Third modest quake within week sends message: Be prepared!

A 3.6 magnitude earthquake this morning (Thursday, Oct. 27) – the third small quake in a week on the Hayward Fault near UC Berkeley – should serve as a wake-up call to complacent Bay Area residents who don’t have earthquake kits at the ready, according to one campus expert.

Epicenter of Oct. 27 3.6 magnitude earthquake.

The red stars shows the epicenter of the Oct. 27 3.6 magnitude earthquake. (Courtesy of USGS)

“Things like this happen all the time on the Hayward Fault, and it doesn’t mean that the big one is going to happen. But it doesn’t mean it isn’t,” said UC Berkeley seismologist Peggy Hellweg, who currently is attending a conference on earthquake early warning at the U.S. Geological Survey headquarters in Menlo Park. “These are gentle reminders that we live in earthquake country.”

The most recent quake struck at 5:36 a.m. today and was centered along a segment of the fault at the foot of the Berkeley hills, which have been sculpted by past movement of the Hayward Fault.

No damage was reported on campus.

Two similar quakes struck last week: The first and largest – a modest 4.0 – rattled Bay area residents on Thursday afternoon, Oct. 20, while a 3.8 aftershock struck later that evening, at 8:16 p.m..

A post last week on the Berkeley Seismological Laboratory’s blog noted that, as a result of the 4.0 quake, “The area west of the fault, that is, the lowlands of Berkeley, Oakland and Albany, moved a few tenths of an inch to the North with respect to the Berkeley Hills. This northward movement is caused by the sliding of the Pacific Plate against the North American Plate.”

The blog noted, too, that even smaller quakes had occurred last Thursday along the same segment of the fault, most of them unnoticed by Berkeley residents.

According to Hellweg, three or more small quakes within a week along the same segment of the fault are not unusual and should not raise concern.

“Little quakes occur along the Hayward fault all the time, and the fact that they are in a different spot than usual is to be expected,” she said.