Seismo Blog

Next ETS Expected any time now

January 24, 2017

by Steve Malone

The next 14-month Magnitude 6+ slow earthquake (Episodic Tremor and Slip) event is expected after a quiet period in Cascadia... or has it been that quiet..  (skip to: Winter 2017 ETS page)

Tremor throughout Cascadia seems to have been relatively quiet over the past four months; only 5,600 tremor locations from the wech-o-meter compared to an average of 15,300 for the six previous four month periods.  In fact the whole past year seems quieter than previous years.  Here is a table of number of tremor locations for the past seven years (Jan 15 - Jan 15).

Yearly tremor locations
 Year  # Tremor locations
2010   40,000
2011   42,000
2012   53,000
2013   49,000
2014   56,000
2015   48,000
2016   28,000

Because this seemed so unusual we wanted to make sure it was not due to a problem with the wech-o-meter or some trace data problem and so started looking at the details of when things changed and why. Ken Creager made some interesting plot comparisons that showed which seismic stations participated in generating tremor over the past few years and also what stations have been dead for various reasons.  Here is an example of a plot showing the tremor detections at each station in the Northern California sub-group (NC) by month (blue is Jan., yellow is Dec.) for the past three years.

It is difficult to interpret this in detail without knowing more about station histories.  But it is obvious that more stations participated in more tremor detections in 2014 than in 2016.  Some stations such as LGB stopped working midway through 2015 and others like M02C and WDC stopped working in the fall of 2016.  Others such as WOOD and CAVE started working some time after those others stopped working.

Here is a plot of the times over the whole last year that all the stations in the wech-o-meter generated data for tremor detection.  Again, it is not obvious how the outages might effect the tremor detections since the wech-o-meter is amazingly robust to minor outages now and then.  However, after lots of looking, checking, testing we have come to the conclusion that the decrease in tremor detections in the far south and far north is probably mostly (all?) due to station change and/or outages.

  Here is a detailed summary of the changes in sensitivity by sub-region progressing from south to north we have gleaned from these and other plots:

CC - Because of the loss of four important stations in May 2016 it seems that this subnet’s sensitivity was greatly reduced from then on.  The addition of new stations on Jan 23, 2017 may restore that sensitivity but remains to be seen.

 

NC - The loss of the above mentioned stations had little effect here. This regions sensitivity was only very slightly degraded until end of Sep 2016 when the TA stations were removed.  The combination of this loss and another station in Oct has made this subnet quite insensitive until new stations were added on Jan 23.  It remains to be seen if this will restore the previous sensitivity.

 

SO - All was OK here until end of Sep when the TA stations were removed.  Even with their loss some tremor at the end of a northward moving ETS was located into Oct.  Some replacement UO stations for the lost TA ones came on line near the end of Oct and was fully restored by late Nov.  While this region has not had many locations since then we think its sensitivity has only been slightly decreased (other than the ~3 week period in early-mid Oct.

 

CO -  This is the same as SO.  Only degraded for ~3 weeks.  This region has traditionally had very few tremor locations other than during the big central Oregon ETS.

 

NO, SW, NW, BC - Do not have any obvious degradation.  While there is a station or two down from time to time, nothing systematic or significant enough to make much difference in sensitivity.

NV - On or about Nov 12 three key stations went down that likely has reduced sensitivity here.  They are still down and may be for a while yet.  However, we have asked the Canadians to send us some more/different stations in this area that may improve things a bit.  Tremor in central and nothern Vancouver Island is being detected from time to time despite missing these stations.

On Jan 23 we updated the configuration of the wech-o-meter to make sure it is running as well as it can.  In particular the southern three subgroups have had new stations added so we may again see an average amount of tremor in the far south start showing up again.  Unfortunately there are no additional stations in the far north and so we must wait for repairs or some new stations on northern Vancouver Island before the system will be fully sensitive in that region.

With the next main ETS likely to occur within the next month or two we are again starting up a blog to track this event.  Though we don't expect anything much different than previous ones.  Check it out at ETS Event of Winter 2017.

Another Seahawks game experiment - Jan 7

January 6, 2017

by Steve Malone

Seahawks fans shake up the PNSN instruments.... again.
This Thursday, 50 million people around the world will drop, cover, and hold on for the 8th Annual Great ShakeOut, the largest earthquake drill in the world. This year at the PNSN, our motto is “drop, cover, hold on, and do something else too". We are thinking about other ways that we can enhance our preparedness for a major earthquake. This week on the SeismoBlog, we are outlining a few other strategies to supplement this year’s drill.

Cascade Volcano Seismology - a Tutorial

October 5, 2016

by Steve Malone

A newly modified tab on each volcano page gives a nice overview of each's earthquake history. Here is an introduction and some hints for interpreting these plots.

iMUSH: Adventures in the Field

September 12, 2016

by Lauren Burch

Seismology graduate student Mika Thompson shares a thrilling tale of wasps, fallen trees, and other impediments to science.

The Long Trek to MH09

September 8, 2016

by Shelley Chestler

Sometimes uninstalling a seismic monitoring station doesn't go quite as planned. Here is tale of my team's first attempt to take out a particularly stubborn station for the iMUSH (Imaging Magma Beneath St. Helens) project:
Both the Cascade Mountains and the Olympic Mountains are products of subduction, but not all mountain ranges are created in the same way.

Another debris flow avalanche at Mount Baker

June 15, 2016

by Steve Malone

Seismic signals on May 25 are evidence for the size and timing of yet another on of these avalanches.

