Engineering geology

ENGINEERINGGEOLOGY:
Engineering geology is the application of the geological
sciences to engineering study for the purpose of assuring
that the geological factors regarding the location, design,
construction, operation and maintenance
of engineering works are recognized and accounted
for. Engineering geologists provide geological and
geotechnical recommendations, analysis, and design
associated with human development and various types of
structures. The realm of the engineering geologist is
essentially in the area of earth-structure interactions, or
investigation of how the earth or earth processes impact
human made structures and human activities.
Engineering geology studies may be performed during the
planning, environmental impact analysis, civil or structural
engineering design, value engineering and construction
phases of public and private works projects, and during
post-construction and forensic phases of projects. Works
completed by engineering geologists include; geological
hazard assessments, geotechnical, material
properties, landslide and slope
stability, erosion, flooding, dewatering,
and seismic investigations, etc. The principal objective of
the engineering geologist is the protection of life and
property against damage caused by various geological
conditions.
ATMOSPHERE:
The atmosphere of Earth is the layer
of gases surrounding the planet Earth that is retained by
Earth's gravity. The atmosphere protectslife on Earth by
absorbing ultraviolet solar radiation, warming the surface
through heat retention (greenhouse effect), and reducing
temperature extremes between day and night (the diurnal
temperature variation.
Principal layers
In general, air pressure and density decrease with altitude
in the atmosphere. However, temperature has a more
complicated profile with altitude, and may remain
relatively constant or even increase with altitude in some
regions (see the temperature section, below). Because the
general pattern of the temperature/altitude profile is
constant and recognizable through means such as balloon
soundings, the temperature behavior provides a useful
metric to distinguish between atmospheric layers. In this
way, Earth's atmosphere can be divided (called
atmospheric stratification) into five main layers. Excluding
the exosphere, Earth has four primary layers, which are the
troposphere, stratosphere, mesosphere, and
thermosphere.[7]
From highest to lowest, the five main
layers are:
Exosphere: 700 to 10,000 km (440 to 6,200 miles)
Thermosphere: 80 to 700 km (50 to 440 miles)[8]
Mesosphere: 50 to 80 km (31 to 50 miles)
Stratosphere: 12 to 50 km (7 to 31 miles)
Troposphere: 0 to 12 km (0 to 7 miles)[9]
Earth's atmosphere Lower 4 layers of the atmosphere in
3 dimensions as seen diagonally from above the exobase.
Layers drawn to scale, objects within the layers are not to
scale. Aurorae shown here at the bottom of the
thermosphere can actually form at any altitude in this
atmospheric layer
The Different Levels of the Atmosphere are:
Troposphere: This is the lowest atmospheric layer and is
about seven miles (11 km) thick. Most clouds and weather
are found in the troposphere. The troposphere is thinner at
the poles (averaging about 8km thick) and thicker at the
equator (averaging about 16km thick). The temperature
decreases with altitude.
Stratosphere: The stratosphere is found from about 7 to 30
miles (11-48 kilometers) above the Earth’s surface. In this
region of the atmosphere is the ozone layer, which absorbs
most of the harmful ultraviolet radiation from the Sun. The
temperature increases slightly with altitude in the
stratosphere. The highest temperature in this region is
about 32 degrees Fahrenheit or 0 degrees Celsius.
Mesosphere: The mesosphere is above the stratosphere.
Here the atmosphere is very rarefied, that is, thin, and the
temperature is decreasing with altitude, about –130
Fahrenheit (-90 Celsius) at the top.
Thermosphere: The thermosphere starts at about 55
kilometers. The temperature is quite hot; here temperature
is not measured using a thermometer, but by looking at the
motion and speed of the rarefied gases in this region,
which are very energetic but would not affect a
thermometer. Temperatures in this region may be as high
as thousands of degrees.
Exosphere: The exosphere is the region beyond the
thermosphere.
