2 moderate earthquakes along the Northern California coast

Last update: July 21, 2012 at 11:45 am by By Ashish Khanal

2 moderate earthquakes along the Northern California coast
While looking into the details about these earthquakes, we found a number of coincidences which may be realated to each other. The series started with a M4.0 earthquake at a depth of 10.1 km (6.3 miles) along the Blanco fracture zone in front of the Oregon coast. Nothing special as the stress in the part of the fault is generating regular earthquakes up to M6.0.
1 hour and 18 minutes later a more powerful M5.1 earthquake occurred along the Gorda ridge fault (separating plates), but this time more to the south in the Californian sector. The depth was set to 10 km or 6.2 miles but this is the usual depth which is set if the data are not accurate enough.
Finally (at least up to now) a M5.2 earthquake occurred at a depth of 0.6 km approx. in the same sector than the earlier M5.1 earthquake. The depth of the last M5.2 earthquake (even poorly constrained) is attracting our attention. We do not sea anything special on the sea floor except some stress scars and ridges (red lines on the three maps below).
There is certainly no proved relation in between the Oregon and California events, but if ER detects patterns, we like to share them with our readers. The separating plates (spreading center) have been related in the past to a number of volcanic ridge eruptions (like they often are occurring in the spreading ridges of the Oceans). Evidence of such an eruption may be noticed by a coloring of the surface waters. Satellite imagery will probably give us a clue later today.
Only few people at the Eureka coast have reported the shaking at USGS. All of them reported a weak to very weak shaking.