Seismo Blog

We are going to have The Big One. That’s a fact.

 

The final blog about The M9 Project is going to focus on you. What are you going to experience during a megathrust earthquake? How do we connect science and community? What should you do to be prepared?

 

The Next Stages of The M9 Project

 

Seismologists are not the only contributors to The M9 Project. Civil engineers, urban design and planners, statisticians, social scientists and public policy researchers also play a role in determining earthquake risk, safety measures, and public response to hazards.

 

Understanding the hazards and mechanisms of an earthquake is one thing, communicating effectively to the public is a completely different ball game. The next steps of The M9 Project focus on how we define and discuss hazards with communities.

 

For example, how does the way we design hazard maps affect how communities approach hazard planning? (See photo below) Or, how can hazards planning be steered towards rebuilding to community-specific values?

 

 

From assessing the utility of hazard maps (see image below), to hosting community planning workshops , The M9 Project’s research into “long term” preparedness- mitigation, response, and recovery focuses on how to best help you. We will discuss what to expect when the big one hits, as well as some resources so you can take steps to prepare .

 

Learning about Cascadia from other Large Earthquakes

 

The last megathrust earthquake on the Cascadia Subduction Zone occurred in 1700 AD, before written records were kept in the region. In addition to The M9 Project research at UW, we can also look to observations of other major earthquakes worldwide, to help us predict what The Big One may look like in the Pacific Northwest.

 

Ground Shaking

 

A magnitude 9 earthquake will generate very strong shaking for several minutes. The intensity, measured by the Modified Mercalli Intensity Scale (MMI), is determined by observations during an earthquake. Shaking tends to decrease farther away from the fault and will vary with local soil conditions, so intensity will vary by location. A more detailed description on intensity can be found here.

 

Below is a comparison of the shaking intensity from the 2001 Nisqually earthquake, compared to a hypothetical  M9.0 earthquake scenario. A megathrust earthquake will be felt over a much larger area, and generate stronger shaking.

 

 

 

You can find more about how magnitude and intensity are related here.

 

As part of The M9 Project, UW civil engineers are researching building response to strong ground shaking from a magnitude 9.0 earthquake in Seattle. This video from Kinetica Dynamics shows skyscrapers in Tokyo shaking from the 2011 M9.0 Japan earthquake.

 

 

Tsunami

 

Large earthquakes on a subduction zone are capable of generating large tsunamis. For example, the 2004 M9.1 Sumatra earthquake resulted in a 30+ meter high tsunami on the west coast of Sumatra (source). For more about tsunamis, visit our tsunami overview page.

 

This NOAA video models the tsunami from the 1700 Cascadia earthquake, which caused damage and loss of life as close as the west coast of North America, and as far away as Japan.  

 

 

We expect the next great Cascadia earthquake to be similar. As mentioned in our first M9 Project blog post, the record of past megathrust earthquakes can be found in muddy estuaries on the coast of the Pacific Northwest. In the layers of coast that have subsided and been filled again, there are bands of sand brought inland by tsunami waves, time and time again. Here is a article written by the American Museum of Natural History with more information on the Ghost Forests on the PNW.

 

Liquefaction

 

For liquefaction to occur, three things must happen. (1) Young, loose and grainy soil (2) needs to be saturated with water, and (3) experience strong ground shaking. The USGS, in coordination with California Geological Survey, give a summary of liquefaction and its effects here.

 

This video from the 2011 M9.0 Japan earthquake shows dramatic cracks in the ground, as well as liquefaction.

 

 

Our webpage on liquefaction includes video of the 2011 Christchurch earthquake, as well as links to liquefaction hazard maps for Washington and Oregon.

 

Landslides

 

Strong shaking can increase susceptibility to landslides.

 

This blog from the American Geophysical Union details some of the significant landslides in Paupa New Guniea that were triggered by a M7.5 earthquake on February 25th, 2011.

 

The Pacific Northwest is susceptible to landslides due to seasonal conditions, and strong shaking will increase landslide risk. Here are some resources from the states of Washington and Oregon.

 

Building Damage and Fires

 

The 1989 Loma Prieta earthquake caused widespread damage to infrastructure, such as the collapse of the Cypress Viaduct in Oakland, and fires in the San Francisco area.

 

Major cities in the Pacific Northwest would be just as susceptible to fire damage, and the construction of the Cypress Viaduct bears a striking resemblance to Seattle’s Alaskan Way Viaduct.

 

 

So, What Can I Do?

 

In order to prepare effectively, it is important to be aware of all earthquake-related hazards, such as the ones listed above. The following websites are great resources for earthquake hazards and preparedness in the Pacific Northwest. We encourage you to know your risks, be prepared, mitigate against hazards, respond safely, and enagae in holistic recovery planning.

 

In the event of an earthquake, don't forget to drop, cover and hold!

 

Special Thanks To

 

Dr. Erin Wirth, Affiliate Professor, University of Washington

Lan T. Nguyen, Doctoral Student, Interdisciplinary Urban Design and Planning, University of Washington

 

 

Landslide Study with Nodal Seismographs

March 26, 2018

by Amanda Thomas

A special seismic array for studying the RattleSnake Landslide. March 26, 2018

Seismology in the air

March 22, 2018

by Steve Malone

A bolide explosion off the coast is recorded on many seismic stations allowing us to get an approximate location.