Ionosphere: The ionosphere overlaps the other atmospheric
layers, from above the Earth. The air is ionized by the
Sun’s ultraviolet light. These ionized layers affect the
transmittance and reflectance of radio waves. Different
ioniosphere layers are the D, E (Heaviside-Kennelly), and
F (Appleton) regions. The ionosphere is a region of the
atmosphere that is ionized by solar radiation. It is
responsible for auroras. During daytime hours, it stretches
from 50 to 1,000 km (31 to 621 mi; 160,000 to
3,280,000 ft) and includes the mesosphere, thermosphere,
and parts of the exosphere. However, ionization in the
mesosphere largely ceases during the night, so auroras are
normally seen only in the thermosphere and lower
exosphere. The ionosphere forms the inner edge of
the magnetosphere. It has practical importance because it
influences, for example, radio propagation on Earth.
The ozone layer is contained within the stratosphere. In
this layer ozone concentrations are about 2 to 8 parts per
million, which is much higher than in the lower
atmosphere but still very small compared to the main
components of the atmosphere. It is mainly located in the
lower portion of the stratosphere from about 15–35 km
(9.3–21.7 mi; 49,000–115,000 ft), though the thickness

varies seasonally and geographically. About 90% of the
ozone in Earth's atmosphere is contained in the
stratosphere.
The ionosphere is a region of the atmosphere that is
ionized by solar radiation. It is responsible for auroras.
During daytime hours, it stretches from 50 to 1,000 km (31
to 621 mi; 160,000 to 3,280,000 ft) and includes the
mesosphere, thermosphere, and parts of the exosphere.
However, ionization in the mesosphere largely ceases
during the night, so auroras are normally seen only in the
thermosphere and lower exosphere. The ionosphere forms
the inner edge of the magnetosphere. It has practical
importance because it influences, for
example, radio propagation on Earth.
HYDROSPHERE
A hydrosphere is the total amount of water on a planet.
The hydrosphere includes water that is on the surface of
the planet, underground, and in the air. A planet's
hydrosphere can be liquid, vapor, or ice. On Earth, liquid
water exists on the surface in the form of oceans, lakes
and rivers. It also exists below ground—as groundwater,
in wells and aquifers. Water vapor is most visible
as clouds and fog. The frozen part of Earth's hydrosphere
is made of ice: glaciers, ice caps and icebergs. The frozen
part of the hydrosphere has its own name,
the cryosphere. Water moves through the hydrosphere in a
cycle. Water collects in clouds, then falls to Earth in the
form of rain or snow. This water collects in rivers, lakes
and oceans. Then it evaporates into the atmosphere to start
the cycle all over again. This is called the water cycle.
Approximately 75% of the Earth's surface,an area of some
361 million square kilometers (139.5 million square
miles), is covered by ocean. The average salinity of the
Earth's oceans is about 35 grams of salt per kilogram of
sea water
LITHOSPHERE
The internal structure of the earth
Although we can't see into the earth, and the deepest drill-
hole is only 13 km, we have a
reasonably good picture of its internal structure and
composition. Firstly, we can observe
material which has been pushed up to surface from great
depth - including parts of the ocean
floor, and kimberlitic material from deep within the
mantle3, the rocks in which diamonds are found.
Secondly, we can observe meteorites, most of which are
thought to be parts of broken up planets or planetesimals
(little planets). Most importantly, however, we can study
and understand seismic waves.
Seismic waves are physical disturbances in a body of rock
- caused by earthquakes or artificial
explosions - which travel through the rock like a wave
across a body of water. They are divided
into two types:
P (Primary, compressional or push) waves - like a coil
spring (or slinky)
S (Secondary or shear) waves - like a piece of rope which
has been flicked
Wave velocity depends on density and elasticity of the
rock. Seismic wave velocities generally
increase with depth because density and elasticity of the
rocks increase with depth. There are also some velocity
anomalies related to temperature variations and
compositional differences.
Some of these are discussed below.
P-waves are faster then S-waves4. P-waves will travel
through a liquid, while S-waves will not.

