Earthquakes

What are Earthquakes?• Earthquake - sudden movement of the ground

caused by the release of energy when the rocks move along a fault.– Fault - a break in rock where movement occurs.

Where do most earthquakes occur?

• Most earthquakes occur at plate boundaries, where there is a lot of stress.

• Some happen at fault zones

Anatomy of an earthquake

Anatomy of an Earthquake

• Focus - where the first movement occurs in the earth’s crust.

• Epicenter - point on the earth’s surface where the earthquake is felt first.

Seismic Waves

• Body waves - travel thru the earth’s interior.Includes:– P waves - primary• Fastest waves, first to be detected.•Move back and forth parallel to the

motion of the wave.•Move thru solids, liquids and gases.

– S waves - secondary• Second fastest•Move perpendicular to motion of wave.•Move only thru solids

Seismic Waves

• Surface waves - travel along the earth’s surface.–Slowest moving waves–Move rock side to side

and up and down–Cause the most

damage during earthquakes

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Seismology

• Seismology is the study of earthquakes.

• Seismograph - instrument that records seismic waves.

Earthquake ScalesMercalli Scale

a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude usually reported for an earthquake (sometimes misreported as the Richter magnitude), which is a measure of the energy released

Richter Scalea numerical scale for expressing the magnitude of an earthquake on the basis of seismograph oscillations.

Measuring Earthquakes

• Magnitude - strength of an earthquake.– Richter scale

• Intensity - how much damage an earthquake causes.– Mercalli scale