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Depths of earthquakes - particularly deep earthquakes

  1. Oct 6, 2016 #1

    Astronuc

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    Staff: Mentor

    I just read a headlines about "Earthquakes in California are discovered more than 15 miles deep."
    https://www.yahoo.com/news/m/e994149f-34a9-3ab4-b16f-fd382e41b607/ss_earthquakes-in-california-are.html [Broken]
    Apparently that's a surprise for California. The article is attributed to the LA Times.

    Then there is the first sentences, "Scientists in California have found that earthquakes can occur much deeper below the Earth’s surface than originally believed, a discovery that alters their understanding of seismic behavior and potential risks. Seismologists have long believed that earthquakes occur less than 12 to 15 miles underground in the planet’s brittle, rocky crust." However, we've been watching deep earthquakes, deeper than 15 miles for decades. One can find records on deep earthquakes on USGS.

    For example,
    M5.0 - 14km SSE of Las Navas, Philippines
    2016-10-06 19:09:50 UTC 12.211°N 125.076°E
    61.5 km depth
     
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Oct 6, 2016 #2

    fresh_42

    Staff: Mentor

    Have you read about the second fault next to the San Andreas fault they allegedly have found some days ago?
     
  4. Oct 7, 2016 #3
    Localized seismic deformation in the upper mantle revealed by dense seismic arrays---http://science.sciencemag.org/content/354/6308/88. [Broken] I was a bit stunned by all the media hype. Interestingly, the paper presents it more matter-of-factly. The real surprise in their work was that the Newport-Inglewood Fault possibly extended down to the mantle. In my last years of oil exploration in California, we had seismic data that showed major boundary faults in California and Nevada extended to the mantle. By 2001, that knowledge was the basis for pretty redefining the tectonic model of the western US. I don't recall quake intensities and depths along those faults, but it should be no great surprise that they would be deep.
     
    Last edited by a moderator: May 8, 2017
  5. Oct 7, 2016 #4
    The "discovery" of the Salton Trough Fault is a bit odd. I can understand how the underwater portion might have been missed all these years, but it apparently tracks close to the San Andreas Fault onshore. Not so close that it couldn't be distinguished from the SAF.
     
  6. Oct 7, 2016 #5

    Astronuc

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    Well, it looks like they recently announced the discovery in the current issue of the Bulletin of the Seismological Society of America.

    Geophysical Evidence for a San Andreas Subparallel Transtensional Fault along the Northeastern Shore of the Salton Sea
    http://www.bssaonline.org/content/106/5/1963.abstract
    "This study posits that the extensional deformation is due to a previously unmapped fault, here named the Salton trough fault (STF)."

    New Southern California earthquake fault found near San Andreas
    http://www.desertsun.com/story/weat...trough-fault-salton-sea-earthquakes/91609892/

    Valerie Sahakian, a researcher with the U.S. Geological Survey and lead author of the study, said the newly named Salton Trough Fault has no connection to the recent quake swarm and the timing of the announcement is coincidental.

    http://time.com/4521244/new-fault-line-california-salton-trough/

    http://earthquake.usgs.gov/hazards/qfaults/map/#qfaults (is it the red dotted line on the eastern side of the Salton Sea?)
     
  7. Oct 7, 2016 #6

    davenn

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    seems typical of really bad reporting and mis-interpretation of what the seismologists probably said
    this sort of mis-information really annoys me

    we all know ( those of us into this stuff, at least) that quakes go much deeper than 10 - 15km
    eg. the Philippines one mentioned and on terms of deep earthquakes, that one is really shallow
    when the large subduction zones are looked at with quake depths to well over 600 km


    Dave
     
    Last edited by a moderator: May 8, 2017
  8. Oct 11, 2016 #7
    Indeed. The detection of ever deeper quakes, defining a descending plane, was one of the key pieces of evidence leading to the recognition and acceptance of plate tectonics. It astounds, frustrates and angers me when popular accounts make such egregious errors.
     
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