Earthquakes 2015

8/19/2019 Earthquakes 2015

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Dead - More than 3,000•A report of U.S. Army

relief operations recorded:•498 deaths in San

rancisco•!4 deaths in Santa

"osa•#0$ deaths in and near

San %ose

Stanford University 1906 Earthquakedama e.


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Earthquakes

• Vibration of the Earth produced by therapid release of energy.

• ….. Massive energy!

• Earthquakes occur along plate boundaries at points called faults.

• Energy is stored in the rocks which

produces stress and strain… until the rock breaks! Releasing stored energy in the formof seismic waves.


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Earthquakes

Energy radiates out from the focus of theearthquake.

he focus is the place within the Earthwhere the rock breaks producing an

earthquake. Energy moving outward

from the focus of an earthquake travels

in the form of seismic waves.


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%tress and %train on Rock

&s we are dealing with a generally solidrigid plates we can e'pect tremendous

stress strain and tension to build up as the plates bend especially in the areas aroundthe boundary of the plates. hese stressesstrains and tensions produce stress and strain

cracks on the plates which are called faults.


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%tress and %train( Rock )ehavior

%train * the result of stress or deformation

elastic deformation * when stresses are removedrock returns to original shape

plastic deformation * permanent deformation.when stresses are removed rock stays bent

rupture * breakage and fracturing of the rockcausing an earthquake.

Brittle materials break during elastic deformation.


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%tress and %train( the forces of

the earthquake• ectonic forces apply stress to rock in three basicforms

1. ompression( pushing together or

compression!. "ension#E$tensional ( %tress that acts to

lengthen an ob+ect or pull it apart.

%. Shear#"ransform( %tress that acts parallelto a surface. ,t can cause one ob+ect to slideover another. he most general definition isthat shear acts to change the angles in an

ob+ect.


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Elastic Rebound


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%tress and %train along "aults


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%tress and %train along faults


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Stress and Strain &Energy

'eleased -hen stress and strain on certain parts of the

plates e'ceed the threshold that can besustained by the elasticity of the rocks in that

area the plate ruptures releasing strainenergy which is called an earthquake.

his energy is transmitted through the platesin the form of seismic waves heat and

sound. he amount of energy released willdetermine the magnitude or strength of theearthquake.


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"aults( rigin of the Earthquake

& fault is a large crack in the Earth#s crust where one part of the crust has moved against another part.

he parts of a fault are

/01 the fault plane/21 the fault trace

/31 the hanging wall and

/41 the footwall.


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he fault plane is

where the action is. ,t

is a flat surface thatmay be vertical or

sloping. he line it

makes on the Earth#ssurface is the fault

trace.

"aults( rigin of the Earthquake


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"ault ypeshere are three basic fault

types

1. (ormal faults form

when the hanging wall

drops down.

he forces that create

normal faults are pullingthe sides apart or

e$tensional.


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"ault ypes

here are three basic faulttypes

2. 'everse faults form

when the hanging wall

moves up.

he forces creating reverse

faults are compressional pushing the sides together.


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"ault ype%. Strike)slip faults have walls that move sideways

not up or down.hat is the slip occurs along

the strike not up or down the

dip.

,n these faults the fault plane is

usually vertical so there is no

hanging wall or footwall. he f

orces creating these faults are

lateral or hori5ontal carrying

the sides past each other.


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*+U,"S


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Faults


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6ormal "ault


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Reverse "ault


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%trike*%lip

"ault


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%trike %lip

"ault


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%trike %lip

"ault


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%eismic -aves

1. Seismic -eformation -hen an earthquake fault ruptures it causes

two types of deformation( static7 anddynamic. %tatic deformation is the

permanent displacement of the ground dueto the event.

&fter the earthquake the formerly straight

line is distorted into a shape havingincreasing displacement near the fault a process known as elastic reound.


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%eismic -aves

2. Seismic /aves he second type of deformation dynamic

motions are essentially sound waves

radiated from the earthquake as it ruptures.-hile most of the plate*tectonic energy

driving fault ruptures is taken up by static

deformation up to 089 may dissipate

immediately in the form of seismic waves.


