Earthquake

Outline

What is an Earthquake?

Cause of Earthquake

Measuring Earthquake

Earthquake’s Epicenter Located?

Size and Strength of an Earthquake Measured?

Destruction from Earthquake

Earthquake Prediction

Remedial Measures

Case Studies

Earthquakes

What Is an Earthquake?

• Focus or hypocenter is the point within Earth where the

earthquake starts.

• Epicenter is the location on the surface directly above

the focus.

An earthquake is the vibration of Earth

produced by the rapid release of energy

Focus and Epicenter

Focus, Epicenter, and Fault

•At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When a large earthquake epicenter is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.

•Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, Meteorite strike and nuclear tests.

Types Of Earth Quakes Shallow Focus EQ

Earthquakes occurring at a depth of less than 10 km are classified as 'shallow-focus' earthquakes.

Intermediate Focus EQ Those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes.

Deep Focus EQ •In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers). • These seismically active areas of subduction are known as Wadati-Benioff zones. •Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.

Cause of Earthquakes

Elastic Rebound Theory

Most earthquakes are produced by the rapid release of

elastic energy stored in rock that has been subjected to

great forces.

When the strength of the rock is exceeded, it suddenly

breaks, causing the vibrations of an earthquake.

Rupture occurs and the rocks quickly rebound to an un

deformed shape

Energy is released in waves that radiate outward from the

fault

Three Types of Faults

Strike-Slip Thrust

Normal

Slippage along a Fault

Elastic Rebound Theory

Strike-slip Fault Example

Normal Fault Example

Dixie Valley-Fairview Peaks, Nevada earthquake

December 16, 1954

Thrust Fault Example

Thrust Fault Example

Earthquake Effects - Ground Shaking

Northridge, CA 1994

Earthquake Effects - Ground Shaking

Northridge, CA 1994

Earthquake Effects - Ground Shaking

KGO-TV News ABC-7

Loma Prieta, CA 1989

Earthquake Effects - Ground Shaking

Kobe, Japan 1995

Earthquake Effects - Ground Shaking

Kobe, Japan 1995

Earthquake Effects - Surface Faulting

Landers, CA 1992

Earthquake Effects - Liquefaction

Source: National Geophysical Data Center

Niigata, Japan 1964

Earthquake Effects - Landslides

Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989

Source: National Geophysical Data Center

Earthquake Effects - Fires

KGO-TV News ABC-7

Loma Prieta, CA 1989

Earthquake Effects - Tsunamis

Photograph Credit: Henry Helbush. Source: National Geophysical Data Center

1957 Aleutian Tsunami

Margalla Tower,Islamabad

Total Slip in the M7.3 Landers Earthquake

Rupture on a Fault

Depth Into the

earth

Surface of the earth

Distance along the fault plane

100 km (60 miles)

Slip on an earthquake fault

START

Slip on an earthquake fault Second 2.0

Slip on an earthquake fault Second 4.0

Slip on an earthquake fault Second 6.0

Slip on an earthquake fault Second 8.0

Slip on an earthquake fault Second 10.0

Slip on an earthquake fault Second 12.0

Slip on an earthquake fault Second 14.0

Slip on an earthquake fault Second 16.0

Slip on an earthquake fault Second 18.0

Slip on an earthquake fault Second 20.0

Slip on an earthquake fault Second 22.0

Slip on an earthquake fault Second 24.0

Causes • While most earthquakes are caused by

movement of the Earth's tectonic plates.

• Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides.

• Violent Volcanic eruptions may cause E.Q.

• If ,Meteorite strikes the earth.

• While most earthquakes are caused by movement of the Earth's tectonic plates, human activity can also produce earthquakes. Four main activities contribute to this phenomenon: storing large amounts of water behind a dam (and possibly building an extremely heavy building), drilling and injecting liquid into wells, and by coal mining and oil drilling.

