## Finding Earthquake Epicenters

Yevgeniy Miretskiy and Mikhail Sabaev
*Project Java Webmaster: Glenn A. Richard*

Mineral Physics Institute

SUNY Stony Brook

### How to Use this Applet

This applet illustrates the utilization of the arrival times of P and S waves at
seismic stations to determine the location of earthquake epicenters. Since P waves travel
through the shallow parts of Earth at about 8 kilometers per second, and S waves travel at
about 5 kilometers per second, the P waves will arrive first at a seismic station after a
quake occurs. In fact, the delay time between the arrival of the P waves and the arrival
of the S waves increases with distance and can be used to compute the distance from the
event.

The distance of the epicenter form each station can be repsresented by a circle of
appropriate radius. With data from three or more stations, circles can be drawn on a map
that intersect at the epicenter.

In this version of the *Finding Earthquake Epicenters* applet, you can drag the
seismic stations to locations of your choice, and you can enter values for the S - P
arrival time delay at each station. If the three circles intersect at a point, the
location of the epicenter will be shown. If they do not meet at a point, but overlap an
area, the applet will draw three chords that join the points where each pair of circles
intersects. The epicenter will be shown at the point where the three chords intersect.
This is one method of compensating for errors in the data. If the circles neither
intersect nor overlap an area, an epicenter will not be computed. Click the *Details*
button to see the distances computed for the data. You can change the scale of the map by
entering a number in the *Scale* field.

### Mathematical Concepts

- Arc intersection
- Chords
- Compensation for errors
- Velocity

Source List for the Three Versions of Quake

Yevgevniy Miretskiy: eugene@invision.net

Mikhail Sabaev: sabaevm@ug.cs.sunysb.edu

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