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California’s top geologist has said the 6.0 earthquake in Napa Valley on Sunday surprised seismic scientists because it appears to be linked to an obscure fault previously deemed inactive.
“We would not have predicted an earthquake on this particular fault,” Dr. John Parrish, the chief of the California Geological Survey, told Sacramento television station KCRA (link to KCRA report).
Dr. Parrish said the Carneros fault, now believed to be the source of the Napa Valley earthquake, had been deemed inactive because it had not produced quake activity in the past 150,000 to 200,000 years.
The Napa Valley quake on the Carneros fault “tells us we can have a magnitude 6.0 anywhere,” Dr. Parrish told KCRA. “It tells us [earthquakes] are unpredictable.”
Dr. Parrish's observations “should be a wakeup call for L.A. city officials and residents” because even the geologist hired by the developer of the controversial twin-skyscraper Millennium project in Hollywood has conceded there are faults on the Millennium site, said attorney Robert P. Silverstein. He represents community activists fighting the Millennium twin-skyscraper project.
“Opponents of the Millennium project have believed all along that the faults underlying the Millennium site are active,” Silverstein added. “Now we are finding that even very ancient, and supposedly inactive, minor faults can suddenly spring into action and pose a threat to life and property. It begs the question: Do we need more safety limits than we now have on major construction on top of faults?”
KCRA also reported Dr. Parrish said the Napa Valley earthquake could force officials statewide to reassess the risk posed by faults that are not now deemed active and dangerous.
“The Millennium developer must be quaking in his boots over the prospect that the Napa Valley quake might trigger a rewrite of the rules about what constitutes an active fault,” said George Abrahams, a Hollywood community leader and Millennium project opponent.
Dr. Parrish is the official who will make the final determination about the Hollywood Fault map, including whether the fault is active and runs through the Millennium property, the site for a proposed 1.1 million square foot development involving two skyscrapers 39 and 35 stories tall.
State law forbids construction of a habitable structure within 50 feet of an active earthquake fault. California government rules now say faults are active if they have experienced earthquake activity within the past 11,000 years.
Otherwise, they are considered inactive. Under current rules, construction can proceed on top of an inactive fault.
The California Geological Survey, which Dr. Parrish heads, produced a preliminary map in January showing the path of the Hollywood Fault. Two traces of an active fault crossed the Millennium site. State law, however, gives property owners the right to challenge the preliminary maps. As part of that process, the Millennium hired Group Delta, a geology firm, to dispute the preliminary map.
Mr. Schwada, of MediaFix Associates, may be contacted at john.schwada@gmail.com
