San Jacinto Fault Zone
The SJFZ is a component of the larger San Andreas transform system and is considered to be the most seismically active fault zone in the area.
[3] Thirty year probabilities for segment-rupturing earthquakes were estimated using three separate models then a preferred weighted result was presented for each segment.
The Clark strand, which is separated from the Casa Loma by a small compressional step in the city of Hemet, continues southeastward out of the valley.
A paleoseismic investigation on this segment at Hog Lake indicated three historical surface-rupturing events occurred around 1210, 1530, and 1750 with an average recurrence period for a magnitude 7.0–7.5 earthquake of 250 years.
Kenneth W. Hudnut and Kerry Sieh examined the surface rupture (along with a trench investigation) in 1989 and estimated the slip rate for the prior 330 years to be 2 – 6 mm/yr (±1 mm).
A trench investigation by Larry Gurrola and Thomas Rockwell near the north shore of ancient Lake Cahuilla dated the events to 885–1440.
[7] With at least six and as many as ten large events since 1890, the right-lateral strike-slip SJFZ is southern California's most restless fault, with the exception of several sections which have seen less frequent activity.
In a paper published in the journal Science, Christopher Sanders plotted the earthquakes of the SJFZ by time and location and found that a uniform pattern became apparent.
[10] Uncertainty surrounds the details of this earthquake but recent studies suggest that a joint rupture of both the SAF and the San Jacinto Fault Zone to the southeast more closely match the damage pattern recorded about this event.
[14] (33°48′N 117°00′W / 33.8°N 117.0°W / 33.8; -117.0) On April 9, a magnitude 6.4 ML earthquake with a maximum perceived intensity of MM VII hit the extreme eastern San Diego County area and created a 31 km (19 mi) surface break along the Coyote Creek Fault.
California State Route 78 was damaged with cracks near Ocotillo Wells and large boulders blocked the Montezuma-Borrego Springs Highway.
Taller buildings swayed in both Los Angeles and San Diego and power outages affected numerous areas, primarily in the cities of Imperial Valley.
A brick wall collapsed at a laundromat in Westmorland (in the El Centro Metropolitan Area) but no one was injured, and in the seaside neighborhoods of San Diego county several hundred windows were broken.
Charles Richter, a Caltech seismologist, stated that the earthquake was centered near Ocotillo Wells about 120 mi (190 km) southeast of Los Angeles.
The Worthington Road bridge, at the New River, failed due to liquefaction and at the Desert Test Range Control Center, water tanks toppled into the building and other equipment crashed through a window.
According to the spokesperson for the state of Baja California, a motor vehicle accident east of Mexicali that claimed the lives of a mother and her four-year-old son was blamed on the earthquake.
Thomas H. Heaton, a USGS seismologist, stated that the faults in the area are difficult to track down because of the sediment deposited in the valley, which had been an intermittent drainage basin of the Colorado River.
