There was a magnitude 5.6 earthquake in Northern California at 1:07 PM, at a depth of 20 miles. It took place in a lightly populated area, but I assume it was felt in Eureka and other north coast towns. It occurred on land between Eureka and Crescent City, roughly between Redwood Creek and the Klamath River, very close to the Hoopa Reservation.
As can be seen in the map above, earthquakes are not unusual in this area. It lies north of the triple junction where three tectonic plates come together (the Gorda, Pacific and North American). A subduction zone is forcing the Gorda Plate beneath the North American continent, and earthquakes are to be expected. There have been a series of magnitude 7 quakes in the region over the years, including the Petrolia earthquake of 1992. Ultimately the descending plate starts to melt, producing the magmas responsible for California volcanoes like Lassen Peak and Mt. Shasta.
As can be seen from the seismicity map of California above, there have been plenty of earthquakes within the last week, but there is nothing happening that is out of the ordinary. California averages several hundred earthquakes a week, although most are not felt.
Get the official details at this site:
http://earthquake.usgs.gov/earthquakes/recenteqsus/Quakes/nc71734741.php#details
Keep track of all the quakes in California here:
http://earthquake.usgs.gov/earthquakes/recenteqscanv/
Perhaps I'm being nit-picky here, but instead of "A subduction zone is forcing the Gorda Plate beneath the North American continent..." wouldn't it be better to say "Plate motions cause the subduction of the Gorda Plate under the North American plate..."?
ReplyDeleteAnd thanks for the heads up! I'll be sure to mention this to my classes this afternoon.
Garry, where did you get that map of historical quakes in the Eureka area? I can only find the map for the whole state. Thanks
ReplyDeleteAlso, Bay Area Volcanos-- the whole of the north Napa valley is the remnants of an old volcano. (Go to Calistoga every year to enjoy the hot waters).
Then there's the Clear Lake volcano field. Do you happen to know if there's any monitoring going on there?
The historical quakes came from this page: http://neic.usgs.gov/neis/eq_depot/2012/eq_120213_nc71734741/nc71734741_h.html
ReplyDeleteRandy, yeah, I was writing quickly. One could even say the Gorda plate is sinking, perhaps.
And now an M6 off the coast of Oregon. I wonder if something interesting might be starting in the area...
ReplyDeletehttp://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usb00080ib.php
I am a new student to geology and enjoyed this post. I look forward to learning more about earthquakes. Goodstuff. Thank you for sharing.
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