Seismographic stations report the following S-wave–P-wave arrival time intervals for an earthquake: Dallas, S-P 5 3 minutes; Los Angeles, S-P 5 2 minutes; San Francisco, S-P 5 2 minutes. Use a map of the United States and the travel-time curves in Figure 13.9 to obtain a rough location for the epicenter of the earthquake.
Describe two scales for measuring the size of an earthquake. Which is the more appropriate scale for measuring the amount of faulting that caused the earthquake? Which is more appropriate for measuring the amount of shaking experienced by a particular observer?
How much more energy is released by a magnitude 7.5 earthquake than by a magnitude 6.5 earthquake?
In Southern California, a magnitude 5 earthquake occurs about once per year. Approximately how many magnitude 4 earthquakes would you expect each year? How many magnitude 2 earthquakes?
What are the fault mechanisms of earthquakes at the three types of plate boundaries?
Destructive earthquakes occasionally occur within lithospheric plates, far from plate boundaries. Why?
At a location along the boundary between the Nazca Plate and the South American Plate, the relative plate movement is 80 mm/year. The last large earthquake there, in 1880, showed a fault slip of 12 m. Should local residents begin to worry about another large earthquake?