Magnitude 6.4 Earthquake Off the Coast of Oregon
Wednesday, January 10, 2008 at 1:37:18 UTC
(Tuesday 5:37.18 PM Pacific Standard Time)`
Epicenter: Latitude43.883°N, Longitude 127.228°W
Depth: approximately 10 kilometers.
The circle with surrounding rings on left-side map above illustrates the epicenter of this earthquake as determined by the US Geological Survey. The configuration of Juan de Fuca, Pacific, and North American plates off the Pacific Northwest Coast is shown on the right-side map. This event almost certainly occurred on the Blanco Fracture Zone that is a transform boundary between the Juan de Fuca and Pacific plates. The direction of relative motion between these plates along the Blanco Fracture Zone is (right-lateral) horizontal (strike-slip) as shown by the yellow arrows on the map. Although earthquakes occur frequently along the Blanco Fracture Zone, they are rarely felt in Oregon or Washington because they are moderate magnitude and a significant distance from the coast. The transform motion does not produce tsunamis because the horizontal motion of the plates does not raise or lower the seafloor as is required to produce a tsunami.
The seismogram for this earthquake recorded by the AS-1 instrument at the University of Portland (UPOR) is shown above. The first P-wave arrival is quite clear but the S-wave arrival is not. This is a common situation for a regional event recorded on a vertical-component instrument like the AS-1.
The seismogram for this earthquake recorded by the AS-1 instrument (CHOR) in Corvallis, Oregon, is shown above. The first P-wave arrival is quite clear. The S-wave arrival is marked by an abrupt increase in period.