1. The document discusses seismology, the internal structure of the Earth, plate tectonics theory, and earthquake waves.
2. The Earth's interior is composed of a crust, mantle, and core. The mantle acts as a viscous fluid that causes convection currents, which in turn exert shear stresses on tectonic plates.
3. Plate tectonics theory proposes that the lithosphere is broken into plates that move relative to each other at plate boundaries. This movement generates earthquakes and other geological activity.
Concept of isostatic adjustment and isostatic models parag sonwane
This document discusses the geological concept of isostasy, which refers to the equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density. It presents several theories of isostasy, including Airy's theory which proposes that thicker crustal areas sink deeper into the mantle, and Pratt's theory which suggests areas of lower crustal density project higher. The document also discusses isostatic effects from processes like deposition, erosion, and past ice sheets, as well as concepts like phase changes and Heiskanen's modification of Airy's theory.
The document summarizes key topics related to Earth's structure and relief formation. It describes the internal layers of the Earth including the crust, mantle, and core. It discusses plate tectonics and how the movement of tectonic plates leads to collisions and separations that form mountains and ocean ridges. It also outlines three main types of relief - continental, coastal, and ocean - and provides examples of associated landforms like mountains, valleys, beaches, and ocean trenches.
The document discusses concepts related to plate tectonics and the Earth's internal structure and processes. It defines key terms like crust, lithospheric plates, volcanoes, earthquakes, and plate boundary types. It also summarizes Alfred Wegener's evidence for continental drift theory. Specifically, it notes he provided evidence that continents fit together like puzzle pieces, that similar geological formations are found far apart, and that fossil distributions also indicate continents have moved. It also asks questions to help explain plate tectonics concepts like the causes of internal activity and how convection currents form due to heat rising and cooling.
1) Isostasy refers to the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere. The elevation and thickness of the Earth's crust depends on its density and thickness to maintain balance.
2) Alfred Wegener first proposed the theory of continental drift in 1915, which states that continents slowly drift due to convection currents in the mantle. Wegener provided evidence that all present-day continents were once joined together in a supercontinent called Pangea.
3) Plate tectonics explains continental drift as the movement of tectonic plates across the Earth's surface over geological time, caused by convection currents in the upper mantle. Pangea broke apart into smaller continents that have
Plate tectonics involves the movement of tectonic plates via divergent, convergent, and transform plate boundaries. The Earth's crust is divided into these tectonic plates which move apart from each other at divergent boundaries, collide at convergent boundaries, or grind past each other at transform boundaries. These plate movements cause volcanic activity and earthquakes, and create geological features such as mid-ocean ridges, trenches, and mountains.
The document discusses the interior structure of the Earth. It is divided into four major layers:
1) The crust is the outermost solid rock layer and is divided into continental and oceanic crust.
2) Below the crust is the mantle, which makes up most of the Earth's volume. The upper mantle includes the asthenosphere and transition zone.
3) In the Earth's core, seismic waves indicate the outer core is liquid while the inner core is solid.
4) Evidence from earthquake waves, density measurements, and mineral properties help reveal the composition of each layer and boundaries between them like the Mohorovicic discontinuity.
1. The document discusses concepts in geophysics including isostasy, density, susceptibility, and resistivity of rocks. Isostasy refers to equilibrium between the earth's lithosphere and asthenosphere. Density is a measure of how tightly packed molecules are in a material. Susceptibility measures a material's magnetization in response to an external magnetic field. Resistivity quantifies a material's opposition to electric current flow.
2. Igneous rocks generally have higher density, susceptibility, and resistivity compared to metamorphic and sedimentary rocks. This is because igneous rocks contain more mafic minerals and have undergone less alteration from their original state than other rock types. Factors like pore space,
Ophiolites provide evidence for the composition and structure of oceanic crust and the upper mantle. They represent sections of oceanic crust and upper mantle that have been obducted or thrust onto continental margins. Studying ophiolites like the Samail ophiolite in Oman has helped scientists understand the layered sequence of rocks that make up oceanic crust, including extrusive basalts, dikes, and intrusive gabbros.
Concept of isostatic adjustment and isostatic models parag sonwane
This document discusses the geological concept of isostasy, which refers to the equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density. It presents several theories of isostasy, including Airy's theory which proposes that thicker crustal areas sink deeper into the mantle, and Pratt's theory which suggests areas of lower crustal density project higher. The document also discusses isostatic effects from processes like deposition, erosion, and past ice sheets, as well as concepts like phase changes and Heiskanen's modification of Airy's theory.
The document summarizes key topics related to Earth's structure and relief formation. It describes the internal layers of the Earth including the crust, mantle, and core. It discusses plate tectonics and how the movement of tectonic plates leads to collisions and separations that form mountains and ocean ridges. It also outlines three main types of relief - continental, coastal, and ocean - and provides examples of associated landforms like mountains, valleys, beaches, and ocean trenches.
The document discusses concepts related to plate tectonics and the Earth's internal structure and processes. It defines key terms like crust, lithospheric plates, volcanoes, earthquakes, and plate boundary types. It also summarizes Alfred Wegener's evidence for continental drift theory. Specifically, it notes he provided evidence that continents fit together like puzzle pieces, that similar geological formations are found far apart, and that fossil distributions also indicate continents have moved. It also asks questions to help explain plate tectonics concepts like the causes of internal activity and how convection currents form due to heat rising and cooling.
1) Isostasy refers to the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere. The elevation and thickness of the Earth's crust depends on its density and thickness to maintain balance.
2) Alfred Wegener first proposed the theory of continental drift in 1915, which states that continents slowly drift due to convection currents in the mantle. Wegener provided evidence that all present-day continents were once joined together in a supercontinent called Pangea.
3) Plate tectonics explains continental drift as the movement of tectonic plates across the Earth's surface over geological time, caused by convection currents in the upper mantle. Pangea broke apart into smaller continents that have
Plate tectonics involves the movement of tectonic plates via divergent, convergent, and transform plate boundaries. The Earth's crust is divided into these tectonic plates which move apart from each other at divergent boundaries, collide at convergent boundaries, or grind past each other at transform boundaries. These plate movements cause volcanic activity and earthquakes, and create geological features such as mid-ocean ridges, trenches, and mountains.
The document discusses the interior structure of the Earth. It is divided into four major layers:
1) The crust is the outermost solid rock layer and is divided into continental and oceanic crust.
2) Below the crust is the mantle, which makes up most of the Earth's volume. The upper mantle includes the asthenosphere and transition zone.
3) In the Earth's core, seismic waves indicate the outer core is liquid while the inner core is solid.
4) Evidence from earthquake waves, density measurements, and mineral properties help reveal the composition of each layer and boundaries between them like the Mohorovicic discontinuity.
1. The document discusses concepts in geophysics including isostasy, density, susceptibility, and resistivity of rocks. Isostasy refers to equilibrium between the earth's lithosphere and asthenosphere. Density is a measure of how tightly packed molecules are in a material. Susceptibility measures a material's magnetization in response to an external magnetic field. Resistivity quantifies a material's opposition to electric current flow.
2. Igneous rocks generally have higher density, susceptibility, and resistivity compared to metamorphic and sedimentary rocks. This is because igneous rocks contain more mafic minerals and have undergone less alteration from their original state than other rock types. Factors like pore space,
Ophiolites provide evidence for the composition and structure of oceanic crust and the upper mantle. They represent sections of oceanic crust and upper mantle that have been obducted or thrust onto continental margins. Studying ophiolites like the Samail ophiolite in Oman has helped scientists understand the layered sequence of rocks that make up oceanic crust, including extrusive basalts, dikes, and intrusive gabbros.
Plate tectonics, earthquakes, and volcanism final(3)1Grace Espago
The document discusses plate tectonics theory and the evidence that supports it. Plate tectonics theory proposes that the Earth's outer layer is made up of rigid plates that move over the asthenosphere below. Plates move by separating at mid-ocean ridges and colliding in other areas. When plates collide, one plate generally subducts under the other. The theory is supported by paleomagnetism data, the distribution of earthquakes along plate boundaries, the ages of seafloor sediments, and hotspot tracks.
The document provides an introduction to seismology and the study of earthquakes. It discusses the formation of the Earth and its layers. The Earth is divided into the inner core, outer core, mantle, and crust. The core is mostly iron and nickel, the mantle consists of silicate compounds, and the crust is made of less dense materials. Earthquakes are caused by the sudden movement of tectonic plates or rupture along faults. The theory of plate tectonics explains the distribution of seismic activity and ties together concepts like continental drift.
The document discusses the geological concept of isostasy. Isostasy refers to the principle of buoyancy where land masses float on the denser underlying mantle material. It explains that mountains create indentations in the earth's crust similar to placing a heavy object on a rubber ball. It also describes early theories on isostasy from Clarence Dutton, who coined the term, and Sir George Airy, who proposed that land masses float with varying thickness but uniform density. The concept was later refined by A. Pratt to propose uniform depth but varying density between land masses.
The document discusses the concept of geosynclines, which refers to thick piles of sediments deposited in deep marine basins that were later compressed, deformed, and uplifted to form mountain ranges. Geosynclines developed in three phases - first sediments accumulated in a subsiding trough (geosynclinal phase), then the deeply buried sediments folded under heat and pressure (tectonic phase), and finally horizontal compression forces uplifted the folded rocks to form mountains tens of thousands of meters high (orogenic phase). Geosynclines are classified as orthgeosynclines like eugeosynclines that formed far from continents with volcanic rocks, or parageosynclines like miogeosyn
Geodynamics studies mantle convection and plate tectonics to understand phenomena like seafloor spreading and mountain building. It provides fundamentals for how the solid Earth works as a heat engine. Early theorists like Wegener and Du Toit proposed continental drift to explain geological similarities between continents. In the 1960s, seafloor mapping and studies of magnetic pole positions in rocks supported plate tectonics, where convection in the mantle drives the motion of rigid tectonic plates. This theory was accepted when it provided a unifying framework and mechanism to explain observations of geology and geophysics.
The document discusses the Earth's internal structure and processes. It describes two models that explain the Earth's internal layers: the geochemical model which divides the Earth into crust, mantle, and core, and the dynamic model which divides it into lithosphere, asthenosphere, mesosphere, and endosphere. The primary cause of Earth's internal activity is convection currents transferring heat from the core outward. This movement of heat drives the movement of tectonic plates at convergent, divergent, and transform boundaries, resulting in geologic processes such as volcanoes and earthquakes.
The Earth has three main layers - a core, mantle, and crust. The crust is made up of tectonic plates that slowly move due to convection currents in the mantle. Alfred Wegener first proposed the theory of continental drift in the early 1900s, but it was not widely accepted until the 1950s when studies of the ocean floor provided supporting evidence. For the past 200 million years, the atmosphere has been around 78% nitrogen and 21% oxygen, though it was likely different in the early Earth with more carbon dioxide and less oxygen. Human activities like burning fossil fuels are increasing carbon dioxide levels today.
Ch.5.less.2.what happens when earth plates movebassantnour
German geologist Alfred Wegener proposed the theory of continental drift in 1912, which hypothesized that the continents were once joined together in a single landmass called Pangaea before drifting apart to their current locations. Wegener provided three key pieces of evidence to support this: the continental margins fit together like puzzle pieces, matching fossil and rock formations were found on separated continents, and the same fossils of non-marine animals were discovered on continents far apart. Later, scientists developed the theory of plate tectonics to explain the forces causing the continental drift, proposing that movements in underground plates pushed the continents apart or together.
The document summarizes key concepts in plate tectonics. It describes how the Earth is divided into layers including the crust, mantle, and core. It explains that the crust is broken into plates that move around on the asthenosphere. There are three main types of plate boundaries: convergent where plates collide, divergent where they move apart, and transform where they slide past each other. Plate tectonics helps explain geological events like continental drift, mountain building, and volcanic activity.
Isostasy refers to the equilibrium between blocks of Earth's crust and the underlying mantle. Lighter crustal blocks "float" higher, while heavier blocks sink deeper into the mantle. There are three models of isostasy: the Airy-Heiskanen model where crustal thickness changes with topography; the Pratt-Hayford model where lateral density changes accommodate topography; and the flexural isostasy model where the lithosphere bends under local loads. Deposition and erosion affect isostatic equilibrium as crust rises when loaded and sinks when unloaded, like an iceberg. Plate tectonics and ice sheets also impact isostasy through crustal thickening during collisions and post-gl
The document provides information about a Geosphere Ecology class taught by Mr. Nettles. It includes the class agenda for several days, learning objectives about the composition and structure of the Earth, and discussions of plate tectonics, earthquakes, volcanoes, and erosion. Students are assigned to create labeled diagrams of the Earth's layers and complete worksheets. A quiz on the material is scheduled for the following week.
The document discusses the Earth's internal energy and how it causes tectonic plate movement and related geological phenomena. The main points are:
1) The Earth has internal heat from radioactive elements and impacts that causes plate tectonics and results in volcanoes, earthquakes, and mountain building.
2) Alfred Wegener proposed continental drift in 1912 to explain how the continents were once joined together before drifting apart, as evidenced by matching continental shelves.
3) The Earth's solid crust is made up of tectonic plates that move due to convection currents in the mantle, resulting in earthquakes and volcanic activity at plate boundaries.
1) Earthquakes are caused by the sudden release of elastic strain energy that builds up in tectonic plates due to their slow relative movements.
2) The Earth's interior is differentiated into layers with the outer core, mantle, and crust composed of lighter rocks overlying denser materials towards the center.
3) Convection currents in the mantle cause the crust and some mantle to break into tectonic plates that move relative to one another, building up elastic stress at plate boundaries.
Internal structure of earth with repect to seismic wavesShah Naseer
This document discusses the structure and composition of Earth's interior as revealed through seismic wave studies. It describes the major layers as follows:
The crust, which is thinner and denser under the oceans than continents. Below is the mantle, which extends to a depth of 2,890 km and is denser than the crust. The lower mantle has higher seismic wave velocities than the upper mantle. The core lies below the mantle, with the liquid outer core surrounding a solid inner core. Seismic waves have provided evidence of this internal structure.
Earthquakes occur along faults in the Earth's crust where blocks of rock move due to stress. There are three main types of faults - normal faults where one block moves down, reverse faults where one block moves up, and strike-slip faults where blocks move horizontally. When stress is released, energy radiates outward from the focus in the form of seismic waves, including primary, secondary, and surface waves. Seismographs can detect and record these waves to locate the epicenter and measure the earthquake's magnitude. Earthquakes can cause severe damage through ground shaking, landslides, fires and liquefaction, but damage can be reduced through monitoring, predicting earthquake activity, and enforcing strict building codes for earthquake-resistant construction.
This document discusses earthquakes, including their causes and global distribution. It begins by defining earthquakes and describing the different types of seismic waves generated. There are two main types of body waves (P and S waves) and two main types of surface waves (Love and Rayleigh waves). Earthquakes are primarily caused by tectonic plate movement and faulting, as well as volcanic activity. They most commonly occur along plate boundaries and zones of historical mountain building. India has been divided into different seismic zones based on earthquake risk, with Zone V representing the highest risk.
Earthquakes are caused by the sudden release of energy along faults in the Earth's crust due to the buildup of stress. Seismographs are used to measure seismic waves from earthquakes and locate their epicenters. The Richter scale is used to measure earthquake strength, with weaker quakes occurring more frequently. Areas along faults that have not recently experienced quakes are more likely to experience strong future quakes. Cities can reduce earthquake damage through building design techniques like base isolators and cross-braces that help structures withstand shaking.
The Earth's crust is divided into 12 major tectonic plates that are constantly moving due to convection currents in the underlying mantle. There are three main types of plate boundaries - divergent where plates move apart, convergent where they collide, and transform where they slide past each other. Plate tectonics explains global patterns of volcanic and earthquake activity which predominantly occur at plate boundaries as the plates interact, collide and subduct.
This document provides an overview of elements of seismology. It defines an earthquake as the shaking of the Earth's surface from a sudden release of energy in the lithosphere. Seismology is the scientific study of earthquakes and elastic wave propagation through the Earth. Engineering seismology applies seismology to assess earthquake hazards for engineering purposes. It involves studying earthquake history and strong ground motions to evaluate expected shaking in a region. The document also discusses plate tectonics, types of plate boundaries, causes of earthquakes, and types of rock faults.
1) Alfred Wegener proposed the continental drift theory which stated that the Earth was once a single supercontinent called Pangaea surrounded by an ocean.
2) Evidence for continental drift includes fossils of the same plants and animals found on different continents, matching rock formations, and glacial deposits found in areas that were once near the South Pole.
3) Arthur Holmes suggested thermal convection in the Earth's mantle as the driving force behind continental movement, likening it to a conveyor belt. This led to the development of the theory of plate tectonics.
This document provides information about plate tectonics and is designed to meet South Carolina science standards. It discusses the layers of the Earth, tectonic plates and their movement, and the three types of plate boundaries - convergent where plates collide, divergent where they separate, and transform where they slide past each other. Specific examples are given for each boundary type, including discussions of sea floor spreading at mid-ocean ridges, subduction zones creating volcanoes and trenches, and the San Andreas Fault as a transform boundary.
The document summarizes the structure and dynamics of the Earth. It describes how the Earth is composed of layers with different densities, including the crust, mantle, and core. It explains that the lithosphere is divided into tectonic plates that move over the asthenosphere due to convection currents in the mantle. There are three main types of plate boundaries - divergent where new crust forms, convergent where plates collide and one is subducted, and transform where plates slide past each other. Plate tectonics involves the creation of oceanic crust at mid-ocean ridges and recycling of crust through subduction.
Plate tectonics, earthquakes, and volcanism final(3)1Grace Espago
The document discusses plate tectonics theory and the evidence that supports it. Plate tectonics theory proposes that the Earth's outer layer is made up of rigid plates that move over the asthenosphere below. Plates move by separating at mid-ocean ridges and colliding in other areas. When plates collide, one plate generally subducts under the other. The theory is supported by paleomagnetism data, the distribution of earthquakes along plate boundaries, the ages of seafloor sediments, and hotspot tracks.
The document provides an introduction to seismology and the study of earthquakes. It discusses the formation of the Earth and its layers. The Earth is divided into the inner core, outer core, mantle, and crust. The core is mostly iron and nickel, the mantle consists of silicate compounds, and the crust is made of less dense materials. Earthquakes are caused by the sudden movement of tectonic plates or rupture along faults. The theory of plate tectonics explains the distribution of seismic activity and ties together concepts like continental drift.
The document discusses the geological concept of isostasy. Isostasy refers to the principle of buoyancy where land masses float on the denser underlying mantle material. It explains that mountains create indentations in the earth's crust similar to placing a heavy object on a rubber ball. It also describes early theories on isostasy from Clarence Dutton, who coined the term, and Sir George Airy, who proposed that land masses float with varying thickness but uniform density. The concept was later refined by A. Pratt to propose uniform depth but varying density between land masses.
The document discusses the concept of geosynclines, which refers to thick piles of sediments deposited in deep marine basins that were later compressed, deformed, and uplifted to form mountain ranges. Geosynclines developed in three phases - first sediments accumulated in a subsiding trough (geosynclinal phase), then the deeply buried sediments folded under heat and pressure (tectonic phase), and finally horizontal compression forces uplifted the folded rocks to form mountains tens of thousands of meters high (orogenic phase). Geosynclines are classified as orthgeosynclines like eugeosynclines that formed far from continents with volcanic rocks, or parageosynclines like miogeosyn
Geodynamics studies mantle convection and plate tectonics to understand phenomena like seafloor spreading and mountain building. It provides fundamentals for how the solid Earth works as a heat engine. Early theorists like Wegener and Du Toit proposed continental drift to explain geological similarities between continents. In the 1960s, seafloor mapping and studies of magnetic pole positions in rocks supported plate tectonics, where convection in the mantle drives the motion of rigid tectonic plates. This theory was accepted when it provided a unifying framework and mechanism to explain observations of geology and geophysics.
The document discusses the Earth's internal structure and processes. It describes two models that explain the Earth's internal layers: the geochemical model which divides the Earth into crust, mantle, and core, and the dynamic model which divides it into lithosphere, asthenosphere, mesosphere, and endosphere. The primary cause of Earth's internal activity is convection currents transferring heat from the core outward. This movement of heat drives the movement of tectonic plates at convergent, divergent, and transform boundaries, resulting in geologic processes such as volcanoes and earthquakes.
The Earth has three main layers - a core, mantle, and crust. The crust is made up of tectonic plates that slowly move due to convection currents in the mantle. Alfred Wegener first proposed the theory of continental drift in the early 1900s, but it was not widely accepted until the 1950s when studies of the ocean floor provided supporting evidence. For the past 200 million years, the atmosphere has been around 78% nitrogen and 21% oxygen, though it was likely different in the early Earth with more carbon dioxide and less oxygen. Human activities like burning fossil fuels are increasing carbon dioxide levels today.
Ch.5.less.2.what happens when earth plates movebassantnour
German geologist Alfred Wegener proposed the theory of continental drift in 1912, which hypothesized that the continents were once joined together in a single landmass called Pangaea before drifting apart to their current locations. Wegener provided three key pieces of evidence to support this: the continental margins fit together like puzzle pieces, matching fossil and rock formations were found on separated continents, and the same fossils of non-marine animals were discovered on continents far apart. Later, scientists developed the theory of plate tectonics to explain the forces causing the continental drift, proposing that movements in underground plates pushed the continents apart or together.
The document summarizes key concepts in plate tectonics. It describes how the Earth is divided into layers including the crust, mantle, and core. It explains that the crust is broken into plates that move around on the asthenosphere. There are three main types of plate boundaries: convergent where plates collide, divergent where they move apart, and transform where they slide past each other. Plate tectonics helps explain geological events like continental drift, mountain building, and volcanic activity.
Isostasy refers to the equilibrium between blocks of Earth's crust and the underlying mantle. Lighter crustal blocks "float" higher, while heavier blocks sink deeper into the mantle. There are three models of isostasy: the Airy-Heiskanen model where crustal thickness changes with topography; the Pratt-Hayford model where lateral density changes accommodate topography; and the flexural isostasy model where the lithosphere bends under local loads. Deposition and erosion affect isostatic equilibrium as crust rises when loaded and sinks when unloaded, like an iceberg. Plate tectonics and ice sheets also impact isostasy through crustal thickening during collisions and post-gl
The document provides information about a Geosphere Ecology class taught by Mr. Nettles. It includes the class agenda for several days, learning objectives about the composition and structure of the Earth, and discussions of plate tectonics, earthquakes, volcanoes, and erosion. Students are assigned to create labeled diagrams of the Earth's layers and complete worksheets. A quiz on the material is scheduled for the following week.
The document discusses the Earth's internal energy and how it causes tectonic plate movement and related geological phenomena. The main points are:
1) The Earth has internal heat from radioactive elements and impacts that causes plate tectonics and results in volcanoes, earthquakes, and mountain building.
2) Alfred Wegener proposed continental drift in 1912 to explain how the continents were once joined together before drifting apart, as evidenced by matching continental shelves.
3) The Earth's solid crust is made up of tectonic plates that move due to convection currents in the mantle, resulting in earthquakes and volcanic activity at plate boundaries.
1) Earthquakes are caused by the sudden release of elastic strain energy that builds up in tectonic plates due to their slow relative movements.
2) The Earth's interior is differentiated into layers with the outer core, mantle, and crust composed of lighter rocks overlying denser materials towards the center.
3) Convection currents in the mantle cause the crust and some mantle to break into tectonic plates that move relative to one another, building up elastic stress at plate boundaries.
Internal structure of earth with repect to seismic wavesShah Naseer
This document discusses the structure and composition of Earth's interior as revealed through seismic wave studies. It describes the major layers as follows:
The crust, which is thinner and denser under the oceans than continents. Below is the mantle, which extends to a depth of 2,890 km and is denser than the crust. The lower mantle has higher seismic wave velocities than the upper mantle. The core lies below the mantle, with the liquid outer core surrounding a solid inner core. Seismic waves have provided evidence of this internal structure.
Earthquakes occur along faults in the Earth's crust where blocks of rock move due to stress. There are three main types of faults - normal faults where one block moves down, reverse faults where one block moves up, and strike-slip faults where blocks move horizontally. When stress is released, energy radiates outward from the focus in the form of seismic waves, including primary, secondary, and surface waves. Seismographs can detect and record these waves to locate the epicenter and measure the earthquake's magnitude. Earthquakes can cause severe damage through ground shaking, landslides, fires and liquefaction, but damage can be reduced through monitoring, predicting earthquake activity, and enforcing strict building codes for earthquake-resistant construction.
This document discusses earthquakes, including their causes and global distribution. It begins by defining earthquakes and describing the different types of seismic waves generated. There are two main types of body waves (P and S waves) and two main types of surface waves (Love and Rayleigh waves). Earthquakes are primarily caused by tectonic plate movement and faulting, as well as volcanic activity. They most commonly occur along plate boundaries and zones of historical mountain building. India has been divided into different seismic zones based on earthquake risk, with Zone V representing the highest risk.
Earthquakes are caused by the sudden release of energy along faults in the Earth's crust due to the buildup of stress. Seismographs are used to measure seismic waves from earthquakes and locate their epicenters. The Richter scale is used to measure earthquake strength, with weaker quakes occurring more frequently. Areas along faults that have not recently experienced quakes are more likely to experience strong future quakes. Cities can reduce earthquake damage through building design techniques like base isolators and cross-braces that help structures withstand shaking.
The Earth's crust is divided into 12 major tectonic plates that are constantly moving due to convection currents in the underlying mantle. There are three main types of plate boundaries - divergent where plates move apart, convergent where they collide, and transform where they slide past each other. Plate tectonics explains global patterns of volcanic and earthquake activity which predominantly occur at plate boundaries as the plates interact, collide and subduct.
This document provides an overview of elements of seismology. It defines an earthquake as the shaking of the Earth's surface from a sudden release of energy in the lithosphere. Seismology is the scientific study of earthquakes and elastic wave propagation through the Earth. Engineering seismology applies seismology to assess earthquake hazards for engineering purposes. It involves studying earthquake history and strong ground motions to evaluate expected shaking in a region. The document also discusses plate tectonics, types of plate boundaries, causes of earthquakes, and types of rock faults.
1) Alfred Wegener proposed the continental drift theory which stated that the Earth was once a single supercontinent called Pangaea surrounded by an ocean.
2) Evidence for continental drift includes fossils of the same plants and animals found on different continents, matching rock formations, and glacial deposits found in areas that were once near the South Pole.
3) Arthur Holmes suggested thermal convection in the Earth's mantle as the driving force behind continental movement, likening it to a conveyor belt. This led to the development of the theory of plate tectonics.
This document provides information about plate tectonics and is designed to meet South Carolina science standards. It discusses the layers of the Earth, tectonic plates and their movement, and the three types of plate boundaries - convergent where plates collide, divergent where they separate, and transform where they slide past each other. Specific examples are given for each boundary type, including discussions of sea floor spreading at mid-ocean ridges, subduction zones creating volcanoes and trenches, and the San Andreas Fault as a transform boundary.
The document summarizes the structure and dynamics of the Earth. It describes how the Earth is composed of layers with different densities, including the crust, mantle, and core. It explains that the lithosphere is divided into tectonic plates that move over the asthenosphere due to convection currents in the mantle. There are three main types of plate boundaries - divergent where new crust forms, convergent where plates collide and one is subducted, and transform where plates slide past each other. Plate tectonics involves the creation of oceanic crust at mid-ocean ridges and recycling of crust through subduction.
Earth's internal heat comes from three main sources:
1) The accretion of dust and gas particles during the Earth's formation released gravitational potential energy and caused internal heating.
2) Radioactive decay of elements in the Earth's core and mantle, such as uranium and potassium, continues to generate heat.
3) Frictional heating from convection currents in the mantle also contributes to the Earth's internal heat. Seismic waves have allowed scientists to indirectly learn about the Earth's layered structure despite only drilling about 7 miles deep.
The document discusses the possible causes of plate movement, including convection currents in the mantle, ridge push, and slab pull. Convection currents cause the mantle to circulate, ridge push is the force that causes plates to move away from mid-ocean ridges as new crust is formed, and slab pull occurs as dense oceanic plates are pulled into the mantle at subduction zones. The document also summarizes seafloor spreading theory, which proposes that new crust is formed at mid-ocean ridges due to upwelling magma.
1. The document provides an overview of earthquakes, their causes, characteristics, effects, and preparedness measures. It describes how earthquakes are caused by the movement of tectonic plates and buildup of elastic strain energy that is suddenly released.
2. Key characteristics discussed include the different types of seismic waves that cause shaking and damage, the measurement scales used to describe magnitude versus intensity, and secondary hazards like landslides, liquefaction, and tsunamis.
3. Typical effects of earthquakes outlined are physical damage to structures, infrastructure and property, casualties, and public health issues in the aftermath.
The document provides an overview of the structure and composition of the Earth's layers, including the crust, mantle, and core. It then discusses plate tectonics and evidence that supports the theory of continental drift, such as matching geological formations and fossil distributions between continents before they drifted apart. The development of the modern theory of plate tectonics to explain continental movement is also outlined.
The document provides an overview of the structure and composition of the Earth's interior based on evidence from seismology and other studies. It describes the different layers from outer to inner as:
1) The lithosphere and crust, composed mainly of silicate rocks with densities around 3.5.
2) The mantle, extending to a depth of 2900km and divided into upper and lower zones. It has a mean density of 4.6.
3) The core, extending from 2900km to the center. It is divided into a liquid outer core and solid inner core, and has the highest densities in the Earth ranging from 10 to 13.6.
This is the entire CSEC geography syllabus (some things might be missing). The information was collected from various websites and textbooks. The topics are:
- Internal forces
-External forces
-Rivers
-Limestone
-Coasts
-Coral reefs and Mangroves
-Weather and Climate
- Ecosystems (vegetation and soils)
-Natural hazards
- Urbanization
-Economic activity
-Environmental degradation
CSEC Geography- Internal Forces - Plate Tectonics and EarthquakesOral Johnson
This document looks at the Earth's internal forces. The main layers of the earth are described. The history surrounding plate tectonics is discussed. The different types of plate boundaries is also explained.
that is associated with broad upwarping of the overlying litho.docxmattinsonjanel
that is associated with broad upwarping of the overlying lithosphere (figure 5.1 iA). As a result, the lithosphere is stretched, causing the brittle crustal rocks to break into large slabs. As the tectonic forces continue to pull the crust apart, these crustal fragments sink, generating an elongated depression called a continental rift (figure 5.1 ib).
A modern example of an active continental rift is the East African Rift (figure s. i 2). Whether this rift will eventually result in the breakup of Africa is a topic of continued research. Nevertheless, the East African Rift is an excellent model of the initial stage in the breakup of a continent. Here, tensional forces have stretched and thinned the crust, allowing molten rock to ascend from the mantle. Evidence for recent volcanic activity includes several large volcanic mountains including Mount Kilimanjaro and Mount Kenya, the tallest peaks in Africa. Research suggests that if rifting continues, the rift valley will lengthen and deepen, eventually extending out to the margin of the landmass (r;<;ur.E 5.1 ic). At this point, the rift will become a narrow sea with an outlet to the ocean. The Red Sea, which formed when the Arabian Peninsula split from Africa, is a modern example of such a feature. Consequently, the Red Sea provides us with a view of how the Atlantic Ocean may have looked in its infancy (figure 5.1 id).
QEOD^
Forces Within sSWHBe Plate Tectonics
New lithosphere is constantly being produced at the oceanic ridges; however, our planet is not growing larger—its total surface area remains constant. A balance is maintained because older, denser portions of oceanic lithosphere descend into the mantle at a rate equal to seafloor production. This activity occurs along convergent (con = together, vergere = to move) boundaries, where two plates move toward each other and the leading edge of one is bent downward, as it slides beneath the other.
Convergent boundaries are also called subduction zones, because they are sites where lithosphere is descending (being subducted) into the mantle. Subduction occurs because the density of the descending tectonic plate is greater than the density of the underlying asthenosphere. In general, oceanic lithosphere is more dense than the asthenosphere, whereas continental lithosphere is
(
Upwarping
figure 5.11
Continental rifting and the formation of a new ocean basin.
A.
The initial stage of con tinental rifting tends to include upwelling in the mantle that is associated with broad doming of the lith-osphere.Tensional forces and buoyant uplifting of the heated lithosphere cause the crust to be broken into large slabs.
b.
A
s the crust is pulled apart, large slabs of rock sink, generating a rift valley.
C.
Further spreading generates a narrow sea, similar to the present-day Red Sea.
D.
Eventually, an expansive ocean basin and ridge system are created.
)less dense and resists subduction. As a consequence, only oceanic lithosphere will subd ...
The document discusses plate tectonics and the structure of the Earth. It describes how seismic waves can reveal layers inside the Earth like the crust, mantle, and core. It explains continental drift and how the theory of plate tectonics developed. Plates move at boundaries where they can spread apart, collide, or slide past each other, causing earthquakes and building landforms.
This document provides an introduction to seismology. It discusses how seismology studies earthquakes and the propagation of energy through the Earth's crust. It then describes the formation of the Earth and its layers, including the crust, mantle, outer core, and inner core. It explains what causes earthquakes, such as the movement of tectonic plates and the rupture of rocks along faults. Finally, it discusses evidence that supported Alfred Wegener's theory of continental drift and how plate tectonics helps explain the distribution of earthquakes and volcanic activity at plate boundaries.
The document discusses the causes and types of earthquakes. It begins by noting that records of earthquakes date back thousands of years in some areas. It then explains that earthquakes are caused by the sudden movement of tectonic plates deep below the earth's surface. The major types of plate boundaries are divergent boundaries where new crust forms, convergent boundaries where plates collide and crust is destroyed, and transform boundaries where plates slide past each other. Specific examples like the Mariana Trench and San Andreas Fault are also described.
The document summarizes key concepts in plate tectonics including:
1) The Earth's interior is divided into layers based on composition and physical state, including the crust, mantle, and core.
2) Seismic waves provide evidence of discontinuities between layers like the Mohorovicic discontinuity between the crust and mantle.
3) Early theories proposed continental drift but plate tectonics explains the movement of lithospheric plates at boundaries like divergent boundaries that create ocean floor.
This document provides an overview of seismicity and earthquakes. It discusses seismic waves, earthquakes and faults, measures of earthquakes including magnitude and intensity, ground damage from earthquakes, tsunamis caused by earthquakes, and earthquake resistant construction. Specific topics covered include the 2001 Gujarat earthquake in India and the devastating 2004 Indian Ocean tsunami. The document aims to introduce students to key concepts regarding seismicity and earthquakes.
Continental drift is the hypothesis that the Earth's continents have moved over geologic time relative to each other. Plate tectonics studies the movement of continents on tectonic plates. There are three main types of tectonic plate boundaries: subduction zones where plates converge, divergent margins where plates spread apart, and transform margins where plates slide past each other. Seafloor spreading occurs at divergent boundaries as heat from the Earth's mantle causes the seafloor crust to crack and new crust is formed, pushing the plates apart over millions of years. The 2004 Sumatra-Andaman earthquake, measured at over 9.0 on the Richter scale, was caused by movement along the Sumatra fault line and
The document summarizes plate tectonics, providing details on:
1) The structure of the Earth's core and mantle, and how convection currents cause plate movements.
2) Evidence for plate tectonics including seafloor spreading and magnetic reversals in ocean crust.
3) The three types of plate boundaries and associated geological features like ocean trenches and volcanic activity.
The document discusses the design of water distribution systems. It states that the design must satisfy water needs and maintain minimum residual pressures. It discusses pressure variations and velocity limits in distribution systems. It introduces the Hazen-Williams equation for calculating head loss in pipes based on flow rate, length, diameter and roughness coefficient. The document outlines Hardy's Cross Method for balancing flows in distribution networks using loop equations. It provides an example of applying the method to calculate pipe diameters and flows in a sample network.
The document contains information to estimate water requirements for different communities including design population, per capita demand, average water demand, maximum daily demand, peak hourly demand, and fire flow requirements. It provides the calculations to estimate the total water requirement considering both regular demand and fire demand for communities with populations of 22,000, 55,000 and 120,000. Fire flow rates and daily amounts are also estimated for different building types and floor areas.
The flooding in western Japan in July 2018 killed over 200 people and left 44 missing. Torrential rains fell over several days, with some areas receiving over 25 inches of rain. The extreme downpour caused rivers to overflow and triggered landslides, destroying homes and infrastructure. Rescue efforts involving over 70,000 workers continued for days to search for survivors amid the wreckage and receding floodwaters. The disaster highlighted Japan's vulnerability to increasingly heavy rains and landslides caused by climate change.
The document summarizes the history of pavement development from ancient times to modern roads. It describes how ancient human pathways evolved into animal tracks and then wheeled vehicles required harder road surfaces. The Romans constructed extensive road networks with gravel surfaces. Later, the French developed roads using compacted stone layers, while the British engineer Macadam introduced using broken stone layers which was more economical. Modern roads now use bituminous concrete and cement concretes, and employ new construction technologies.
This document discusses roads in Pakistan, including CPEC roads, motorways, and national highways. It provides details on 5 CPEC road projects costing over $5 billion that are planned or under construction. It also lists 14 existing and under construction motorways running over 5,000 km, as well as over 20 national highways spanning the country and totaling nearly 20,000 km. The motorways and national highways facilitate domestic and international transportation across Pakistan.
Highway engineering involves planning, designing, constructing, operating, and maintaining roads and bridges. A highway connects towns and cities via intersections and traffic lights, while a motorway connects important cities at higher speeds without intersections. The history of paved roads dates back to ancient Egypt and the Roman Empire, while modern highway construction began in the 20th century. There are two main types of pavements: flexible pavements made of asphalt layers over granular material, and rigid concrete pavements that distribute loads over a wide area.
The document discusses China-Pakistan Economic Corridor (CPEC) roads network, including motorways and national highways. It outlines 15 major CPEC road projects that are either under construction or planned. These include expanding the Karakoram Highway, upgrading the Peshawar-Karachi motorway, and reconstructing the ML-1 rail line from Peshawar to Karachi. CPEC aims to boost regional connectivity and benefit not just China and Pakistan but also other countries through increased trade and economic cooperation.
This document contains information submitted by Muhammad Noman, a student with roll number 15-CLT-36 at Nfc Institute Of Engineering And Fertilizer Research in Faisalabad. The document is for the course Concrete Technology –II (PR) and was submitted to Engg. Basit.
The document summarizes the history and current status of Pakistan's motorway system. It begins with a brief history of road construction dating back to ancient Rome and Egypt. It then provides details on 15 existing and planned motorways in Pakistan, including their planned completion dates, lengths, number of lanes and exits. The total length of operational motorways has grown from 632 km in 2010 to over 1,000 km presently. The first motorway opened in 1997 between Peshawar and Islamabad.
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Eq chapter
1. 1
Chapter 1
Seismology
1.1. Introduction
A study of earthquake engineering calls for a good understanding of geophysical
process that causes earthquakes and various effects of earthquakes. Seismology is
the study of the generation, propagation and measurement of seismic waves through
earth and the sources that generate them. The word seismology originated from
Greek words, ‘seismos’ meaning earthquake and ‘logos’ meaning science. The study
of seismic wave propagation through earth provides the maximum input to the
understanding of internal structure of earth.
1.2. Internal Structure of Earth
The earth’s shape is an oblate spheroid with a diameter along the equator of about
12740 km with the polar diameter as 12700km. The higher diameter along equator is
caused by the higher centrifugal forces generated along the equator due to rotation
of earth. Though the specific gravity of materials that constitute the surface of earth
is only about 2.8, the average specific gravity of earth is about 5.5 indicating
presence of very heavy materials towards interior of earth. The interior of the earth
can be classified into three major categories as Crust, Mantle and Core (refer Figure
1.1).
Figure 1.1 Cross-section of interior of earth.
Crust, 5-70 km
Outer mantle, 2900 km
Inner mantle, 2200 km
Core, 1370 km radius
2. 2
Crust: or the lithosphere, is the outer part of the earth is where the life exist. The
average thickness of crust beneath continents is about 40km where as it decreases
to as much as 5km beneath oceans. The oceanic crust is constituted by basaltic
rocks and continental part by granitic rocks overlying the basaltic rocks. Compared to
the layers below, this layer has high rigidity and anisotropy.
Mantle: is a 2900 km thick layer. The mantle consists of 1) Upper Mantle reaching a
depth of about 400 km made of olivine and pyroxene and 2) Lower Mantle made of
more homogeneous mass of magnesium and iron oxide and quartz. No earthquakes
are recorded in the lower mantle. The specific gravity of mantle is about 5. The
mantle has an average temperature of about 2200degree Celsius and the material is
in a viscous semi molten state. The mantle act like fluid in response to slowly acting
stresses and creeps under slow loads. But it behaves like as solid in presence of
rapidly acting stresses, e.g. that caused by earthquake waves.
Core: has a radius of 3470 km and consists of an inner core of radius 1370 km and
an outer core (1370 km < R < 3470 km). The core is composed of molten iron,
probably mixed with small quantities of other elements such as nickel and sulphur or
silicon. The inner solid core is very dense nickel-iron material and is subjected to
very high pressures. The maximum temperature in the core is estimated to be about
3000 degree Celsius. The specific gravity of outer core is about 9-12 where as that
of inner core is 15.
1.3. Continental Drift and Plate Tectonics
1.3.1. Continental drift theory
German scientist Alfred Wegener, in 1915, proposed the hypothesis that the
continents had once formed a single landmass before breaking apart and drifting to
their present locations. His observations were based on the similarity of coastlines
and geology between south America, Africa and Indian peninsula, Australia and
Antarctica, Figure 1.2. He proposed that a large continent termed Pangae existed in
earth around 200 million years ago and was surrounded by an ocean called
Panthalassa. It was postulated that this super continent broke into several pieces
that formed the present continents. These pieces have subsequently drifted into their
current position. Although, he presented much evidence for continental drift, he was
unable to provide a convincing explanation for the physical processes which might
have caused this drift. He suggested that the continents had been pulled apart by the
centrifugal pseudo force of the Earth's rotation or by a small component of
astronomical precession. But the calculations showed that these forces were not
sufficient cause continental drift.
3. 3
Figure 1.2 Similarity between the coastlines continents and distribution of fossils of
ancient biota [Source: http://facstaff.gpc.edu/~pgore /Earth&
Space/images/Fig4.gif].
1.3.2. Plate tectonics
The theory of plate tectonics, presented in early 1960s, explains that the lithosphere
is broken into seven large (and several smaller) segments called plates as shown in
Figure 1.3.
Figure 1.3 Tectonic plate map of the world.
The upper most part of the earth is considered to be divided into two layers with
different deformation properties. The upper rigid layer, called the lithosphere, is
about 100 km thick below the continents, and about 50 km under the oceans, and
consists of Crust and rigid upper-mantle rocks. The lower layer, called the
asthenosphere, extends down to about 700 km depth. The rigid lithospheric shell is
broken into several irregularly shaped major plates and a large number of minor or
secondary plates. The lithospheric plates are not stationary, on the contrary, they
float in a complex pattern, with a velocity of some 2-10 cm/year on the soft rocks of
the underlying asthenosphere like rafts on a lake.
4. 4
Figure 1.4 The state of convection currents below the earth’s surface and their effect
on plate movement (From http://www.pbs.org/gbh/aso/ tryit/
tectonics/intro.html].
This theory requires a source that can generate tremendous force is acting on the
plates. The widely accepted explanation is based on the force offered by convection
currents created by thermo-mechanical behavior of the earth’s subsurface. The
variation of mantle density with temperature produces an unstable equilibrium. The
colder and denser upper layer sinks under the action of gravity to the warmer bottom
layer which is less dense. The lesser dense material rises upwards and the colder
material as it sinks gets heated up and becomes less dense (refer Figure 1.4).
These convection currents create shear stresses at the bottom of the plates which
drags them along the surface of earth.
Figure 1.5 Map of distribution of earthquake epicentres around the world.
The continental sized plates are African, American, Antarctic, Indo-Australian,
Eurasian and pacific plate. Apart from this, several smaller plates like Andaman,
Philippine plate also exist. As plate glides over the asthenosphere, the continents
and oceans move with it. Because the plates move in different directions, they
knock against their neighbors at boundaries. The great forces thus generated at
5. 5
plate boundary build mountain ranges, cause volcanic eruptions and earthquakes.
Most of the Earth’s major geological activity occurs at plate boundaries, the zones
where plates meet and interact. Figure 1.5 depicts the distribution of earthquake
epicentres around the world.
The earthquake that occurs at a plate boundary is known as inter-plate earthquake.
Not all earthquakes occur at plate boundaries. Though, interior portion of a plate is
usually tectonically quiet, earthquakes also occur far from plate boundaries. These
earthquakes are known as intra-plate earthquakes. The recurrence time for an intra-
plate earthquake is much longer than that of inter-plate earthquakes
1.4. Movement of Plate Boundaries
Owing to the difference in movement between the plates that are in motion, three
types of plate boundaries are found to exist along their edges:
1) Spreading ridges
Spreading ridges or divergent boundaries are areas along the edges of plates move
apart from each other, Figure 1.6. This is the location where the less dense molten
rock from the mantle rises upwards and becomes part of crust after cooling. Highest
rate of spreading or expansion between plates is found to occur near Pacific Ocean
ridges and the lowest rate of spreading occurs along mid-Atlantic ridges. Generally,
spreading ridges are located beneath the oceans. A few areas where the spreading
occurs along the continental mass are East African rift valley and Iceland.
Figure 1.6 A cross-section of the divergent plate boundary.
2) Convergent boundaries
The convergent boundaries are formed where the two plates move toward each
other. In this process, one plate could slip below the other one or both could collide
with each other.
a. Subduction boundaries
These boundaries are created when either oceanic lithosphere subducts beneath
oceanic lithosphere (ocean-ocean convergence), or when oceanic lithosphere
subducts beneath continental lithosphere (ocean-continent convergence), Figure 1.7.
The junction where the two plates meet, a trench known as oceanic trench is formed.
6. 6
Figure 1.7 Creation of subduction boundaries [From: http://www.tulane.edu/
~sanelson/geol204/struct&materials.htm].
When two plates of oceanic lithosphere run into one another, the subducting plate is
pushed to depths where it causes melting to occur. When a plate made of oceanic
lithosphere runs into a plate with continental lithosphere, the plate with oceanic
lithosphere subducts because it has a higher density than continental lithosphere.
The subducted plate melts as it encounters higher temperature regime inside earth
melts and produces magma. This magma rises to the surface to produce chains of
volcanos and islands known as island arcs. One of the areas around Indian
peninsula where subduction process is in progress is near Andaman-Sumatra
region, where the Indo-Australian plate is subducting below the Andaman and Sunda
plates, Figure 1.8.
Figure 1.8 Subduction process along Andaman-Sumatra arc, [From Geological
Survey of India, http://www.portal.gsi.gov.in/gsiDoc/pub/cs_sumatra.pdf].
b. Collision Boundaries
When two plates with continental lithosphere collide, subduction ceases and a
mountain range is formed by squeezing together and uplifting the continental crust
on both plates, Figure 1.9. The Himalayan Mountains between India and China were
formed in this way.
7. 7
Figure 1.9 Creation of collision boundaries [From
http://www.tulane.edu/~sanelson /geol204/struct&materials.htm].
3) Transform boundaries
Transform boundaries occur along the plate margins where two plate moves past
each other without destroying or creating new crust, Figure 1.10.
Figure 1.10 A typical profile of a transform plate boundary.
1.5. Faults
The term fault is used to describe a discontinuity within rock mass, along which
movement had happened in the past. Plate boundary is also a type of fault.
Lineaments are mappable linear surface features and may reflect subsurface
phenomena. A lineament could be a fault, a joint or any other linear geological
phenomena. Most faults produce repeated displacements over geologic time.
Movement along a fault may be gradual or sometimes sudden thus, generating an
earthquake.
8. 8
Figure 1.11 Various terminolgies assocaited with the rupture plane of a fault.
(a) (b)
(c) (d)
Figure 1.12 Types of faults (Arrow shows direction of relative displacement)
(a) Normal fault; (b) Reverse fault; (c) Strike-slip fault; (d) Oblique fault.
There are two important parameters associated with describing faults, namely, dip
and strike, Figure 1.11. The strike is the direction of a horizontal line on the surface
of the fault. The dip, measured in a vertical plane at right angles to the strike of the
fault, is the angle of fault plane with horizontal. The hanging wall of a fault refers to
the upper rock surface along which displacement has occurred, whereas the foot
wall is the term given to that below. The vertical shift along a fault plane is called the
throw, and the horizontal displacement is termed as heave.
Faults are classified in to dip-slip faults, strike-slip faults and oblique-slip faults based
on the direction of slippage along the fault plane, Figure 1.12. In a dip-slip fault, the
slippage occurred along the dip of the fault, Figure – 1.12(a) and (b). In case of a
strike-slip fault, the movement has taken place along the strike, Figure 1.12(c). The
movement occurs diagonally across the fault plane in case of an oblique slip fault,
Figure 1.12(d). Based on relative movement of the hanging and foot walls faults are
classified into normal, reverse and wrench faults. In a normal fault, the hanging wall
has been displaced downward relative to the footwall, Figure 1.12(a). In a reverse
fault, the hanging wall has been displaced upward relative to the footwall, Figure
1.12 (b). In a wrench fault, the foot or the hanging wall do not move up or down in
9. 9
relation to one another, Figure 1.12 (c). Thrust faults, which are a subdivision of
reverse faults, tend to cause severe earthquakes.
Faults are nucleating surfaces for seismic activity. The stresses accumulated due to
plate movement produces strain mostly along the boundary of the plates. This
accumulated strain causes rupture of rocks along the fault plane.
1.6. Elastic Rebound theory
As the plate try to move relative to each other, strain energy gets built up along the
boundaries. When the stress buildup reaches the ultimate strength of rock, rock
fractures and releases the accumulated strain energy, Figure 1.13. The nature of
failure dictates the effect of the fracture. If the material is very ductile and weak,
hardly any strain energy could be stored in the plates due to their movement. But if
the material is strong and brittle, the stress built up and subsequent sudden rupture
releases the energy stored in the form of stress waves and heat. The propagation of
these elastic stress waves causes the vibratory motion associated with earthquakes.
Figure 1.13 Elastic rebound across a fault.
The region on the fault, where rupture initiates is known as the focus or hypocenter
of an earthquake. Epicenter is the location on the earth surface vertically above the
focus. Distance from epicenter to any place of interest is called the epicentral
distance. The depth of the focus from the epicenter is the focal depth. Earthquakes
are sometime classified into shallow focus, intermediate focus and deep focus
earthquakes based on its focal depth. Most of the damaging earthquakes are
shallow focus earthquakes.
After rupture
Fault
Fault
Unstressed
Stressed
Elevation
A`
A`
A`
10. 10
1.7. Earthquakes
Figure 1.14 General depiction of an earthquake rupture scenario.
Earthquake is the vibration of earth’s surface caused by waves coming from a
source of disturbance inside the earth (refer Figure 1.14). Most earthquakes of
engineering significance are of tectonic origin and is caused by slip along geological
faults.
The typical characteristics of earthquake depends on
1. Stress drop during the slip
2. Total fault displacement
3. Size of slipped area
4. Roughness of the slipping process
5. Fault shape( Normal fault, Reverse fault, Strike slip fault)
6. Proximity of the slipped area to the ground surface
7. Soil condition
As the waves radiate from the fault, they undergo geometric spreading and
attenuation due to loss of energy in the rocks. Since the interior of the earth consists
of heterogeneous formations, the waves undergo multiple reflections, retraction,
dispersion and attenuation as they travel. The seismic waves arriving at a site on the
surface of the earth are a result of complex superposition giving rise to irregular
motion
Buildings
Continental crust
Surface waves
Earthquake
focus
11. 11
1.8. Earthquake Waves
Earthquake vibrations originate from the point of initiation of rupture and propagates
in all directions. These vibrations travel through the rocks in the form of elastic
waves. Mainly there are three types of waves associated with propagation of an
elastic stress wave generated by an earthquake. These are primary (P) waves,
secondary (S) waves and surface waves. In addition, there are sub varieties among
them. The important characteristics of these three kinds of waves are as follows:
1.8.1. Primary (P) Waves
These are known as primary waves, push-pull waves, longitudinal waves,
compressional waves, etc. These waves propagate by longitudinal or compressive
action, which mean that the ground is alternately compressed and dilated in the
direction of propagation, Figure 1.15. P waves are the fastest among the seismic
waves and travel as fast as 8 to 13 km per second. Therefore, when an earthquake
occurs, these are the first waves to reach any seismic station and hence the first to
be recorded. The P waves resemble sound waves because these too are
compressional or longitudinal waves in nature. Hence, the particles vibrate to and fro
in the direction of propagation (i.e. longitudinal particle motion). These waves are
capable of traveling through solids, liquids and gases.
Figure 1.15 Nature of propagation of P waves.
The P-waves propagates radial to the source of the energy release and the velocity
is expressed by
(1 )
(1 )(1 2 )
p
E
V
−ν
=
ρ + ν − ν (1.1)
where E is the Young’s modulus; ν is the Poisson’s ratio (0.25); and ρ is the density.
1.8.2. Secondary (S) Waves
These are also called shear waves, secondary waves, transverse waves, etc.
Compared to P waves, these are relatively slow. These are transverse or shear
waves, which mean that the ground is displaced perpendicularly to the direction of
propagation, Figure 1.16. In nature, these are like light waves, i.e., the waves move
perpendicular to the direction of propagation. Hence, transverse particle motion is
characteristic of these waves. These waves are capable of traveling only through
solids. If the particle motion is parallel to prominent planes in the medium they are
12. 12
called SH waves. On the other hand, if the particle motion is vertical, they are called
SV waves. The shear wave velocity is given by
2 (1 )
s
E G
V = =
ρ +ν ρ (1.2)
where
2(1 )
E
G =
+ν
is the shear modulus.
Figure 1.16 Nature of propagation of S waves.
They travel at the rate of 5 to 7 km per second. For this reason these waves are
always recorded after P waves in a seismic station.
1.8.3. Surface Waves
When the vibratory wave energy is propogating near the surface of the earth rather
than deep in the interior, two other types of waves known a Rayleigh and Love
waves can be identified. These are called surface waves because their journey is
confined to the surface layers of the earth only. Surface waves travel through the
earth crust and does not propagate into the interior of earth unlike P or S waves.
Surface waves are the slowest among the seismic waves. Therefore, these are the
last to be recorded in the seismic station at the time of occurrence of the earthquake.
They travel at the rate of 4 to 5 km per second. Complex and elliptical particle
motion is characteristic of these waves. These waves are capable of travelling
through solids and liquids. They are complex in nature and are said to be of two
kinds, namely, Raleigh waves and Love waves.
(a) (b)
Figure 1.17 Nature of propagation of (a) Rayleigh waves and (b) Love Waves
(from http://earthquake.usgs.gov)
The Rayleigh surface waves are tension-compression waves similar to the P-waves
expect that their amplitude diminishes with distance below the surface of the ground.
Similarly, the Love waves are the counterpart of the “S” body waves; they are shear
waves that diminishes rapidly with distance below surface, Figure 1.17.
13. 13
The damage and destruction associated with earthquakes can be mainly attributed
to surface waves. This damage potential and the strength of the surface waves
reduce with increase in depth of earthquakes.
1.9. Earthquake Terminology
The motion of plates results in stress buildup along plate boundaries as well as in
interior domain of the plate. Depending on the state of buildup of stress and amount
of resistance offered by the fault strata, rupture is initiated as stress exceeds the
capacity of the strata. Generally, the rupture causing earthquakes initiates from a
point, termed as hypocenter or focus, which subsequently spreads over to a large
area. Depending on the characteristics of strata where rupture occurs, the shape of
the ruptured area could be highly irregular and the amount of interface slip along the
ruptured surface could also vary. Several terms associated with earthquake
rupture/propagation are discussed given below:
Figure 1.18 Various distance measurements associated with earthquake.
The place of origin of the earthquake in the interior of the earth is known as focus or
origin or centre or hypocenter (refer Fig. 1.18). The place on the earth's surface,
which lies exactly above the centre of the earthquake, is known as the 'epicenter'.
For obvious reasons, the destruction caused by the earthquake at this place will
always be maximum and with an increasing distance from this point, the intensity of
destruction also decreases. The point on earth's surface diametrically opposite to the
epicenter is called the anti-center. An imaginary line which joins the points at which
the earthquake waves have arrived at the earth's surface at the same time is called a
'co-seismal'. In homogeneous grounds with plain surfaces, the iso-seismals and co-
seismals coincide. Of course, in many cases due to surface and subsurface
irregularities, such coincidence may not occur.
SITE
EPICENTRAL DISTANCE
FOCALDEPTH
FOCUS OR HYPOCENTER
HYPOCENTRAL
DISTANCE
EPICENTER
14. 14
Figure 1.19 Schematic of a
seismograph [Source: IIT-K
BMTPC Eq Tips – 02].
1.10. Recording Earthquakes [Murty, 2005]
The vibratory motion produced during an earthquake could be measured in terms of
displacement, velocity or acceleration. A seismologist is interested in even small
amplitude ground motions (in terms of
displacement) that provides insight into the wave
propagation characteristics and enables him to
estimate the associated earthquake parameters.
As accelerations are the causative phenomena
for forces that damage structures (Force = mass
x acceleration), engineers are more concerned
with the earthquake causing structural damage,
hence are interested in acceleration
measurement.
The instruments measure the ground
displacements and are called seismographs.
The record obtained from a seismograph is
called a seismogram.
The seismograph has three components – the sensor, the recorder and the timer.
The principle on which it works is simple and is explicitly reflected in the early
seismograph – a pen attached at the tip of an oscillating simple pendulum (a mass
hung by a string from a support) marks on a chart paper that is held on a drum
rotating at a constant speed. A magnet around the string provides required damping
to control the amplitude of oscillations. The pendulum mass, string, magnet and
support together constitute the sensor; the drum, pen and chart paper constitutes the
recorder; and the motor that rotates the drum at constant speed forms the timer,
Figure 1.19. By varying the characteristics of equipment one could record
displacement, velocity or acceleration during an earthquake
The devises that measure the ground accelerations are called accelerometer. The
accelerometers register the accelerations of the soil and the record obtained is called
an accelerogram. Further discussions on accelerograms and its engineering
applications are covered in section 2.
1.11. Determination of Hypocenter or Earthquake Focus
Seismologists use the elapsed time between the arrival of a P-waves and S-waves
at a given site to assist them in estimating the distance from the site to the center of
energy release. The distance of focus from the observation station is determined by
the relative arrival times of the P and S waves. The distance from hypocenter to
observation point is given by
1 1
s p
T
S
V V
=
−
(1.3)
15. 15
where, T=difference in time of arrival of P and S waves at an observation point; S=
distance from hypocenter to observation point; and Vp and Vs are the velocity of P
and S waves, respectively.
The time T can be taken as the time of duration of the initial tremor to it built-up while
Vp and Vs are geological properties for a given locations. Thus, the distance from the
hypocenter to the observation point is approximately proportional to the time of
duration of the initial tremor; the coefficient of proportionality is about 8 km/sec.
When S has been determined for each of three observation points the hypocenter is
located as the point of intersection of these spheres.
1.12. Size of Earthquakes
The size of earthquake could be related to the damage caused or parameters like
magnitude. These two useful definitions of the size of earthquakes are sometimes
confused.
1.12.1. Intensity of Earthquakes
The intensity of an earthquake refers to the degree of destruction caused by it. In
other words, intensity of an earthquake is a measure of severity of the shaking of
ground and its attendant damage. This, of course, is empirical to some extent
because the extent of destruction or damage that takes place to a construction at a
given place depends on many factors. Some of these factors are: (i) distance from
the epicenter, (ii) compactness of the underlying ground, (iii) type of construction (iv)
magnitude of the earthquake (v) duration of the earthquake and (vi) depth of the
focus. Intensity is the oldest measure of earthquake.
The seismic intensity scale consists of a series of certain key responses such as
people awakening, movement of furniture, damage to chimneys, and finally - total
destruction. Numerous intensity scales have been developed over the last several
hundred years to evaluate the effects of earthquakes, the most popular is the
Modified Mercalli Intensity (MMI) Scale. This scale, composed of 12 increasing levels
of intensity that range from imperceptible shaking to catastrophic destruction, is
designated by Roman numerals. It does not have a mathematical basis; instead it is
an arbitrary ranking based on observed effects. The lower numbers of the intensity
scale generally deal with the manner in which the earthquake is felt by people. The
higher numbers of the scale are based on observed structural damage. An
abbreviated version of the MMI scale is given in Table 1.1 as per IS-1893:1984.
Another intensity scale is Mendvedev-Spoonheuer-Karnik scale (MSK 64). This
scale is more comprehensive and describes the intensity of earthquake more
precisely. Indian seismic zones were categorized on the basis of MSK 64 scale.
Some of the other intensity scales used are Rossi-Forel (RF) scale, Japanese
Meteorological Agency (JMA) intensity scale, etc. Figure 1.20 gives a comparison of
the various seismic intensity scales used worldwide.
An imaginary line joining the points of same intensity of the earthquake is called an
'iso-seismal'. In plan, the different iso-seismals will appear more or less as concentric
circles over a plain, homogeneous ground if the focus of the earthquake is a point.
On the other hand, if the focus happens to be a linear tract, the iso-seismals will
16. 16
occur elongated. Naturally, the areas or zones enclosed by any two successive iso-
seismals would have suffered the same extent of destruction.
Over the years, researchers have tried to develop more quantitative ways for
estimating earthquake intensity. One of such relationships correlating earthquake
intensity to peak ground velocity is given by
10
10
log 14
MMI=
log 2
gV
(1.4)
where Vg is the peak ground velocity in cm/sec.
Another such relation reported by Wald et.al, (1999) based on Californian
earthquake database is
MMI = 3.47 log(Vg) + 2.35 (1.5)
In addition to peak ground velocity, empirical relationships correlating peak ground
acceleration to MMI has also been reported. For e.g.,
MMI = 3.66 log (Peak Ground Acceleration in cm/sec/sec) – 1.66 (1.6)
17. 17
Figure 1.20 A comparison of various seismic intensity scales used worldwide.
18. 18
Table 1.1 Modified Mercalli Intensity Scale (IS-1893:1984).
MMI
Intensity
Remarks
I Not felt except by a very few under specially favourable circumstances
II Felt only by a few persons at rest, specially on upper floors of buildings; and
delicately suspended objects may swing.
III Felt quite noticeably indoors, specially on upper floors of buildings but many
people do not recognise it as an earthquake; standing motor cars may rock
slightly; and vibrations may be felt like the passing of a truck.
IV During the day felt indoors by many, outdoors by a few, at night some awakened;
dishes, windows, doors disturbed; walls make creaking sound, sensation like
heavy truck striking the building; and standing motor cars rock noticeably.
V Felt by nearly everyone; many awakened; some dishes, windows, etc, broken; a
few instances of cracked plaster; unstable objects overturned; disturbance of
trees, poles and other tall objects noticed sometimes; and pendulum clocks may
stop.
VI Felt by all, many frightened and run outdoors; some heavy furniture moved; a few
instances of fallen plaster or damaged chimneys; and damage slight.
VII Everybody runs outdoors, damage negligible in buildings of good design and
construction; slight to moderate in well built ordinary structures; and some
chimneys broken, noticed by persons driving motor cars.
VIII Damage slight in specially designed structures; considerable in ordinary but
substantial buildings with partial collapse; very heavy in poorly built structures;
panel walls thrown out of framed structures; falling of a chimney, factory stacks,
columns, monuments, and walls; heavy furniture overturned, sand and mud eject
in small amounts; changes in well water; and disturbs persons driving motor cars
IX Damage considerable in specially designed structures; well designed framed
structures thrown out of plumb; very heavy in substantial buildings with partial
collapse; building shifted off foundations; ground cracked conspicuously; and
underground pipes broken.
X Some well built wooden structures destroyed; most masonry and framed
structures with foundations destroyed; ground badly cracked; rails bent; landslides
considerable from river banks and steep slopes; shifted sand and mud; and water
splashed over banks.
XI Few, if any, masonry structures remain standing; bridges destroyed; broad
fissures in ground, underground pipelines completely out of service; earth slumps
and landslips in soft ground; and rails bent greatly.
XII Total damage; waves seen on ground surfaces; lines of sight and levels distorted;
and objects thrown upward into the air.
19. 19
1.12.2. Magnitude of Earthquake
The magnitude of an earthquake is related to the amount of energy released by the
geological rupture causing it, and is therefore a measure of the absolute size of the
earthquake, without reference to distance from the epicenter. While earthquake
intensity is depicted in Roman numerals and is always a whole number, magnitude is
depicted in Arabic numerals and need not be a whole number. Similar to intensity
scales, over the years, a number of approaches for measurement of magnitude of an
earthquake have come into existence.
1.12.3. Richter Magnitude, ML
A workable definition of magnitude was first proposed by C.F. Richter. He based on
the data from Californian earthquakes, defined the earthquake magnitude as the
logarithm to the base 10 of the largest displacement of a standard seismograph
(called Wood-Anderson Seismograph with properties T=0.8 sec; m=2800; and
damping nearly critical ≈ 0.8) situated 100 km from the focus.
10M=log A (1.7)
where A denotes the amplitude in micron (10-6
m) recorded by the instrument located
at an epicentral distance of 100 km; and M is the magnitude of the earthquake.
When the distance from the epicenter at which an observation is obtained other than
100 km, a correction is introduced to the equation as follows:
10
100
M=M -1.73log∆
∆ (1.8)
where M is the magnitude of the earthquake; ∆=distance from epicenter (km), M∆=
magnitude of the earthquake calculated for earthquake using the values measured
at a distance ∆ from the epicenter. The graphical form of this procedure is given in
Figure 1.21.
20. 20
Figure 1.21 A graphical form of the estimation of Gutenberg – Richer magnitude
[From Lay and Wallace, 1995].
Because of the logarithmic nature of the definition a difference of 1.0 in the
magnitude represents a difference of 10 in the seismograph amplitude. Magnitude
observations by different recording stations usually differ quite widely, often by as
much as one magnitude, which is later corrected taking into account the recordings
from a large number of instruments.
1.12.4. Moment magnitude
Over the years, scientists observed that different magnitude scales had saturation
points and the magnitudes estimated by different approaches did not point to a
unique value of earthquake size The Richter magnitude saturates at about 6.8, and
the surface wave magnitude at about 7.8. In addition, these magnitude estimates did
not have a linear relation with the energy released due to earthquake rupture. To
address these short falls, Hanks and Kanamori, in 1979 proposed a magnitude
scale, termed as ‘moment magnitude’, based on the seismic moment due to
earthquake rupture. The moment magnitude is given by
( )1.9log
3
2
010 −= MM w (1.9)
where Mw is the moment magnitude, M0 is the seismic moment in N-m.
In addition to the magnitude scales as discussed, Surface wave magnitude, Ms,
based on the amplitude of Rayleigh waves having a period of about 20 seconds,
body wave magnitude, Mb based on the amplitude of first few P wave cycles are also
being used.
A comparison of various magnitude scales are given in Figure 1.22. It can be noted
from Figure that the moment magnitude does not saturate.
21. 21
Figure 1.22 A comparison of different magnitude scales.
