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 characteristicsRight-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