San Andreas - San Francisco

The San Andreas Fault is a geologic transform fault that runs a length of roughly 800 miles (1,300 km) through California in the United States. The fault's motion is right-lateral strike-slip (horizontal motion). It forms the tectonic boundary between the Pacific Plate and the North American Plate.
The fault was first identified in Northern California by UC Berkeley geology professor Andrew Lawson in 1895 and named by him after a small lake which lies in a linear valley formed by the fault just south of San Francisco, the Laguna de San Andreas. Following the 1906 San Francisco Earthquake, it was Lawson who also discovered that the San Andreas Fault stretched well southward into Southern California.

Earthquakes - San Francisco

The region is particularly exposed to hazards associated with large earthquakes, owing to a combination of factors:
- Numerous major active faults in the region.

- A combined thirty year probability of a major earthquake in excess of seventy percent.

- Poorly responding native soil conditions in many places near the bay and in inland valleys, soils which amplify shaking as shown in the map to the right.

- Large areas of filled marshlands and bay muds that are significantly urbanized, with most subject to liquefaction, becoming unable to support structures.

- A large inventory of older buildings, many of which are expected to perform poorly in a major earthquake.

- Extensive building in areas subject to landslide, mudslide, and in some locations directly over active fault surface rubble zones.

- Most lowrise construction is not fireproof and water systems are likely to be extensively damaged and so large areas are subject to destruction by fire after a large earthquake.

The coastal location makes the region vulnerable to Pacific Ocean tsunamis. Some of these hazards are being addressed by seismic retrofitting, education in household seismic safety, and even complete replacement of major structures such as the eastern span of the San Francisco – Oakland Bay Bridge.For an article concerning a typical fault in the region and its associated hazards see Hayward Fault Zone. (from wikipedia)