Living on the Edge - Unit 1 Prework
The study area for this unit is the boundary between the Pacific and North American plates, in California. This is a transform plate boundary, with the two plates sliding past each other with a right-lateral sense of motion. Along this boundary, there is no active volcanism but there are many faults and frequent earthquakes.
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In most maps of tectonic plates, this plate boundary is drawn along the San Andreas Fault, which stretches 1300 km (800 miles) across western California. Review the map below1 and consider the distribution of earthquakes along this plate boundary. Is tectonic activity only present along the San Andreas Fault? How well is this boundary characterized by the single line of the San Andreas Fault? Explain your answer using information from the map.
Epicenters of earthquakes with magnitudes >= 5.0, 1973-2012
Direction of plate motion
San Andreas fault
Other faults active within the last 130,000 years
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The map below shows the population density of California, as well as the epicenters of 9 earthquakes that are significant either because of their magnitude or because of the amount of deaths/damage that they caused. The accompanying chart lists information for these earthquakes.
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What are the similarities between the earthquakes? What are the differences?
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Is there a direct relationship between the size (magnitude) of the earthquake and the amount of deaths/property damage? Explain, giving examples that support your answers.
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Besides earthquake magnitude, what other factor(s) do you think might affect the amount of deaths/property damage caused by an earthquake?
California population density
2010 census data
Credit: US Census Bureau
Source of image for overlay: http://commons.wikimedia.org/wiki/File:California
_population_map.png Accessed: December 2013
Data for Selected California Earthquakes
|
Epicenter
|
Year
|
fault(s) involved
|
Magnitude
|
Deaths
|
Damages
|
San Francisco
|
1906
|
San Andreas
|
7.8
|
3000+
|
$ 480 million (1906 dollars);
80% of San Francisco destroyed
|
Kern County
|
1952
|
White Wolf
|
7.3
|
12
|
$ 40 million
|
Coalinga
|
1983
|
Anticline Ridge
|
6.5
|
0
|
$ 10 million
|
Whittier Narrows
|
1987
|
Whittier
|
5.9
|
8
|
$ 358 million
|
Loma Prieta
|
1989
|
San Andreas
|
6.9
|
63
|
$ 7,500 million ($7.5 billion)
|
Landers
|
1992
|
Camprock, Emerson, Homestead
|
7.3
|
3
|
$ 92 million
|
Northridge
|
1994
|
Pico
|
6.7
|
60
|
$20,000 million ($20 billion)
|
Hector Mine
|
1999
|
Lavic Lake, Bullion
|
7.1
|
0
|
minor
|
Parkfield
|
2004
|
San Andreas
|
6.0
|
0
|
minor
|
30-year Probability for
M >= 6.7 Earthquakes
The map below shows 30-year probabilities for earthquakes of magnitude 6.7 or greater2 (you will be doing similar calculations in class). The Los Angeles area shows particularly high probabilities over a broad area; yet it has not had such an earthquake in the past 30 years. How do you suppose scientists are able to calculate probabilities of earthquakes of sizes that have not occurred?
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