MINI GRAND CHALLENGE PRESENTATIONThe Great California ShakeOut
(i) Plate boundaries in California(ii) California, “Earthquake Country”(iii) Faults of the San Francisco Earthquake(iv) Locating faults in California
(i) Plate boundaries in California(ii) California, “Earthquake Country”(iii) Faults of the San Francisco Earthquake(iv) Locating faults in California(v) Focal mechanisms and Seismic Data(vi) Earthquakes’ dependency on faults
(i) Plate boundaries in California(ii) California, “Earthquake Country”(i) Plate boundaries in California(ii) California, “Earthquake Country”(iii) Faults of the San Francisco Earthquake
(i) Plate boundaries in California(i) Plate boundaries in California(ii) California, “Earthquake Country”(iii) Faults of the San Francisco Earthquake(iv) Locating faults in California(v) Focal mechanisms and Seismic Data
Outline
The Great California ShakeOut
Types of Plate Boundaries in California
The Great California ShakeOut
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.
The Great California ShakeOut Types of Plate
Boundaries
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
The Great California ShakeOut Plate Boundaries
in California
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SCEC-VDO Visualization
ReferencesKious, 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/e-learning/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
References“Plate Tectonics.” Pacific Northwest Seismic Network. Web.
18 June 2013. <http://www.geo.fu-berlin.de/fb/e-learning/geolearning/en/mountain_building/plate_tectonics/index.html>.
The Great California ShakeOut
The Great California ShakeOut
Finding Fault in California
Basin and Range Province
The Great California ShakeOut Normal Faults
Fault Scarps
The Great California ShakeOut Reverse and
Thrust Faults
Offset stream channels
Sag Ponds (Elizabeth Lake)
1906 San Francisco Earthquake
The Great California ShakeOut Strike-Slip Faults
The Great California ShakeOut
SCEC-VDO Visualization
ReferencesBolt, 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 are visualization models that show:
• direction of slip in an earthquake• attitude of movement along the
fault • orientation of stress
Strike Slip Right Lateral
Fault PlaneAuxiliary Plane
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Focal Mechanisms and Seismic Data
Seismologists analyze the first P-waves from the Earth that either compress or dilate the ground at multiple stations.
First Motion Ground MovementCompression UP
Dilation DOWNNull 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.
Reverse Fault
A B A
A AB
Illustrations by Ani Pytlewski
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.
The Great California ShakeOut
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
The Great California ShakeOut
SCEC-VDO Visualization
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ReferencesCronin, 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://all-geo.org/highlyallochthonous/2009/12/5-focal-mechanisms/>.
Do Earthquakes Always Occur on Faults?
The Great California ShakeOut
The Great California ShakeOut
NO• Caused by sudden release of energy• Tectonic earthquakes are focused on a fault• Induced seismicity• Volcanism
• Earthquakes caused by the movement of magma through the earth’s crust
• Magma releases energy that causes shaking
Mount St. Helens Erupting
The Great California ShakeOut Volcanism
The Great California ShakeOut Induced
Seismicity• Extraction of fossil fuels or ground water• Reservoirs• Mining• Geothermal energy
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SCEC-VDO Visualization
ReferencesChong, 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.
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