Download The Northridge Earthquake

MONTEREY PENINSULA COLLEGE
GEOLOGY 2
HOMEWORK: DETERMINE THE EPICENTER OF THE 1994 NORTHRIDGE EARTHQUAKE
Seismic waves, felt as the shaking motion when an earthquake occurs, are generated when energy is released during an
earthquake. The difference in time is takes for the two primary types of seismic body waves—P waves and S waves—to
travel to and be recorded by a seismometer, is used to determine where the epicenter of the earthquake is located. Primary
waves (P waves) travel faster than secondary waves (S waves), therefore the P waves will arrive at a recording station first.
First, visit http://www.sciencecourseware.com/VirtualEarthquake/VQuakeExecute.html, read each web page carefully,
and determine the epicenter for at least one earthquake in one of the four regions. Attach a print-out of your
epicenter triangulation page and Richter magnitude confirmation page to this homework. (You may also apply for a
Certificate of Completion as a Virtual Seismologist.)
Next: View Figures 1 through 3 (attached), and carefully read instructions below.
To use a seismogram (the picture generated by a seismograph) to calculate the distance between the recording
station and the epicenter of an earthquake:
a) Identify the first arrival of the P waves (the first appearance of a wave image; Figure 1);
b) Identify the first arrival of the S waves (when the wave image is amplified; Figure 1);
c) Measure the lag time (∆T) between the P and S wave arrivals in seconds (ts - tp);
d) Find the distance (D) that corresponds to that lag time using a travel-time curve (Figure 2); or use the following equation:
D = ∆T/(1/vs – 1/vp),
Where D = distance, ∆T = the lag time, vs = the speed of the S wave in the crust, and vp = the speed of the P wave in the crust;
e) Using a compass, draw a circle with a radius equal to D and its center at the seismic station that recorded the P and S
waves; and,
f) Repeat steps (a) through (e) for at least 2 more stations, and you will have “triangulated” the location of the earthquake
epicenter.
1.
Complete the following table using steps a, b, and c (above).
Station
Code
tp (seconds)
ts (seconds)
∆T (ts – tp)
Distance (km)
Barrett Dam
BAR
35
64
29
245
Goldstone
GSC
Needles
NEE
Pasadena
PAS
Pinion Flat
PFO
Seven Oaks Dam
SVD
Victorville
VTV
2.
Using the data from the table above and following steps d, e, and f, determine the epicenter location of the 1994
Northridge earthquake in latitude and longitude (plot it on Figure 3).
3.
Is the earthquake’s epicenter located on one of the major faults shown in Figure 3?