ETS Event of Summer 2019
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Blog for ETS of Summer 2019
Deep Tremor News: Spring - Summer. 2019
This BLOG-like page is being generated in a form similar to previous ETS ones to document and provide information on a Northern Washington ETS that should start sometime between April and May, 2018. There are no special experiments in the field for this ETS. We will be tracking and reporting on this ETS using data only from the real-time regional networks (UW, UO, CN, PB, CA) and/or information reported to us by others.
Produced by Steve Malone, PNSN Professor Emeritus
Information will be posted on this page (latest at the bottom) and references to figures from time to time.
NEWS (latest is at the bottom):
Apr. 8, 2019 - As of right now the expected main Puget Sound - Vancouver Island ETS event is probably still several months away. It should start in July-Aug plus or minus a month if the interval between events stays similar to the past and depending if it starts in Puget Sound (earlier) or Vancouver Island (later). However, this blog is starting early because there has been tremor activity in the spring of 2019 that has some characteristics of a Puget Sound ETS event. Many observers have been questioning if this is a classical northern-Washington ETS event taking place very early. As of now, we think it is NOT but rather is a strange inter-ETS sequence of tremor. A "regular "Observations" report has been posted with some thoughts about what we (I) think may be taking place. This current ETS blog will be updated in the summer when the real thing gets going.
Apr. 11, 2019 - Oops. I discovered some problems with my "regular "Observations" page I posted a few days ago and have had to post an "Oops, retraction/correction Observation" page in response. More will continue here as this situation develops.
Apr. 15, 2019 - I just add a bit more here even though the main northern Puget Sound ETS has not yet gotten going. The southern Puget Sound and southern Washington has continued to have some tremor. After a brief pause in tremor activity from Apr 9 -11 tremor again picked up on Apr 12 and has continued to slowly migrate south. As mentioned in the "regular "Observations" page and a previous Observations page by Mouse Reusch one of the central Oregon ETS events propagated north into southern Washington a little over a year ago. Current tremor activity is overlapping this area just northwest of Portland right now. The main Oregon ETS events in the past have had inter-event times of almost two years, thus the current activity extending into Oregon again seems too early if it is covering some of the same region. Time will tell.
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.
There are even small patches up on Vancouver Island and down near Medford, OR. The strongest batches seem to be from Seattle south a ways, one in northern Oregon and another recent and continuing one in central Oregon. There seems to be enough tremor in these batches to represent significant slow slip. Remember that Aaron "tremor-man" Wech believes and states that ALL tremor represents slow slip. It is just not observable on GPS data until it goes on long enough.
So, at the risk of being booted out of the ETS seismologists club I decided to pretend that I was an ETS geodesist. With some careful checks (I really don't know enough to know what to check) I have analyzed a bunch of data from GPS stations in the region to try and determine where and how much slip was going on. My data sources are basically from the very good PANGA web site that presents processed and de-trended displacement data for a huge number of sites all over western North America. I also used a private data repository and display interface from the Cascade Volcano Observatory for some presentations. In the following map I show the locations of what I interpret to be the recent (March-May) displacements or slow-slip movements (red circles) and the locations where I don't see any such displacements (magenta squares). The small yellow circles are the locations of stations for which there was no data or the data were too noisy to decide one way or another if there was motion.
One can look on the PANGA web page for these station and decide for oneself if this seismologist is interpreting geodetic data reasonably well. But as examples of a couple of stations that clearly show movement (P423, P425) compared with a couple that don't (P424, P437) I provide the following time series for the last 18 months of their data. Note that in all four cases one can easily see the previous ETS events (Jan, 2018 in the south and Apr, 2018 in the north).
Based on this seismologists attempt at being a geodesist I will claim that one or maybe several ETS events are taking place to the south of Seattle but that the "main" one north of Seattle has not yet started. This, of course begs the question about this southern movement being too early. Indeed, central Oregon ETS events have tended to be on about a two year cycle in the past so this is almost a year early if that is what it is. I have not attempted to looks at the GPS data in Oregon myself but suspect that it might show slow slip going on there now. I will leave that as an exercise for the reader and keep my attention more focused on the traditional 14 month ETS area.
BTW (By The Way) A heads up! Dr. Professor Wech has been working hard on a new wech-o-meter over the past several months. It and its new web interface may be ready for releasing to the public soon. Stay tuned for exciting technical developments, if not geophysical ones.
May 22, 2019 - NOTE: The new tremor location and display system is realeased as of noon today. Check it out in the same old place at pnsn.or/tremor and also a complete description of why, how and what in our Observations blog.
Not much new regarding where or what the tremor is doing. It continues as of yesterday now in south central Oregon but may be near the end of its run. We now wait on something really getting going in northern Washington and/or southern Vancouver Island, maybe within a month.
May 28, 2019 - Indeed the central Oregon tremor bunch seems to have recently gotten much weaker; however some have noticed that there has been again tremor in the Olympic mountain area (northern Puget Sound region). Yep, but. probably not the beginning of the expected MAIN northern Puget Sound - Southern Vancouver Island - 14 month ETS..... probably. It seems with tremor jumping around in different places looking like it's really going to take off it can be confusing. I am confused but then I often am. However, I am also patient and still waiting for the real thing to start. Of course, as Dr. Wech of the new Wechometer-2 says: "all tremor represents slip". I agree, but still am intrigued with the fairly regular schedule this 14-month batch has taken in the past and so am waiting for it to be about 14 months since the last one before screaming "it has started".
BTW, speaking of the Wechometer-2 (it is pronounced in only two syllabales, "weh - cometer" rather than the previous version that was a "wech - o - meter") it has been running now for almost a week and we feel it is working well. However, we are also interested in your impressions. Please fill out the google form survey with your comments and/or impressions (raves are incouraged).