"The challenge, she noted, is that scientists are still learning about earthquake swarms, which are collections of dozens or hundreds of small, usually harmless quakes. And they don't have strict parameters for when swarms start or conclude. There isn't a good way to officially define when swarms begin and end, Minson said. If there was more activity now we would probably call it a new swarm."
"The swarm has been subsiding. It appears to have quieted down, he said. But these swarms aren't like having a large earthquake on a fault followed by a series of aftershocks. They are still a bit of a mystery. Many of the quakes that have jostled San Ramon in recent months are so small that people living in the suburban Contra Costa County town of 85,000 didn't feel most of them."
The earthquake swarm near San Ramon began on Nov. 9 and produced 91 earthquakes of magnitude 2.0 and above, with the largest registering 4.0 on Dec. 19. No event of that magnitude has occurred since Jan. 10, when magnitudes of 2.3 and 2.0 were recorded, and seismic activity has paused for about two weeks. Earthquake swarms are collections of dozens or hundreds of small quakes and lack strict parameters for formal start or end definitions. The mechanisms behind swarms remain not fully understood. Most events were too small to be felt, and no damage or injuries were reported.
Read at www.mercurynews.com
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