California earthquake: A new threat emerges
In the 1980s, scientists initiated a study to uncover the mystery behind an orphan tsunami that struck Japan in the year 1700.
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“Geologist [I'm Climate Change]”
Since: Mar 07
#1 Mar 17, 2014
Goldfinger et al, did a study on seismogenic turbidites.
The multi phase events are the result of triggered landslide tsunamis rolling down different length channels after being triggered @ the same time. These events appear to be the results of the tsunamigenic megathrust earthquakes covering the zone of the arc in the catchment (& in many cases covering the California & Oregon sectors NW or WNW vectors (basin & range), and in all others covering the entire arc up to the midpoint of Vancouver island with vectors ranging from WNW to W to WSW and occasionally SW.
The penultimate event was a particularly big one that relaxed the entire arc in the SW. The last in 1700 was a multi vector type with the event initiating @ the Cascadia/Gorda junction box (lassen area), and extending through to Washington in a WNW vector to the Cascadia-garibaldi junction box (glacier peak area) with a LARGE runout in central Oregon. This event gave the 7 wave train in Japan lasting most of the morning. This event was also responsible for the decompression of the USA in a great circle through New Madrid & Charleston to S of Bermuda in the triangle through to the mid Atlantic ridge. This decoupled crust with no friction left the garibaldi arc unsupported & the stress overcame the young's modulus of the garibaldi arc which then let go WSW as a classical arc runout from Washington-central Vancouver island.
As an arc runout, this 2nd part of the 1700AD quake was a low magnitude & low tsunami with as a result, thin magma filled fractures being formed in the arc. These fractures have since been squeezed into the N. Cascadia volcanoes by recompression of the arc resulting in the recent activity (historic) in the N. of Cascadia. The same volcanism has also occurred post 1700 in the south of the arc where the runout was also low. The magma filled fractures in central Cascadia are still squelching around heading for the least compressed bit (near the 3 sisters & Newberry).
The WNW vector in S. Cascadia has left the W. part of the Gorda arc near Mendocino compressed with only the outer forearc sliced & decompressed. The result is that the Gorda arc is still compressed & the descending Gorda plate is locked near Mendocino. The Mendocino forearc has occasional big thrust quakes. The last event was a transform fault involving the decompressed part of the Gorda plate sliding past the locked part E. of the Mendocino lockup.
now the fun bit:
Goldfinger et al also did a study on seismoturbidites in the fans off the N. san Anrdeas (NW of Frisco). All these appear to be singe pulse events relating to individual transform fault quakes of san andreas type. and show a periodicity of around 250-300 years or so. One notable event stands out from the rest.
This event occurred ~360AD (240-470AD) and is notable because it is a multiphase event with several pulses of sand down the channel @ the same time. This appears to be a particularly large & long lived transform event & is most likely the date of the last megathrust event affecting Mendocino & the Gorda arc which is compressing as a result of gulf of California rift spreading vs. the Gorda plate.
Interesting thing is that Goldfinger notes that tsunamiites in all cases of deep marine turbidites off NW frisco region were not found implying (loosely) that an earthquake landslide trigger is most likely.
Now plug in his result vs. the S. Cascadia turbidites.
Worth googling references for that one (hard to find).
have a nice day: Ag
#2 Mar 20, 2014
hope it slides into the ocean soon,taking care of the illegals in that state.
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