Evidence found of low slip earthquakes impeding progression of large destructive quakes

Evidence found of low slip earthquakes impeding progression of large destructive quakes
Installing S-net seafloor observation equipment. Data included seismograms collected by this equipment. Credit: National Research Institute for Earth Science and Disaster Resilience

A team of researchers affiliated with several institutions in Japan has found evidence of slow slip earthquakes impeding the progression of large destructive quakes. In their paper published in the journal Science, the group describes their study of both types of earthquakes and the events surrounding the large Tohoku-Oki quake in 2011, and what they found. Heidi Houston, with the University of Southern California, has published a Perspective piece on the work done by the team in the same journal issue. She also outlines the two large earthquake tracking systems that have been installed in Japan and on the bottom of the ocean along the Japan Trench.

The Japan Trench is a seafloor depression off the coast of Japan—it was created by tectonic forces as the Pacific plate was pushed beneath the continental Okhotsk Plate, a process that continues today. It is also the site of many undersea earthquakes, which can lead to tsunamis, at least in its midsection, according to evidence found by the researchers with this new effort.

As part of their study of slip (slow) earthquakes, the researchers were studying data recorded by the Hi-net seismograph array, which covers Japan with about approximately 800 seismometers, and GEONET, which is an array of sensors on the seabed in the Japan Trench. Slip earthquakes are much slower-moving earthquakes, so they do not shake the ground or cause damage. But they are also harder to detect. To detect them, new technology has been developed that looks for tremors, very-low-frequency earthquakes, and slow slip events (those that migrate enough to show up on sensors).

  • Evidence found of low slip earthquakes impeding progression of large destructive quakes
    S-net observation equipment before installation. Credit: National Research Institute for Earth Science and Disaster Resilience
  • Evidence found of low slip earthquakes impeding progression of large destructive quakes
    A ship installing the S-net observation equipment. Credit: National Research Institute for Earth Science and Disaster Resilience

The researchers report that they found a lot of slip earthquakes happening in the northern and southern parts of the Japan Trench, but very few of them in the center section. Conversely, they found evidence of large earthquakes happening in the center section, but not in the northern or southern sections. And they also found that during the large Tohoku-Oki quake, the shaking occurred mostly in the center section—seismic waves stopped when they reached the boundaries of the northern and southern sections. Houston suggests this finding will need to be confirmed in other places, but for now, it appears that it might help with large quake forecasting efforts in the years ahead.


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Rumbling from ocean trenches could be sign that Japan faces mega earthquake

More information: T. Nishikawa el al., "The slow earthquake spectrum in the Japan Trench illuminated by the S-net seafloor observatories," Science (2019). science.sciencemag.org/cgi/doi … 1126/science.aax5618
Journal information: Science

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Citation: Evidence found of low slip earthquakes impeding progression of large destructive quakes (2019, August 23) retrieved 19 September 2019 from https://phys.org/news/2019-08-evidence-earthquakes-impeding-large-destructive.html
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Aug 23, 2019
Makes sense: If part of the fault can creep and slip, there may not be enough accumulated stress to transmit a 'fast' quake to next section.
Hopefully, slow-slip sections like this on US & Canada West Coast will prevent the San Andreas & Co un-zipping when the Mega-Thrust cuts loose, and vice versa...

Aug 24, 2019
Hopefully, slow-slip sections like this on US & Canada West Coast will prevent the San Andreas & Co un-zipping when the Mega-Thrust cuts loose, and vice versa...
...but it won't. Too many feet behind and long overdue for correction. Like otto always say, you might postpone the inevitable but you can't avoid it.

Any day now. The recent split in the desert only a foreshock. Quakes accelerating in frequency and magnitude there and everywhere else in the world. Something fishy going on.
https://earthquak...kes/map/

-Switch on '7 days, all magnitudes US' for a thrill.

Aug 24, 2019
"-Switch on '7 days, all magnitudes US' for a thrill."

Sorry, TGO, not convinced. Remember USGS etc recently emplaced *many* local sensors to catch those recent Cal quakes' very small aftershocks, better map the crossing faults.

My point is such slow-slip sections *may* sufficiently isolate zones such the entire seaboard won't unzip as one from Mexico to Alaska...
Sure, any serious quake on any section will be very, very bad, totally 'Be Not There'. But, given the logarithmic scale, even a bunch of nasty 5~~7 is preferable to one 'Great Quake', a vast 8~~9 which slumps half the Cal / Oregon etc coast into sea, souses the rest with a tsunami train...
"San Andreas Fault: Twinned with the North Anatolian..."

Aug 25, 2019
My point is such slow-slip sections *may*...
"Once in a while, the North American plate slides just a little bit, a few inches toward the west. So, the region that's just under the Olympic Peninsula or on Vancouver Island is moving just a few inches to the west during these slow slip events," said Harold Tobin, director of the Pacific Northwest Seismic Network.

"But what's concerning for some seismologists, and there is a difference in opinion about this, is that the slow-slip event will slightly increase the chances of earthquakes, or even the "big one." Typically the plates are locked, according to Tobin. But because the plates are moving, there is concern that the "slip" will cause an earthquake."

-So are you done guessing yet? What is locked is locked. Ancillary movement only transfers more load to the locked region.

Aug 25, 2019
""We have an increased chance of a big earthquake initiation because the slip is adding load to the bottom edge of the fully locked zone of the Cascadia Fault," said PNSN seismologist Bill Steele."

-The question is whether the slow slip will hasten the big earthquakes on the US west coast, not whether it will lessen their severity. Nothing is being dissipated, only transferred.

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