navi science

8/3/2019 Navi Science

1/19

` The shaking or trembling caused by the suddenrelease of energy

` Usually associated with faulting or breaking of

rocks

` Continuing adjustment of position results inaftershocks


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What is the Elastic Rebound Theory?

y Explains how energy is

stored in rocks

Rocks bend until the

strength of the rock isexceeded

Rupture occurs and

the rocks quickly

rebound to an

undeformed shape

Energy is released inwaves that radiate

outward from the fault


3/19

The Focus and Epicenter of anEarthquake

The point within

Earth where faultingbegins is the focus,

or hypocenter.

The point directly

above the focus on

the surface is the

epicenter.


4/19


5/19

Seismographsrecord earthquake

events

At convergent boundaries,

focal depth increases

along a dipping seismic

zone called a Benioffzone


6/19

Building collapse

Fire

Tsunami

Ground failure


7/19

Response of material to thearrival of energy fronts released

by rupture Two types:

Body waves

P and S

Surface waves R and L


8/19

Body waves P or primary waves

x fastest waves

x travel through solids,liquids, or gases

x compressional wave,

material movement is inthe same direction aswave movement

S or secondary waves

x slower than P waves

x travel through solids

onlyx shear waves - move

material perpendicularto wave movement


9/19

Surface Waves: R and L waves

y Surface Waves Travel just below or along the grounds surface

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

movement

Especially damaging to buildings


10/19

How is an Earthquakes Epicenter Located?

Seismic wave behavior

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

y Average speeds for all these waves is known

y 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.


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LOCATIONOF AN EPICENTER ON

MAP

Three seismograph stations

are needed to locate the

epicenter of an earthquake

A circle where the radius

equals the distance to the

epicenter is drawn

The intersection of the

circles locates the

epicenter


12/19

How are the Size andStrength of an

Earthquake Measured?

Intensity subjective measure

of the kind ofdamage done andpeoples reactionsto it

Iso seismal linesidentify areas ofequal intensity


13/19

MAGNITUDE OF EARTHQUAKE

Magnitudey Richter scale

measures total amountof energy released byan earthquake;

independent ofintensity

y Amplitude of thelargest wave producedby an event iscorrected for distanceand assigned a valueon an open-endedlogarithmic scale


14/19

amplitude, duration, anddamage increases in poorlyconsolidated rocks.

Injury and loss of life

Collapse

Road and bridge damage Lack of basic necessities

Spread of diseases

Property damage

These are the destructions

caused by by earthquakes.


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Can Earthquakes be Predicted?Can Earthquakes be Predicted?

Earthquake Precursors changes in elevation or tilting of land surface,fluctuations in groundwater levels, magneticfield, electrical resistance of the ground

seismic dilatancy model seismic gaps


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Earthquake Prediction Programs include laboratory and field studies of rocks before, during, and after

earthquakes

monitor activity along major faults

produce risk assessments


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Can Earthquakes be Controlled?Can Earthquakes be Controlled?

y Graph showing the

relationship between the

amount of waste injected

into wells per month and

the average number ofDenver earthquakes per

month

y Some have suggested

that pumping fluids into

seismic gaps will cause

small earthquakes while

preventing large ones


18/19

Steps To Control Earthquakes

1.To prevent an earthquake hazard the

building should be properly designed.

2. Do not construct houses on high risk

prone areas.

3. In case of an earthquake move out of thebuilding and came in the open but not

panic.

4. Do not use lifts in case of an

earthquake.

5. If indoors , and lying on the bed then lie

straight and cover your head with the

pillow.


19/19

Project on Earthquakes

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