Is Mount St. Helens seismicity increasing?

July 29, 2014

by Steve Malone

The Mount St. Helens area has received a lot of attention recently.  The apparent big increase in located events seen on the "Quakes near volcanoes" plot has generated some interest and questions from the public.  So, is this activity unusual?  Does it mean the volcano is preparing to erupt?  There is, of course the iMUSH experiment taking place there now that includes some explosions that the PNSN locates.  But these are only  half a dozen of the 87 events located near the mountain in the past month.

 

Another way of looking at the changing seismicity rate is a cumulative seismicity plot in which the number of events occurring before a certain date are plotted against that date.  Above is a last 6-month cumulative seismicity plot for the area around Mount St. Helens (shown in the map below).  The obvious increase in slope starting in mid-june and again in early July represents increases in event rate.  This is exactly the kind of plot that alerts a volcano seismologist to volcanic unrest that could lead to an eruption.

BUT, BE CAREFUL!  Interpreting such plots without understanding the nature of the data used can be highly misleading.  Note that the data used is for a region around the Mountain from north of Spirit Lake to south of the Swift River reservoirs and many of the events showing up are not from the volcano at all.


Here is a seismicity map of the Mount St. Helens region for the past three months.  The symbol colors are proportional to the event depth; red les than 1 km deep progressing to blue for events deeper than 10 km.  The star symbols are for known and probable explosions (quarry blasts and iMUSH shots). While many of the events, particularly small ones, are located right under the volcano there are also many events at quite a distance away.  Such distant events are rarely related to pre-eruption unrest.


However, much more important to the interpretation of the apparent seismicity increase is the way the event catalog was produced.  With the installation of iMUSH passive experiment seismic stations starting in mid-june much greater care has been taken to detect and locate every possible seismic event in the region.  Typically the PNSN uses an automatic seismic event detector that recognizes when seismic signals on several stations becomes significantly larger than the normal background signals and interprets this as an earthquake of possible interest.  This technique works very well for most earthquakes, certainly those large enough to be felt or of much significance.  However, very small events whose signals are not much different than background levels are missed.  During the iMUSH project PNSN staff are spending extra time examining the seismic records by hand and using special versions of the records such as spectrograms to detect the absolute smallest events.  Also, Dr. John Vidale, the PNSN director, has adapted some research software to run specifically on Mount St. Helens data to help detect the very smallest of small events.

To illustrate this change in detection threshold above is a plot of individual event magnitude versus time. Note that in May and early June few events were around magnitude 0 (zero) or less. (NOTE: keep in mind that magnitude is an open-ended logarithmic scale in which earthquakes of magnitude 0 are ten times smaller than magnitude 1 and magnitude -1 is yet 10 times smaller than a magnitude 0).   After mid-June most of the events are less than magnitude 0. That is, the detection of the very smallest events since mid-June gives the impression that many more events are occurring when in fact it is just an artifact of the extra care being taken to detect very small events.

Thus, while for a volcano seismologist it would be quite interesting and even exciting to observe a real increase in seismicity related to the volcano, it looks as if that is not the case.  We see no evidence of volcanic unrest what so ever, just the results of curious scientists looking closer at normal, background activity.

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.
The last great Cascadia Subduction Zone Earthquake occurred 313 years ago. We need to do more before the next one strikes.

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