San Francisco Bay Region Geology and Geologic Hazards

About Quaternary Faults > Why Do Geologists Study Faults?

Why Do Geologists Study Faults?

Active faults generate earthquakes. Geologists study them to better understand where and when future earthquakes will occur.

Geologists study faults to better understand where large earthquakes originate. The Earth's plates are constantly moving, but most faults are motionless, locked by friction, until the day when the force on the fault builds up enough to overcome the resistance. When that happens, the rocks on either side of the fault lurch into motion, releasing pent-up energy in an earthquake. Most earthquakes are so small that special instruments are needed to detect them, but a few release huge amounts of energy, causing widespread destruction. During most earthquakes, fault motion stays below the Earth's surface, but in large earthquakes, fault motion may break through to the surface, offsetting rocks and sediments, as well as anything built on the fault, as much as ten feet or more.

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Earthquake shaking can cause widespread destruction, as is shown by newspaper drawings made after the 1868 earthquake on the Hayward Fault and photos taken after the 1906 earthquake on the San Andreas Fault.

Knowing the location of active faults is important so that planners and developers can avoid building houses or other structures, which would be destroyed when the fault breaks the Earth's surface, on the faults. Geologists also study the faults to find out how quickly the stress on them is building, as well as when the last large earthquake on them was and how often large earthquakes are caused by them. This information together gives them a general idea of how soon to expect the next Big One on a particular fault. The eventual goal is accurate and precise earthquake prediction, but geologists still haven't developed the tools required to do that. Geologists also study faults because they can affect the distribution of oil, underground water, and mineral resources. Faults also can serve as conduits for volcanic eruptions. Finally, studying faults can help to better understand how both the Earth's crust and the surface landscape formed.

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During earthquakes, faults can offset the ground surface by many feet, as shown by the offset of this fence across the San Andreas Fault after the 1906 earthquake.

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Fault offset destroyed this house during the 1906 earthquake.  


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