ask a geologist

I was wondering about the earthquakes off the bay area coast in the last week. So I decided to use ask-a-geologist



To: Ask-A-Geologist@usgs.gov

Subject: earthquakes off shore near San Francisco Bay area ?'s





I've noticed 3 earthquakes in the San Francisco area



a 3.6

a 2.9

a 3.4



2 off shore and one nearby the peninsula of the San Francisco bay.



Any relation to each other? Can you tell me what the fault(s) might be?



Is this the Pacific Shelf subduction zone?



thanks,



Rick Stuart

KFOG FM

San Francisco



here's the reply:



From: smills@usgs.gov

Subject: Re: earthquakes off shore near San Francisco Bay area ?'s



Greetings.



Given the depth of these events, less than 10 km, these are normal

side-slip movements along either the San Anreas fault or on its close

adjoining faults. The deeper events, the 12-25 miles deep ones, are in the

subduction zone. Just remember that, in about 15 million years, Los

Angeles will be alongside San Francisco; imagine running through Watts

during the Bay-to-Breakers.



The actual subduction zone is a bit farther north. That is characterized

by the presence of the volcanoes (Hood, Ranier, St Helens, Lassen),

although Mt Tamalpais, Mt Diablo, and the caldera at Scramento are extinct

volcanoes.



Cheers.