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California earthquake swarm

Discussion in 'Environmental Discussion' started by tochatihu, Jul 6, 2019.

  1. William Redoubt

    William Redoubt Senior Member

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    I was in my cabin along the Colorado River north of Blythe, California. Very significant shaking there, lasting for about 40 seconds Back and forth motion north to south. I did not hear the p wave, but the stereo was on playing Top Country (more sh*t on my boots).

    2019-07-05 7.1 Quake.jpg
     
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  2. tochatihu

    tochatihu Senior Member

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    Folks without earthquakes deserve to know about these interesting things. P (pressure) wave(s) are the leading edge of rock-compression transmission. If you have higher land or buildings nearby you get that through air (audio).

    S (shear) waves arrive later, telling about rocks moving to their new positions. This longest phase can reveal just how large movements were. When 'my' building wiggled for more than a minute in 2008, I knew that somewhere, it was very bad. See Sichuan 2008.

    north to south@21. Can you even imagine that before seismometers were deployed, such observations would have been very important?
     
  3. tochatihu

    tochatihu Senior Member

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    Let it be known that earthquake-energy release is way above linear on oft-reported 'magnitude' scales. How much more? Read something. I'm not tellin'.
     
  4. William Redoubt

    William Redoubt Senior Member

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    The p wave is very distinct from any other acoustic experience. In 2001, I was working in my office east of Seattle on the second floor of an engineering firm. For the previous 5 years, or so, I had collaborated with scientists on producing design manuals for earthquake-related bridge construction. I recall several fascinating discussions with the science team related to the p-wave. On that morning, I heard the sound of the p-wave, and immediately left the building. Seconds later the s-waves hit. A 6.9, the Nisqually quake caused billions in damage. Although our building only suffered from fallen objects (a file cabinet in my office tipped over), it was a very memorable experience.

    This most recent Cali Quake is the largest in over 20 years, and much larger than the Northridge event of 1994.
     
  5. William Redoubt

    William Redoubt Senior Member

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    Magnitude is not linear. It's exponential. Essentially, each successive magnitude is 33 times larger than the last. That means a magnitude-8.0 earthquake is 33 times stronger than a 7.0, and a magnitude-9.0 earthquake is 1,089 (33 x 33) times more powerful than a 7.0 — the energy ramps up fast.
     
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  6. tochatihu

    tochatihu Senior Member

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    My best p-wave 'audition' was in Pasadena CA, long ago. A minor shake moved through NW -> SE and it sang so clearly.
     
  7. tochatihu

    tochatihu Senior Member

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    Folks who think about decibels (and bels) may see a similarity.
     
  8. fuzzy1

    fuzzy1 Senior Member

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    I was in an engineering facility north of Seattle, also on the second floor. I heard what sounded like rumblings in the mezzanine below, before we figured out it was a quake. The space under the nearest table was quickly fully occupied, so I headed for an exit instead, getting hit by multiple falling ceiling tiles on the way. As I got out, my impression was that half the facility's ceiling tiles had come down. But upon re-entry, discovered that it was less than two dozen fallen total, I just happened to be under the place that lost the most.

    There was lots of other acoustic ceiling tile damage though. The main building, the stairwell structures on the sides, and the suspended fire sprinkler system, all moved and swayed separately. The result was that many sprinkler heads greatly enlarged their holes through the tiles. And there were many partially crunched tiles adjacent to those stairwells.

    Workers with south side window views could see the surface waves approaching through the parking lot.
     
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  9. Diemaster

    Diemaster Active Member

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    how I learned about earthquakes :)

    RIP Mark Spits (The Lab Rat)
     
  10. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I've been fortunate not to get stuck in a big one. I felt many minor ones, and two medium ones between living in Alaska and California.

    Oddly enough the Northridge quake affected me in an automotive context even though I lived in Massachusetts that year. My VW had rusted out its exhaust and I ordered a new system... from a shop in LA county. It was an extra week or so for the parts to show up. Looking back, I'm kind of impressed it was that little of a delay.
     
    #30 Leadfoot J. McCoalroller, Jul 8, 2019
    Last edited: Jul 8, 2019
  11. hill

    hill High Fiber Member

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    my favorite earthquake fun fact read recently was that in order to reach magnitude 12, the Earth would have to split in half.
    I'd watch that

    .
     
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  12. bisco

    bisco cookie crumbler

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    from your living room.

    i only know enough not to move to cali
     
  13. Diemaster

    Diemaster Active Member

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    Wise move. were making plans to move out of CA as soon as possible.
     
  14. bisco

    bisco cookie crumbler

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    don't come here, it's horrible!:p
     
  15. Diemaster

    Diemaster Active Member

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    no were 98% sure were moving to AZ or TX.
     
  16. William Redoubt

    William Redoubt Senior Member

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    Don't move to the Northwest. The Cascadia Subduction Zone along the Washington/Oregon/ BC coast will be source of the big one. And don't install gas appliances. That's what causes the fires. Multi-story buildings? No dice -- soft story collapse. Stay away from oceans -- tsunamis. Non-flat areas: watch out for landslides.
     
  17. bisco

    bisco cookie crumbler

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    hmm...

    i don't think i'd be happy in either place year round. but if you're used to the heat, it's different i suppose
     
  18. Diemaster

    Diemaster Active Member

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    heat I can handle as long as it's a dry heat with as little humidity as possible. heat+humidity is the killer.
     
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  19. bisco

    bisco cookie crumbler

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    agreed
     
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  20. tochatihu

    tochatihu Senior Member

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    "data gets to the scoring judges" :)

    Most quakes are scored by programmed criteria (machine judges). A few get reviewed by wetware. Chosen mostly by size*. Less by newsworthiness I think.

    Scoring includes focal mechanism, which looks like a beach ball :)

    ==
    Daily aftershocks (M 2.5+) are now down to 116. That was nearly 700 initially.

    *Quakes chosen by size, not the geologists. That might not have been completely clear :)