Earthquake_Lab_Worksheet_SP23
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Florida International University *
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Course
1010
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
9
Uploaded by ElderSeaUrchinMaster101
1
Earthquake Lab Worksheet
–
GLY 1010 Lab
Student Name:
__________________________
•
Examine
Figure 1
closely.
Identify the P and S wave arrival times, S-P interval, and amplitude.
Figure 1: Example Seismogram
2
Finding the Epicenter of an Earthquake
Task 1: Find the S-P travel Times
Estimate the time interval between the arrival of the P and S waves (the S-P Interval on the seismograms
from Figure 2, 3, and 4). See Figure 1 for identifying the elements of a seismogram.
Figure 2: Tokyo, Japan
Tokyo S-P Time Interval: ____________________________
Figure 3: Akita, Japan
Akita S-P Time Interval: ____________________________
3
Figure 4: Pusan, South Korea
Pusan S-P Time Interval: ____________________________
Task 2: Finding the Earthquake distance from the recording station
Determine the distance from each seismic recording station to the earthquake’s epicenter by using the
know travel times of the S and P waves. Using
Figure 5
, determine the distance from the earthquake to
each recording station.
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4
Figure 5: S-P Travel Time Curve
Answers:
•
Tokyo, Japan distance (km): ______________________________
•
Akita, Japan distance (km): _______________________________
•
Pusan, South Korea distance (km): _________________________
5
Task 3: Finding the epicenter
Figure 6: Map of Japan region
The line showing the scale on the map is not long enough to measure the radius for each circle.
Use the scale: 9 cm = 800 km.
Drawing a 9 cm line with the subdivisions will help to measure the radius.
6
Instructions for locating the epicenter of the earthquake:
1)
Locate Akita, Tokyo, and Pusan in the map above.
2)
Using a compass and a ruler, draw a circle for each of the seismograph stations (Akita, Tokyo,
and Pusan) with radii corresponding to your answers for
Task 2
.
Make sure the units are in
kilometers
.
Save each circle after drawing them.
3)
Once you have drawn all three circles and located the point where all three intersect, you will
have successfully located (triangulated) the epicenter of the earthquake.
Identify the location of
the epicenter by selecting the closest city.
Closest city to the epicenter:
_____________________________
Task 4: Finding the magnitude of an earthquake
The Richter magnitude scale (Figure 7) was developed in 1935 by Charles F. Richter of the California
Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of
an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.
Adjustments are included for the variation in the distance between the various seismographs and the
epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and
decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a
strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each
whole number increase in magnitude represents a tenfold increase in measured amplitude; as an
estimate of energy, each whole number step in the magnitude scale corresponds to the release of about
31 times more energy than the amount associated with the preceding whole number value.
Figure 7: Richter magnitude scale (
Image is from Richter's (1958) book Elementary Seismology.
)
(USGS Earthquake Hazards Program)
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7
Instructions for estimating magnitude of an earthquake
•
To estimate the Richter magnitude for an earthquake, one must know the distance in kilometers
of a seismograph station from the earthquake epicenter and the maximum amplitude in
millimeters of the S wave on that station
’s seismogram (
see figure 1
).
•
The magnitude can be estimated by drawing a line from the distance axis to the S-wave
amplitude axis using the values for that seismograph station.
Where the line crosses the
magnitude axis is the Richter magnitude for the earthquake.
Again, it is best to use
seismograms from at least three seismographs to converge on a single best answer.
•
Estimate the Richter magnitude based on where the lines for the three seismographs cross the
center axis of the Richter nomogram (they may not intersect perfectly).
Figure 8: Richter nomogram
What is the Richter magnitude for this earthquake? _________________________
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Task 5
: Calculate the following
1. An earthquake of magnitude 6.6 releases how many times more energy than the earthquake of
magnitude 4.0 ?
2. The following questions refer to the Figure 9 below.
Figure 9. S and P Travel Time curve
A)
If the travel time of the S wave is 21 minutes and 50 seconds, what is the distance between the
epicenter and the seismic station?
B)
How long will the P wave take to travel the same distance (in minutes and seconds)?
9
C)
Determine the time lag.
D)
If the P wave arrived at the seismic station at 12: 25: 10 PM, at what time did the earthquake
occur?
3. Refer to Figure 9
above
.
A.
If the S-P time interval is 7 minutes, what is the distance between the seismic station and the
epicenter?
B.
What is the travel time of the S wave?
What is the travel time of the P wave?
C.
If the P wave arrived at the seismic station at 7: 30 AM, when did the S wave arrive at the same
seismic station?
D.
At what time did the earthquake occur?
Answer the following Questions
1.
Define earthquake in geologic term.
2.
How are faults, foci, and epicenters related?
3.
List the major differences between P and S waves?
4.
Explain why P waves move through solids, liquids, and gases, whereas S waves move only through
solids.
5.
Distinguish between the Mercalli scale and the Richter scale.
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