example, about 60 tourists and park employees drowned but few large animals. Three
elephants were seen fleeing to higher ground. On closer inspection, the elephants with
tracking collars appeared to have exhibited normal movements for the day. If indeed animals
sense danger from earthquakes or tsunamis, scientists do not know what it is they could be
sensing, but they would like to find out.
Lesson Summary
- Seismologists use seismograms to determine how strong an earthquake is, how far away
it is, and how long it lasts. - Epicenters can be calculated using the difference in the arrival times of P-and S-waves
from three seismograms. - The intensity of an earthquake can be determined in many ways. The Mercalli Scale
identifiesthedamagedoneandwhatpeoplefeel,theRichterScalemeasuresthegreatest
amplitude of the earthquake, and the moment magnitude scale measures the total
energy released by an earthquake. - Despite some successes, seismologists have not come too far in their ability to predict
earthquakes.
Review Questions
- How can a seismograph measure ground shaking if all parts of it must be attached to
the ground? - On a seismogram, which waves arrive first, second, third and which arrive last?
- What information is needed for seismologists to calculate the distance that a seismic
station is from an earthquake’s epicenter? - If a seismogram records P-waves and surface waves but not S-waves, where was the
earthquake epicenter located relative to the seismograph and why? - Like the Richter scale, the magnitude moment scale is logarithmic. What is the differ-
ence in the amount of energy released by an earthquake that is a 7.2 versus an 8.2 in
magnitude? A 7.2 versus a 9.2? - Why do you need at least three seismographs to locate an earthquake epicenter?
- While the Mercalli scale is still used for measuring earthquake magnitude, why is it
not the only scale used? Where does it fall short relative to the Richter and Moment
Magnitude scales? - Why is the moment magnitude scale thought to be more useful than the Richter scale
for measuring earthquake magnitudes? - What is the difference in energy released between a 6 and a 7 on the Richter scale?
How about a 6 and a 7 on the moment magnitude scale? - How do seismologists use earthquake foreshocks to predict earthquakes? Why are
foreshocks not always an effective prediction tool?