Scientists revise Rose Canyon Fault earthquake forecast

SAN DIEGO -- Although a major earthquake along the Rose Canyon Fault in San Diego County is not imminent, researchers found that it produces powerful earthquakes more frequently than previously believed.

The Rose Canyon Fault runs alongside the northern San Diego County coast, comes inland around La Jolla, extends under downtown San Diego and winds up offshore again off Imperial Beach.

San Diego State University scientists determined that the system generates a 6.5- to 6.8-magnitude earthquake about once every 700 years, refuting earlier research that indicated that such quakes occur every 1,000 to 1,500 years, The San Diego Union-Tribune reported. Prior to 1990, the Rose Canyon Fault was believed to be inactive.

"We could see the history of ruptures in the soil of Old Town, and that told the story," doctoral student Drake Singleton said.

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The researchers also found evidence at a site in Old Town that the fault has produced at least two additional quakes in the magnitude 5.0 to 6.0 range in recent centuries. Temblors of that magnitude likely wouldn't break the surface of the ground, but could cause liquefaction in San Diego and Mission Bays, according to the Union-Tribune.

Last fall, Singleton and Seismologist Tom Rockwell dug a trench on the Presidio Hills Golf Course and studied the sediment for traces of past earthquakes. They found that a major quake had occurred before the Mission San Diego de Alcala was founded in 1769, according to the Union-Tribune.

Their initial results were submitted as an abstract to the Geological Society of America.