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The Northern San Andreas Fault


The northern part of the San Andreas fault, some 300 kilometers long, ruptured from end to end on 18 April 1906, producing an earthquake of approximately magnitude 7.8. For several decades afterward, very little seismic activity occurred along this stretch, which reaches from Shelter Cove southeastward to San Juan Bautista. However, earthquakes have been increasing roughly since the 1980s, a period that includes the 17 October 1989 Loma Prieta event, of magnitude 7.1, in the San Francisco Bay area. While moderate and large earthquakes like 1989's are of concern and can cause deaths and damage, another great event the size of the 1906 quake is not anticipated for at least a century.

This tour of the San Andreas fault begins at the north end. The next part of the fault, beyond San Juan Bautista, is the creeping section.

San Andreas fault home page

Images 1-12 of 37
Lay of the landIndex Map of the Northern San Andreas FaultWhere it all beginsMouth of Alder CreekMarks of movementFault Trace at Alder CreekA common phenomenonDeflection of Alder Creek
Moving the goalpostShutter Ridge at Alder CreekBig ditch in the deep woodsSan Andreas Fault North of Skaggs Springs RoadDistinctive sandstonesRocks of the Gualala BlockSigns of movementSan Andreas Fault at Fort Ross Road
A secret wet spotSag Pond in Fort Ross OrchardA rumpled hillsideFault Trace South of Fort RossHigh and dryAbandoned Course of Mill GulchView to an offsetFault Trace at Mill Gulch
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