December 2017 Oregon Tremor Event - Update
December 27, 2017
by Nancy Sackman
Tremor has continued in Oregon since the last post on December 15th. Current tremor activity has been ongoing since about 12/5/2017 (figure 1).
Figure 1. Age progression of tremor in central Oregon for the past two weeks. Earliest tremor locations start from 12/5/2017 and propagate northerly and southerly. Last update was December 26, 2017.
Since December 19th, tremor has now migrated northerly toward Portland and southerly toward Medford (figure 2).
Figure 2. Tremor activity from 12/19 to 12/26 showing progression in a northern and southerly direction.
More FAQs on Slow Slip and Tremor
On our previous blog post, we briefly discussed what ETS (episodic tremor and slip) is. Let’s go through a couple of more frequently asked questions.
1.What is tremor?
Tremor in the Cascadia Subduction Zone is the seismic noise of slow moving earthquake along the interface of the subducting Juan de Fuca Plate and the North American plates. Compared to normal earthquakes, tremor has lower frequency energy and can last for minutes, hours or weeks.
2. What about volcanic tremor?
Tremor can also be volcanic. But ETS is deep, non volcanic signatures that are a result of plate motion, not magmatic movement.
3. How deep are the tremors?
As it states on our website - “This is a topic of ongoing research.” But research suggests that it occurs near the plate interface at approximately 30 - 40 km deep.
4. What is the magnitude of tremor?
Tremor is probably made up of many tiny individual earthquake-like sources each with a "magnitude" of less than 1. Since tremor is an on-going continuous signal assigning a magnitude to it is never done.
Check out the map on our web page: