What we will be studying today: The Earth’s structure What are Tectonic plates and what do they have to do with an Earthquake? The different types of plate boundaries. What is an Earthquake? How does it occur? How do we measure an Earthquake? Can we predict Earthquakes? What are the impacts of an Earthquake?
The Earths Structure The earth consists of several layers. The three main layers are the core, the mantle and the crust. The core is the inner part of the earth, the crust is the outer part and between them is the mantle.
Tectonic PlatesBefore we can understand Tectonic plates, lets take a look at Continental drifts: In 1912, a German scientist called Alfred Wegener proposed that South America and Africa were once joined together and had subsequently moved apart. He believed that all the continents were once joined together as one big land mass called Pangaea and this was intact until about 200 million years ago. The idea that continents are slowly shifting their positions is called continental drift.
Tectonic Plates What are Tectonic plates? the two sub-layers of the earths crust (lithosphere) that move, float, and sometimes fracture and whose interaction causes continental drift, earthquakes, volcanoes, mountains, and oceanic trenches. the two sub-layers of the earths crust (lithosphere) that move, float, and sometimes fracture and whose interaction causes continental drift, earthquakes, volcanoes, mountains, and oceanic trenches The ocean floors are continually moving, spreading from the centre and sinking at the edges. At the edges of these plates (plate boundaries) earthquakes and volcanoes occur. Convection currents in the mantle move the plates. The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.
Two Types of PlatesOceanic Plates Continental PlatesOceanic plates, as the name goes, Continental plates are crust that are crusts which carry the have continents (Large land oceans above it. It is made of masses) and some areas of lighter but denser materials than ocean on them. They are usually the continental crust. named after the continents they carry. Because they are made of lighter and less dense substances than an oceanic plate
Plate names North Eurasian AmericanPacific Pacific African South Nazca American Indo-Australian Plate Antarctic
EarthquakesWhat are they? How do they Occur? Earthquakes are vibrations caused When two blocks of rock or two by earth movements at plate plates are rubbing against each boundaries and at major fault lines other, they stick a little. They (cracks in the earth’s surface). dont just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure thats built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again.
What are the different Tectonic Plate Boundaries that cause Earthquakes?Divergent Boundaries: At divergent boundaries new crust is created as two or more plates pull away from each other. Oceans are born and grow wider where plates diverge or pull apart. As seen below, when a diverging boundary occurs on land a rift, or separation will arise and over time that mass of land will break apart into distinct land masses and the surrounding water will fill the space between them. The pressure from the break and heat from the rising lava can cause an earthquake
Why do the plates move? The plates that form the crust of the earth are floating on the molten interior of the planet, and they are constantly moving and pushing each other because of the heat escaping.
What are the different TectonicPlate Boundaries that causeEarthquakes? In plate tectonics, a convergent boundary, also known as a destructive plate boundary is an actively changing region where two (or more) tectonic plates move toward one another and collide. The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries. When two plates move towards one another, they form either a subduction zone or a continental collision.
What are the different Tectonic PlateBoundaries that can causeEarthquakes? Conservative plate margins At a conservative margin two plates try to slide past each other slowly. Quite often, the two plates stick and pressure builds up; the release of this pressure creates a severe earthquake.
How is an EarthquakeMeasured?This measures the magnitude of a tremor (how powerful itis) using an instrument called a seismograph.On the Richter Scale, magnitude is expressed in wholenumbers and decimal fractions. Although the Richter Scalehas no upper limit, the largest earthquake ever recordedwas in 1960 in Chile. It measured 9.5 on the Richter Scale.It is a logarithmic scale which means that a size ‘6’ on theRichter Scale is 10 times larger than a size ‘5’ and 100 timeslarger than a size ‘4’.The Haiti Earthquake measured 7.0 on the Richter Scale!The Christchurch Earthquake measured 6.3The earthquake in Japan measured a whopping an 8.9
Mercalli Scale The Mercalli scale measures how much damage is caused by the earthquake based on observations. It is measured on a scale between 1 and 12. Mercalli Scale
I Felt by almost no one.II Felt by very few people.III Tremor noticed by many, but they often do not realise it is an earthquake.IV Felt indoors by many. Feels like a truck has struck the building.V Felt by everyone; many people are awakened. Swaying trees and poles may be observed.VI Felt by all; many people run outdoors. Furniture is moved.VII Everyone runs outdoors. Poorly built structures considerably damaged. Slight damage elsewhere.VIII Specially designed structures damaged slightly, others collapse.IX All buildings considerably damaged, many shift off foundations. Noticeable cracks in the ground.X Many structures destroyed. Ground badly cracked.XI Almost all structures fall. Bridges wrecked.XII Total destruction. Waves seen on ground surfaces.
Can we Predict anEarthquake?YES AND Seismologists study the activity ofNO! plate boundaries and the earths crust in order to gain a better understanding of when Earthquakes will occur. Currently they are able to predict an earthquake within a decade or so, however this is not specific to year, month, day or time.
Impacts of an Earthquake?:Deaths Impact on economyInjuries Government fundingDestruction of houses Families lose everything and have toCollapsed buildings like: schools, rebuild their liveshospitals, aged care, universities, Loss of loved onesshops, skyscrapers, hotels, fire Food supply is affectedstations, police stations No electricityRoads are cracked Water supply can become contaminatedWater, sewage and storm pipes are Severe injuries can impact on andamaged individuals entire lifeElectricity and Reception poles/cables Disease outbreakare damages Not enough resources to treat the sickNatural habitat and injured Start to think about these impacts! We will look at this more in the Socio-Economic Natural Disaster Toolbox!