314 years ago Sunday, a megathrust ea...

314 years ago Sunday, a megathrust earthquake devastated the region ... ready for another?

There are 1 comment on the Seattle Post-Intelligencer story from Jan 29, 2014, titled 314 years ago Sunday, a megathrust earthquake devastated the region ... ready for another?. In it, Seattle Post-Intelligencer reports that:

THE CASCADIA SUBDUCTION ZONE: The geography of northern California, Oregon, Washington, and southern British Columbia is shaped by the Cascadia subduction zone, where the North American Plate collides with a number of smaller plates: the largest of these is the Juan de Fuca Plate, flanked by the Explorer Plate to the north and the Gorda plate to ... (more)

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“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#1 Jan 29, 2014
Nice article.

The article missed the vectors of the last event.

Initial was California-Central Washington @ WNW vector, with the largest runout @ central Washington relaxing the crust through the Colorado Hotspot & onward through New Madrid & the Charleston-S. Bermuda area along a great circle as wide as the arc. Runout for that event was a backarc basin type involving an initial lurch and a later slow crawl. The slow crawl was responsible for the later waves of 7 wave tsunami train in japan which was still rather large on arrival.

2nd stage was the WSW vector from central Washington northward to central BC Vancouver island and south into Oregon to overprint with the slow crawl from the stage 1 earlier (by several minutes or so).

The missing vectors still compressing are the NW vector from California & the Gorda arc which appears to have been missed out in 1700; and SW vector involving the Garibaldi arc and extending into Cascadia and backed up by the Chilcotin hotspot.

The Garibaldi/Chilcotin vector is a long recurrence interval. The California Gorda arc vector however is the usual source location & vector of short segment earthquakes typical of S. Cascadia & more numerous than the full area runout type. There is a recurrence interval of ~500 years for the California-Gorda vector but this may have occurred as the initiator of the 1700 event and been overprinted by the main event WNW vector runout. In that scenario the next Cascadia event with Gorda-California vector is about 200 years away or so.

Currently Cascadia is largely relaxed & largely aseismic, recompression is generally noted by volcanism involving compression of long magma filled fractures @ the base of the crust initiated during the short WSW vector runout in the N. part of the arc and the lowermost part of the arc short runout in N. California (Shasta & Lassen). As the forearc is more compressed than the arc the forearc moves inward en masse without internal recompression quakes @ present.

W. Vancouver @ the slowly compressing long interval garibaldi arc is rather more noisy. Also compressing nowadays is the forearc of the Gorda arc NE of Cape Mendocino near Petrolia.

Would have liked to see that one in the article.

Have a nice day: Ag

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