The Pacific Marin Enviromental Laboratory"s (PMEL) VENTS program, which accesses the U.S. Navy's SOund SUrveillance System (SOSUS) to monitor ocean sound, indicates that a large seismic swarm along the northern end of the Juan de Fuca spreading ridge near the junction of the Nootka and Sovanco Fracture Zones began on September 6. (See earlier Seismo-Watch Report.) This is the triple point junction between the Pacific Juan de Fuca and Explorer tectonic plates.

The activity escallated on September 7 when a tremor measuring M4.2 was recorded and was followed by an intense sequence that produced a series of five tremors in the M4 range, including two measuring as large as M4.5 on September 8. See a list of current events here.

Although the robust microseismicity continued, moderate activity waned over the next few days but still managed to produce two more quakes in the M4 range, one measuring M4.5 on the 10th.

Activity jumped again on September 12 when another seven M4+ tremors were recorded, including one as large as M5.0. It occurred at 12:50 UTC (5:50 a.m. local time), September 12.

According to PMEL, the Pacific Geoscience Center of the Geological Survey of Canada has recorded and produced moment tensor solutions for two of the larger events that indicate strike-slip motion. Both events are oriented parallel to Juan de Fuca orientation (N15°E) and are likely associated with the ridge system.

The triple point junction between the Pacific, Juan de Fuca and Explorer tectonic plates has been a source of abundant seismicity over the years but activity has been relatively quiet since a M6.1 earthquake happened on January 11 earlier this year. See a list of events from 1999-2001.

Felt Reports
The quakes are centered too far from shore to have been felt.