EarthquakesEarthquakes

Earth shaking Earth shaking

Basic Earthquake Words: Basic Earthquake Words: The epicenter and focusThe epicenter and focus

Forcepushing Force

pushing

Fault is a crackThat forms

Along the break

An Earthquake is thegroup of waves

that spread awayfrom the focus

Earthquakes require a brittle-solid that breaks – the lithosphereEarthquakes require a brittle-solid that breaks – the lithosphere- force builds but no shape changing shape, not plastic- force builds but no shape changing shape, not plastic- break/shatters when force large enough- break/shatters when force large enough- Earth material (rock) goes twang, energy released- Earth material (rock) goes twang, energy released

as earthquake waves as earthquake waves Lithosphere:(plate)

brittle solid,strong

earthquakes

Mantle:plastic –oozes

Outer Core:liquid

Inner Core:solid

Earthquakes Earthquakes are are

concentrated concentrated around plate around plate boundariesboundaries

Depth ofFocus:

0-70 km70-300 km300-700 km

Plates

(Garrison, 1993)

• Pressure, Primary (P) waves: - squeeze - slinky push-pull - faster than sideways wave in Earth - travels through solids and liquids - Ex: sound only pressure wave

• Sideways, Secondary (S) waves: - rope wiggle - slower than pressure wave in Earth - travels through solids, NOT liquids

• Solids transmit P and S waves - Sudden force in a solid makes P and S together, usually cannot separate - Example: smack board with hammer

Earthquakes Exist In the Form of Waves: Most expressed are P & SEarthquakes Exist In the Form of Waves: Most expressed are P & S

Actually, there are three types of Earthquake wavesActually, there are three types of Earthquake waves

P=Pressure waveSlinky push-pull,

Caterpillar scrunchFastest, 1st to arrive

S=Shear waveSideways wiggle

Slinky sideways wiggleRope wiggle

Slower, 2nd to arrive

Surface WaveOnly travels on a surface,

Maximum movement on surface,Movement decreases away

from surface, Movement disappears far enough

away from surfaceSlowest, 3rd to arrive

Causes Most of the Damage

2Flavors

OfSurfacewaves

An earthquake in lithosphere (plate) makes An earthquake in lithosphere (plate) makes P, S and Surface wavesP, S and Surface waves

that spread outward in all directionsthat spread outward in all directions

If the Earth were uniform,stronger P and S waves would

travel inside in straight linesthrough the entire Earth.

= focusSurfaceWaves

Only travel On the

surface

Seismometer Recording of an Earthquake:Seismometer Recording of an Earthquake:A record of the winners of a race with A record of the winners of a race with P arriving first, S second, Surface lastP arriving first, S second, Surface last

P & S waves P & S waves inside the Earth inside the Earth - do - do notnot travel in travel in straight lines straight lines- take different- take differentroutes routes

Can’t B

e

Observed

Explanation requiresA

Non-uniform Earth

The San Andreas Fault:Our nearest plate boundary

Lakes.Lakes.

                                                           <>

Japan’sJapan’sEarthquakesEarthquakes

The EndThe End