Earthquake Swarm, Including Magnitude 4.0, Shakes East Bay Cities

KPIX San Francisco ^ | May 3, 2015 | AP/CBS

[John W]

CONCORD (CBS/AP) — A string of moderate earthquakes has rattled the East Bay Sunday, shaking buildings. There were no immediate reports of injuries or damage.

The U.S. Geological Survey says an earthquake with a preliminary magnitude of 4.0 hit at 2:13 p.m. Sunday. It was centered a mile south of Concord.

Three smaller quakes shook the area in the moments before and after the larger one. A magnitude 2.5 earthquake hit at 2:01 p.m., followed by the 4.0 at 2:13, and a 2.7 magnitude quake at 2:14 p.m. A magnitude 2.4 shook the area again at 2:28 p.m. A magnitude 1.6 hit at 2:56 p.m.

[dandiegirl]

There was one in Dallas this morning at 10:15. A 3.2

[Nuc 1.1]

Why does the shallow depth cause concern?

[Polynikes]

A shallow depth EQ’s shaking and resultant damage can be much worse at lower magnitude than one that is deeper but larger. If these relatively small EQ’s are precursors to a larger EQ but at the same depth and it is something say in the 5.0’s at 1km or then the damage/shaking will be greater than if the EQ is at say 20-30 km.

[Nuc 1.1]

Ah. Thanks.