What is an earthquake?

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Physical Geology 1330
116-S&R 1
Earthquakes
Dr. Mike Murphy
[email protected]
333-S&R-1
www.uh.edu/~mamurph2/homepage.html
What is an earthquake?
Vibration of the Earth caused by the rapid
release of energy. Often, earthquakes are
caused by slip on faults.
Elastic Rebound
1.
2.
3.
4.
Faults Move (Slip) in Two Ways:
Fault Creep – slow gradual movement. Produces small earthquakes.
Stick-Slip: Faults stay locked storing up elastic energy, then suddenly slip releasing the
stored energy. Produces large earthquakes.
Focus Epicenter –
Fault Scarp – a feature resulting from displacement of the earth’s surface due to slip
(motion) on fault.
Seismographs –
Components of a Seismograph –
Body Waves – P waves
S waves
S Waves P Waves
Speed
Amplitude
Period
Medium
Locating Earthquakes is based on the velocity difference between S waves and P
waves.
How many Seismographs do you need to locate an earthquakes epicenter?
Modified Mercalli Intensity Scale – assesses the damage of an earthquake at a specific
location. Intensity measures the damage of an earthquake – which in turn depends on:
Richter magnitude scale –
1. Determines EQ magnitude from deflections on seismographs.
2. Uses a logarithmic scale to express magnitude.
3. Scale ranges from 0.1 to 9.
4. For each increase of 1 unit in magnitude, the Shaking (wave amplitude) increases
by a factor of 10.
5. For each increase of 1 unit in magnitude, the Energy increases by a factor of 32.
Magnitude vs. Amplitude vs. Energy
Summary of Earthquake Hazards
1.
2.
3.
4.
5.
Fault Rupture
Ground Shaking
Liquefaction of Sediment
Landslides
Tsunamis
6. Dam Failure
7. Fires
In Class Video – “When the Bay Area
Quakes”
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