Three Cascadia ETS events in past month??

September 4, 2014

by Steve Malone

There is a 9/5/2014 update and a 9/11/2014 update

Here is a plot of most of the past month of tremor locations in Cascadia color coded by time (red - most recent, blue oldest).

 

This plot is for the period, 8/10 - 9/4/2014 but not all sections started at the same time. The first segment to light up was in northern California starting on Aug 10 with scattered activity stretching from near Red Bluff almost to the Oregon border. There was then a couple of days break before it jumped up into southern Oregon half way between Roseburg and Medford and then mostly progressed smoothly  to the south.

The next section to start was in central Vancouver Island.  This sequence started with a burst in both the north and south on Aug 15 and then the northern part continued and smoothly moved south.  This appears to have stopped on Sep 2 but a burst further south near Nanaimo started up about the same time the main burst was dying out.

And finally the northern Puget Sound (traditional 14 month ETS zone) started up on Aug 23.  It started in southern Puget Sound on the down-dip side and then seems to have migrated up-dip and spread slightly to the north and a bit to the south.  This may be an inter-ETS event and die out in the next couple of days.  If it is the start of the main ETS event then it is early.  The previous main ETS event went from Sep 7 to Oct 8, 2013 and so this would be less than a year between events.

We have not yet heard anything from any geodesists about detecting actual slow-slip accompanying any of this tremor.  This blog will be updated if we hear anything or more interesting patterns develop.


 Update #1 - 9/5/2014

After posting this blog yesterday I heard from David Mencin and Kathleen Hodgkison of UNAVCO.  They report that strain meter site B018 (just south of Olympia) is showing a typical slow-slip strain event.

 

Here is the 30-day plot from strain site B018.  The smoothed (red) curve clearly shows the transient strain event starting by at least Aug. 27, only two days after the ealiest tremor.  The higher frequency regular oscillations (black curve) are the strain due to solid earth tides (pull of sun and moon).  Other plots of this instrument and all of the UNAVCO strain instruments can be found at the UNAVCO strain data web page.

While not yet having heard from GPS geodesists and not being one myself and thus reluctant to interpret their data I can suggest looking at the PANGA web site for very nice displays of GPS data

Here is a plot of the last couple of years from the longitudinal component of the Willapa Hills (WWH) grouping of stations from PANGA.  Note that, in particular for stations P430, TWHL, P420 and P415 there seems to be an obvious and sudden downward (west) jump over the latest several weeks.  However, if the time scale is correct then this change seems to have started back in June (month 6) so there must be something wrong with the plot or my interpretation.

 


OK, maybe the Puget Sound activity is NOT the main 14 month ETS starting early. It seems to have died out about three days ago without propagating very far at all.  The fact that there appeared to be some geodetic motion seems strange for such a short tremor episode (just over 2 weeks), but there have been a few other similar episodes in the past.  The Vancouver Island tremor did not continue but the northern California set is still going on.

Is Mount St. Helens seismicity increasing?

July 29, 2014

by Steve Malone

Looking at the "Quakes near volcanoes" plot today shows that 87 earthquakes have been recorded at Mount St. Helens over the past 30 days. This is way above the average for the past many years. Is this significant? Actually, no. Its called a sampling artifact that gives the impression of increased activity. For the details......
Several days of very warm weather has resulted in a couple of large snow avalanches at Mount St Helens but apparently no unusually large ones at other volcanoes. The seismic network at Mount St. Helens is particularly good at picking up the shaking due to large snow avalanches. Two such events on the afternoon of May 14 got our attention. For copies of seismograms and photos......
A large explosion was reported in the early morning hours of April 25 in North Bend, WA. I reviewing the seismic records we find signals consistent with this report. For a preliminary report.....
PNSN instruments picked up the ground vibrations generated by the deadly Oso landslide.

Legacy web site content returns

March 17, 2014

by Steve Malone

Two years ago the PNSN web site changed format in a big way. New features and capabilities were added and the look and feel was greatly improved. But, many of the old popular pages were left behind. We have now converted many of these pages to generic documents that can be linked from the new pages but are still in the old format. For a summary of what we have now....

Ice avalanches on Cascade volcanoes

February 28, 2014

by Steve Malone

With the recent heavy snows in the mountains after a long, cold dry spell the Cascades could be primed for big snow avalanches. However, just in the past couple of days we have seen two big seismic sources that we interpret to be, at least initiated as ice avalanches at Mount Rainier and Glacier Peak. For some details and photos...... (and an update)

A New View On What's Shaking on the Cascade Volcanoes

February 26, 2014

by Jon Connolly

We have added a new interactive graphic to the PNSN home and volcano page that provides a quick summary of the latest Cascade volcanic seismicity. This graphic replaces a table view of the same data. We have strived to make the PNSN landing page a quick summary view of immediate information that allows a user to drill down for more info if desired. The table view for recent volcanic seismicity was a bit clumsy and fell short of this goal.

Seismic Spectrograms - A new way to look at wiggles

February 13, 2014

by Steve Malone

Many people are familiar with seismograms - charts showing vibrations from a seismograph over time - but far fewer know or understand spectrograms. Still, these plots showing the strength of seismic vibrations over time at different frequencies are very useful for seismic analysts once they have some experience with them. At the PNSN we have been using them for several years, particularly for volcano stations. Now we are providing them for anyone to look at. For an introduction........

