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
Like this post? Subscribe to my RSS feed and get loads more!
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).