Two separate seismograph stations receive indication of an earthquake in the for

Question

Two separate seismograph stations receive indication of an earthquake in the form of a wave traveling to them in a straight line from the epicenter and shaking the ground at their locations. Station B is 50 due east of station A. The epicenter is located due north of station A and 30 north of due west from station B. Determine the distance from the epicenter to A. Determine the distance from the epicenter to B. Station C is located an additional 10 east of B. At what angle does C report the direction of the epicenter to be?

Explanation / Answer

You can't determine the distance to the epicenter given only one time. You need the difference in P- and S-wave travel times to determine the distance. Otherwise, all that you'd know is that the ground shook. Could have been a mile away, could have been 100 miles away. P-waves travel anywhere between ~1 and ~14 km/sec, while the S-waves are the slower ones, 1 to 8 km/sec. This in mind, given *only* a single 1:40... you can do a distance = rate * time D = (14 km/s) * (100 s) D = 1,400 km or D = (1 km/s) * (100 s) D = 100 km That's a pretty broad range of distances that does not help you one bit. You're missing data that you need. HOWEVER!!! If you mean to indicate that there's a difference of 100s between P- and S-wave arrival time, you would do this: distance from earthquake * ( 1/ (S-wave speed) - 1 / (P-wave speed) ) Then use average values for P-wave and S-wave travel times of 3.45 km/s (S-wave) and 8 km/s (P-wave).

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