A 4.4 magnitude earthquake struck without warning on a Tuesday afternoon, its epicenter 120 miles north of San Francisco in remote Mendocino County wine country. Felt across the entire Bay Area by millions,

Many of the state’s largest earthquakes have struck near the junction, where the Pacific, North American and Gorda plates meet. This area also forms the boundary between two infamous threats: the San Andreas Fault system, which runs across most of California, and the Cascadia subduction zone, which goes up to Vancouver Island, Canada.

Dozens of small earthquakes have shaken the San Francisco Bay Area over the last month, rattling nerves and raising fears that more seismic events may be on the horizon. The clusters of earthquakes — the latest of which struck Monday — have all been ...