Earth Science
Names: _____________________________
Locating an Earthquake Epicenter
Purpose:
» to plot data and create a time-travel graph
» to learn how an earthquake epicenter is created
Background: The rocks of the lithosphere are hard and brittle. When stress builds up in the rock, it bends and
then break. When it breaks, energy is released, and waves are sent out in all directions. The place along the fault
where the earthquake occurred is known as the focus. The epicenter is the point on the surface directly above the
focus.
There are three types of earthquake waves. The P-wave, (or primary wave), is the fastest, the S-wave, (or secondary
wave), is the medium speed wave, and the L-wave, (or Long wave) is the slowest wave. Since each wave travels at a
constant speed, the longer they travel, the farther each waves gets apart from the next. (See picture 2)
Materials:
Ruler
Graph Paper
Drafting Compass
Paper Clips
Data Table:
Distance From
Epicenter in Kilometers
500 km
1000 km
1500 km
2000 km
2500 km
3000 km
3500 km
4000 km
4500 km
5000 km
5500 km
Arrival Time of the
P-wave after earthquake
1.31
2.39
3.46
4.38
5.38
6.07
6.80
7.49
8.21
8.73
9.27
minutes
minutes
minutes
minutes
minutes
minutes
minutes
minutes
minutes
minutes
minutes
Arrival Time of the
S-wave after earthquake
2.58 minutes
4.53 minutes
6.30 minutes
7.84 minutes
9.42 minutes
10.64 minutes
11.89 minutes
13.12 minutes
14.36 minutes
15.39 minutes
16.38 minutes
Difference in arrival times of
S and P waves.
(S-P Lag Time)
1.27
2.14
2.84
3.46
Questions:
1.
Describe how you determine the S-P lag time?
2.
A single seismic station can not determine the epicenter of an earthquake by itself, all it is able to
determine is:
3.
Describe how you determined how far the epicenter was located from a particular seismic station.
4.
What is the approximate location of Earthquake number 1.
5.
What is the approximate location of Earthquake number 2.
6.
Why might the circles not all cross at exactly the same point? Describe.
****Determine the locations of the earthquake epicenters using the following information****
Earthquake Number 1
City, State
S-P Lag Time
Boston, MA
5.71 minutes
Boulder, CO
2.70 minutes
Dallas, TX
3.69 minutes
Distance in Km.
Distance in cm on map
****Determine the locations of the earthquake epicenters using the following information****
Earthquake Number 2
City, State
S-P Lag Time
Boulder, CO
1.93 minutes
Phoenix, AZ
2.95 minutes
Dallas, TX
3.27 minutes
Distance in Km.
Distance in cm on map