Gorda Ridge Seismic Event 2001: Land Seismic Arrays
	RESULTS FROM LAND SEISMIC ARRAYS: The Pacific Northwest Seismograph Network (PNSN) operates seismograph stations and locates earthquakes in Washington and Oregon. PNSN data help scientists understand Pacific Northwest earthquake hazards, predict volcanic eruptions at Cascade volcanoes, and determine the location of faults and volcanic magma chambers. Besides earthquakes in Washington and Oregon, we often record earthquakes offshore along the boundaries of the Juan de Fuca Plate. The PNSN by itself is not able to determine the location and magnitude of these offshore events as precisely as it can earthquakes located on shore.
	John Nabelek at Oregon State University's College of Oceanic and Atmospheric Sciences has posted moment-tensor solutions for the larger earthquakes detected by the PNSN. The solutions indicate normal faulting oriented parallel to the strike of the Gorda Ridge. Similar events during the 1996 event on the North Gorda segment were interpreted to represent movements along the axial valley boundary faults in response to the removal of magma in the subsurface underlying the vallet floor. The solutions are posted at: http://quakes.oce.orst.edu/moment-tensor/special/GordaRidge0104/index.html
	The following report was provided by Amy Tieman, University of Washington Geophysics Program Between April 4-5, the PNSN has recorded approximately 18 moderate sized earthquakes in the offshore region where the Gorda ridge eruption has occurred. We have used a technique for calculating the magnitude of the Gorda ridge earthquakes that is based on the seismic amplitudes recorded at our stations and which is tied to magnitudes determined for some of these events by the National Earthquake Information Center (NEIC). The estimated magnitudes fall in a range of 3.5 - 4.5 for the located Gorda ridge earthquakes. Here is a table of our 18 events: GORDA RIDGE EARTHQUAKES (NEIC magnitudes are noted by *) Date/time (UTC) Magnitude 010404 01:30 4.0 010404 01:32 4.25 010404 01:41 3.9 010404 01:48 3.95 010404 01:50 4.25 010404 04:06 3.775 010404 05:28 not able to locate 010404 05:41 not able to locate 010404 06:50 3.625 010404 07:23 4.2 010404 07:32 3.885 010404 09:48 3.9 * 010404 14:48 not able to locate 010404 15:38 3.9 * 010404 21:26 3.55 010405 00:10 4.5 * 010405 02:32 not able to locate 010405 05:08 3.55 Pacific Northwest Seismograph Network http://www.geophys.washington.edu/SEIS/PNSN
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	Address inquiries to: Robert Dziak - Seismologist - robert.p.dziak@noaa.gov