Beginning at 0700 GMT on 28 February 1996, intense seismicity was detected in the northeast Pacific Ocean using the T-phase Monitoring System developed by NOAA/PMEL to access the U.S. Navy's SOund SUrveillance System (SOSUS) in the northeast Pacific. The current event is located on the northernmost segment of the Gorda Ridge near 42 40'N and 126 48'W. The nature of the seismicity is very similar to that observed in June 1993 at the CoAxial Segment of the Juan de Fuca Ridge, which was later documented to be a lateral magma injection with subsequent eruption.
The following spectrograms compare this event to CoAxial event's onset.
The time series on the left represents the output of an acoustic beam directed at the respective sites. The color spectrograms represent time in y (1-minute ticks) and frequency in x (0-75 Hz).
Due to current security restrictions, the actual arrival times are not shown;
however, the similarity in the character of the events is obvious.
The black dots represent t-wave epicenters. Red dots include additional arrays. Locations of CTD casts from NOAA Ship McArthur are plotted as crosses (blue for no detected plume; magenta for plume anomaly). Oceanographic profiles for each location are shown below. Location of seafloor lava flow and new plume discovered by WECOMA are marked in red.
Data through 2300Z 3/19/96
NOAA/PMEL is currently investigating the availability of NOAA ships for a field response effort.
Water column measurements would be emphasized in any NOAA effort.
A variety of expeditions are scheduled for the northeast Pacific this summer.
Field response is being coordinated Jim Cowen (U. Hawaii), Bob Embley (NOAA), and Marv Lilley (U. Wash) through the RIDGE Program.
Update 3/4/96 1600 PST The NOAA Ship McArthur will sail from Seattle at 1500 PST on Thursday, March 7 to perform 2-4 days of water column surveys at the site. Ed Baker of PMEL will be Chief Scientist.
Update 3/6/96 1100 PST If the McArthur cruise reveals evidence of "event" type plumes present at the site, there will be strong interest for follow up efforts. One near- term possibility is an open slot in the schedule of the R/V WECOMA, the UNOLS vessel operated by Oregon State University. The WECOMA is presently scheduled to depart San Diego on 28 March and could be available until about 19 April if resources were available to pay for shiptime, etc.
Address inquiries to:
Bob Dziak - Seismic Analysis and Event Detection (robert.p.dziak@noaa.gov)
Bob Embley - Field response, Seafloor Geology (robert.w.embley@noaa.gov)
Ed Baker - Water Column Measurements (edward.baker@noaa.gov)
John Lupton - Helium-3 Measurements, RAFOS (john.e.lupton@noaa.gov)
Dick Feely - Particle Chemistry (richard.feely@noaa.gov)
Gary Massoth - Fluid Chemistry