Mystery 15 Year Quake Drought Raises Stakes In Cascadia MegaQuake Fears
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In 2006, geologists feared the worst - they believed a megathrust earthquake was imminent in the Pacific Northwest. Now in 2016, the Pacific Northwest may be revealing an alarming pattern of missing earthquakes in the same megathrust region that generates MegaQuakes.
Are we prepared for a major quake?
LOS ANGELES, CA (California Network) - On December 7, 2006, deep within the University of Washington's Seismology lab, where the inner sanctum of humming powerful computers, networks, monitors, and scientists dwell, data furiously pours in at a rate of multiple tens of thousands of numerical readings per second from over four hundred channels of seismic stations strategically distributed throughout the Pacific Northwest - is when the seismologists expressed a rare and candid moment, "nervousness". The earth had stopped vibrating. The "heartbeat" of the earth had "flatlined" as the near clockwork timing of the 10-14 month regular interval of a Cascadia Subduction Zone "Silent Earthquake", or Episodic Tremor and Slip (ETS), was not producing the anticipated flurry of deep tremors within in the locked section of the Cascadia Subduction Zone (CSZ).
In the minds of the seismologists, this could only mean one thing - the "Big One". Not willing to publicly infer "The Big One", a code word was used, understood by geologists, and made its way into the status blog. The word? "Parkfield".
Quoting the Dec 7, 2006 UW deep tremor news blog: "We are getting a bit nervous since there is still no tremor. But Herb Dragert, the epitime [sic] of calm gives the following based on his statistics. Nov 25 is the center of the expected window with plus or minus 35 days being the one sigma deviation so we still have some time to go before we may mention the dreaded word, 'parkfield'". The reason for the seismologists concern, over the sputtering out of the "Silent Earthquake", was that this "flatlining" indicated that the Cascadia Subduction Zone slip region was locked, thus risking a trigger of a massive locked plate rupture, creating a Great or even a MegaQuake. Just as the regular intervals, and associated deep fault slip patterns, of strong earthquakes at Parkfield California, the Cascadia Subduction Zone may have reached its "interval moment" to its next expected "The Big One".
Seismologists concerns peaked weeks later when a very candid blog update was posted Jan 3, 2007, stating: "Stop the ETS! This is frustrating. Since early on Jan 1 there has been no apparent tremor activity anywhere. What the^%^$#?".
Mother Nature had defied the seismologists' "one sigma deviation", of +-35 days, and had blown past this mark on December 30, 2006. Their frustration was understandable as the lack of tremors had the implication of a pending massive rupture - or in other words - the dreaded MegaQuake. Why wasn't a preliminary warning issued to the public? The only unofficial warning, if you were a techno-nerd following this blog, was "What the^%^$#?".
It wasn't until mid January 2007, did the anticipated ETS "heartbeat" begin and the crisis was averted. Here's the point - anyone following the blog would have noted serious alarm from decoding what the seismologists let slip out - "dreaded megathrust","35 days after Nov 25", then four days after passing this "one sigma deadline", scientists effectively said, to put it mildly, "Oh *blank*". The seismologists really did believe that there was a serious megathrust earthquake threat from this never-seen-before ETS type of "flatlining" behavioral pattern. Only having a rich paleoseismic history of past behavioral patterns are scientists able to adequately judge the significance of new aberrations. Since 2007, scientists have studied a number of ETS events, including in other subduction zones, and have concluded that ETS events are not as critical as a predictor of a potential large earthquake.
Fig 1. Regular Episodic Tremor and Slip (ETS) events have been occurring every 10-14 months since the 1990's in the PNW. 2016 Image shows the tiny deep tremors (time color coded dots) on a map where the CSZ is slowly slipping in a "slip zone" in the North American Plate and Juan de Fuca plate/Explorer plate. Image courtesy of PNSN.
However, for the last fifteen years, a new crisis may be developing. The crisis is "quiet". Again, scientists do not have enough of a rich paleoseismic behavioral pattern history to compare against in the CSZ to answer what this new anomaly means. This very unusual pattern of quiet has been developing within the Pacific Northwest where there is an unnatural absence of moderate to larger earthquakes within Oregon and Washington. Yet, at the same time, a notable increase of earthquakes are racking up just off the coast of Oregon and Washington from the Subduction Accretion Zone to the middle of the subducting Juan de Fuca plate. John Vidale, a principal investigator, professor, and state seismologist, with the Pacific Northwest Seismic Network (PNSN), originally identified the missing "onshore Oregon and Washington" phenomenon, back in 2012, in a PNSN Nov 11 blog story titled "Six-year drought of large Pacific Northwest earthquakes". But, it was simply concluded that the anomaly was due to just "random chance".
