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NORTHERN GORDA RIDGE

4.5 (NEIC) - largest of s series of events

n/a

01/04/05
00:10
42.15N:
127.05W
<5.0 km

Seismo-Watch Significant Earthquake Report- No. 01-009

Northern California, April 7, 2001 (Seismo-Watch) -- A recent volcanic eruption seems to be happening in the deep waters of the Eastern Pacific Ocean off the coast of Crescent City, California.

Data collected by US Navys SOund Surveillance System (SOSUS) and interpreted by the National Oceanographic and Atmospheric Association's (NOAA) Pacific Marine Environmental Laboratory (PMEL), located in Newport, Oregon, has revealed that a robust seismic sequence similar to a submerged volcanic eruption began late on April 3 about 150 miles west-northwest of Crescent City along Gorda Ridge.

At least 14 moderate tremors measuring between M3.5 - M4.5 have been detected amongst a robust series of background events (See preliminary list from NEIC which show slightly different magnitude calculations). The initial rate of seismicity was on the order of 100 eq/hour, but seems to have relaxed somewhat and now is producing activity at about 10-20 eq/hour.

The activity appears to be centered along the Jackson segment of the central Gorda Ridge and is too far from shore to propose any risk.

A reconnaissance expedition of the waters above the site is currently underway and is being coordinated by partnership between NOAA and Scripps Institution of San Diego, California, funded by the National Science Foundation (NSF). They plan on using the sophisticated scientific exploration vessel, the New Horizon, which is has been dispatched from San Diego and is on its way to Eureka, California.

The Gorda Ridge is a tectonic spreading center where two plates, the Pacific and Gorda, are moving in opposite directions from each other. Volcanic eruptions characterize the geology as magma from the mantle injects into the voids produced by movement by the tectonic plates.

The Gorda Ridge has produced two similar eruptions in recent times, one in 1996 and another in 1998. PMEL has some great descriptions of these events on their web page.

UPDATE: April 7, 2001: PMEL reports that seismicity continues at a rate of about 10-20 eq/hour. The New Horizon ocean scientific exploration vessel is on it way to Eureka, CA and is being slowed by strong wings and ocean currents.

UPDATE: April 9, 2001: PMEL reports that seismicity continues at a moderate rate. Nearly 2,500 events have been recorded in the series thus far. The New Horizon is expected to arrive at Eureka, CA Monday, April 9. Research scientist are traveling to Eureka to meet the vessel.

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Epicenter Map, from NOAA's PMEL


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