All waves are bent (refracted) at a boundary between rocks
of different composition or physical state (e.g., solid
versus liquid).
Some important discoveries about the internal
characteristics of the earth were made in the early 1900's.
For one thing, it was noted that S waves from a large
earthquake could not be detectedbeyond 103° away from
the source. This was interpreted as indicating that at least
part of the core must behave as a liquid . While P-waves
are transmitted through a liquid medium, there is also a P-
wave shadow zone extending from 103 to 143° away from
the source of a seismic event. Based on an understanding
of the refraction of seismic waves, this is also consistent
with the idea that part of the core is liquid. Another
important discovery based on seismic data was that there is
a significant difference in the seismic velocity - and hence
geological properties - between the crust and the
underlying
material (the mantle). Measurements made at different
distances from earthquake epicentres showed that seismic
waves that travelled downward, and then were refracted
laterally actually moved more quickly than those that just
travelled laterally. The dividing line between the crust and
the mantle is known as the Mohoroviçic Discontinuity, or
Moho
The crust is approximately 5 km thick under the oceans
and 30 to 60 km thick on the continents.
The average global thickness is about 20 km, which
represents 0.3% of the total radius of the
earth. This is roughly equivalent to the thinnest layer of
skin on the outside of an onion.
The mantle has a total thickness of 2885 km and comprises
more than 80% of earth's volume
(the upper part has the composition of the rock peridotite -
which includes the minerals olivine
and pyroxene). The temperature increases towards the base
of the mantle, but not as much as expected - so we
conclude that there must be convection within the mantle
to transmit some of
the internal heat out towards the surface. It is assumed,
therefore, that the mantle behaves in a
'plastic' way. We know that it is essentially solid because it
can transmit S-waves, but it will
'flow' in response to long-term stress. The uppermost 100
km of the mantle is solid, and this zone, along with the
crust, is known as the lithosphere. The lithosphere does not
participate in the convection, and thus the temperature
gradient in this zone is quite steep. Immediately below the
lithosphere - from 100 km to 200 km - there is a layer of
partial melting - also called the low velocity zone because
seismic waves are slowed within it As we will see later,
the existence of this partially liquid layer is important to
the mechanics of plate tectonics. The low-velocity zone
makes up part of the asthenosphere5 that is a relatively
mobile part of the mantle. The core has a total radius of
3486 km- and although itcomprises only one-sixth of the
volume of the earth, it represents almost one third of its
mass. It is predominantly made up of
metallic iron along with some nickeland smaller
amounts of sulphur and oxygen - the proportion of iron
increasing towards the centre. The outer
core is liquid, while the inner core (which is actually
hotter) is solid. This apparent anomaly can be explained
partly by the differences in their composition, but mostly
by the difference inpressure. The pressure within the inner
core is too great for it to part of the core is in motion - and
it is this motion - of a material that conducts electricity -
that gives the earth its magnetic field.Seismologists
continue to study data from both natural and man-made
seismic events using
increasingly sensitive instruments and sophisticated data
processing methods. With the type of information now
available it is possible to generate three-dimensional
models of the temperature variations within the mantle.
The results provide evidence of where hot material is
moving upward from the lower mantle, and where
relatively cool material is moving down.
ORIGIN OF EARTH
Earth, along with the other planets, is believed to have
been born 4.5 billion years ago as a solidified cloud of dust
and gases left over from the creation of the Sun. For
perhaps 500 million years, the interior of Earth stayed
solid and relatively cool, perhaps 2,000°F. The main
ingredients, according to the best available evidence, were
iron and silicates, with small amounts of other elements,
some of them radioactive. As millions of years passed,
energy released by radioactive decay—mostly of uranium,
thorium, and potassium—gradually heated Earth, melting
some of its constituents. The iron melted before the
silicates, and, being heavier, sank toward the center. This
forced up the silicates that it found there. After many
years, the iron reached the center, almost 4,000 mi deep,
and began to accumulate. No eyes were around at that time
to view the turmoil that must have taken place on the face

of Earth—gigantic heaves and bubblings on the surface,
exploding volcanoes, and flowing lava covering
everything in sight. Finally, the iron in the center
accumulated as the core. Around it, a thin but fairly stable
crust of solid rock formed as Earth cooled. Depressions in
the crust were natural basins in which water, rising from
the interior of the planet through volcanoes and fissures,
collected to form the oceans. Slowly, Earth acquired its
present appearance.
