Question

Finding An Earthquake's Epicenter Lab

Introduction:
To pinpoint the epicenter, analyze the P-wave
and S-wave data recorded at seismic stations.
Analysis:
1. Obtain a map of the western hemisphere from your
teacher and mark the seismic stations listed in the table.
2. For each station, calculate and record the arrival
time differences by subtracting the P-wave
arrival time from the S-wave arrival times.
3. Use the arrival time differences and the travel-time curve to find the distance
between the epicenter and each seismic station. Record the distances.
P-wave S-wave
Arrival Arrival
Time
(PST) (PST)
Newcomb, NY
8:39:02 8:44:02
Idaho Springs, CO 8:35:22 8:37.57
Darwin, CA
8:35:38 8:38:17
4. Draw a circle around each station. Use the distance from the epicenter
as the radius for each circle. Repeat for each seismic station.
5. Identify the epicenter of the earthquake.
Thinking Critically
1. Explain why you need to find the difference in time of arrival
between P-waves and S-waves for each seismic station.
Seismic
Station
So You can
2. Identify sources of error in determining an earthquake's epicenter.
3. Explain why data from more seismic stations
would be useful for finding the epicenter.
can use
Time since earthquake occured (min)
16
15
14
13
12
11
10
9
8
96
Name Caden Homa,
Date \ \\/ 2 Hour
5
4
3
2
1
the time
Arrival
Distance
Time
from
Time Difference Epicenter
(min) (km)
min 3,300
2:39 1,450.
Typical Travel-Time Curves
S-wave curve
P-wave curve
1000 2000 3000 4000 5000
Distance from epicenter (km)

Answer 1

Determining an earthquake's epicenter involves precise measurements of the time difference between P-waves and S-waves reaching seismic stations. However, various factors introduce potential errors into this process.

Recording Accuracy Inaccuracies in noting the exact arrival times of seismic waves at stations can occur due to human error, equipment malfunctions, or signal distortions.

Even minor discrepancies in time recording can significantly impact the calculated distances.

Travel Time Curve and Wave Speed Utilizing a travel time curve, which outlines the expected time intervals for waves to reach various distances, is crucial.

Any inconsistencies or deviations from these expected values can introduce errors.

Additionally, variations in wave propagation speeds due to different types of rock or ground conditions can affect accuracy.

Propagation Speed Uncertainty The precise propagation speeds of seismic waves can vary depending on geological structures encountered.

Uncertainties in these speeds can lead to inaccuracies in calculating distances.

To enhance accuracy, data from more seismic stations are invaluable. Triangulating the epicenter using data from multiple stations creates intersecting circles of possible epicenter locations, narrowing down the actual source.

More data points enable a better defined convergence point, reducing errors and providing a more precise location of the earthquake's origin. The use of a broader network of stations aids in mitigating inaccuracies stemming from isolated recording issues at individual stations, improving the overall reliability of determining seismic event locations.