Transcript Largest discontinuity along the San Andreas fault San Andreas fault

Southern California
Earthquake Center
Mini Grand Challenge
Lindsay Arvin
Daniel Philo
Ryan Meier
Jing Yuan
Kelvin Vasquez
Ngoc Kiem
Southern California
Earthquake Center
• How the San Andreas is not strictly a strike-slip fault.
• Why the San Andreas can be divided into segments.
• How the major segments of the San Andreas have
different recurrence intervals.
• What is the big bend and why is it important
• How the San Gorgonio Pass is an earthquake “traffic
jam”.
• How the extensional forces cause the Salton Trough.
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Transform Faults
(1)
(2)
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Compression Along the San Andreas
(3)
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References
“Earth’s crust: transform faults.” Art. Encyclopædia Britannica Online. Web. 20
Jun. 2013. <http://www.britannica.com/EBchecked/media/1178/Twotransform-faults-offsetting-a-mid-oceanic-ridge>.
"Geologic History of the San Andreas Fault System." Western Region Geology
and Geophysics Science Center. United States Geological Survey, 26 May
2006. Web. 20 June 2013.
<http://geomaps.wr.usgs.gov/archive/socal/geology/geologic_history/san
_andreas_history.html>.
3. "Southern California Is Earthquake Country." Earthquake Country. Southern
California Earthquake Center, n.d. Web. 20 June 2013.
<http://www.earthquakecountry.info/roots/socal.html>.
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Segments of the San Andreas Fault
• Historically, the San
Andreas has been divided
up into individual fault
segments that range from
tens to hundreds of
kilometers.
• These include the Big
Bend, Coachella, &
Parkfield fault segments.
Several segments of the San Andreas fault in Southern California.
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Segments of the San Andreas Fault
• The San Andreas can be divided
up into three larger segments as
well.
• Southern, Central, and
Northern.
• Complex fault geometries of the
Southern and Northern allow
for large earthquakes (Li and
Liu, 2006).
• Central segment is dominated
by aseismic creep.
The trace of the San Andreas fault in California (Lynch, 2006).
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Earthquake Center
References
Lynch, David, 2006. “Can San Andreas Break At Once? Study Says
Maybe.” KPBS. < http://www.kpbs.org/news/2013/jan/10/can-sanandreas-break-once-study-says-maybe/>
Li, Q., and M. Liu, 2006, Geometrical impact of the San Andreas Fault on
stress and seismicity in California, Geophysical Research
Letters, 33, L08302, doi:10.1029/2005GL025661
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Recurrence Intervals
• Frequency – Average time between past seismic events
– aka “recurrence interval”
• Recurrence Interval =
Average slip per major rupture / Slip Rate
Quote: The next large earthquake on the southern San Andreas Fault could affect 10 million
people or more. “It could (The Big One) be tomorrow or it could be 10 years or more from now”
-Yuri Fialko, September 2005
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Prediction vs. Forecasting
• Recurrence Intervals – Past occurrence of random events.
• Prediction – Determining the hazard of seismic activity of given areas is
important to predict future occurrences.
• Forecasting - Future likelihood of random events.
– Using probability of seismic activity
occurring in a given area during a
given time
– Assessing both the slip rate of the
fault and the risk the fault presents
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Recurrence Intervals Segments
•
Northern Segment
– Average slip rate (1.3 – 1.5 inches per year)
– Meaningful average recurrence interval 200 with an uncertainty of 50 years
– 1906 San Francisco Earthquake 7.8M
•
Central Segment
– Aseismic creep – slips continuously without
causing earthquakes
– 1857 Fort Tegon Earthquake 7.9M
• Few exceptions i.e. Parkfield
•
Southern Segment (Mojave Segment)
– Average slip rate (1.3 – 1.5 inches per year)
Creeping at Hollister, CA
– Meaningful average recurrence interval 200 with an uncertainty of 50 years
– No major earthquake in over 250 years *(1680 7.7M)
• YIKES!
Fun Fact: Probable Magnitudes on the SAF are MW6.8 - 8.0 (Hang on!)
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References
Furnal, Thomas E., Silvio K. Pezzopane, Ray J. Weldon, II, and David P. Schwartz.
"A 100-Year Average Recurrence Interval for the San Andreas Fault at
Wrightwood, California." Science 259 (1993): n. pag. Science.
Web.
"Information and Resources about the San Andreas Fault." Information and
Resources about the San Andreas Fault. Ed. David K. Lynch. N.p., 2009. Web.
June 2013.
