SAN RAMON — The ground has been restless in this community 35 miles east of San Francisco. Since late last year, dozens of earthquakes have rumbled through San Ramon and its tidy neighborhoods and cul-de-sacs, disrupting the suburban calm.

They have been mostly quick, and relatively weak, rumbles occurring here and there, with a few hefty thumps in between. Until this week, they were all magnitude 4 or below — not powerful enough to cause any real damage, but frequent enough to make even longtime residents of this earthquake-prone region puzzle over what’s going on.

Monday brought the biggest jolt yet, and the most active day since the quakes began in November, when an earthquake with a 4.2 magnitude rattled nerves and windows. It was felt as far away as San Francisco.

“Everyone is really on edge here,” said Seema Sophia Aggarwal, who has lived in San Ramon for 2 1/2 years. “The ground was bouncing and jerking from morning until night.”

Seismologists call waves of earthquakes like this swarms. They described the seismic activity as normal — and, crucially, said it was unlikely to be building up to a large, destructive big one. But they don’t know when the shaking will stop, either.

There is no exact definition of an earthquake swarm, but it is generally applied to a series of earthquakes that doesn’t follow a pattern more typical to seismic events. Normally, a large earthquake is followed by aftershocks that become smaller and less frequent over time, usually in a predictable way. Earthquakes in a swarm, though, strike close in time in a concentrated area, and they are usually small and similar in magnitude to one another. They are less predictable.

Annemarie Baltay, a geophysicist with the U.S. Geological Survey, described it as a “continuous hum” of little quakes. A sequence can go on for days or for months, as this one has. This swarm began Nov. 9 and has waxed and waned, with clusters of quakes followed by quiet periods.

Monday brought the most active burst yet. The day kicked off with a magnitude 3.8 earthquake at 6:27 a.m., followed by a half dozen smaller quakes. The 4.2 hit about 30 minutes later.

“I was rolling around in bed,” said Ravi Venkatesh, a San Ramon resident. “It was like being in choppy waters on a cruise ship or on a ferry, except more intense.”

The quakes continued, reaching at least 50 before Monday was over. They were the talk of the town, the conversation topic at school drop-offs and at the start of spin classes. Local online groups lit up with quake chatter every time the ground shuddered: “Here we go again.” “One more.” “They just aren’t stopping.”

Some people said they were feeling “quake drunk,” Venkatesh said.