Southern California faults


Most of central and northern California rests on a crustal block that is being torn from the North American continent by the passing Pacific plate of oceanic crust. Southern California lies at the southern end of this block, where the Southern California faults create a complex and even chaotic landscape of seismic activity.

Fault modeling

Seismic, geologic, and other data has been integrated by the Southern California Earthquake Center to produce the Community Fault Model database that documents over 140 faults in southern California considered capable of producing moderate to large earthquakes. A three-dimensional model has been derived that can be viewed with suitable visualization software. The probability of a serious earthquake on various faults has been estimated in the 2008 Uniform California Earthquake Rupture Forecast. According to the United States Geological Survey, Southern California experiences nearly 10,000 earthquakes every year. Details on specific faults can be found in the USGS Quaternary Fault and Fold Database.

Historical earthquakes

Southern California faults have been responsible for many high magnitude and high-impact earthquakes.

Most active faults

Effect on geography

Southern California's complex rock formations are a result of uplift by the region's active faults. The San Gabriel and San Bernardino Mountains gained their height from the displacement of brittle granite crust by the San Andreas and the Elsinore Faults. Movement of the Sierra Madre and Raymond Fault have both lifted the northern Los Angeles Basin while depressing the southern region. The close proximity of tall mountains and deep valleys in Southern California is a direct result of the closely nestled faults of the region.

Effect on climate

The tall fault block mountains surrounding the Los Angeles region trap moisture and encourage rainfall. Without these natural barriers mediating the local climate, Los Angeles might be as dry and hot as the Eastern deserts of California. On the other hand, it has been noted that the encircling mountains tend to trap smog, causing it to accumulate in the populated region instead of moving out to sea or further inland.