Summer rockfall time, yet again

August 21, 2015

by Steve Malone

On Aug 13, 2015 the seismic station, RER (Emerald Ridge ~ 350m from Tahoma Creek) at Mount Rainier showed signals consistent with a small debris flow in Tahoma Creek. Reports from Rainier National Park confirmed this. The Cascade Volcano Observatory has a short description of this event in their 2015 News Briefs. This debris flow (muddy flood containing rocks, trees and other debris) was likely started by a jökulhlaup from the terminus of South Tahoma Glacier. There were several 'pulses' of the flood over the course of about three hours. A pasted together set of seismograms/spectrograms starting at 9:40 PDT clearly shows the changes in shaking probably reflecting different volumes of water being released.

The warmness of the color is proportional to the strength of ground shaking at any given time. The vertical axis is the frequency of that shaking. Note that for these debris flow events the shaking takes place at all frequencies but most intensely in the 4-10 Hz band. Mount Rainier National Park provides many areal photos of the debris flow source and drainage and a very nice Press Release with other details.

Such debris flows were fairly common in the South Tahoma drainage in the 1990s up to the early 2000s. Here is a partial report on the seismic recordings of such a debris flow in August, 2001.

Other Cascade volcanoes have had recent debris flows as well. A recent one at Mount Baker took place in June, 2013, though this one may have had an avalanche origin rather than a jökulhlaup source.


Rock falls are yet another seismic source common on volcanoes. On Aug 19, 2015 at 11:49:53 AM PDT a seismic event at Mount Rainier fooled the PNSN automatic event detection and location system to thinking a Magnitude 3.2 earthquake had taken place. Since we never trust our computers to get things always right we quickly reviewed the seismic trances by eye and recognized the event to be a large rock fall, not a traditional earthquake (due to fault breakage). Since this event started rather abruptly (which is not always the case) we could time seismic arrivals quite precisely and got a pretty good location. Here are the set of seismograms from many stations located on Mount Rainier for this event. 

The black rectangles on each trace are our estimates of the arrival time of the main P-arrival used to locate the event. Here are the spectrograms for some of the same stations.

Note that the strong signals are much shorter in duration than for the debris flow mentioned above. The strong part lasts for only 10-15 seconds and the whole thing is over in less than two minutes. However, unlike the debris flow that only recorded on a station very nearby this event is recorded all over the mountain and even as far away as White Pass.

Different people picking the seismic arrivals and using different location algorithms all come up with locations very close to the same place as shown in the following oblique Google image.

The orange markers are location estimates done by different people/techniques for the same event. Stars are the nearby seismic stations. Queries to the staff at the Park resulted in the Park Geologist, Scott Beason recognizing what he thought was a rock fall scar on or near the Success Cleaver, very near our location estimate. Scott provided the following photo taken from some distance. The arrow is pointing to the apparent rock fall scar.

This event was no where near as large as several rock falls from Nisqually Cleaver in the summer of 2011.

Avalanches can have somewhat similar seismic signals but generally do not last as long as a debris flow signal but longer than a rock fall. Ice avalanches are fairly common during winter and spring. Of course large landslides such as the Oso event of March, 2014 are a very different story.

 

Why earthquakes disappear

May 31, 2015

by Renate Hartog

Earthquakes have been appearing and disappearing from the U.S.G.S. webpages, this blog explains why.

PNW Earthquake Early Warning prototype goes live

February 18, 2015

by Steve Malone

Earthquake Early Warning (EEW) is now officially working for the Pacific Northwest (Washington and Oregon) in the same way it has in California for the past two years. It even got tested the first night in operations and worked...sort of. A workshop hosted by the PNSN at the University of Washington on Feb 17 introduced the topic and featured software to a group of about forty invited participants. For a few details on the workshop and the system's first live test......
The Seattle Seahawks' win over the Green Bay Packers in over time ended up so exciting that many of us serious scientists forgot to be serious and analyze the seismograms. Yikes! What a crazy ending. In fact, most of the game was seismically quiet (and disheartening for Seahawk fans), but the final half hour produced several seismic events that challenges the original "Beast Quake" for seismic supremacy. For our semi-scientific analysis......

Panther versus Seahawk Game Analysis

January 11, 2015

by Steve Malone

Both the PNSN experiment and the Seahawks were successful Saturday evening. Both got off to a slow start. The PNSN QuickShake display had several bad dropouts during the first half and at half-time the Seahawks were only ahead by four points. When working properly QuickShake provided us with "early Warning" of a successful play that would show up on TV a few seconds later. None of the signals compared to the size of those during the original "Beast Quake" of 2011 but some interesting patterns were seen. For more detailed analysis......
Last year the PNSN used the vibrations generated by enthusiastic Seahawk fans at CenturyLink Field to test instruments, data acquisition and web based displays. Some might say the seismic monitoring inspired fans to greater cheering resulting in the Seahawk's successful Super Bowl run. With new instruments recently acquired and improved data processing and display techniques developed we are again looking for somewhere to test them. With the Seahawks again in the playoffs with home field advantage why not watch/help them again? For the details.....

Canadian ETS morphing to Washington one?

November 18, 2014

by Steve Malone

Over two weeks of tremor in central Vancouver Island has been progressing southward. Though we don't know about the geodetic component we suspect that this represents a slip event that is propagating southward. Since a southern Vancouver Island-Northern Puget Sound ETS is due about now the question is will this current activity continue all the way to southern Puget Sound. For some details.....

Great ShakeOut, Great success!

October 16, 2014

by Angel Ling

Congratulations and thank you for your participation in the Great ShakeOut Earthquake Drill! Hopefully it gave you a great opportunity to practice "Drop, Cover and Hold on", and review and update emergency preparedness plans and kits/supplies. Thanks again to make the Pacific Northwest safer. Read more to see what the Great Washington ShakeOut looks like at the PNSN!

The Great ShakeOut 2014 is Tomorrow!

October 15, 2014

by Angel Ling

Tomorrow is the Great Washington Shake Out 2014! Please join us in the World's largest Earthquake Drill at 10:16 a.m. on October 16. Read more...

Three Cascadia ETS events in past month??

September 4, 2014

by Steve Malone

Since Aug 10 there have been three parts of the Cascadia subduction zone with extended periods of near continuous tectonic tremor. Typically if tremor continues in a zone for more than 10 days then the geodesists can easily see an accompanying slow-slip event coincident with it. While tremor in the three zones has not been exactly synchronous it is somewhat unusual for this much of Cascadia to "light up" this strongly all together. For some of the details....

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.

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