Morgan Hill – South County got a geological jolt at 9:43am Wednesday, when a minor earthquake hit five miles northeast of San Martin. The rumble measured 3.5 on the Richter scale: enough to nudge some residents out of their daydreams, but too weak to knock cans from the shelves at Nob Hill Foods, where employees said they didn’t even feel it.
The quake was followed about an hour later by a microquake emanating from the same point, barely tipping the Richter scale at 1.6. Data from the U.S. Geological Survey estimated a 1 in 1,000 risk of aftershocks through this afternoon.
Gilroy experiences an average of four magnitude-3 earthquakes every year, said David Oppenheimer, a U.S. Geological Survey seismologist. The last moderate quake was a 4.7, measured on June 15, 2006. The rumbles originate from the southern Calaveras Fault, which “creeps a lot,” said Oppenheimer, “but doesn’t look likely to rupture in very big earthquakes.”
The fault last ruptured in 1949, in a 5.2 quake.
In Gilroy, firefighters rolled up fire stations’ garage doors after the morning’s jolt, just in case an aftershock hit and trapped the engines. Fire risk was minimal, said Chief Dale Foster. Police and fire dispatchers reported no damage and no emergency calls.
Emily Alpert covers public safety issues for The Dispatch. She can be reached at 847-7158 or at [email protected].