Example 1.1
Calculate the moment magnitude of an earthquake with the rupture area dimensions
of length 35km, width 15km and slip 1meter. Assume modulus of rigidity, mu = 3.5 x
1010
N/m2
Solution: Given
Length of ruptured area of fault : 35 km
Width of ruptured area of fault : 15km
Average slip : 1 m
Seismic moment = mu x Length x Widthx Slip
= 3.5 x 1010
x (35 x 1000) x (15 x 1000) x 1
= 1.84 x 1019
N-m
Earthquake magnitude, Mw = (2/3) x [log(1.84 x 1019
) – 9.1]
= 6.8
1.13. Energy of an Earthquake
An approximate relationship between surface wave magnitude, Ms, and the energy
released by an earthquake, E, is given by
10 slog E 4.8 1.5M= +
(1.10)
22. 22
where E is measured in joules. Thus the ratio of energies released by two
earthquakes differing by 1 is magnitude is equal to 31.6. The ratio is 1000 for
earthquakes differing by 2 in magnitude, Table 1.2. Comparisons have been made
between natural forces and nuclear weapons. The energy released by a 1 megaton
hydrogen bomb is roughly equivalent to a magnitude 7.4 earthquake. Figure 1.23
shows the variation of the energy released against the magnitude.
Table 1.2: Increase in Energy Release for Various Range of Increase in Value
of Magnitude
Increase in Magnitude Increase in Energy Release
0.2 2 Times
0.447 5 Times
0.67 10 Times
1 31.6 Times
2 1000 Times
4 5 6 7 8 9 10
1E10
1E11
1E12
1E13
1E14
1E15
1E16
1E17
1E18
1E19
1E20
EnergyReleased(J)
Magnitude
Figure 1.23: Energy magnitude relationships.
1.14. Comparison of Magnitude and Intensity
Comparisons between magnitude and intensity are fraught with difficulty. Firstly,
intensity varies with distance from the epicentre. Secondly, a large earthquake may
occur away from inhabited areas and therefore cause little apparent damage. Focal
depth, ground conditions and quality of building construction can have a
considerable effect on subjective assessments of damage. Magnitude-intensity
relationships are not favoured for engineering purposes. However, intensity could be
23. 23
the only information available for large historical earthquakes and the inputs from
intensity measurements would be necessary in estimating the maximum earthquake
potential of the region.
In 1956, Richter proposed a simple relationship between magnitude and epicentral
intensity given by
( ) 1
3
2
0 += IML (1.11)
The equation was derived by comparison of magnitude and epicentral intensity data
of Californian earthquakes.
This relationship could vary from region to region. For e.g., Street and Turcotte in
1977 proposed a magnitude intensity relation specific to North-eastern North
America, given by
66.1)(49.0 0 += ImbLg (1.12)
However, it is found that correlations between intensity and magnitude are not
particularly accurate for estimation of earthquake magnitude. In addition to epicentral
intensity, researchers have attempted to associate other intensity related parameters
like log of area with intensity greater than IV; log of felt area, fall off intensity, etc.,
with varying levels of success. Figure 1.24 shows a comparison of magnitudes
estimated from intensity using different approaches as mentioned above.
Figure 1.24 Correlation between earthquake magnitude and various intensity
measures. [From Reiter L., 1989].
25. 25
1.16 Tutorial Problems
1. Where do earthquakes happen?
2. Where do over 90% of earthquakes occur?
3. Why do earthquakes happen?
4. What are the formulae for P and S velocity?
5. What is an earthquake?
6. Indicate the approximate radius of the earth, inner core, and outer core.
7. How are Earthquake Magnitudes Measured?
8. What is a fault?
9. What are different types of faults?
10.What is the biggest earthquake recorded?
11.What is intensity?
12.The Mohorovicic discontinuity is the seismic boundary between
(A) Crust and mantle.
(B) Asthenosphere and lithosphere
(C) Core and mantle
(D) Mantle and lithosphere
13.Which type of seismic wave does not pass through a fluid?
(A) Surface wave
(B) Body wave
(C) S-wave
(D) P-wave
14.The size and shape of the earth's core can be measured by information from
the
(A) Earth's weight
(B) S-wave shadow zone
(C) nature of meteorites
26. 26
(D) P-wave shadow zone
15.Part of the earth's core is believed to be liquid as indicated by information
from the
(A) Nature of meteorites
(B) S-wave shadow
(C) Earth's magnetic field.
(D) P-wave shadow
16.The least dense rocks are found in
(A) Continental crust.
(B) Oceanic crust.
(C) The mantle.
(D) the core.
17.At a recording station a difference in time of arrival between P waves and S
waves was observed to be 1.5 seconds. What is the approximate distance
from the station at which the event occurred? Assume P wave velocity as 4
km/sec and S wave velocity as 2 km/sec.
18.During an earthquake the maximum amplitude recorded at a site by Wood-
Anderson Seismograph is 20 cm. The maximum ground velocity recorded
was 25 cm/sec. The site was found to be 75 km away from the epicenter.
Determine the Magnitude and Intensity of the occurred earthquake.
19.The epicentral intensity of an earthquake that occurred in 1870 is estimated to
be IX in MMI scale. Estimate the approximate magnitude of the earthquake.
20.Estimate the moment magnitude of an event with rupture length of 100km,
rupture width of 45km and slip of average fault slip of 3m. Take modulus of
rigidity, mu as 3.5 x 1010
N/m2
27. 27
1.17 Answers to Tutorial Problems
1. Earthquakes occur all the time all over the world, both along plate edges and
along faults. Most earthquakes occur along the edge of the oceanic and
continental plates. The earth's crust (the outer layer of the planet) is made up
of several pieces, called plates. Earthquakes usually occur where two plates
are running into each other or sliding past each other.
2. At plate boundaries
3. Earthquakes are usually caused when rock underground suddenly breaks
along a fault. This sudden release of energy causes the seismic waves that
make the ground shake.
4. The P-waves propagates radial to the source of the energy release and the
velocity is expressed by
(1 )
(1 )(1 2 )
p
E
V
−ν
=
ρ + ν − ν
where E is the Young’s modulus; νis the Poisson’s ratio (0.25); and ρis the
density.
The shear wave velocity is given by
2 (1 )
s
E G
V = =
ρ +ν ρ
where
2(1 )
E
G =
+ν
is the shear modulus
5. Earthquake is the vibration of earth’s surface caused by waves coming from a
source of disturbance inside the earth. Most earthquake of engineering
significance is of tectonic origin and is caused by slip along geological faults.
6. The average thickness of crust beneath continents is about 40km where as it
decreases to as much as 5km beneath oceans. Mantle is a 2900 km thick
layer. The mantle consists of 1) Upper Mantle reaching a depth of about 400
km made of olivine and pyroxene and 2) Lower Mantle made of more
homogeneous mass of magnesium and iron oxide and quartz. Core has a
radius of 3470 km and consists of an inner core of radius 1370 km and an
outer core (1370 km < R<3470 km).
7. The magnitude of most earthquakes is measured on the Richter scale,
invented by Charles F. Richter in 1934. The Richter magnitude is calculated
from the amplitude of the largest seismic wave recorded for the earthquake,
no matter what type of wave was the strongest. The Richter magnitudes are
based on a logarithmic scale (base 10).
28. 28
8. A fault is a fracture or zone of fractures between two blocks of rock. Faults
allow the blocks to move relative to each other. Faults may range in length
from a few millimeters to thousands of kilometers.
9. During an earthquake, the rock on one side of the fault suddenly slips with
respect to the other. The fault surface can be horizontal or vertical or some
arbitrary angle in between. Earth scientists use the angle of the fault with
respect to the surface (known as the dip) and the direction of slip along the
fault to classify faults. Faults which move along the direction of the dip plane
are dip-slip faults and described as either normal or reverse, depending on
their motion. Faults which move horizontally are known as strike-slip faults
and are classified as either right-lateral or left-lateral. Faults which show both
dip-slip and strike-slip motion are known as oblique-slip faults
10.The largest earthquake to occur in the twentieth century is the 1960 Chilean
earthquake, which occurred off the coast of South America. The magnitude of
this earthquake has been estimated to be a 9.5. The earthquake created a
deadly tsunami more than 10 m in height along the Chile coast, eliminating
entire villages. Some hours later, the tsunami killed hundreds more in Japan,
more than 13000 km from the earthquake source.
11.Of the two ways to measure earthquake size, magnitude is based on
instrumental readings and intensity is based on qualitative effects of
earthquakes.
12. Ans: A, Ugoslavian scientist Mohorovicic in 1909 discovered the boundary
between the crust and the mantle. The boundary is a zone where seismic P-
waves increase in velocity because of changes in the composition of the
materials.
13.Ans: C, S-wave cannot because you can compress a fluid (P-wave) but you
cannot shear a fluid (S-wave).
14. Ans: D, Seismic P-waves spread throughout the earth from a large
earthquake. These waves are measured by seismic recording stations all
around the world except between 103o and 142o of arc from the earthquake.
This is the P-wave shadow zone,
15.Ans: B, The S-wave shadow zone is formed because S-waves cannot travel
through the earth's core. This, and other seismic data indicate that the outer
part is liquid, or at least it acts like a liquid.
16.Ans: A, continental crust.
17.Given
Vp = 4000m/sec, Vs = 2000m/sec
T = 1.5 sec
Distance = 1.5 / { (1/2000) – (1/4000) }
= 6000m = 6km.
18.Solution: Given Data
29. 29
A=20 cm = 0.2 m = 0.2×106
micron
∆=75km
Vg=25 cm/sec
The magnitude of the earthquake
6
10 10
100
M = log (0.2 10 ) - 1.73log
75
×
= 5.1
The intensity of the earthquake
10
10
log 14 25
MMI =
log 2
×
= 8.45 (say VIII)
19.Solution: Given Data
Epicentral Intensity, I0 = IX.
Equivalent earthquake magnitude = (2/3) I0 +1
= (2/3) * 9 + 1 = 7
20.Solution: Given Data
Fault length = 35km = 35 x 1000 m
Fault width = 15km = 15 x 1000 m
Slip = 1m
Seismic moment = 3.5 x 1010
x 35 x 1000 x 15 x 1000 x 1 = 1.84 x 1019
N-m
Moment magnitude = (2/3)(log10(1.84 x 1019
) – 9.1) = 6.8