There are various scientific theories of origin and
evolution of the earth
Nebular Hypothesis
Planetesimal Hypothesis
Gaseous Tidal Hypothesis
Binary Star Hypothesis
Gas Dust Cloud Hypothesis
Nabular Hypothesis
German philosopher, Kant and French mathematician,
Laplace
Earth, planets and sun originated from Nebula.
Nebula was large cloud of gas and dust. It rotates slowly.
Gradually it cooled and contracted and its speed increased.
A gaseous ring was separated from nebula
Later the ring cooled and took form of a planet
On repetition of the process all other planets came into
being
The central region, nebula became sun.
Objections:
Sun should have the greatest angular momentum because
of its mass and situated in the center,however, it has only
two percent of momentum of the solar system
How the hot gaseous material condensed in to rings
Planetesimal Hypothesis
Chamberlin and Moulton proposed the theory in 1904
The sun existed before the formation of planets
A star came close to the sun.
Because of the gravitation pull of the star, small gaseous
bodies were separated from the sun
These bodies on cooing became small planet's
During rotation the small planets collided and form planets
Objections:
The angular momentum could not be produced by the
passing star.
The theory failed to explain how the planetesimals had
become one planet
Gaseous Tidal Theory
Jeans and Jeffrey proposed the theory in 1925
Large star came near the sun. Due to gravitational pull a
gaseous tide was raised on the surface of the sun.
As the star came nearer,the tide increased in size.
Gaseous tide detached when star move away.
The shape of the tide was like spindle.
It broke into pieces-forming nine planets of the solar
system
Binary Star Hypothesis
The idea was developed by Lyttleton in 1938. Before the
formation of planets, the sunhad a companion star.
Another star passed close to these double stars and
dragged thecompanion star away. A gaseous filament was
torn from the companion star and itremained close to the
sun. The planets were originated from this gaseous
filament inthe same way as described in the gaseous tidal
hypothesis.
The Dust-Cloud Hypothesis
The universe contains huge clouds made up of very large
amounts of dust and
gas. About 6,000,000,000 (billion) years ago, one of these
clouds began to condense.Gravitation--the pull that all
objects in the universe have for one another--pulled the
gasand dust particles together. As the dust cloud
condensed, it began to spin. It spun fasterand faster and
flattened as it spun. It became shaped like a pancake; that
is thick at thecenter and thin at the edges. The slowly
spinning center condensed to make the sun.But the outer
parts of the pancake, or disk, were spinning too fast to
condense in one piece. They broke up into smaller swirls,
or eddies, which condensed separately to make the planets.
The forming sun and planets were made up mostly of gas.
They contained much more gas than dust. The earth was
far bigger than it is now and probably weighed 500 times
as much. The large body of dust and gas forming the
suncollapsed rapidly to a much smaller size. The pressure
that resulted from the collapsecaused the sun to become
very hot and to glow brightly. The newly born sun began
toheat up the swirling eddy of gas and dust that was to
become the earth. The gasexpanded, and some of it flowed
away into space. The dust that remained behind
thencollected together because of gravity. Although the
shrinking earth generated a lot ofheat, most of this heat
was lost into space. Therefore, the original earth was most
likely solid, not molten. This hypothesis was developed by
a scientist, Harold C. Urey in 1952.It is also known as the
Urey's hypothesis. He showed that methane, ammonia, and
water are the stable forms of carbon, nitrogen, and oxygen
if an excess of hydrogen is present. Cosmic dust clouds,
from which the earth formed, contained a great excess of
hydrogen.
