© USGSEpicenter of a magnitude 3.6 earthquake Friday in the East Bay area.
Several magnitude 2 and 3 earthquakes rumbled through the San Francisco Bay Area on Friday.
It's the latest seismic activity to add to a swarm of 60 earthquakes greater than magnitude 1 to hit the Danville area in the past week.The largest in the sequence, a magnitude 3.6 earthquake, came at 12:19 p.m. Friday. The U.S. Geological Survey received reports from more than 1,000 people who said they felt the quake, extending from the East Bay and into San Francisco. The quake was quite shallow, less than a third of a mile under the surface of the earth.
A magnitude 2.8 aftershock was felt two minutes later.
Earthquake swarms like the one that began on Feb. 16 in the Danville area have been common over the past few decades, occurring in 1970, 1976, 1990, 2002, 2003 and 2015. They occur in the San Ramon Valley corridor along Interstate 680 between Walnut Creek and the Dublin and Pleasanton areas, said U.S. Geological Survey research geologist Belle Philibosian.
The Calaveras fault runs right along the San Ramon Valley. In the Danville area, the fault zone transitions and steps over to the Concord fault, which continues north into Concord, Philibosian said. There is a complex zone of small faults in this transition area.
While the San Andreas and Hayward faults are well known to many in the Bay Area for their seismic risk, the Calaveras and Concord faults also pose a substantial risk. The Calaveras fault is as long as the Hayward fault, for instance, and can produce a magnitude 7 earthquake, Philibosian said.
Comment: Following last week's 4.6 magnitude earthquake in the UK, which was felt from Cornwall to Liverpool, a British Geological Survey tweet stated that, "Events of this magnitude only happen in the UK every 2-3 years."
Actually, there have been about 7 similar-strength quakes in the UK in the last 3 years alone...
22 May 2015 - A 4.2 magnitude earthquake 'causes homes to shake' in Kent, UK
25 May 2015 - Magnitude 3.0 earthquake recorded in North Wales
29 Jan 2015 - Britain's second earthquake in 48 hours strikes in East Midlands
7 Mar 2016 - Earthquake 'shook houses' in south-east England
3 Jan 2017 - 3.9 magnitude tremor strikes off UK coast - biggest quake for nearly a decade
4 July 2017 - Earthquake recorded off Shetland was largest in UK for nine years
5 Aug 2017 - Scottish Highlands are rocked by their biggest earthquake for 30 years
We are seeing a marked increase in seismic activity around the world lately, could it be related to scientists' predictions that major earthquakes for 2018 due to slowdown in Earth's rotation?