Download - Earthquake Presentation 08 09

EarthquakesEarthquakesare the vibrationsvibrations caused by sudden

movements of Earth’s rocks.

Forces within the crust cause rocks to

bend or break.

Where do most Earthquakes occur?

12%

88% Ring of Fire

All Others

Most Earthquakes occur:

*along the “Ring of Fire”, a belt which circles the Pacific Ocean

*88% of all earthquakes occur here

Earthquake Belts

along the belts which run through» central Asia» mid-ocean ridges» Mediterranean Sea» Caribbean Sea

Each black dot represents one earthquake over a 10 year period

Earthquake Belts

*due to one or a combination of more than one of three kinds of forces:

1. tension 2. compression 3. shearing

Elastic Rebound

ForcesForces may causerock to:

1. * Fracture » breaks in rock

where no movement has occurred

ForcesForces may causerock to:

2. * Fault » fractures in rock where

movement has occurred» may occur in any direction

along the surface of the break (fault plane)

*Fault Types

»may be one of three types:

1. normal

2. reverse

3. strike-slip (transform)

Normal Fault

Normal Fault Structures

Reverse Fault

Reverse Fault Structures

Strike-slip (Transform) Fault

Strike-Slip Fault

Strike Slip Fault

ForcesForces may cause rock to:

3. *Fold » due to compression» may form one single bend (monocline)» or may form alternating ridges (anticlines)

and troughs (synclines)

monocline

anticlines

synclines

Folded Rocks

anticline

syncline

Where are the oldest rocks exposed at the surface?

Folded Rocks

monocline

rock has a gently dipping bend in the horizontal rock layer.

Seismic Waves

originate from the *focus, the actual point on the fault where movement occurs

affect the point on the earth surface directly above the focus, called the *epicenter

Seismic Waves

may be a *body wave:

1. *P- wave (primary) - rocks particles back and forth, fastest wave, first to arrive

2. *S - wave (secondary) - rocks move forward but vibrate at right angles to the direction of movement, slower than p - wave, arrives later

Seismic Waves

may be a *surface wave:

3. *L- wave (longitudinal) - vibrates the earth’s crust like an ocean wave

is the most destructive

travels very slow compared to P & S – waves

last to reach the seismic station

Seismic Waves

Earthquake DestructionDestruction

Intensityis a measure of the physical damage or geologic change

measured by the

Mercalli Scale

Magnitudeis a measure of the strength of an earthquake recorded by seismographs

measured by the

Richter Scale

How Seismographs Work

Seismograph

Richter Scale

For every increase in 1 on the Richter

Scale….

there is an increase of 32 times the

energy released!

Seismogram

P and S Wave Travel Time Curves

Use the difference in P and S wave arrival times to calculate the distance from the epicenter.

Locating Earthquakes

Station 1Station 1


Station 2


Station 3

Locating Earthquakes - Depth

Seismic Waves in the Earth

Earth’s Interior

P & S waves slow when they hit the upper mantle (asthenosphere)

speed up again when they hit the solid lower mantle

P waves are slowed and deflected when they hit the liquid outer core

Earth’s Interior

S waves do not travel through the liquid outer core

Shadow Zone results between 105o and 140o from an earthquake’s focus

Earth’s Interior

Earth’s Interior

Why is the inner core a solid?

Earth’s Interior

Crust: 3 – 60 miles thick, hard, brittle, continents are thicker than ocean

Mantle: thickest layer, denser than crust, upper mantle is plastic-like (flows under pressure)» Separated from the crust by the Moho or

Mohorovicic Discontinuity» Made of silicon, oxygen, magnesium, iron

Earth’s Interior

Core: innermost layer, made of iron and nickel

» Inner core is solid

» Outer core is liquid

Earthquake Damage

Earthquake Safety

Outdoors – move to an open area» Stay away from chimneys, buildings, trees» Stay away from beaches

Indoors » move away from windows, large objects» Seek shelter under table, desk, doorway, basement stairs» Turn off electricity, water, gas if possible

Tsunamis

Probably Caused by Submarine Landslides

Travel about 400 m.p.h.

Pass Unnoticed at Sea, Cause Damage on Shore

Tsunamis

Whether or Not Damage Occurs Depends on: » Direction of Travel » Harbor Shape » Bottom topography» Tide & Weather

Tsunamis

Satellite images from NASA show the destruction caused by a tsunami to the Indonesian province of Aceh. The left photo shows the town of Lhoknga before the tsunami hit on Dec. 24, 2004.

Tsunamis