rocks of different types
Igneous Rocks
Igneous rocks are crystalline solids which form directly
from the cooling of magma. This is an exothermic process
(it loses heat) and involves a phase change from the liquid
to the solid state. The earth is made of igneous rock - at
least at the surface where our planet is exposed to the
coldness of space. Igneous rocks are given names based
upon two things: composition (what they are made of) and

texture (how big the crystals are).Igneous rocks are formed
when melted rock cools and solidifies. Minerals
crystallise and interlock as the melt cools and solid rock
forms. Eventually the entire melt forms a cool solid rock
composed of crystals with no open spaces and usually
showing no preferred grain alignment. The rock may be
entirely composed of one mineral but is usually made of
several mineral types. The composition and range of types
of minerals is determined by the magma. The size of the
crystals is determined by the cooling history. In general,
slow cooling will result in large crystals forming while
rapid cooling will produce smaller crystals. Very rapid
cooling may result in non-crystalline glass forming as part
of or even all of the rock. If some slow cooling is followed
by rapid cooling a fine grained rock with a scattering of
larger crystals, called a porphyry, can result Melted rock
may come in the form of magma, when it is found
underneath the Earth’s surface. It can also come in the
form of lava, when it is released unto the Earth’s surface
during a volcanic eruption. Magma can be intruded into
other rocks within the crust or it can be erupted onto the
surface. Intrusive igneous rocks, sometimes called plutonic
rocks, are often coarse grained while the extrusive igneous
rocks erupted or extruded at a volcano are often fine
grained. When erupted magma flows across the landscape
it is called lava.
Some examples of igneous rocks are granite, scoria,
pumice, and obsidian.
Pumice, for instance, is formed when lava made up of
melted rock, water, and trapped gas is ejected from a
volcano during a violent eruption. As the ejected material
undergoes very rapid cooling and depressurization, some
of the trapped gas escape, leaving holes and gas bubbles
on the solidified material.
Sedimentary Rocks
In most places on the surface, the igneous rocks which
make up the majority of the crust are covered by a thin
veneer of loose sediment, and the rock which is made as
layers of this debris get compacted and cemented together.
Sedimentary rocks are called secondary, because they are
often the result of the accumulation of small pieces broken
off of pre-existing rocks. There are three main types of
sedimentary rocks:
Clastic: your basic sedimentary rock. Clastic sedimentary
rocks are accumulations of clasts: little pieces of broken up
rock which have piled up and been "lithified" by
compaction and cementation.
Chemical: many of these form when standing water
evaporates, leaving dissolved minerals behind. These are
very common in arid lands, where seasonal "playa lakes"
occur in closed depressions. Thick deposits of salt and
gypsum can form due to repeated flooding and evaporation
over long periods of time.
Organic: any accumulation of sedimentary debris caused
by organic processes. Many animals use calcium for shells,
bones, and teeth. These bits of calcium can pile up on the
seafloor and accumulate into a thick enough layer to form
an "organic" sedimentary rock.
Sedimentary rocks form from sediments deposited from
water or air. Each grain in the rock was originally separate
from all the others. When it stopped moving it settled
down, touching severalother grains but leaving pores
spaces between the grains in places where they cannot
touch. Compaction under the weight of the accumulating
sediments may have distorted soft grains, reduced the
porosity and increased the cohesion between grains.
Minerals precipitating out of watery solution filling the
pores may have formed a cement, further securing the
minerals to each other to form a solid rock. Common
sedimentary rocks include sandstone, mudstone,
conglomerate and limestone. Grains in a sedimentary rock
can be either distinct minerals or fragments of rocks.
Either way,they have usually been sourced from the
weathering and erosion of other rocks. Grain shape can be
very angular or very rounded or anywhere in between.
They can also vary from rod-like to platy to spherical.
Some sedimentary processes form homogeneous grain
assemblages while others result in much more variable
groupings. Grain size and grain type are used to further
classify sedimentary rocks .Sedimentary rocks start
forming when soil and other materials on the Earth’s
surface are eroded and finally settle down, forming one
layer of sediments. As time passes,more and more
materials get eroded and settle on the older layers. Thus,
layer upon layer is formed. The lower layers undergo
intense pressure due to the weight of the upper layers,
eventually evolving into rocks.
