""This is a lot of shaking for the people in the San Ramon area to deal with," Sarah Minson, a research geophysicist with the U.S. Geological Survey's Earthquake Science Center at California's Moffett Field, told SFGATE. "It's quite understandable that this can be incredibly scary and emotionally impactful, even if it's not likely to be physically damaging or related to any sort of threat of a larger magnitude earthquake.""
"These sequences, technically called "swarms," involve many earthquakes in a small region that don't fit the pattern of aftershocks following a mainshock. The recent rumblings around San Ramon began on Nov. 9 with a magnitude 3.8. Mostly tiny earthquakes followed, with only 71 of the some 330 quakes recorded larger than magnitude 2. By comparison, the 2015 event included 89 earthquakes over magnitude 2 in a two-month period."
More than 300 earthquakes have occurred in the San Ramon area since early November, with recent maxima of magnitude 4.0 and 3.9. The sequence began Nov. 9 with a magnitude 3.8 and comprises about 330 events, 71 above magnitude 2. Similar swarms have happened at least six times since 1970, including 2015. The pattern differs from aftershock sequences and likely reflects pressurized fluids moving through the crust and opening fluid-filled cracks between converging faults such as the Calaveras Fault. Residents report unsettling shaking, though the activity is unlikely to cause major damage.
Read at SFGATE
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