MINI GRAND CHALLENGE PRESENTATION
The Great California ShakeOut
The Great California ShakeOut
Outline
(i)
(ii)
(iii)
(iv)
(v)
(vi)
Plate boundaries in California
California, “Earthquake Country”
Faults of the San Francisco Earthquake
Locating faults in California
Focal mechanisms and Seismic Data
Earthquakes’ dependency on faults
The Great California ShakeOut
Types of Plate Boundaries in California
The Great California ShakeOut
Types of Plate Boundaries
Divergent Boundaries:
Two plates pull apart
Convergent Boundaries:
Two plates push together
Transform Boundaries:
Two plates slide horizontally against one another
Plate boundary zones:
Sometimes boundaries are not well defined, especially if they involve more than two plates.
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Plate Boundaries in California
Transform boundary between the Pacific and North
American plates along the San Andreas Fault
Convergent boundary at the Cascadia Subduction
Zone
Convergent boundary at the bend in the San
Andreas Fault
Divergent boundary at the Brawley Seismic Zone
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SCEC-VDO Visualization
The Great California ShakeOut
References
Kious, W. J., and Robert I. Tilling. "Understanding Plate Motions." This Dynamic Earth, USGS. United States
Geological Survey, Feb. 1996. Web. 18 June 2013.
<http://pubs.usgs.gov/gip/dynamic/understanding.html>.
"The Salton Seismic Imaging Project." Earthquake Hazards Program. United States Geological Survey, 11 Dec.
2012. Web. 18 June 2013. <http://earthquake.usgs.gov/research/structure/salton/>.
"Plate Boundaries." Department of Earth Sciences. Freie Universität Berlin, 31 Mar. 2008. Web. 18 June 2013.
<http://www.geo.fu-berlin.de/fb/elearning/geolearning/en/mountain_building/plate_tectonics/index.html>.
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The State of California: “Earthquake Country”
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SCEC-VDO Visualization
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References
“Plate Tectonics.” Pacific Northwest Seismic Network. Web. 18 June 2013. <http://www.geo.fuberlin.de/fb/e-learning/geolearning/en/mountain_building/plate_tectonics/index.html>.
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Finding Fault in California
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Normal Faults
Basin and Range Province
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Reverse and Thrust Faults
Fault Scarps
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Strike-Slip Faults
Offset stream channels
1906 San Francisco Earthquake
Sag Ponds (Elizabeth Lake)
The Great California ShakeOut
SCEC-VDO Visualization
The Great California ShakeOut
References
Bolt, Bruce A. Earthquakes. 5th ed. New York: W.H. Freeman, 2003. Print.
Hough, Susan Elizabeth. Finding Fault in California: An Earthquake Tourist's Guide. Missoula, MT: Mountain
Pub., 2004. Print.
Michaelsen, Joel. "Basin and Range (Transierra) Region Physical Geography." Basin and Range Region. U.C.
Santa Barbara, n.d. Web.
"The San Andreas Fault." The San Andreas Fault - V. Surface Features. Department of the Interior, U.S.
Geological Survey 11 Jan. 2013. Web.
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Focal Mechanisms and Seismic Data
Focal mechanisms are visualization models that show:
•
direction of slip in an earthquake
•
attitude of movement along the fault
•
orientation of stress
Fault Plane
Auxiliary
Plane
Strike Slip
Right Lateral
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Seismologists analyze the first P-waves from the Earth that either
compress or dilate the ground at multiple stations.
First Motion
Ground Movement
Compression
UP
Dilation
DOWN
Null
No apparent motion
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At each seismograph station:
First motion P-waves are analyzed to show orientation of stress and slip along
the fault.
A
B
A
Reverse Fault
A
B
Lower Hemisphere Projection
Areas of compression and dilation are plotted on stereonet projection and the best fit line
separating the zones of stress is drawn, creating the “beach ball” diagram.
Illustrations by Ani Pytlewski
A
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How do geologists determine the Fault Plane ?
• Aftershocks
• Seismic history
• Field evidence for strike, dip, and rake of the fault
(correlate to focal mechanism)
• Ray Path geometry
Additional field data is
needed to differentiate
between the auxiliary
and fault plane.
The Great California ShakeOut
SCEC-VDO Visualization
The Great California ShakeOut
References
Cronin, V., 2004, A draft primer on focal mechanism solutions for geologists, Baylor University, p. 1-14
Johnson, Jenda. “Focal mechanism.” Incorporated Research Institutions for Seismology. 2013. Web. 18 June
2013. <http://www.iris.edu/hq/programs/education_and_outreach/ animations/25 >.
Lillie, R. J., 1998, Earthquake seismology, Whole earth geophysics: An introductory textbook for geologists &
geophysicists, p. 185-220
Rowan, Chris. “5 focal mechanisms.” 29 December 2009. Web. 18 June 2013. <http://allgeo.org/highlyallochthonous/2009/12/5-focal-mechanisms/>.
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Do Earthquakes Always Occur on Faults?
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NO
• Caused by sudden release of energy
• Tectonic earthquakes are focused on a fault
• Induced seismicity
• Volcanism
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Volcanism
• Earthquakes caused by the movement of magma through the earth’s crust
• Magma releases energy that causes shaking
Mount St. Helens Erupting
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Induced Seismicity
• Extraction of fossil fuels or ground water
• Reservoirs
• Mining
• Geothermal energy
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SCEC-VDO Visualization
The Great California ShakeOut
References
Chong, Kian H. "Fault Plane." USGS. N.p., n.d. Web.
"Earthquake." Wikipedia. Wikimedia Foundation, 06 June 2013. Web. 13 June 2013.
"Induced Seismicity." Wikipedia. Wikimedia Foundation, 06 Nov. 2013. Web. 19 June 2013.
"Mexico City, September 19, 1985." ANIMAL. N.p., n.d. Web. 20 June 2013.