Earthquakes

An earthquake is…

• The shaking of the earth’s crustshaking of the earth’s crust caused by a release of energyrelease of energy.

• Earthquakes can be caused by:– 1. Eruption1. Eruption of aof a volcanovolcano– 2. Collapse of a cavern2. Collapse of a cavern– 3. Impact of a meteorite3. Impact of a meteorite– 4. Strain4. Strain built up along boundaries built up along boundaries between between

platesplates

A fault is…

• A break in the lithosphere along which

movement has occurred. Most earthquakes occur in this way.– Friction between plates prevents them from

moving, so strain builds up. The rock deforms. Eventually, the strain becomes great enough that the rock moves, and returns to normal shape. This causes an earthquake (elastic rebound theory).

• Focus: the point at which the rock first breaks and moves in an earthquake. Below the surfaceBelow the surface.

• Epicenter: the point on the earth’s surface directly above the focus.

Seismic Waves

• The energy released in an earthquake travels in waves. There are three types:

–Primary waves (P waves)

–Secondary waves (S waves)

–Surface waves (Love and Rayleigh)

Primary Waves• Called P wavesP waves

• Compression waves- squeeze and stretch rock (Push and Pull)(Push and Pull)

• Can travel through any material- solid, solid, liquids, and gasesliquids, and gases

• Travel the fastest

Secondary Waves• S waves

• Side to Side movement.

• Can travel only through solid material, not liquids or gases

• Travel a little more than half the speed of P waves

Surface Waves• Seismic waves that travel along Earth’s

Surface

• When P and S waves reach the surface, they make Surface waves

• There are two typestwo types, Love waves and Rayleigh waves

• Cause lots of damage

Measuring Earthquakes• Seismograph:

Instrument used Instrument used toto measure an measure an EarthquakeEarthquake

• Seismogram: The The paper paper record of the record of the Earthquake data Earthquake data (shaking) (shaking) is called a seismogram

The S-P Time The S-P Time Interval is theInterval is the time between time between

the start of the the start of the p wave and the p wave and the

s wave.s wave.

Locating Earthquakes

• Because P waves and S waves travel at P waves and S waves travel at different speedsdifferent speeds, the difference in their arrival times can be used to determine the DISTANCE away an earthquake occurred.

Locating Earthquakes• If you know the distance an earthquake

occurred from at least three different seismic stations, you can determine the location of the epicenter.

• Triangulation:Using theUsing the S-P S-P time interval time interval data from 3 data from 3 stationsstations to to determine the determine the epicenterepicenter

http://upload.wikimedia.org/wikipedia/commons/thumb/0/02/Epicenter_Hypocenter.png/800px-Epicenter_Hypocenter.png

Earthquake Magnitude: strength measured by the amount of released energy

•Richter Scale by Charles Richter

•Each increase in number represents 10x an increase in power.

•Example: a 4.0 is ten times stronger than a 3.0

Earthquake Hazards

• FireFire: Causes the most damage in an Earthquake, some utility lines and roads get damaged

• LiquefactionLiquefaction: When the ground turns to quicksand due to the shaking

• TsunamisTsunamis: Are caused by underwater earthquakes that make a big wave.

http://cosmos.ucdavis.edu/2002/FinalProjects/Cluster4/smith/Page%202