Some examples of sedimentary rocks are sandstone,
limestone, shale, conglomerate, and gypsum.
Metamorphic Rocks
The metamorphic get their name from "meta" (change) and
"morph" (form). Any rock can become a metamorphic
rock. All that is required is for the rock to be moved into
an environment in which the minerals which make up the
rock become unstable and out of equilibrium with the new
environmental conditions. To metamorphose or simply to
morph means ‘to change in form’. Metamorphic rocks are
actually products of rocks that have undergone changes.
Thus, a metamorphic rock may have originally been an
igneous, sedimentary, or even another metamorphic rock.
The changes occur when the original rocks are subjected to
extreme heat and pressure beneath the Earth’s surface.
They may also occur when the original rocks are caught in

the middle of two colliding tectonic boundaries. Without
actually melting, some mineral assemblages redistribute
the elements within the starting minerals to form new
suites of minerals that are more stable at the new pressures
and temperatures. Metamorphic rocks formed from
magmatic intrusions heating country rock (the cool rock
around the magma) are called thermal or contact
metamorphic rocks. Metamorphic rocks resulting from
wide spread temperature and pressure changes caused by
tectonic processes are called regional metamorphic rocks.
In most cases, this involves burial which leads to a rise in
temperature and pressure. The metamorphic changes in the
minerals always move in a direction designed to restore
equilibrium. Common metamorphic rocks include slate,
schist, gneiss, and marble.
Earthquake
Body waves = seismic vibrations that move through the
Earth's interior. They are classified into:
Primary waves or P waves: push-pull waves, waves move
back and forth in the direction in which the wave is
travelling. Change both volume and shape of material in
which they pass. Affect and can pass through solids,
liquids, and gasses (as they all exhibit resistance to change
in volume). Also calledLongitudinal Waves= wave motion
(amplitude) is parallel to direction of travel, e.g. accordion
motion, to and from.
Secondary waves or S waves = vibrations occurring at
right angles to direction of wave propagation. They are
shake-waves (shear waves), vibrating side-to-side. They
are not as fast as P-waves and result in changing only
shape of material they travel through. Affect and can pass
through only solid materials (only solids offer resistance to
change in shape). Also called Transverse Waves = wave
motion (amplitude) is perpendicular to direction of travel,
e.g. spring bobbing, up and down.
Aftershocks = smaller earthquakes that occur after the
main earthquake in the same place as the mainshock.
Aftershocks are linked to the size of the mainshock and if
this is large can continue for many weeks,months or years.
Earthquake = shaking or slipping movement of the earth’s
crust, followed by seismic waves and vibrations.
Earthquake Fault = earthquake faults are fractures where
displacement is on either side relative to one another and
parallel to the fracture.
Epicentre = the point on the Earth's surface vertically
above the focus of an earthquake, i.e. directly above the
true centre of the seismic disturbance from which the
shock waves of an earthquake seem to radiate. The
epicentre usually registers the strongest shaking.
Fault = a crack in the Earth’s crust along which the rocks
slide. Faults are found at the edges of the plates where the
crust is moving in different directions.
Fault plane = the planar (flat) surface along which two
blocks of the earth's crust suddenly slip past one another
during an earthquake
Focus = the point inside the Earth where the rock breaks
off and pressure is released, The focus point generally
occurs 45 miles below the ground.
Focal depth of an earthquake = the depth of the hypocentre
below the Earth's surface.
Foreshocks = these are smaller earthquakes in the same
area as the following larger earthquake. Until the larger
earthquake hits scientists are unable to predict if they are
foreshocks.
Hypocentre = the location below the Earth’s surface where
an earthquake rupture begins.
Magnitude = a number that categorizes the amount of
energy released during an earthquake.
Mainshock = the largest, main earthquake.
