Mini Grand Challenge Presentation

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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

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

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>.

The State of California: “Earthquake Country”

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>.

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

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.

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

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

At each seismograph station:First motion P-waves are analyzed to show orientation of stress and slip along the fault.

Reverse Fault

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.

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.

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?

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

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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