Why are there no faults in the Great Valley of central California?
The Great Valley is a basin, initially forming some ~100 million years ago as a low area between the subducting ocean plate on the west (diving down under the North American plate) and the volcanoes to the east (now the Sierra Nevada mountains). Since its formation, the Great Valley has continued to be low in elevation. Starting about 15 million years ago the tectonics changed in California and instead of the ocean plate diving down under the North American plate, it began to slide along it, with the ocean plate moving northward. This movement occurs along the San Andreas fault and the many other faults that are roughly parallel to it.
The faults on the east side of the Great Valley, mostly in Nevada, are the result of the North American plate pulling apart there, in a different tectonic setting that results in the linear mountain ranges and long valleys you can see there. The faults just to the east of the Great Valley are mostly old faults and may or may not still be active today. So there is movement of faults in two separate regimes: sideways motion along the San Andreas system to the west-southwest, and pull apart motion along the faults mostly in Nevada to the east-northeast of Sacramento.
(contributed by Heidi Stenner)
What is the relationship between faults and earthquakes? What happens to a fault when an earthquake occurs?
USGS will track cause and extent of ground sinking near California Aqueduct. The latest satellite tracking data will be used to help scientists gain a better understanding of how land subsidence is affecting the state-owned California Aqueduct in California's San Joaquin Valley.
Maps showing the potential for destructive mudflows in the wake of recent Southern California wildfires were made available to the public and emergency responders today by the U.S. Geological Survey (USGS).
The maps estimate the size of potential debris flows, commonly known as mudflows, and the areas that could be affected when rainfall begins on recently-burned areas.
The U.S. Geological Survey has a new website that offers a virtual tour of the Hayward fault.
Three-dimensional perspective view of the likelihood that each region of California will experience a magnitude 6.7 or larger earthquake in the next 30 years (6.7 matches the magnitude of the 1994 Northridge earthquake, and 30 years is the typical duration of a homeowner mortgage).
Photograph taken during a Land Cover Trends Project field trip in California of a valley with residential housing.
Irrigation systems in Central California Valley Ecoregion: Single-field irrigation ditch.