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%eismic -aves( )ody -aves

here are two types of body waves

:*-aves or :rimary -aves

%*-aves or %econdary -aves


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:*-aves

: waves arrive first. :rimary pressure waves.

&nalogous to sound waves.

:article motion is along the direction of travel /propagation1 of the wave

i.e. longitudinal waves.

: waves can travel through solids liquids or gases.


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Earthquake Waves


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:*-ave ;otion

:ush*:ull ;otion


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%*-ave ;otion

%*shake or shear wave

% i


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%*-ave ;otion

S waves are characteri5ed by a sideways movement. he rock materialsare moved from side to side as the wave passes.

S waves are like water waves the wave pulses travel along by moving themedium from side to side. &s the pulse moves along each section ofrope moves to the side then back again in succession. Rocks are moreresistant to sideways motion so the S wave travels more slowly.


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%urface -aves

he surface waves are the slowest of the three earthquake wave types.

wo basic types of surface waves

0.


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0.


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Seismic Wave Motion


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>sing %eismic -aves to %tudy

Earth#s ,nterior

%eismic -aves travel through the entire

Earth

)oth % and : waves travel throughout the

body of the earth and can be picked up

by seismometers * machines that recordearthquakes * anywhere in the world.


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Seismic waves as $)rays to look

inside the earth

• :*-aves travel

through solid and

liquid


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• ?owever it turnsout that % waves

cannot travelthrough the coreand only : wavesare recorded in

some places(

S)/aves travel only through solids

Seismic waves as $)rays to look

inside the earth


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• %eismic waves travel

faster through denser

material.

• )ecause of this the

path traveled by a

seismic wave is bent

towards the surface.

>sing %eismic -aves to %tudy

Earth#s ,nterior


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+ i t d th


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Seismometers

• + seismometer records the

virations from

earthquakes. 2echanical

versions work y way of alarge mass3 freely

suspended.

• 4n the e$ample on the left3

a rotating drum records a

red line on a sheet of

paper. 4f the earth moves

5in this case from left to

right the whole machine

will virate too.

• 7owever3 the large mass

tends to stay still3 so the

drum shakes eneath the

pen3 recording a squiggle8


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%eismograph


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Seismographs

M i E th k


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Measuring Earthquakes

There are at least 20diferent types omeasures

3 o them are theMercalli scale, Richterscale, and theMoment Magnitudescale

Magnitude is a

measurement oearthquake strengthbased on seismicwaes and moementalong aults


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The Richter Scale

The Richter scale is a ratingof the size of seismic waves asmeasured by a particular typeof mechanical seismograph Developed in the !"#$s%ll over the world& geologistsused this for about '# years

Electric seismographseventually replaced themechanical ones used in thisscale(rovides accuratemeasurements for small&nearby earthquakesDoes not work for big& farones


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Earthquake Strength

2. he ;ercalli %cale

• ;easures the amount of damage from an

earthquake• Ranges from , to @,,

• )ased on common earthquake occurrences

such as Anoticeable by peopleA Adamage to buildingsA chimneys collapseA Afissuresopen in the groundB.

Th M lli S l


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The Mercalli Scale

Developed in the twentieth

century to rate earthquakesaccording to their intensityThe intensity of anearthquake is the strength ofground motion in a given place)s not a precise measurement

*ut& the + steps e,plain thedamage given to people& landsurface& and buildingsThe same earthquake couldhave different Mercalliratings because of thedifferent amount of damage

in different spots

-The Mercalli scale uses Roman numeralsto rank earthquakes by how much damagethey cause

The Moment Magnitude


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The Moment MagnitudeScale.eologists use this

scale today)t$s a rating system thatestimates the total energyreleased by an earthquake/an be used for any kind ofearthquakes& near or farSome news reports maymention the Richter scale&but the magnitude numberthey quote is almost alwaysthe moment magnitude forthat earthquake


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0ow Earthquakes /ause Damage

The severe shakingprovided by seismicwaves can damage ordestroy buildings andbridges& topple utilitypoles& and damage gasand water mains 1ith their side to side&up and down movement& S

waves can damage ordestroy buildings&bridges& and fracture gasmains2


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Earthquake damage in &nchorage on ;arch 2C 0D4


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"sunami -amage3leeruk3 4ndonesia


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Tsunami

Earthquakes 2015

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