The United States Geological Survey recorded a Magnitude 2.5 Earthquake at a depth of 100 m, in San Bernardino County, California, 61 km to the north of Joshua Tree, slightly before 11.40 am local time (slightly before 6.40 pm GMT) on Sunday 15 September 2013. This is a small quake, unlikely to have caused any damage or casualties, particularly as it occurred in a remote location, though it may have been felt locally.
The approximate location of the 15 September 2013 San Bernardino County Earthquake. Google Maps.
California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.
Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.
See also Magnitude 4.1 Earthquake in northeast Baja California, Magnitude 2.8 Earthquake in Baja California, Magnitude 3.6 Earthquake in Inyo County, northern California, Magnitude 3.1 Earthquake to the north of the Gulf of California and Magnitude 3.2 Earthquake in southern California.
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