Seventy-five tremors hit San Ramon, a small California city on 2. Here's what caused the swarm and why it isn't entirely ...

Earthquakes are unsettling, but a swarm of earthquakes can be downright scary, and some San Francisco residents are worried the Big One is near.

An earthquake swarm is a series of small quakes that “may occur in a region for months without a major earthquake,” according to Britannica.. Getty Images/iStockphoto A swarm of a half-dozen ...

19 Earthquakes Rock San Francisco Bay Area in 2 Hours on a Fault Feared to Trigger 'The Big One' ...

San Ramon, Calif., has been rattled by dozens of small earthquakes in recent months. Even in a region used to regular shaking, it’s been a lot.

The jolt of seismic activity Monday was among the busiest of a swarm that began nearly 3 months ago. Until the quake Friday, an earthquake swarm that began Nov. 9 around San Ramon had delivered 91 ...

Earthquakes usually strike without warning. But sometimes they come in clusters — dozens or even hundreds of small quakes concentrated in one area over days or weeks. Geologists call these clusters ...