Sorry to be such a fly in the ointment... but, your description still requires some modification. The fault that moved is NOT between the Gorda and Pacific plates. The January 9 earthquake was caused by left-lateral movement on a strike-slip fault WITHIN the Gorda plate. This produced about 2 meters of horizontal displacement. Movement on similar faults (within the Gorda plate) caused the Nov. 1980, two of the April 92, the Dec 94, and June 2005 earthquakes.
...and to be more precise, faults are not "lines" but planes or surfaces.
Thanks again for your interesting article
...and thanks for your detailed article.
Your readers may be interested to know that the USGS downgraded the probability of a damaging >5.0 aftershock in the 7 days following Saturday's earthquake from 78% to 38% (it may be even lower today). The 78% number is still posted on the USGS web site referenced above.
The following is incorrect:
"a vast slab of the earth's crust, known as the Gorda plate, slipped vertically against the much larger North America plate, releasing years of accumulated pressure"
The earthquake was caused by HORIZONTAL slip on a left-lateral, strike-slip fault WITHIN the Gorda plate. There was very little vertical motion. That is why these faults do not typically produce a tsunami (although secondary ocean displacement can cause a local tsunami).
The stress on the Gorda plate (from interactions with both the North American and Pacific Plates) causes the Gorda plate to deform and essentially break up. This deformation is represented by numerous left-lateral, strike-slip faults - similar to the one that moved on Saturday. Motions on these faults are the most common sources of damaging earthquakes in our area.
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Apr 16, 2015
vol XXVI issue 16
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