All the mountains, oceans, and islands on Earth exist because of plate tectonics. Different plate boundaries produce different geologic features: divergent boundaries spread apart to form mid-ocean ridges and rift valleys, transform boundaries slide past one another to form strike-slip faults like the San Andreas, and convergent boundaries collide to form tall mountains, deep trenches, and volcanoes. This type of plate boundary is responsible for the numerous volcanic arcs around the Pacific Rim (often called the “Ring of Fire”), and formed our iconic Cascade Volcanoes. Here in the Pacific Northwest, the Juan de Fuca plate is subducting beneath the North American plate along a convergent plate boundary called the Cascadia Subduction Zone (CSZ). Subduction zones like this are the only fault systems capable of producing very large megathrust earthquakes, but they only do so occasionally - over the last 100 years, there have been 84 earthquakes of magnitude 8.0 or greater worldwide, and only 4 of them were greater than an M9.

 


The simplest answer to the question “Will there be another large earthquake on the CSZ?” is yes. However, the question of “when” is much more difficult to answer. Seismologists don’t know exactly when the next large earthquake will occur on the CSZ, but we do have a good picture of when they have happened over the past 10,000 years. If we divide 10,000 years by the number of ~M9 earthquakes found in that time period, the average recurrence rate for M9 earthquakes along the CSZ is roughly 550 years. We are 316 years past the last great CSZ earthquake in 1700, and we estimate that there is about a 15 % chance that an M9 will occur on this fault within the next 50 years. However, research on submarine landslide deposits shaken loose by big earthquakes indicate that M8+ earthquakes occasionally strike off the coast of Oregon in between “full rip” M9 events. This research suggests that there is a greater probability of reoccurence of a great earthquake in Southern Oregon than off the Washington coast, but there is not a consensus within the geophysical community as to specifically how much greater the hazard is.

One is a guess, and the other is an educated guess.
Earthquakes happen on faults, but where are the faults in Oregon and Washington? The new "Display Faults" tool on the PNSN Recent Events map can help you explore the locations of faults in the Pacific Northwest.

Exotic Events (not erotic events)

April 1, 2016

by Steve Malone

Seismically recorded non-earthquakes now have their own page at the PNSN.

Negative depth earthquakes?

March 30, 2016

by Steve Malone

Why do some earthquakes in our list have negative depths now?

Explosion "Earthquakes"

March 10, 2016

by Steve Malone

Two recent large explosions generated acoustic waves recorded on seismographs.

West Coast Earthquake Early Warning System on the Horizon

February 9, 2016

by Shelley Chestler

Last week the White House hosted the first ever Earthquake Resilience Summit. One of the main goals of the meeting was to discuss the potential for fully funding a west coast earthquake early warning system.

Back-to-back ETS events, maybe

February 6, 2016

by Steve Malone

Following the recent "standard" northern Washington ETS another has apparently started heading south toward Oregon.

Slow Earthquake Trembles beneath Vancouver Island

January 7, 2016

by Shelley Chestler

Did you know that there is a type of earthquake that happens so slowly that we can’t feel it? One of these slow earthquakes is happening under Vancouver Island and northern Washington right now!

A Perspective on Tremor Activity

January 7, 2016

by Aaron Wech

With tremor activity occurring in the Pacific Northwest, it's important to provide perspective.

Don't Sweat the Little Ones

December 14, 2015

by Shelley Chestler

The recent earthquakes around the Puget Sound are probably not indicative of the “big one.”

A new look for pnsn.org

December 4, 2015

by Jon Connolly

The new pnsn.org website aims to provide a better user experience for all devices, prioritize features, and provide robust availability during a seismic event.
The July 2015 New Yorker article “The Really Big One,” by Kathryn Schulz, shook up the Pacific Northwest (PNW) more than any earthquake has since the Magnitude-6.8 Nisqually earthquake in 2001. In the article’s most dooming statement, the head of the Cascadia FEMA division was quoted saying, “everything west of I-5 will be toast.” This assertion scared the living daylights out of PNW residents, creating a sense of terror and hopelessness that was the antithesis of what the article meant to do: to spur the region into preparing for this potentially devastating event.

Unusual earthquake swarm south of Bend, OR

October 23, 2015

by Steve Malone

A somewhat unusual earthquake swarm started early on Oct 22, 2015 in an area about 65 km (40 miles) southwest of Bend, OR (25 km WSW of La Pine, OR). 36 events have been detected and located by the PNSN as of noon on Oct. 23, the largest only Magnitude 2.5. This ongoing swarm is in the same area that had similar swarms in 2001 and 2012 and is likely just the same sort of thing taking place again. For more details and updates....

How big was that earthquake?

September 24, 2015

by Steve Malone

Determining an earthquake's size seems to often result in different and inconsistent estimates. The "Magnitude" of an earthquake can be determined by several different methods, all of which should have some relationship to one another and, at least be consistent one earthquake to another. Unfortunately that's often not the case. PNSN seismologists spend lots of time estimating (measuring and calculating) earthquake magnitudes and end up discussing (arguing over) different techniques and complaining (whining) about inconsistencies and criticizing (belittling) certain results. Recently some effort is being made to try and refine (improve) our standard, routine ways of determining magnitude. We are starting to upgrade our published catalog with these "improved" magnitude estimates so you may see these estimates change from what was in the catalog before. Don't worry. The earthquakes have not changed, just our estimate of how big they are. For the gory details of how this is being done......

Summer rockfall time, yet again

August 21, 2015

by Steve Malone

With hot dry weather it is not surprising that the seismic records for volcano stations show lots of signals consistent with rockfall/avalanches and other exotic seismic events. In fact it is a bit of a surprise that we have not seen more and bigger such events this summer........ so far. Recent activity at Mount Rainier has included a debris flow (probably related to a jökulhlaup) and a moderate sized rockfall from high on the southwest side of the volcano. For some of the seismic details.....

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.