Southern California

Earthquake Center

Mini Grand ChallengeLindsay ArvinDaniel PhiloRyan MeierJing Yuan

Kelvin VasquezNgoc 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.

Outline

Southern California

Earthquake CenterTransform Faults

(1)

(2)

Southern California

Earthquake CenterCompression Along the San Andreas

(3)

Southern California

Earthquake CenterReferences

“Earth’s crust: transform faults.” Art. Encyclopædia Britannica Online. Web. 20 Jun. 2013. <http://

www.britannica.com/EBchecked/media/1178/Two-transform-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>.

Southern California

Earthquake CenterSegments 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.

Southern California

Earthquake CenterSegments 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).

Southern California

Earthquake CenterReferences

Lynch, David, 2006. “Can San Andreas Break At Once? Study Says Maybe.” KPBS. < http://www.kpbs.org/news/2013/jan/10/can-san-andreas-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

Southern California

Earthquake CenterRecurrence 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

Southern California

Earthquake CenterPrediction 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

Southern California

Earthquake CenterRecurrence 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)– 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!)

Creeping at Hollister, CA

Southern California

Earthquake Center

ReferencesFurnal, 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. 17

June 2013.

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.e-education.psu.edu/earth501/content/p4_p8.html>.

Southern California

Earthquake CenterSan 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 …

Southern California

Earthquake CenterGarlock Fault

(King et al, 1985)

Southern California

Earthquake CenterGarlock Fault

(King et al, 1985)

Southern California

Earthquake CenterBig Bend Evolution

(Dolan et al, 2007)

Southern California

Earthquake CenterReference

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 long-term 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

Southern California

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

San Gorgonio Pass

Southern California

Earthquake Center

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 north-dipping San Gorgonio Pass–Garnet Hill fault system at depth

Stars show epicenter of earthquakes on faults outside of San Gorgonio Pass

Active and Inactive Faults

Southern California

Earthquake CenterSlip Rate Comparison

Southern California

Earthquake Center

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: 10.1130/0016-7606(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.

References

Southern California

Earthquake Center

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.

 

Salton Trough

Southern California

Earthquake Center

 • 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

Physical Features and Characteristics of the Salton Trough Area

Southern California

Earthquake Center

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=a9e0022c-

ee64-4a24-9c7d-afc3a5830a8c>.

References