The Puente Hills Fault, or the Puente Hills thrust system, is a thrust fault located across the Los Angeles Basin, discovered in 1999. It runs about 25 miles from the Puente Hills region in the southeast to just south of Griffith Park, Los Angeles in the northwest. The fault is often referred to as a blind thrust fault due to a lack of superficial ground features normally associated with thrust faults that have recently experienced seismic activity. The fault is distinct in that it runs across the Los Angeles Basin, and is separate from the Whittier Fault.
The frequency of a major rupture in the Puente Hills Fault is on the order of once per several thousand years. This frequency of occurrence is relatively rare compared to the San Andreas Fault, which is a transform fault. More specifically, geologists have determined that the fault has ruptured at least four times in the past 11,000 years. The magnitudes of such earthquakes are considered to have been 7.0 - 7.5 Mw.
The location of the fault directly below metropolitan Los Angeles leads it to be of great concern for the public, with various predicted scenarios in the event of an earthquake. If a similar earthquake were to happen today, the projected losses by the USGS say about "250 Billion in property damage" and 3,000-18,000 deaths would happen.
The 4.4 2010 Pico Rivera earthquake, at 4:04 AM on March 16, 2010, may have been caused by movement on this fault according to CALTECH and USGS.
According to Dr.Hutton from CALTECH, the chance that the early morning tremor was a foreshock to a larger quake was initially 5 percent but would rapidly decline to 1 percent after 24 hours.[1]
The quake was slightly unusual because hours later there still had been no aftershocks.[1]