History of San Ramon earthquake swarms stretches back decades
By John Ramos
While earthquakes are not uncommon in the Bay Area, one city has been experiencing a swarm of quakes since November.
San Ramon sits atop the Calaveras Fault, and for some reason that scientists don’t quite understand, tiny earthquakes happen there on a fairly regular basis.
“We’ve seen them historically,1970, 1976, 1990, 2002, 2003, 2015, 2018, and now, we had a small swarm in November and another swarm now,” said Dr. Annemarie Baltay, a geophysicist and seismologist with the US Geological Survey.
But on Monday morning, the neighborhood around Alcosta Boulevard was particularly active, with seven mini-earthquakes between 2:00 and 10:00 AM. Dr. Baltay said how the quakes cluster can be unpredictable.
“We don’t know exactly why these swarms are occurring exactly where they do,” she said. “But we’ve seen that they can be very focused, and in 1990, we saw one that kind of moved along in time. We think it’s some small, sort of micro movements along the fault, or along smaller faults in the area. And that’s just generating a couple little earthquakes that just pop off and trigger each other.”
They were triggering all around Saif Hameed’s neighborhood, including one 2.7 magnitude tremor recorded directly beneath his home.
“2:00 AM was the first one. We were sleeping. The bed shook. And I went to the kids to check them, and they were up,” he said. “Yeah, both kids were up, 5-year-old, 7-year-old. They thought it was cool, they were excited. I was a little scared.”
Hameed said it’s a little unnerving to discover that an earthquake was happening in his own yard, albeit, about 9 kilometers deep in the Earth. But he said the one that really got his attention was the quake, initially registered at 3.7, that happened less than a mile away.
“It is exciting in a way, but it’s also scary,” Hameed said. “As long as it’s a small earthquake, it’s fine. But I don’t want this to be, like, a big one.”
Across the street, his neighbor Lisa Bargenquast said she actually got tired of all the shaking and began yelling at the Earth to settle down.
“You could hear the blinds, you could hear the house cracking and that was just, I keep wondering, OK, when is the second story going to come down on us, you know?” she said. “And then you get to the point where it’s just like, OK, c’mon, are we done yet? Because we’re on the third one, the fourth one, from that day! So, yeah.”
Of course, the big question is, are the mini quakes leading to something bigger? Dr. Baltay said anything can happen at any time, but what’s occurring in San Ramon is still pretty typical.
“Yeah, I don’t know if I believe that, but I hope she’s right,” said Hameed, laughing. “You never know. Nature can be unpredictable.”
Dr. Baltay said, for practical reasons, earthquakes are only registered after they reach 2.0 on the scale. She said the Earth is constantly shifting underground and some amount of movement is happening at all times. Small earthquake swarms often occur when the massive plates move a little bit and then take some time to readjust. She said then things tend to quiet down for a while, which will be welcome news to the people living off Alcosta Boulevard.
