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Ch. 15 Earthquake Notes
1. An Earthquake is movement of the Earth’s crust caused by a release of energy.
2. Elastic Rebound is when the rock snaps back to its shape when the built up stress is
released.
3. Where the rock actually breaks is called the focus. The point directly above the focus
on the surface is called the epicenter.
Earthquake Faults –(See Mountain Building Notes)
Normal Fault
Reverse Fault
Strike Slip Fault
4. Earthquake energy travels in WAVES
P-Wave or Primary, travels fastest through all the Earth in a push and pull, back
and forth motion. These waves are usually not felt (6-10km/sec). Can travel thru
any material. (solid, liquid or gas)
S-Waves or Secondary waves travel at right angles to their direction in a Side to
Side motion. These waves travel only through solids. (3-6Km/sec)
L-Waves are the last and slowest (1-3km/sec). L-waves travel on the surface like
waves on water. This is called liquefaction.
5. Seismographs
Can detect and record the time, length and magnitude of an earthquake.
Three are needed to locate an epicenter.
6. A seismogram is used to measure earthquake lag time and magnitude. The time
between the arrival of the P and S wave is called Lag Time.
7. Earthquake magnitude is measured on the Richter Scale (1-10) Each step has 32X
more energy released.
8. Damage is measured on the Mercali Scale (1-12).
9. Aftershocks are smaller earthquakes that occur later in the same location.
10. Seismic sea waves caused by EQ’s are Tsunamis.