• Perhaps the best known example is the 2008 Sichuan earthquake in China's Sichuan Province in May; this tremor resulted in 69,227 fatalities and is the 19th deadliest earthquake of all time. The Zipingpu Dam is believed to have fluctuated the pressure of the fault 1,650 feet (503 m) away; this pressure probably increased the power of the earthquake and accelerated the rate of movement for the fault.

• The greatest earthquake in Australia's history is also claimed to be induced by humanity, through coal mining. The city of Newcastle was built over a large sector of coal mining areas. The earthquake has been reported to be spawned from a fault that reactivated due to the millions of tonnes of rock removed in the mining process.

Bigger Faults Make Bigger Earthquakes

1

10

100

1000

5.5 6 6.5 7 7.5Magnitude

Kilo

me

ters

8

Bigger Earthquakes Last a Longer Time

1

10

100

5.5 6 6.5 7 7.5 8

Magnitude

Seconds

What Controls the Level of Shaking?

• Magnitude More energy released

• Distance Shaking decays with distance

• Time Span How long E.Q stays in a locality

• Local soils/rock conditions Amplify the shaking

M5

M6

M7

Cause of Earthquakes

• An aftershock is a small earthquake that

follows the main earthquake. Continuing

adjustment of position results in aftershocks.

• A foreshock is a small earthquake that often

precedes a major earthquake.

Aftershocks and Foreshocks

Earthquake Waves

Measuring Earthquakes

Seismographs are

instruments that

record earthquake

waves.

Seismograms are

traces of amplified,

electronically

recorded ground

motion made by

seismographs.

Seismograph

At convergent boundaries, focal depth increases along a

dipping seismic zone called a Benioff zone

Seismotectotics Seismotectonics is the study of the relationship between the earthquakes, active tectonics and individual faults of a region. It seeks to understand which faults are responsible for seismic activity in an area by analyzing a combination of regional tectonics, recent instrumentally recorded events, accounts of historical earthquakes and geomorphologic evidence. This information can then be used to quantify the seismic hazard of an area.

Measuring Earthquakes

What are Seismic Waves? Response of material to the arrival of energy fronts

released by rupture

Body Waves: P and S waves

Surface Waves: R and L waves

Body Waves: P and S waves

• Body waves

– P or primary waves

• fastest waves

• travel through solids, liquids, or gases

• compressional wave, material movement is in the same direction as wave movement

– S or secondary waves

• slower than P waves

• travel through solids only

• shear waves - moves material perpendicular to wave movement

Surface Waves: R and L waves

• Surface Waves

– Travel just below or along the ground’s surface

– Slower than body waves; rolling and side-to-side

movement

– Especially damaging to buildings

Seismic wave behavior

– P waves arrive first, then S waves, then L and R

– Average speeds for all these waves is known

– After an earthquake, the difference in arrival times at a

seismograph station can be used to calculate the distance

from the seismograph to the epicenter.

How is an Earthquake’s Epicenter Located?

How is an Earthquake’s Epicenter Located?

Earthquake Distance

• Travel-time graphs from three or more

seismographs can be used to find the

exact

location of an earthquake epicenter.

• A circle where the radius equals the

distance to the epicenter is drawn.

• The intersection of the circles locates

the epicenter

• The epicenter is located using the

difference in the arrival times between P

and S wave recordings, which are related

to distance.

• About 95 percent of the major

earthquakes occur in a few narrow

zones.

Earthquake Direction

Earthquake Zones

Locating an Earthquake

The farther away a seismograph is from the focus of an earthquake,

the longer the interval between the arrivals of the P- and S- waves

How is an Earthquake’s Epicenter Located?

Earthquake Distance

• Travel-time graphs from three or more

seismographs can be used to find the

exact

location of an earthquake epicenter.

• A circle where the radius equals the

distance to the epicenter is drawn.

• The intersection of the circles locates

the epicenter

• The epicenter is located using the

difference in the arrival times between P

and S wave recordings, which are related

to distance.

