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EART 10 - Geologic Principles			NAME____________________
Fall 1995
EARTHQUAKE EPICENTER
due date: November 16, 1995
	
Refer to the text (Hamblin, 7th ed.): pp. 498-501.
and appropriate pages in the Laboratory Manual (Zumberge/Rutford, 9th ed.)

YOU WILL NEED A COMPASS FOR THIS EXERCISE.

The following table gives arrival times of P and S waves from three
seismograms that recorded a magnitude 6.6 earthquake in southern California
in January 1994.  The seismic stations for each seismogram are shown on the
map on the reverse page by solid circles at Los Angeles (LA), Ventura (VEN),
and in the Mohave Desert (MD).

Station		Arrival Times		Ts-Tp		Epicentral Distance 
	P Wave (Tp)	S Wave (Ts)	(s)		D (km)

LA	8:36:09.26	8:36:15.87	__________	_______________

VEN	8:36:09.93	8:36:17.03	__________	_______________

MD	8:36:11.00	8:36:18.86	__________	_______________


PART A.	Calculate the epicentral distances (D) for each station from the
following equation.
D/Vs - D/Vp = Ts - Tp , where

	D = epicentral distance (km)
	Ts = S-Wave arrival time (s)
	Tp = P-Wave arrival time (s)
	Vs = average S-Wave velocity (3.5 km/s)
	Vp = average P-Wave velocity (6 km/s)

Show your work and put your answers in the table above.

PART B.	Plot the epicenter of the earthquake on the map on the reverse
side of this paper by drawing circles centered on the seismic stations with radii
that represent the epicentral distances.  The intersection of the three circles
defines the earthquake epicenter.  (NOTE: map scale is in miles; 1 mi = 1.61
km)

PART C.	Why is the earthquake epicenter not on a fault trace?