17
Nester, Irene K. "San Andreas Transform Fault Zone." San Andreas Transform Fault
Zone. Emporia State University, 25 Apr. 2008. Web. 13 June 2013.
<http://academic.emporia.edu/aberjame/student/nester1/sandreas.htm>.
Richardson, Eliza. "Different Methods for Determining Recurrence
Interval." Welcome to the Dutton E-Education Institute!Pennsylvania State
University, n.d. Web. 14 June 2013. <https://www.eeducation.psu.edu/earth501/content/p4_p8.html>.
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San Andreas Big Bend
• A geometric feature
• Restraining the relative plate
motion
• Nature’s solution
•



Impacts include:
patterns of faults, seismicity
Rupture propagation
Possibility of multi-fault
ruptures
…
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Garlock Fault
(King et al, 1985)
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Garlock Fault
(King et al, 1985)
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Big Bend Evolution
(Dolan et al, 2007)
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Reference
King, G., Nábělek, J., 1985, Role of Fault Bends in the Initiation
and Termination of Earthquake Rupture Asperity and
Barriers, Science, Vol. 228, No. 4702, pp. 984-987
Dolan, J., Bowman, D., Sammis, C., 2007, Long-range and longterm fault interactions in Southern California, Geology, v.
35 no. 9 p. 855-858
Li, Q., Liu, M., 2006, Geometrical impact of the San Andreas Fault
on stress and seismicity in California, Geophysical Research
Letters, Vol 33, L08302
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Earthquake Center
• Largest discontinuity along the San Andreas
fault
• San Andreas fault slip decreases to a minimum
of 5–10 mm/yr at the SGP, from 24 ± 3.5 mm/yr
at Cajon Pass on the northwest and 12–22 mm/yr
at Indio on the southeast
• The San Andreas fault curves abruptly
southward from its normal southeast trend and
butts into the eastward-trending Banning fault at
45
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Traces of active faults are
show in red
Inactive faults are shown in
black
Beach-balls show epicenter
and oblique slip during
earthquakes on the northdipping San Gorgonio Pass–
Garnet Hill fault system at
depth
Stars show epicenter of
earthquakes on faults
outside of San Gorgonio
Pass
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Allen C.R. 1957, San Andreas fault zone in San Gorgonio Pass,
Southern California: Geological Society of America
Bulletin, v. 68, p. 315– 350, doi: 10.1130/00167606(1957)68[315:SAFZIS]2.0.CO;2.
Cooke, M. L., & Dair, L. C. (2011). Simulating the recent evolution
of the southern big bend of the san andreas fault, southern
california. Journal of Geophysical Research.Solid
Earth, 116(4) doi:http://dx.doi.org/10.1029/2010JB007835
"The Enigmatic San Gorgonio Pass." The Enigmatic San Gorgonio
Pass. University Of Southern California, Feb. 2009. Web. 20
June 2013.
Salton Trough
Salton Trough area :
• Coachella
• Imperial Valleys
• Western half of the Mexicali Valley
• The Colorado River Delta in Mexico
Formation :
• Small scale : A complex transition zone
between the right-lateral motion of the
San Andreas transform fault system,
and the northwestward progressing
spreading ridge complex of the Gulf of
California segment.
• Large scale: A deep sedimentary basin
formed by the extensional forces
associated with an underlying tectonic
plate boundary.
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Physical Features and Characteristics of
the Salton Trough Area
• A graben is a strip of land bounded on
opposite sides by roughly parallel faults.
Through movement of the faults, the strip
of land sinks in a process called
subsidence.
• The region around the south San Andreas
fault is actively being stretched due to
extensional deformation. Numerous faults,
high levels of seismicity and a series of
young volcanic buttes suggest this region
may be a source for future geo-hazards
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References
Alles, David L. "Geology of the Salton Trough." Western Washington
University, 28 Oct. 2011. Web.
<http://fire.biol.wwu.edu/trent/alles/GeologySaltonTrough.pdf>.
"Salton Sea Tectonic Research." Salton Sea Tectonic Research. Scripps
Institution of Oceanography, 1 June 2010. Web. 20 June 2013.
<http://quakeinfo.ucsd.edu/~dkilb/NG/SaltonSea/Introduction.html
>.
Viento, Pasar. "Garben Laguna Salada by the Horns." Geocaching.
Groundspeak, 14 July 2007. Web. 20 June 2013.
<http://www.geocaching.com/seek/cache_details.aspx?guid=a9e0022cee64-4a24-9c7d-afc3a5830a8c>.