March 03, 2007
The moderate quake that struck near Lafayette on Thursday night has geologists weighing in on the potential for bigger earthquakes in the area. The magnitude 4.2 earthquake could be a sign that larger quakes are possible in the area. Or it could indicate that smaller earthquakes are the norm in this area. The epicenter of the Lafayette quake was about 10 miles below the surface, so the nature of the fault is unclear. The location of Thursday's quake is near the trace of a relatively unknown fault called the Reliez Valley fault. The locations of about a dozen small aftershocks following Thursday's earthquake don't match up with the north-northwest trending Reliez Valley fault. "As aftershocks started to occur, they progressed in a west-southwest direction." Therefore, the fault that hosted Thursday's quake is likely a relatively harmless one in the block of earth between the larger Calaveras and Hayward faults that isn't capable of bigger shocks.
People close to the epicenter reported violent shaking; others farther away said they felt an ongoing rumble. Residents calling a local television station couldn't believe it was "only" a 4.2 earthquake — they said it felt worse. A few water pipes broke.