Two Magnitude 6.5 earthquakes on Queen Charlotte Islands Fault.
Saturday, January 5, 2008

Summary by Professor Robert Butler, Portland Universiyt

First event: 11:01:05 UTC
Epicenter: Latitude 51.299N, 130.713W.
Depth: approximately 10 kilometers.
Second event: 11:44:48 UTC
Epicenter: Latitude 51.171N, 130.556W.
Depth: approximately 10 kilometers.

During the predawn hours (Pacific Time) of January 5, 2008, two magnitude 6.5 earthquakes occurred within 45 minutes of each other. These events were located near the intersection of three plate boundaries: (1) the Queen Charlotte Fault that forms a transform boundary between the Pacific and North American plates; (2) the Cascadia subduction zone boundary between the Juan de Fuca and North American plates; and (3) the Explorer Ridge, a spreading ridge that separates the Pacific and Juan de Fuca plates. The epicenters of these two earthquakes were within a few kilometers of each other at the location shown by the star on the map below. The faulting mechanism for both earthquakes was right-lateral strike-slip motion that would be consistent with motion along the Queen Charlotte Fault. The seismogram recorded by the AS-1 seismometer at the University of Portland is shown on the next page.  Although local storms are causing large ocean waves with resulting microseismic noise, the P, S, and surface waves arrivals are quite clear on this record.


University of Portland AS-1 seismogram.


College Hill, Corvallis, (CHOR) AS-1 seismogram.


CHOR Magnitude Calculation