Wierd Thrust Earthquake Somewhere Near the Queen Charlotte Fault

Was watching a movie last night when the Mw7.7 earthquake went off somewhere near the Queen Charlotte Fault.  The USGS location is under land, the islands now called Haida Gwaii (Formerly Queen Charlotte).  I think the fault is still the Queen Charlotte Fault though.  The Harvard location is on the fault, different than all four of the other network locations on NEIC

(see the image, the red thingy is the USGS location, the pushpin is the Harvard solution).  Given the location, even though it was big, I went back to the movie, assuming it was a strike slip earthquake like the 1949 one (Mw 8.1!!) and there would be no tsunami.  But then saw the warnings coming through and the evacuation of Hawaii in the middle of the big Halloween party going on in Honolulu.  That seemed a bit overcautious given the strike slip fault.  But low and behold, it turned out to be a thrust earthquake, so the warnings were warranted, though that wasn’t known at the time.  Can you say strain partitioning?   How long had this strike-slip fault been saving up compressional strain to produce this earthquake?  The 1949 earthquake in the same areas was almost pure strike slip, and 500 km long.   Small increments of compressional strain could have been accumulating there for many hundreds, maybe thousands of years, something like the way Tohoku accumulated more and more compressional strain, all the while having M7.8-8.5 earthquakes for over 1000 years before the big one let go.  Every one of these things has lessons for us….

Here’s  a brief phone interview with Daily Planet about this earthquake:  http://www.youtube.com/watch?v=_B65voERptc&feature=youtu.be

 
Today Jeff Beeson and I ran a Coulomb stress model to see what sort of stress change might be expected from this earthquake on the northern tip of the Cascadia/Explorer megathrust.  With reasonable guesses about some of the parameters, the stress transfer might be 0.01-0.02 bars, a very small increase that’s in the noise.

Here’s the mechanism:

October 28, 2012, QUEEN CHARLOTTE ISLANDS REGION, MW=7.7

Meredith Nettles
Goran Ekstrom

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201210280304A  
DATA: II LD IU DK CU MN G  IC GE
L.P.BODY WAVES:149S, 387C, T= 50
MANTLE WAVES:  150S, 405C, T=150
SURFACE WAVES: 153S, 408C, T= 50
TIMESTAMP:      Q-20121028073457
CENTROID LOCATION:
ORIGIN TIME:      03:04:39.2 0.1
LAT:52.47N 0.00;LON:132.13W 0.01
DEP: 15.0  0.2;TRIANG HDUR: 18.2
MOMENT TENSOR: SCALE 10**27 D-CM
RR= 4.120 0.015; TT=-2.560 0.011
PP=-1.560 0.009; RT= 2.900 0.123
RP=-0.906 0.110; TP= 2.140 0.006
PRINCIPAL AXES:
1.(T) VAL=  5.205;PLG=70;AZM=  3
2.(N)      -0.058;    10;    122
3.(P)      -5.147;    17;    215
BEST DBLE.COUPLE:M0= 5.18*10**27
NP1: STRIKE=320;DIP=29;SLIP= 111
NP2: STRIKE=116;DIP=63;SLIP=  79

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