"This has happened many times before here in the past, and there were no big earthquakes that followed,"
"We think that this place keeps having earthquake swarms due to a lot of fluid-filled cracks, thanks to very complex fault geometry - unlike, say, the San Andreas Fault, which is this nice clean edge."
"It lit up, and then was quiet for a little over a week and then lit up again,"
"That's fairly typical. These might last as long as a couple months, waxing and waning. And then the area typically shuts off for five years or even longer before another swarm pops up."
Around 90 small earthquakes occurred near San Ramon, beginning Nov. 9 with a magnitude 3.8. Most follow-up temblors were smaller and largely unfelt, though a 3.2 shook nearby commuters. The region has experienced at least six similar swarms since 1970, including one in 2015. Scientists attribute the repeated swarms to complex fault geometry and fluid-filled cracks rather than a single clean fault like the San Andreas. Swarms typically wax and wane over weeks to months and then become quiet for years. The November sequence may consist of aftershocks if the first event was the largest.
Read at SFGATE
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