# How do you find the distance from the epicenter?

Apr 27, 2010
in
Earthquake Questions

i know how to find the time and all but i dont know how to use the earth science reference table for the epicenter

for example if the time is 1:40 seconds what is the distance from the epicenter.

can you please explain the steps? thanks

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One comment

Earth Man on April 27, 2010 at 6:33 pm

Follow me on this. 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).