San Francisco Bay Region Geology and Geologic Hazards

About Quaternary Faults > Do All faults Cause Earthquakes?

Do All faults Cause Earthquakes?

Faults with no Quaternary activity are least likely to cause an earthquake. Holocene-active faults are considered the most active.

There are literally hundreds of faults in the San Francisco Bay region alone. All faults are the result of movement in the Earth's crust, and all but the tiniest probably have generated earthquakes. However, much of that movement and most of those earthquakes occurred far in the Earth's past. Because the pattern of stress in the crust changes over geologic time, faults are formed, slip for a time, and then are abandoned. Geologists focus their studies on Quaternary-active faults, faults that have ruptured in Quaternary time. Faults that have not broken in the last 1.8 million years are probably abandoned, or at least they cause an earthquake so infrequently as to be less important. On the other hand, faults that have ruptured in Holocene time (the last 11,500 years) are considered the most active and dangerous faults.

Photo - description below
This map of faults (red lines) includes many older faults that are not on the main map. These faults do not show evidence of having broken in Quaternary time, and so they are considered less likely to cause future earthquakes.



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Page Last Modified: 8/18/2006