M3.6 in Oregon, M4.2 off Oregon Coast, M3.0 in England

ETS from 5/16 through 5/18/2019

Although seismic activity is relatively low right now across the globe, there have been some interesting events the past day or so. Also, ETS (episodic tremor and slip) has been ongoing for a while now along the Oregon Coast. Well, just to the east of the coast. I will show some plots to these events. If you haven't already, please click the title of this post or "read more" to continue...

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Oregon Earthquakes

Above is a map showing the locations of the 2 earthquakes that recently struck Oregon. If you wish to see the location of any seismic station used in this entire blog post, then please CLICK HERE.

M4.2 off Oregon Coast

USGS event page

On May 18, 2019 (Happy Mt. St. Helens day!) at 20:43UTC a M4.2 earthquake struck off the coast of Oregon along the Blanco Fracture Zone. Surprisingly, although the earthquake struck far off the coast, 4 people reported to USGS that they felt this event. Very intriguing! I wonder how 4 people felt it? It supposedly struck at 10km in depth but I believe it could have been deeper seeing that people did feel this event far from the epicenter. Below are the 3 plots from the closest seismic station.

M3.6 strikes Oregon - ENE of Lincoln City

USGS event page

On May 19, 2019 at 16:23UTC (9:23am PST, same date) a strong M3.6 earthquake rocked NW Oregon. It struck at 42.4km in depth and was reportedly felt by 36 people, even some feeling the event in Portland! The reason people felt this small of an earthquake that far away is due to the strength and depth of the event. Let's say a M7 struck at 10km in depth. Now let's say a M7 struck at 100km in depth. The deeper M7 would be felt much further from the epicenter than the shallower event. Below are the plots of this M3.6 from one of the closest seismic stations.

Now it is very interesting to note that this earthquake struck not far from the ongoing tremor and slip that is occurring in Western Oregon. You can see this in the image on the right, the M3.6 is marked for you.

Could this earthquake have been caused by the ongoing tectonic slip that is occurring? I believe it is possible. However the depth seems to be a little too deep, however I am not a professional so the connection to the ETS may still remain. The image on the right is of reported tectonic tremor from 5/16 through 5/18/2019.

ETS, episodic tremor and slip, is caused by tectonic slip along the Cascadia Subduction Zone. Tremor is likely caused by lubrication of the Juan De Fuca plate and North American plate "grinding" against one another. I personally believe that if we did not have this high of plate lubrication that we would see many M6 and M7 events (at a far greater rate than is currently witnessed). Thank God for plate lubrication!

Now the ETS episode lately has been interesting. It first started a month or so ago under the Olympic Peninsula in WA. However it calmed and then another ETS episode broke out, this time along the western coast of Oregon. ETS has been acting very odd lately, something even PNSN agrees with. We are obviously seeing another ETS episode, but it is kind of early. However geological phenomena, such as ETS, does not hold an exact schedule 100% of the time, even if it has in the past. I believe this is the start of the Summer 2019 ETS episode. Once again, it started in a way that has people puzzled. Why has ETS been acting so erratic lately? And why is the ETS episode starting early? Only time will tell. I suggest you CLICK HERE to keep an eye on PNSN updates about the ongoing tremor and slip.

Below are two images of seismogram, spectrogram, and spectra plots for one of the tectonic tremor events. I took the data from two stations to prove this was not surface noise. As you can see this is a typical low frequency, non-volcanic (tectonic) tremor. Here is what tectonic tremor looks like:

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M3.0 in the U.K.

On May 19, 2019 at 9:51UTC, a M3.0 earthquake struck 7km ESE of Swanage, United Kingdom. The location of the event is shown above, as well as the USGS event page for this earthquake. We see 3 people reported to USGS that they felt this event. Shaking was extremely weak and earthquakes like this do happen from time to time in the U.K. However it is noteworthy whenever one occurs so I thought I would post about it.

Below are the plots from the closest seismic station to this event. Sadly, it seems the seismic instrument does not detect frequencies beyond 10Hz so the spectrogram plot may look a little weird. Keep an eye out for more activity and I will be back soon!