How do you locate an earthquake epicenter/focus?

Question

How do you locate an earthquake epicenter/focus?

Answer 1

If you'd like to learn how to find the epicenter of an earthquake, Geology On-Line Labs has a great (and easy!) tutorial to teach you how:

http://nemo.sciencecourseware.org/Virtua...

Answer 2

You would have to look at the records of earthquakes in your area or the area that you are researching and see the exact points on the fault line and then graph them on a map then you can find the most likely epicenter of the next or previous earthquake

Answer 3

The difference in velocities of P (primary) and S (secondary) waves is a method used to locate the epicenter of an earthquake.

I suggest you research a bit on "seismograms" and "travel time graphs" if you want to go further in depth and understand how earthquake epicenters and focus are precisely located. The focus is located right beneath the epicenter. So if you have located the epicenter then you have found the focus as well.

Epicenters can sometimes be easily pinpointed from physical evidence. However, seismograms and travel time graphs give a more precise location.

Answer 4

First of all the focus and epicenter are not the same thing.  The focus is the location underground where the slippage that starts the earthquake occurs.  The above-ground epicenter is the point directly above the focus.

The epicenter of an earthquake can be found using the triangulation method.  Earthquakes form, among other waves, P and S waves.  P waves travel faster than S waves.  That means the greater the distance from the epicenter, the greater the time between the arrival of p waves and s waves.  To use this fact, seismologist obtain the difference in arrival times from three different monitoring stations.  They use this information to determine the distance to the epicenter.  (there are tables for this).  Then they draw a circle around one of the monitoring stations with the radius equal to the distance to the epicenter.  Then they know that the epicenter falls somewhere on that circle.  That is not very exact.  However, adding the same information from a second station will show that the two circles intercept in two locations.  Now that's quite a bit better.  By adding the info from a third station, the epicenter will be revealed by where all three circles intercept.  There will be only one point that this occurs.  That is the epicenter.