Plate tectonics = plate tectonics are the science of the
process where rigid plates move across hot molten
material. It helps explain the formation of mountains and
the distribution of earthquakes and volcanoes.
Richter Scale = the magnitude of seismic energy released
during an earthquake is measured by the Richter scale. A
quake magnitude is determined by measuring the
amplitude of the largest wave recorded on the seismogram.
The larger the amplitude,the greater is the displacement
of the recording pen and the greater the earthquake.
plate tectonic concept

QUESTION BANK
1. define: atmosphere, ozone depletion, green
house effect, petrology, metamorphism,
Tsunami, Seismology, body waves, epicenter,
focus, crystallography, clastic, extrusive, fault,
mineralogy
2. what is plate tectonic?
3. what are the effects of earthquakes?
4. what are igneous ,sedimentary and
metamorphic rocks?
5. how are the 3 types of rocks formed ?
6. differentiate between 3 types of rocks.
7. explain the different layers of atmosphere
8. write the theories on which evolution of
earth depends
9. what are requirements for mineral
composition of rocks?(write in brief)
10. differentiate between the following:
 extrusive and intrusive rocks
 intensity and magnitude
 clastic and chemical
 lava and magma
 erosion and weathering
 mantle and core
 atmosphere and biosphere
 epicenter and hypocenter
 aftershock and foreshocks
 p-waves and s-waves
note: no need to learn the exact text ...u can write
the answers in your own language. write all
answers in brief.
**** refer question 3 from internet
****refer contribution of engineering geology in
civil engineering.

Folding and faulting in the
Earth's crust
Diastrophicprocesses - folding and faulting
occurwhen pressure deep within the
lithosphere cause the earth=s surface to
buckle, bend and even split apart.
Folding - when the earth=s crust is pushed up
from its sides
- occurs at a very slow rate
- Fold mountains occurwhere the crust
is pushed up as plates collide which
causes the crust to rise up in folds.
Examples: Andes, Himalayas, Juras in
Switzerland, Appalachians
Types of Folds 1. Anticline- the peak or
hill of folded rock layers
2. Syncline - the trough or
valley of folded rock layers
3. Tightfold - a sharp-
peaked anticline fold
4. Overfold - bending or
warping of folding rock layers
5. Recumbentfold - a fold
that is bent so much that it is no longer
vertical.
6. Nappe- a fold that has
overturned so much the
rock layers have fractured.
Faulting - when tension and compression
associated with plate movement is so
great that blocks of rock fracture or
break apart.
- process canoccurvery rapidly
- this rapid movement causes the
ground to shake and vibrate, resulting in
earthquakes.
Types of Faults 1. Normal- rocks move
away from each other due
to land moving apart.
2. Rift valley/graben -two
normal faults occur
parallel to each other and
the land sinks between the
two faults
3. Reverse Fault - opposite
of normal; rocks are
compressed suchthat one
plate moves up while the
other decends below it
4. Horst - land rises
between parallel faults.
5. Tear fault/strike-slip -
two plates slide laterally
past each other.
Figure 1:
Topographic relief of the Earth's terrestrial surface
and ocean basins. Ocean trenches and the ocean floor have
the lowest elevations on the image and are colored dark
blue. Elevation is indicated by color. The legend below

shows the relationship between color and elevation.
(Source: National Geophysical Data Center, NOAA).
The topographic map illustrated in Figure 1
suggests that the Earth's surface has been
deformed. This deformation is the result of
forces that are strong enough to move ocean
sediments to an elevation many
thousands meters above sea level. This
displacement of rock can be caused
by tectonic plate movement and subduction,
volcanic activity, and intrusive igneous
activity.
Deformation of rock involves changes in the
shape and/or volume of these substances.
Changes in shape and volume occurwhen
stress and strain causes rock to buckle and
fracture or crumple into folds. A fold can be
defined as a bend in rock that is the response
to compressional forces. Folds are most
visible in rocks that contain layering. For
plastic deformation of rockto occura number
of conditions must be met, including:
 The rock material must have the ability to
deform under pressure and heat.
