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7.0 Earthquake off Northern California coast

bjdeming

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It hit just before 11 a.m., local time, and they briefly issued a tsunami warning but that was canceled. It wasn't a thrust type of movement that would displace water, but an almost classic sideways (strike-slip) movement, according to the beachball graphic on the USGS event page.

That page also has aftershock forecasts, but this was in the Mendocino Fracture Zone and strong seismicity isn't unusual. There will be aftershocks for a while.

We're way north of the area and didn't feel a thing, of course. Did anyone else?

I only just heard about it and read a general report of "damage," but hopefully there are no injuries.
 

bjdeming

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Visuals always help. The geology here is so complex in so many ways!

 

thundersnow

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Help me understand the map with the arrows and GPS motion. Are those generated from points that moved in a direction relative to each other during the event?
 

bjdeming

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Check with Earthscope for reliable details (they're good about answering questions), but I believe those arrows are vectors showing the direction and perhaps also amount of the transient fixed-station movement as seismic waves rolled through from the 7-pointer.

That's a good point about station movement relative to other stations. I might be wrong but do think that the change in direction is there because of the more powerful regional tectonics that are in control here, for example, the plate triple junction (how powerful? Before the Mendocino triple junction formed, what's now the San Andreas fault used to be a subduction zone; because of complex plate interactions the triple point is migrating northward, and I've read some papers that suggest that this might be slowly shutting down Cascade volcanism).

Regional tectonics beats local point slippage and/or fracture most of the time, though this is all oversimplification because California tectonics are very complex and I can't comprehend very much of it.

Those waves briefly illuminated how the ground tends to move here when a force is applied, because of the stress field generated by slooow overall plate motions that are there all the time.
 

bjdeming

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Another account popped up in my feed today, and while exploring it I found this post -- an intriguing look at what it's like to be on the inside of offficial response to a geologic event (with a California spin: the coop and planned power outages).
 
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