1. Earthquakes
Chapter 19

2. San Francisco

3. Focus vs. Epicenter Focus Epicenter
_________– where the rock breaks and seismic waves begin; can be at deep or shallow depths
_________ – point on the surface directly above the focus; usually what is used to locate the position of an earthquake
Epicenter

4. Seismic Waves Primary Secondary Surface
_______ (P) Wave – fastest, able to travel through liquids, energy travels in the same direction wave is traveling
________ (S) Wave – slower, not able to travel through liquids, energy travels at right angles to direction wave is traveling
________ (L) Wave – travels along the surface, knocks down and destabilized structures.
Secondary
Surface

5. The interior structure of the earth is determined by the pattern of seismic waves. The __________ is liquid so s-waves can not pass through.
outer core

6. The difference in arrival times between p-waves and s-waves is called __________.
lag time
The greater the lag time (shown here as the distance between the two curves) the _________ the distance away from the earthquake.
greater

7. To locate the epicenter of an earthquake, a minimum of ____ seismograph stations is needed. The location is where all circles _______.
three
intersect

9. How do we measure earthquakes
Earthquakes are measured on 2 scales
Richter Scale measures _magnitudes
Modified Mercalli Scale measures damage