2. What is an Earthquake? An earthquake is the vibration of the Earth caused by a rapid release of energy. The focus is point in the Earth where the release of energy originates. The location on the surface of the Earth directly above the focus is called the epicenter.

3. An earthquake occurred on the Erie Fault 5 km below Ashtabula. Damage from the earthquake was greatest in nearby Chardon. The furthest report of shaking was recorded in Akron. Where was the earthquake's epicenter? 1.The Erie Fault 2.Ashtabula 3.Chardon 4.Akron

4. The Elastic Rebound Theory Earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to stresses. Once the strength of the rock is exceeded, it suddenly ruptures, causing the vibrations of an earthquake.

5. Fault Movement A fault is a fracture in Earth’s crust that shows evidence of movement or displacement. Movement along faults can be sideways or horizontal (strike-slip) or vertical (dip-slip) as shown here.

6. Earthquake Detection Seismographs are instruments that record earthquake waves. Essentially, a weight is suspended from a support that is attached to bedrock. When the bedrock vibrates, a pen records the earthquake on a rotating drum.

7. Seismic Records Records of the ground motion are called seismograms. These are the sheets of paper removed from the rotating drum of the seismograph.

8. Seismic Waves Seismograms reveal that there are two types of seismic waves generated by rock slippage: Surface waves travel along the Earth’s outer layer Body waves travel through the Earth’s interior. Body waves are further divided into primary and secondary waves.

9. Seismic Waves P waves are push-pull waves. P waves compress and expand in the direction the wave is traveling. S waves move up and down at right angles to their direction of travel.

10. Seismic Wave Arrivals Location: Off the coast of Central America Date: January 13, 2001 Time: 17:33:29 Magnitude: 7.1 Mw P waves arrive at the recording station first, then S waves, and finally surface waves. P waves travel about 1.7 times faster than S waves.

11. Examine the seismogram below that shows a 26-minute long record of the seismic waves from the 1906 San Francisco earthquake as it was received by a seismograph station in Germany. Approximately how much time elapsed between the arrival of the first P and S waves? 1.60 seconds 2.4 minutes 3.10 minutes 4.20 minutes

12. Locating Earthquakes The difference in velocities of P and S waves provides a method for locating the epicenter. The greater the length of the time between the first arriving P and S waves, the greater the distance the earthquake is away. In this example, an interval of 5 minutes indicates the earthquake was 3400 km away from the recorder.

13. Locating Earthquakes From the travel-time graph we get the distance to the earthquake, but how can we figure out the direction?? The precise location can be found if three seismic stations recorded the earthquake.

14. Earthquake Distributions Earthquakes occur in narrow zones marking the boundaries of the main plates. Circum-Pacific Belt Oceanic Ridge System