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GEO 6950 Reviews in Earth Science, Fall 2011Topic 2 Tectonics of Western North America
11. San Andreas Fault SystemCarrie Welker and Alex Turner
Geography of the SAFS
The entire system is a zone approximately 3000 km long.
It is bounded in the north by the Mendocino trench – transform – transform triple junction off north western California.
It is bounded in the south by the Rivera ridge – trench – transform triple junction near the mouth of the Gulf of California.
A splay off the SAFS called the Eastern California shear zone is connected with the main fault system south of the big bend. It trends north along the eastern front of the Sierra Nevada, where it is known as the Walker Lane belt.
SAFS Physical and geological characteristics
Right-lateral transform plate boundary between Pacific and North American tectonic plates.
Pacific plate moving northwestward at 28-34 mm yr-1
~550 km of total displacement since formation 15-20 Ma
Both seismic and aseismic slip occur on locked and creeping segments of SAF
San Andreas Fault Observatory at Depth (SAFOD) at Parkfield, CA
Fault Core contains the weak smectite clay mineral saponite aseismic slip?
North American Plate
Pacific Plate
Crust and Lithosphere Properties
SAFS Important ChronologyFormation - 15-20 Ma the Pacific-North American plate boundary transitions from a subduction to a transform boundary (Farallon subduction to right-lateral strike-slip on SAF)
Historical Earthquakes
Year Magnitude Name Location Fatalities/damage1857 7.9 Fort Tejon Earthquake Central SAFS 1
1906 7.8 San Francisco Earthquake North SAFS 3000 / $524 million
1933 6.4 Long Beach Earthquake Southern SAFS 115 / $40 million
1989 6.9 Loma Prieta Earthquake North SAFS 63 / $6 billion
1994 6.7 Northridge Earthquake Southern SAFS 60 / ~$15 billion
2010 7.2 Easter Earthquake Southern SAFS (Baja CA)
2 / most damage in Mexico