May 18, 2019– Mary Greeley News – Dozens of tremors recorded over the past weeks have “continued to excite and confuse all of us tremor watchers,” according to a recent Pacific Northwest Seismic Network blog post.
Since early April, patches of tremors along the West Coast, including in the Puget Sound region and down through Oregon, have persisted. The strongest, according to the author of the blog post, “seem to be from Seattle south a way.”
“There seems to be enough tremor in these batches to represent significant slow slip.”
Episodic tremor and slip have been affecting the Pacific Northwest about every 14 months since at least the 1990s. The name refers to a process that occurs well below Earth’s surface along faults that form the boundaries of tectonic plates. The events involve one plate sliding over another, accompanied by a tremor.
Shaking from these events typically aren’t felt and don’t mean an earthquake is imminent. However, researchers believe the slip events are building up pressure at the fault, which will eventually lead to a long-predicted magnitude 9 earthquake.
Though it appears several slip events are occurring, the latest data doesn’t seem to indicate the “main” event has started north of Seattle.
In early April, the main event between Puget Sound and Vancouver was expected to start somewhere around July and August. Researchers began publishing findings early because of tremor activity in the spring that has similar characteristics.
May 16, 2019 – Tremor bursts have continued to excite and confuse all of us tremor watchers over the past month; but still I don’t think we have seen the start of the regular 14-month northern Washington-Southern BC ETS patch. Below I show the wech-o-mter tremor locations for Apr 12 – May 15 color coded by time (blue – oldest, red – latest). It is far from obvious that there has been a normal, mostly unilateral progression of tremor up or down the region. Rather tremor has jumped around with significant batches concentrated in an area for a while and then either moving a bit or dying out.
credit: In part with https://www.king5.com/article/weather/earthquakes/tremor-bursts-south-of-seattle-continue/281-0c9be3cd-6b81-406d-96bd-e6328ad3684d