Expert Geosphere
Investigating Earthquakes

Essay/Short Answer Problems

Name_____________________________
1. What are the three most important parts of a seismogram?
 
 The three most important parts of a seismogram are:
 
                             1.the amplitude of the ground movement
                             2.the time of first P-wave arrival
                             3.the time of first S-wave arrival
 
 
2. How can you tell how far away the epicenter of an earthquake is?
 
 The difference in arrival times indicates how far away the epicenter is located. This is because P-waves propagate through the Earth much faster than S-waves propagate. Note the first P-wave arrival and the first S-wave arrival
 
 
3. How are seismic waves generated?

The crust of the earth when it is subject to tectonic forces, bends slightly. But, because the crust is rigid, when the stress or pressure exceeds the strength of the rocks, the crust breaks and snaps into a new position. Vibrations called seismic waves are generated and travel both through the earth and along its surface. These seismic waves cause the movement we call earthquakes.
 

4.  What are some ways you could suggest to make buildings safer during earthquakes?

There is no known way to prevent earthquakes, but it is possible to lessen the impact. The amount of devastation from an earthquake can be greatly diminished by building structures using earthquake resistant design, making the interiors of buildings safe from falling objects, and educating people about earthquake safety.
 

5.  How is location of earthquakes similar to triangulation?  What other physical features are often measured by triangulation?

Given a single seismic station, the seismogram records will yield a measurement of the S-P time, and thus the distance between the station and the event. Multiply the seconds of S-P time by 8 km/s for the kilometers of distance. Drawing a circle on a map around the station's location, with a radius equal to the distance, shows all possible locations for the event. With the S-P time from a second station, the circle around that station will narrow the possible locations down to two points. It is only with a third station's S-P time that you can draw a third circle that should identify which of the two previous possible points is the real one.