Fast forward to today in 2016. This "random chance" is now looking to be not-so-random but a true anomaly that may be of a big concern for the Pacific Northwest. This "Six-year drought" is now a "Fifteen-year drought" and counting, when looking at moderate (M5.0) or greater earthquakes. From 1990 to mid-2001, there have been ten moderate to stronger earthquakes within Oregon and Washington (see Fig 2). Yet, from mid-2001 to mid-2016 there have been zero. Starkly contrasting this "drought" is what may be called an off-shore "flood", no pun intended. This "flood" is a dramatic increase of off-shore earthquakes to seventy one in contrast with thirty seven earthquakes in the same comparable time periods. This is not explainable by any statistical "Monte Carlo" probability applied "Probability Density Function" to yield an earthquake recurrence answer. So what does this drought & flood mean? Is this an "Oh *blank*" moment?
Prior to the MegaQuake and tsunami in Japan, scientists noted that the earth was not as active in earthquakes. Agence France-Presse quotes Toshiyahu Nagao, Head of Earthquake Prediction Research Centre at Tokai University on how the earth became quiet before Japan's 2011 MegaQuake. "Considering the geographic location of Japan, we can say the current activities are rather normal and it was too quiet [before the 2011 earthquake]," Nagao told AFP.
Fig 2. Alarming MegaQuake Zone Mystery. A Quake Drought in Oregon and Washington while off-shore quakes have nearly doubled. Image base courtesy of Google Earth.
In reference to Toshiyahu Nagao regarding a "rather normal" reference in occurrence of earthquakes in a region, another important perspective, to this localized PNW mystery, is illustrated by looking at the worldwide rate of moderate (M5.0) or greater earthquakes (see fig 3). The data indicates that there has been no downtrend of moderate to stronger earthquakes worldwide during the timeframe of the PNW "drought". In contrast, the data slightly infers an average "increase" in worldwide moderate or stronger earthquakes from 2001 to 2015. So what is happening in the Pacific Northwest in the MegaThrust Cascadia Subduction Zone?
Scientists are quickly seeking to provide answers, as they were tasked by the National Earthquake Prediction Evaluation Council (NEPEC). The first step was a 2015 USGS Open File Report 2015-1151, titled "Earthquake Forewarning in the Cascadia Region", which outlines methods of recognizing critical geologic process changes, or any pattern changes that may yield "direct" and "indirect" forewarning conditions. "Direct forewarning" is from changes in actual observed geologic processes and/or patterns. "Indirect forewarning" is largely based on model predictions of increased earthquake risk via probabilities. Within this report, scientists have recognized that there's been a recent and much lower rate of seismicity in the Cascadia region, quoting "In the Cascadia region, similar methods may be applicable, but results have much larger uncertainties because input information has to come from places outside the region (presumed to be similar geologically) and because Cascadia's recent seismicity rates are much lower and its record of past earthquakes less complete relative to California."
It should be noted that a primary stated criteria in this report, to triggering a "direct forewarning", is identified as "Increased rates of moderate earthquakes within the subducting plate". Yet, for fifteen years there has been a stark dichotomy in an "increase" and a "decrease" in moderate quakes in the colliding tectonic plates that make up a dominant section of the Cascadia Region (OR/WA).
Why isn't a "direct forewarning" issued right now?
The report does define "operational earthquake forecasting" to be short term as anticipated to be within days to months. However, the report does not address a pattern that has developed for over a decade or more. Even though some scientists could possibly consider this Earthquake "Drought & Flood" as a proper criteria to give some type of earthquake forewarning, the report reveals a caveat that effectively renders any accuracy of a "forewarning" to be greatly diminished in worth. Quoting, "In short, establishing quantitative linkages between whatever is measured or calculated and earthquake occurrence remains a challenge in the Cascadia region. Even if we can identify extraordinary events, quantitative short-term forecasts will have huge uncertainties because they will be based on observations for which, by definition, no clear precedent exists."
In the end, perhaps this mystery will reveal its secrets as an "Oh *blank*", when the megathrust strikes.
Fig 3. Rate of Worldwide M5.0 or greater earthquakes from 1990 to 2015.
(1) Fall 2006 ETS - Deep Tremor in Cascadia Zone - Special Seismic and Geodetic studies , Nov. 2006 - Jan. 2007 - http://assets.pnsn.org/oldets/fall2006/
(2) Six-year drought of large Pacific Northwest earthquakes, November 11, 2012, by John Vidale - http://pnsn.org/blog/2012/11/11/six-year-drought-of-large-pacific-northwest-earthquakes
(3) Earthquake Forewarning in the Cascadia Region - By Joan Gomberg,1 Brian Atwater,1 Nicholas Beeler,1 Paul Bodin,2 Earl Davis,3 Arthur Frankel,1 Gavin Hayes,1 Vicki McConnell,4 Timothy Melbourne,5 David Oppenheimer,1 John Parrish,6 Evelyn Roeloffs,1 Garry Rogers,3 Brian Sherrod,1 John Vidale,2 Timothy Walsh,7 Craig Weaver,1 and Paul Whitmore8 - http://pubs.usgs.gov/of/2015/1151/ofr20151151.pdf
(4) Japan on alert after powerful earthquake in Pacific - https://www.theguardian.com/world/2015/may/31/japan-alert-powerful-earthquake
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