San Diego at risk of major earthquakes, studies say

New research released this week found that a fault under the heart of San Diego can produce stronger and more frequent earthquakes than previously thought.

It’s the second study in recent months pointing to heightened quake risks in the San Diego area. Here is a breakdown: San Diego’s Rose Canyon fault produces powerful earthquakes more frequently than once believed, according to researchers from San Diego State University.

SDSU scientists who studied the fault in Old Town determined that the system — which before about 1990 was thought to be inactive — generates a magnitude 6.5 to 6.8 earthquake about once every 700 years.

Seismologist Tom Rockwell said that earlier work indicated that such quakes occur every 1,000 to 1,500 years on the 40mile-long fault, which extends from San Diego Bay, through Old Town and across Mission Valley, and up Rose Canyon through Mount Soledad, to offshore at La Jolla.

The fault is known to extend as far north as Oceanside offshore.

“A powerful quake in the midto-upper 6s could cause liquefaction around San Diego and Mission bays and locally in Mission Valley, and cause the land to be offset across the fault, which would damage buildings,” said Rockwell, one of California’s most experienced seismologists.

The research team said they also found evidence at a dig site in Old Town that the strike-slip fault has produced at least two additional quakes in the magnitude 5.0 to 6.0 range in recent centuries — shaking referred to as background seismicity.

In March, scientists proved how San Diego’s Rose Canyon should give residents of Los Angeles and Orange counties something to worry about.

Researchers said the discovery of missing links between earthquake faults shows how a magnitude 7.4 temblor could rupture virtually simultaneously underneath Los Angeles, Orange and San Diego counties.

Such an earthquake would be 30 times more powerful than the magnitude 6.4 Long Beach quake in 1933, which killed 120 people.