© USGS
The earthquake may have measured only 3.9, but it still could make history in Orange County.
Monday's temblor, centered in the southern suburb of Laguna Niguel, could be the first measured on a fault discovered only 13 years ago, which runs along the coast from Newport Beach and Costa Mesa to San Juan Capistrano -- close to the San Onofre nuclear power plant.
The little-known fault - - called the San Joaquin Hills thrust -- is similar to the fault that triggered the deadly Northridge quake 18 years ago in the San Fernando Valley.
Unlike the famous San Andreas fault, which is visible from the ground, the fracture in the Earth's crust that makes up the San Joaquin Hills thrust fault is entirely underground. Because there is no visible break in the Earth's crust at ground level, the fault is perhaps more dangerous because it's unclear exactly where the boundaries of the fault are.
Scientists weren't aware of the blind thrust faults that triggered the 6.7 Northridge quake in 1994, nor the 6.0 Whittier Narrows quake in 1987 until after the ground began shaking.
Experts said Monday's temblor should serve as a wake-up call, particularly to Orange County residents who mistakenly believe that quakes are more an L.A. problem. Scientists believe that the San Joaquin Hills thrust fault is capable of generating a magnitude 7 quake or greater.
The U.S. Geological Survey in 2003 conducted a
scenario of such a quake, and found it could trigger severe shaking all along southern Orange County, including Costa Mesa, Irvine, Lake Forest, Mission Viejo, Newport Beach, Laguna Beach, Dana Point and San Juan Capistrano.
Comment: The article mentions that a 2.1 magnitude earthquake produced a 'loud boom' but it was not recorded on the USGS site. Perhaps the 'loud boom' was from a different source?