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GEOL 1101 LAB #5 EARTHQUAKES AND THE EARTH’S INTERIOR
1. What is the primary cause of naturally occurring earthquakes?
What is the name of the theory describes how this causes the vibrations that are earthquakes?
2. Define earthquake focus (sometimes also called the “hypocenter”) and earthquake epicenter.
3. Name and describe the characteristics of the 2 types of BODY seismic waves.
4. What are the characteristics of the SURFACE seismic waves?
Use the seismogram below and Travel Time Curves #1 to answer questions 5 and 6.
5. Determine the S-P lag time (also called the S-P travel time) for the following seismogram.
bottom time scale is in minutes
S-P lag time = __________
6. Use the lag time and the Travel Time Curves #1 to determine the distance to the epicenter.
Distance to the epicenter =
TRAVEL TIME CURVES # 1 for questions 5 and 6
TRAVEL TIME CURVES #2 for question 7 and 8.
7. Determine the S-P lag time for the following recording stations. Time is written as hours:minutes:seconds (for
example 3:25:45) so when you subtract be sure you remember that there are 60 seconds in a minute!!
Then, use the Travel Time Curves #2 to determine the distance to the epicenter for each station:
LOCATION
P-WAVE
S-WAVE
S-P LAG TIME
DISTANCE TO THE
ARRIVAL TIME
ARRIVAL TIME
EPICENTER (km)
El Paso
7:30:13
7:30:56
Albuquerque
7:30:55
7:32:08
Flagstaff
7:30:15
7:31:13
8. Use the map below, and draw the circles around each station (being sure to use the scale of the map!!!) and
determine the location of the epicenter for this earthquake.
9. Explain the difference between earthquake intensity and earthquake magnitude. What scales are used to
measure each?
10. Earthquake intensity is very useful to estimate strength of historical earthquakes. Use the Mercalli Scale in
your text or the Earthquake Lecture Notes and determine the Earthquake Intensity of the strongest earthquake in
New Mexico history. This earthquake occurred on Nov. 15, 1906. Four chimneys were shaken off the Socorro
County courthouse. Plaster walls fell at the Masonic Temple and part of the roof was thrown onto the floor.
Estimated Intensity =
11. Below is a cross section across the Andes from the Pacific Ocean shore to 1000 km to the east. The
epicenters of 10 earthquakes are shown as circles on the sketch below. Below the sketch are listed the focal
depths for each (that is the depth to the focus for each quake). Plot the focal depth by making a dot at the correct
focal depth for each epicenter.
FOCAL DEPTH OF EARTHQUAKES to plot above:
EQ 1 = 15 km; EQ 2 = 25 km; EQ 3 = 30 km; EQ 4 = 50 km; EQ 5 = 150 km; EQ 6 = 180 km;
EQ 7 = 200 km; EQ 8 = 225 km; EQ 9 = 350 km; EQ 10 = 375 km
12. What do we call this zone of shallow, intermediate, and deep focus earthquakes? Why does this occur?
13. Go to the IRIS earthquake website: http://ds.iris.edu/seismon/
The map shows recent earthquake activity (red circles occurred today, etc.) so you can see just how common
earthquakes are (over 1 million per year that can be recorded on seismometers!). Below the IRIS earthquake map,
click on “Last 30 days earthquakes” which will give you a list of the most recent earthquakes. The time is given as
UTC (+ 6 hours for Mountain daylight savings time and +7 hours for Mountain standard time). Look at the list for
the last week or so and pick the 3 STRONGEST (highest magnitude) earthquakes to complete the chart below.
Clicking on the location will bring up a map showing where the epicenter was located. Above the chart, indicate the
date you looked at the website.
DATE: ___________________________
LOCATION
EQ#1.
EQ#2.
EQ#3.
MAGNITUDE
FOCAL DEPTH (km)
14. Are any of these earthquakes intermediate to deep focus (> 80 km deep)? If so, what is the likely tectonic
setting? (that is, at what type of plate boundary did the earthquake occur?)
15. For each of the earthquakes, determine if the quake occurred along a plate boundary or in the middle of a plate
(an intraplate earthquake). If the quake was along a plate boundary, name the type of plate boundary (convergent,
divergent or transform) that the earthquake occurred in.
EQ#1
EQ #2
EQ #3
16. What is the boundary between the crust and the mantle called? What happens to the velocity of seismic
waves as they pass into the mantle from the crust?
17. What is the S-wave shadow zone? What does it indicate?
18. Complete the following chart, showing the differences between the continental and oceanic crust and the upper
mantle.
OCEANIC CRUST
CONTINENTAL CRUST
UPPER MANTLE
COMPOSITION
(rock type)
DENSITY
THICKNESS
19. Name the layers of the Earth’s interior shown on the sketch below.
Layer from 0 – 100 km:
Layer from 100 to 250 km:
Layer from 250 – 2900 km:
Layer from 5100 – center of the Earth at 6370 km:
Layer from 2900 – 5100 km:
20. Draw in the Moho on the diagram above and label the oceanic and continental crust.
21. In which of the above layers does the Moho occur? (that is, which layer includes ALL of the crust
some of the uppermost mantle?
22. What are the differences in the physical characteristics of the lithosphere and the asthenosphere?
23. Which of these layers is broken into tectonic plates?
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