Seismology: The study of earthquakes and seismic waves produced by earthquakes.
-speed and strength of seismic waves are altered by properties of the region through which they pass

Elastic Rebound Theory (H.F. Reed)
-focus (= hypocenter)
-epicenter
-strike-slip motion
-seismic creep
-frictional lock

P (compressional) - V = 4 miles sec-1
Seismic Waves Body S (shear) - V = 2 miles sec-1; do not travel through liquids
Love V = 1.5 miles sec-1
Surface Rayleigh -period and amplitude of waves vary tremendously

-Seismograph records a seismogram
-Locate epicenter by "triangulation" based on difference in arrival time of P & S waves to at least 3 seismograph stations
-Strength of Earthquake estimated by measuring its magnitude on the Richter scale.
-magnitude is a measure of the intensity of groundshaking and is logarithmic (10X more intense groundshaking in a magnitude 4 earthquake compared to a magnitude 3.0 earthquake)
-for every unit increase in the magnitude scale, there is = 30-fold increase in energy released
-m=2.0 earthquake (= 1 million per year) barely perceptible by a person standing at the epicenter
-m=7.0 - 7.3 (= 15 per year)
-m 8.0 (= 1 every 5 to 10 years)

95% of the energy released by earthquakes is concentrated along plate edges:
-divergent zones: small, shallow earthquakes
-convergent zones: small to large quakes ranging from shallow to great (700 km) depths
-transform boundaries: small to large quakes at shallow depths

Seismic waves are used to determine the location and thickness of Earth's layers (see diagram).
Earthquake Destruction is caused by:
-seismic vibrations
-tsunami (seismic sea waves)
-fires
-landslides and ground subsidence
-liquifaction
The amount of destruction caused by earthquakes depends on:
-magnitude of the quake
-proximity of quake to a populated area
-nature of buildings and the type of ground upon which they are built; rigid buildings and structures built on unconsolidated sediment are most susceptible to destruction.

1. Earthquake A has a Richter magnitude of 4 while earthquake B has a Richter magnitude of 7.
   a. How much more ground motion is associated with earthquake B as compared to earthquake A?
   b. Approximately how much more energy was released by earthquake B than be earthquake A?
2. What is elastic rebound theory and how is it used to explain the generation of seismic waves? What is the difference between stick-slip motion and a seismic creep?
3. Identify three types of plate boundaries and briefly describe the nature of earthquake activity (cause, relative magnitude, depth, etc.) associated with each type of boundary.
4. Why do P and S waves follow a curved rather than a straight-line path through the Earth? Use a labeled diagram to illustrate the direction of curvature for a few waves generated by an earthquake whose epicenter is at the north pole.
5. Describe what happens to both P and S waves when they encounter the core-mantle boundary. Explain why P & S waves behave like they do at this boundary.
6. Use a labeled diagram to explain how the epicenter of an earthquake is located.
7. Where and what is the low velocity zone and why is it an important part of the explanation of plate tectonics?
8. Draw a labeled cross-section of the Earth showing the crust, lithosphere, asthenosphere, upper mantle, lower mantle, core-mantle boundary, fluid outer core, solid inner core. Either draw the cross-section to scale or indicate the depth at which each of these features occurs. What are the major characteristics of each region?

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