March 2019 Washington Tremor

March 2019 Washington Tremor

March 29, 2019

by Mouse Reusch

March 2019 Washington Tremor

Is it ETS? (TLDR: No)

Tremor activity picked up a wee bit west of Bremerton for a couple of days starting around March 7.  Following that, there was a short hop northward to west of northern Whidbey Island. For several days it parked itself in that area, as well as to the south, reaching the northeastern section of the Olympic Peninsula.  Roundabout 3/20/19, the tremor shifted southward to the Olympia area, even going so far as Chehalis.

Figure 1. Tremor Detection Map - Dates from 3/7/2019 - 3/28/2019

Tremor map from the page for northern Cascadia through March 28.  The settings are indicated on the left. The color bar on the right shows earlier detection in blue and later ones in dark red.  Detections are updated at the end of the day at about 6 pm PDT.


If this is an ETS event, there are a couple of things to note.  Typically, we have observed tremor migrating northward.  At this point it has migrated southwards. So, is this an inter-ETS event?  The last ETS event for this part of Cascadia started in May, 2018 and lasted approximately two months.  ETS typically starts about every 12-14 months and lasts weeks to months here. If we are truly seeing another ETS, it would have been about 10 months since the start of the last one.    

BUT, it seems unlikely that this will grow into an ETS event.  According to Ken Creager, seismology professor and chair of the UW Department of Earth and Space Sciences, “It is the third time in the past two years that a similar event (has occurred) slightly to the south with 120 hours of tremor (though it could still grow).”  Emeritus Professor Steve Malone concurs that this is not currently an ETS event and he anticipates writing a further blog post on this in the coming weeks.

Figure 2. Tremor Swarms in Space and Time

Tremor swarms figure with north at the top and south at the bottom.  The X-axis is time for the past 10 years. Each black dot is a tremor epicenter. Red circles have an area proportional to the hours of tremor in a swarm and mark the centroid.  The numbers indicate hours of tremor for the biggest ones. FIgure and most of the caption from Prof. Ken Creager.

Look for more analysis and figures in the weeks to come! (Same tremor channel! Same tremor time?!?!)