Living on the Edge Unit 1 Prework

InTeGrate: Living on the Edge Unit 1: Hazard at Transform Plate Boundaries

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.

1. 
   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

2. 
   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.
   
   1. 
      What are the similarities between the earthquakes? What are the differences?
      
   2. 
      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.
      
   3. 
      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?

1^ Data sources for Google Earth layers:

• 
  San Andreas fault trace - line segments used with permission from Thomas Christian Chust, Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Germany
  
• 
  M 5.0+, 1973-2012 earthquake epicenters compiled using the USGS/NEIC PDE Catalog accessed December 2013
  http://earthquake.usgs.gov/earthquakes/eqarchives/epic/kml/
  
• 
  Source for other faults: USGS, Google Earth layer publically available at http://earthquake.usgs.gov/hazards/qfaults/google.php, accessed December 2013
  

2
^ CA Earthquake Probability Map

Credit: USGS, California Geological Survey, Southern California Earthquake Center

Source for image overlay: http://www.scec.org/core/public/sceccontext.php/3935/13661/

Accessed December 2013