 The higher the temperature of the rock the
more plastic it becomes.
 Pressure must not exceed the internal strength
of the rock. If it does, fracturing occurs.
 Deformation must be applied slowly.
A number of different folds have been
recognized and classified by geologists. The
simplest type of fold is called a monocline
(Figure 2). This fold involves a slight bend in
otherwise parallel layers of rock.
Figure 2: Monocline fold.
(Source:PhysicalGeography.net)
Figure 2: Monocline fold.
An anticline is a convex up fold in rock that
resembles an arch-like structure with the rock
beds (or limbs) dipping way from the center
of the structure (Figure 3).
Figure 3: Anticline fold
center of the fold and are roughly symmetrical. (Source:Physica
Figure 3: Anticline fold.
A syncline is a fold where the rock layers are
warped downward (Figure 4 and 5). Both
anticlines and synclines are the result of
compressional stress.
Figure 4:
Syncline fold. Note how the rock layers dip toward the
center of the fold and are roughly symmetrical.
Figure 4: Syncline fold.

Figure 5:
Synclinal folds in bedrock, near Saint-Godard-de-
Lejeune, Canada. (Source:Natural Resources Canada).
More complex fold types can develop in
situations where lateral pressures become
greater. The greater pressure results in
anticlines and synclines that are inclined and
asymmetrical (Figure 6).
A recumbent fold develops if the center of the
fold moves from being once vertical to a
horizontal position (Figure 7). Recumbent
folds are commonly found in the core
of mountain ranges and indicate that
compressionand/or shear forces were stronger
in one direction. Extreme stress
and pressure can sometimes cause the rocks to
shear along a plane of weakness creating a
fault. We call the combination of a fault and a
fold in a rock an overthrust fault.
Faults form in rocks when the stresses
overcome the internal strength of the rock
resulting in a fracture. A fault can be defined
as the displacement of once connected blocks
of rock along a fault plane. This can occurin
any direction with the blocks moving away
from each other. Faults occurfrom both
tensional and compressionalforces. Figure 8
shows the location of some of the major faults
located on the Earth.
Figure 8:
Location of some of the major faults on the Earth. Note
that many of these faults are in mountainous regions.
There are several different kinds of faults.
These faults are named according to the type
of stress that acts on the rockand by the
nature of the movement of the rock blocks
either side of the fault plane. Normal faults
occurwhen tensional forces act in opposite
directions and cause one slab of the rock to be
displaced up and the other slab down (Figure
9).
Reverse faults develop when compressional
forces exist (Figure 10). Compressioncauses
one block to be pushed up and over the other
block.
Figure 9:
Animation of a normal fault.

Figure 10:
Animation of a reverse fault.
(Source: PhysicalGeography.net)
A graben fault is produced when tensional
stresses result in the subsidenceof a block of
rock. On a large scale these features are
known as Rift Valleys (Figure 11).
A horst fault is the development of two
reverse faults causing a block of rock to be
pushed up (Figure 12).
Figure 11:
Animation of a graben fault.
(Source: PhysicalGeography.net)
Figure 12:
Animation of a horst fault.
The final major type of fault is the strike-slip
or transform fault. These faults are vertical in
nature and are produced where the stresses are
exerted parallel to each other (Figure 13). A
well-known example of this type of fault is
the San Andreas Fault in California.
Folds and faults have an economic
importance. Anticlines and horsts are good
sites for oil accumulation forming oil
reservoirs whereas synclines and grabens are
suitable for water accumulation
forming aquifers or groundwater basins.
Faults represent a weak zone so they should
be avoided or put in mind in any civil
constructions. Also, faults as a weak zone are
suitable for upward leakage of either lava
forming sills or dykes
or groundwater forming springs.
Folding and faulting reflect the effect of the
internal energy of the earth. Consequently, the
criteria of folding and faulting represent a
kind of eath's ability for stability.

Engineering geology

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