Swarm of quakes buzzes Danville

A cluster of small earthquakes continued to shake the Danville area into Friday afternoon, measuring as strong as magnitude 3.5, slowing BART trains, but causing no significant damage, authorities said.

As of 1 p.m., the U.S. Geological Survey had reported 16 quakes in the area, with five of them above magnitude 2.5. The 3.5-magnitude temblor happened at 12:19 p.m. Friday near Diablo, a wealthy community northeast of Danville.

When BART receives reports of earthquakes, it stops trains until it can get information from the Geological Survey. If the magnitude is lower than 3.0, trains can start running under automatic controls. If it’s higher than 3.0, operators run trains at low speeds, under manual control, for about five minutes while conducting visual track inspections.

A 2.8 earthquake at 12:21 p.m. caused BART to halt trains briefly, transit officials said. A 5:53 a.m. quake also led to a 10-minute delay that affected the morning commute.

The quake cluster mostly consisted of shakers too small to feel, but a 3.3-magnitude event struck at 5:28 a.m. about 1 mile northwest of Danville, according to the Geological Survey. In the hours before, quakes of 2.8 and 2.7 shook the area.

“Looking in that general region, I’m counting 55 quakes just in the last week,” said Amy Vaughan, a geophysicist with the Geological Survey. Chronicle staff writer Michael Cabanatuan contributed to this report.