Continued Landslide Monitoring

February 11, 2018

by Steve Malone

Steady landslide motion still of seismic interest. Update on March 26, 2018

January 2018 Oregon Tremor Event Update

January 31, 2018

by Nancy Sackman

Oregon tremor over!
In the previous blog post about The M9 Project, we talked about how the Cascadia Subduction Zone can generate an M9.0 earthquake. However, our understanding of what an earthquake of this scale would actually look like is less advanced. While we have evidence of past earthquakes (e.g., native oral histories, tsunami records), we have no quantitative observations of how strong the shaking would be during a megathrust earthquake in the Pacific Northwest.

Seismic monitoring of a slow landslide

December 30, 2017

by Steve Malone

Active landslide at Union Gap. Updated Jan 31, 2018.

December 2017 Oregon Tremor Event - Update

December 27, 2017

by Nancy Sackman

Update to Central Oregon Tremor - moving toward Portland and Medford

December 2017 Oregon Tremor Event

December 15, 2017

by Nancy Sackman

Over the past 9-10 days, it appears that tremor in central Oregon has picked up.
What is “The Big One” going to look like? How soon will we know it’s coming? How are our cities and communities going to fare?

Entiat area earthquakes and other seismicity

August 9, 2017

by Steve Malone

A few questions have popped up about earthquakes near Entiat, WA. I might as well address these and a few other questions.

Earthquake swarm NE of Bremerton

May 11, 2017

by Renate Hartog

Earthquake swarm near Bremerton; what is going on?

Volcano Preparedness May 2017

May 1, 2017

by Nancy Sackman

May is Volcano Preparedness Month for Washington State
On Monday morning (April 10) the Pacific Northwest Seismic Network (PNSN) was buzzing with activity, but not seismic activity. The Network hosted a press conference to announce the rollout of a new version of the earthquake early warning (EEW) system, ShakeAlert, which is now fully integrated across the entire West Coast of the United States.

Next ETS Expected any time now

January 24, 2017

by Steve Malone

Already over and then going again. Back-to-back ETS and finally over as of Apr 6.

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.

December 2017 Oregon Tremor Event

December 15, 2017

by Nancy Sackman

December 2017 Oregon Tremor Event

 

Over the past 9-10 days, it appears that tremor in central Oregon has picked up (Figure 1).  The last slow slip and tremor event was in February 2016, 22 months ago.  

 

Figure 1

Figure 1. Age progression of tremor in central Oregon for the past 9 days.  Earliest tremor locations start from 12/5/2017 and propagate roughly outward, clustering near Salem and Roseburg.  Last update was December 14, 2017.


 

Tremor is the release of seismic noise from slow slip along the interface of the Juan de Fuca and North American plates and lasts for several weeks to months.  This process is known as Episodic Tremor and Slip (ETS).  Slow slip happens down-dip of the locked zone (Figure 2).  The locked zone is where tectonic stress builds up until it releases in a great earthquake or megaquake.  The recurrence interval of slow slip and tremor varies at different regions along the Cascadia Subduction Zone.  

 

Figure 2

Figure 2. Cross section of the subducting Juan de Fuca Plate.  Figure from Vidale, J. and Houston H.  (2012) Slow slip:  A new kind of earthquake (Physics Today, 2012 pages 38-43).

 

The last ETS event in Cascadia started in February 2017 around the western edge of the Olympic Mountains.  The duration was approximately 35 days with a two-week quiescent period.  Prior ETS events in northern Washington/Vancouver Island area was approximately December 2015.  

 

The last ETS event in central Oregon was 2016 and lasted just over a week before it stopped on March 1, 2016.  

 

ETS events are still being studied to understand the processes about slow slip and megathrust earthquakes.  


More information about slow slip and tremor can be found here on the PNSN website.

December 2017 Oregon Tremor Event - Update

December 27, 2017

by Nancy Sackman

Tremor has continued in Oregon since the last post on December 15th.  Current tremor activity has been ongoing since about 12/5/2017 (figure 1).  

 

Figure 1

Figure 1. Age progression of tremor in central Oregon for the past two weeks.  Earliest tremor locations start from 12/5/2017 and propagate northerly and southerly.  Last update was December 26, 2017.

Since December 19th, tremor has now migrated northerly toward Portland and southerly toward Medford.

 

Figure 2

Figure 2. Tremor activity from 12/19 to 12/26 showing progression in a northern and southerly direction.

More FAQs on Slow Slip and Tremor

 

On our previous blog post, we briefly discussed what ETS (episodic tremor and slip) is.  Let’s go through a couple of more frequently asked questions.

 

1.What is tremor?

 

Tremor in the Cascadia Subduction Zone is the seismic noise of slow moving earthquake along the interface of the subducting Juan de Fuca Plate and the North American plates.  Compared to normal earthquakes, tremor has lower frequency energy and can last for minutes, hours or weeks.

 

2. What about volcanic tremor?

 

Tremor can also be volcanic.  But ETS is deep, non volcanic signatures that are a result of plate motion, not magmatic movement.

 

3. How deep are the tremors?

 

As it states on our website - “This is a topic of ongoing research.”  But research suggests that it occurs near the plate interface at approximately 30 - 40 km deep.   

 

4. What is the magnitude of tremor?

 

More than likely less than a 2.  According to our website, we don’t assign a magnitude during our automatic detection of tremor.  


 

Check out the map on our web page:

 

https://pnsn.org/tremor