The final football game analysis

January 19, 2014

by Steve Malone

The data and notes have been collected for our seismic recording of the NFC championship game between the Seattle Seahawks and San Francisco 49ers and some analysis has been done. While too early yet for a definitive conclusion on all aspects of the data, we can report some interesting results and speculations. This blog will be added to as more analysis is completed. (By the way... The Seahawks won so on to the Super Bowl.) In the meantime for some interesting observations.......

The Football Game Experiment Continues

January 14, 2014

by Steve Malone

During the Seattle Seahawk's-New Orelans Saints Divisional game of Jan 11, 2014 we experimented with adding seismic stations at the stadium, providing live seismogram feeds, near realtime seismograms and some interpretation of recorded events. Since the Seahawks won and will play again in CenturyLink Field, why stop now. We learned some things, are puzzled about some things and changed somethings and doing it again. For all the details......

Seismic Game Analysis

January 11, 2014

by Steve Malone

The PNSN, along with with many fans, took extra interest in yesterday's playoff game. With two extra seismic stations installed at the stadium seismologists watched the seismograms at the same time watching the game on TV. We now have some analysis of the wiggles and other observations on this multipart experiment. For all the details....

PNSN Earth-shaking Seahawks Experiment

January 8, 2014

by Jon Connolly

Here is the content of a press release PNSN issued today about the deployment of two strong motion sensors in CenturyLink Field. We will monitor the vibrations of the structure and ground produced by an excited and energized crowd of Seahawks fans during the playoff game against the New Orleans Saints on Saturday, 11 Jan., 2014. The experiment provides challenges at all turns, but we hope to learn something about how seismic waves are generated within a structure, how to sense them and transmit them in a very challenging environment for data telemetry, and how to process and present them to users in real time. We also hope the Hawks win (although a close game might produce more ground motion!). Go Hawks!

Large Mount Baker debris Avalanche this fall

October 29, 2013

by Steve Malone

Every few years a buildup of ice and snow on the north and west side of Sherman Peak (Mount Baker) produces a large debris avalanche that can go several kilometers down the Boulder Glacier. Such an event occurred recently as determined by a pilot report (with photos). Searching the seismic records for Mount Baker seismographs turned up the seismic signal for this event on the afternoon of Oct 21, much later in the year than for previous such events. For more details.....

Speedy ETS in the works

September 16, 2013

by Steve Malone

It seems that the expected ETS of Oct-Nov, 2013 is already underway. Significant tremor started on Sep 7 in south Puget Sound and has already moved into southern Vancouver Island. This one seems both early and speedy with strange jumps. Update on Oct 11, 2013: It is over. This one went from Sep 7 - Oct 8, 2013. For all the details of this whole event......

Peppy seismic swarm 20 km NW of Mount St Helens

August 24, 2013

by John Vidale

A series of M3 earthquakes are shaking the area of Mount St Helens, in one of the more vigorous bursts of seismic activity in a few years.
Say "jokulhlaup" three times real fast and then run up-slope to get away from it. This icelandic word describes a sudden release of water trapped in a glacier. Such sudden floods can rapidly "bulk up" with sediment scavenged from river banks generating a lahar (mud flow) that can be very dangerous and destructive. Such an event occurred in the early morning hours of May 31 from the Deming Glacier down the Middle Fork of the Nooksack River and was well recorded by the MBW seismic station of the PNSN.
To address our users' desire for a simple user interface to view the latest earthquakes in the Pacific Northwest, we have just released three features: a new recent events list, mobile views, and a Twitter feed that will tweet all PNSN events magnitude 2 or greater.

M3.5 event west of Tacoma early Sunday morning

April 8, 2013

by John Vidale

Deep event is typical of seismicity near Seattle, has some aftershocks.

Oregon ETS is over, but....

April 4, 2013

by Steve Malone

The ETS in central Oregon starting on Feb 24 seems to have finished on Mar 31. But, bursts of tremor continue in other parts of Cascadia. In fact during the Oregon ETS much of Cascadia has seen periods of tremor lasting from one to several days.

Small swarm near Mount McLoughlin last night

March 24, 2013

by John Vidale

It has mostly been seismically quiet recently, although last night and this morning a swarm has been active in southern Oregon.

Earthquake early warning workshop quick report

March 17, 2013

by John Vidale

A workshop with 50 people met last month to chart the path to Earthquake Early Warning in the Pacific Northwest. Progress is encouraging.

thePNSN Facebook discussions

March 15, 2013

by John Vidale

The PNSN's in-depth blogs are here, and meanwhile our liveliest discussions on happening on Facebook.

Deep Tremor over much of Cascadia

March 8, 2013

by Steve Malone

Following three months of relatively little deep tremor in Cascadia the past month has seen bursts of activity up and down the region including what appears to be a full blown ETS starting in northern Oregon and spreading south.

Small earthquakes under Gold Bar

February 28, 2013

by Kate Allstadt

Though the residents of Gold Bar may not have noticed, a swarm of hundreds of tiny earthquakes has been rumbling along just a few kilometers east of town since October 2012.

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