• About 95 percent of the major

earthquakes occur in a few narrow

zones.

Earthquake Direction

Earthquake Zones

How is an Earthquake’s Epicenter Located?

Material P wave Velocity (m/s) S wave Velocity (m/s)

Air 332

Water 1400-1500

Petroleum 1300-1400

Steel 6100 3500

Concrete 3600 2000

Granite 5500-5900 2800-3000

Basalt 6400 3200

Sandstone 1400-4300 700-2800

Limestone 5900-6100 2800-3000

Sand (Unsaturated) 200-1000 80-400

Sand (Saturated) 800-2200 320-880

Clay 1000-2500 400-1000

Glacial Till (Saturated) 1500-2500 600-1000

Size and Strength of an Earthquake

Measured?

Historically, scientists have used two different

types of measurements

intensity

magnitude

How are the Size and Strength of an Earthquake Measured?

• Modified Mercalli Intensity Map

– 1994 Northridge, CA earthquake,

magnitude 6.7

• Intensity

– subjective

measure of the

kind of damage

done and

people’s

reactions to it

– Iso-seismal lines

identify areas of

equal intensity

Modified Mercalli Scale I. Instrumental Not felt except by a very few under especially favorable conditions.

II. Feeble Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects

may swing.

III. Slight Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not

recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a

truck. Duration estimated.

IV. Moderate Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors

disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars

rocked noticeably. Dishes and windows rattle.

V. Rather Strong Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects

overturned. Clocks may stop.

VI. Strong Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books

off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.

VII. Very Strong Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to

moderate in well-built ordinary structures; considerable damage in poorly built or badly designed

structures; some chimneys broken. Noticed by persons driving motor cars.

VIII. Destructive Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial

collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments,

walls. Heavy furniture moved.

IX. Ruinous General panic; damage considerable in specially designed structures, well designed frame structures

thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off

foundations.

X. Disastrous Some well built wooden structures destroyed; most masonry and frame structures destroyed with

foundation. Rails bent.

XI. Very Disastrous Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.

XII. Catastrophic Total damage - Almost everything is destroyed. Lines of sight and level distorted. Objects thrown into the

air. The ground moves in waves or ripples. Large amounts of rock may move.

How are the Size and Strength of an Earthquake Measured?

• Magnitude

– Richter scale

measures total

amount of energy

released by an

earthquake;

independent of

intensity

– based on Amplitude

of the largest wave

produced by an

event is corrected

for distance and

assigned a value on

an open-ended

logarithmic scale

Each unit of Richter magnitude equates to

roughly a 32-fold energy increase

Does not estimate adequately the size of very large earthquakes

Size and Strength of an Earthquake Measured?

Momentum Magnitude

• Derived from the amount of displacement that occurs along the fault zone

• Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes.

• Measures very large earthquakes

(surface area of fault) x (avg. displacement along fault) x (rigidity of rock)

Earthquake Magnitudes

Some Notable Earthquakes

TSUNAMI A tsunami (plural: tsunamis or tsunami; from Japanese: , lit. "harbor

wave" English pronunciation: or also called a tsunami wave train, and

at one time incorrectly referred to as a tidal wave, is a series of water

waves caused by the displacement of a large volume of a body of water,

usually an ocean, though it can occur in large lakes.

Causes Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides and other mass movements, meteorite ocean impacts or similar impact events, and other disturbances above or below water all have the potential to generate a tsunami.

Some meteorological conditions, such as deep depressions that cause tropical cyclones, can generate a storm surge, called a meteo-tsunami, which can raise tides several meters above normal levels. The displacement comes from low atmospheric pressure within the centre of the depression. As these storm surges reach shore, they may resemble (though are not) tsunamis, inundating vast areas of land.

There have been studies and at least one attempt to create tsunami waves as a weapon. In World War II, the New Zealand Military Forces initiated Project Seal which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.

If the first part of a tsunami to reach land is a trough—called a drawback—rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas. A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave's period. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.

Intensity scales The first scales used routinely to measure the intensity of tsunami

were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and

the Imamura-Iida intensity scale, used in the Pacific Ocean.

The latter scale was modified by Soloviev, who calculated the

Tsunami intensity I according to the formula

I= ½ + Log2 H av

where H is the average wave height along the nearest coast. This

scale, known as the Soloviev-Imamura tsunami intensity scale, is used

in the global tsunami catalogues compiled by the NGDC/NOAA and

the Novosibirsk Tsunami Laboratory as the main parameter for the

size of the tsunami.

Magnitude scales The first scale that genuinely calculated a magnitude for a

tsunami, rather than an intensity at a particular location was

the ML scale proposed by Murty & Loomis based on the

potential energy.

Difficulties in calculating the potential energy of the tsunami

mean that this scale is rarely used.

Abe introduced the tsunami magnitude scale , calculated

from,

Mt= a log h + b log R = D

where h is the maximum tsunami-wave amplitude (in m)

measured by a tide gauge at a distance R from the epicenter,

a, b & D are constants used to make the Mt scale match as

closely as possible with the moment magnitude scale.

The Economics and Societal Impacts of EQs

Damage in Oakland, CA, 1989

• Building collapse

• Ground failure / Liquefaction

• Tsunami

• Fire

Seismic Vibrations

Destruction from Earthquakes

The damage to buildings and other structures

from earthquake waves depends on

several factors.

the intensity

duration of the vibrations

the nature of the material on which the

structure is built

the design of the structure.

Significant Causes of Infrastructure Damage

Engineered

(Institutional Buildings)

• Quality of construction and construction materials

• Lack of seismic considerations

• Lack of monitoring

• Building codes

• Governance weakness

Non-Engineered

(Private Buildings/Homes)

• Lack of awareness about seismically resistant design

• Settling of structures

• Aspiration to modernize with insufficient knowledge of safe construction

• Cost

Seismic Vibrations

Destruction from Earthquakes

Liquefaction

• Saturated material turns fluid

• Underground objects may float to surface

Tsunamis: the Japanese word for “seismic sea wave”

Destruction from Earthquakes

Cause of Tsunamis

• A tsunami triggered by an earthquake occurs where a slab

of the ocean floor is displaced vertically along a fault.

• A tsunami also can occur when the vibration of a quake

sets an underwater landslide into motion.

Although tsunamis travel quickly, there is sufficient time to

evacuate all but the area closest to the epicenter.

Other Dangers

Destruction from Earthquakes

• With many earthquakes, the

greatest damage

to structures is from

landslides and ground

subsidence, or the sinking of

the ground triggered by

vibrations.

Landslides

• In the San Francisco earthquake of 1906, most

of the destruction was caused by fires that started when gas and

electrical lines were cut.

Fire

A CO2 fire extinguisher rated for flammable liquids and gasses

A chemical foam extinguisher with contents.

A chemical foam extinguisher with contents.

water extinguisher

Can Earthquakes be Predicted?

Earthquake Prediction Programs

– include laboratory and field studies of rocks before, during,

and after earthquakes

– monitor activity along major faults

– produce risk assessments

Predicting Earthquakes

• So far, methods for short-range predictions of earthquakes have

not been successful.

Short-Range Predictions

• Scientists don’t yet understand enough about how and where

earthquakes will occur to make accurate long-term predictions.

Long-Range Forecasts

Remedial Measures

Increase public awareness about hazard risk management.

Build capacity of professionals and government officials. Safe building practices and earthquake resistant design.

Develop and enforce simple building codes for rural and peri-urban areas.

Seismic Microzonation

• Seismic microzonation is defined as the process of subdividing a potential seismic or earthquake prone area into zones with respect to some geological and geophysical characteristics of the sites such as ground shaking, liquefaction susceptibility, landslide and rock fall hazard, earthquake-related flooding, so that seismic hazards at different locations within the area can correctly be identified.

• Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damages.

• Dynamic characteristics of site such as predominant period, amplification factor, shear wave velocity, standard penetration test values can be used for seismic microzonation purpose.

• On the basis of these information, we review our construction design according to seismic hazards, and take preventive measures for stability of structures.

Earthquake Preparedness

• Earthquake preparedness refers to a variety of measures designed to help individuals, businesses, and local and state governments in earthquake prone areas to prepare for significant earthquakes.

Before Earth Quake • Retrofitting and earthquake resistant designs of new

buildings and lifeline structures (e.g. bridges, hospitals, power plants).

• We should have response doctrines for state and local government emergency services.

• We should train common people by media about Preparedness plans for E.Q.

During Earth Quake

• Drop to the ground • Take Cover by getting under a sturdy table or other piece of furniture. • Hold on until the shaking stops. • If You Are Inside • Kneel under a desk, table, or bench. If there aren’t enough sturdy pieces

of • furniture to get under, kneel next to an interior walls but away from

windows, • overhead light fixtures, and tall pieces of furniture that might fall over. • Stay under cover until the shaking stops (at least one minute). Face away • from windows, and bend your head close to your knees. • Hold on to the table leg or desk (a few inches above the ground to avoid • pinching fingers). Cover your eyes with your other hand. If your “shelter” • moves, move with it. If you don’t have a “shelter” to hang on to, clasp

your • hands on the back of your neck to protect your face.

If You Are Outside

• Move into the open, away from buildings, fences, trees, tall playground

• equipment, utility wires, and street lights.

• • Kneel or sit on the ground and cover your head and face with your

• hands.

• • Once in the open, stay there until the shaking stops.

What You Can Do After an Earthquake

• Is it safe to move in ? • Once the shaking has stopped, look around for possible hazards to determine if it is safe for you to move before getting up and helping others. If time permits and there is a small fire that can be put out

with the fire extinguisher, do that. • 2. If you are inside, decide whether to evacuate or stay put. • Any of the following require immediate evacuation. • Fire, damage to structure, a gas leak, or hazardous materials spill. • In some situations, you may choose not to evacuate or to delay

evacuation. • For example, if there is a slight shaking with no apparent damage and another hazard such as severe weather, it may be more dangerous to

move children outside. • If you smell gas or hear a blowing or hissing noise, open a window and then quickly leave with the children, and shut the gas off at the outside

main meter.

• you must evacuate immediately (because of fire, severe damage to structure, gas leak, or hazardous materials spill), check all children and adults for injuries and give first aid for injuries.

• As time permits, you may need to turn off utilities such as gas, electricity, and water.

• If electrical wires are crackling inside, shut off the gas first, then turn off the master electrical switch.

CASE STUDIES

Kashmir Earth Quake

Chile Earth Quake

Kashmir Earthquake

8th October 2005 7.6-magnitude

earthquake took place on

Saturday 8th October at

08:25 local time.

The epicentre was

Muzzaffarabad the capital

of the Pakistan

administered region of

Kashmir, 80km north-east

of Islamabad.

It was followed by 20

powerful aftershocks

How did the earthquake occur

The earthquake in

Pakistan is the result of

India's long-term,

gradual, geological

movement north into

Asia at a speed of five

centimetres a year - a

millimetre per week.

Plate Boundary ???

http://news.bbc.co.uk/1/hi/world/south_asia/4322582.stm

Discovering Earth’s Composition

Earth’s Layered Structure

Mantle

Crust • Early seismic data and drilling technology indicate that the

continental crust is mostly made of lighter, granitic rocks.

• Composition is more speculative.

• Some of the lava that reaches Earth’s surface comes from

asthenosphere within.

Core

• Earth’s core is thought to be mainly dense iron and nickel, similar

to metallic meteorites. The surrounding mantle is believed to be

composed of rocks similar to stony meteorites.

Thanks

??......