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    Seismologists Are A Little Nervous

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    Don in Hollister

    Posts : 137
    Join date : 2010-02-17
    Age : 83
    Location : Hollister, California

    Seismologists Are A Little Nervous

    Post  Don in Hollister on Sun 11 Jul 2010, 1:36 pm

    Hi All. The quakes down in Southern California are making some seismologists a little nervous including this one. The majority of the quakes near the main event are more then likely aftershocks, but the further you get away from the main even the more likely they are triggered quakes.

    The 7.2M quake occurred on the Laguna Salada which is the Mexican Elsinore fault. The majority of the aftershocks went north along the Laguna Salada/Elsinore fault with the number of aftershocks on the Laguna Salada/Elsinore fault. There was a cluster of quakes further to the north and to the east of the Elsinore fault. This where the 5.2M quake occurred and is most likely associated with the San Jacinto fault.

    This gives a pretty good indication of the direction of stress. We say pretty much the same thing occur between the Landers and Hector mines quake. The time period between those two quakes was about 7 years. It could take the same amount of time for the next major quake to occur or it could occur next week on any one of the faults in the area. It will occur of that there is no doubt. It is just a matter of when. Of course with all the prediction experts we have in the US they should be able to tell us, when, where and how large it will be. However if you are prepared for a major quake you don't need no one predicting it for you. The results will be nearly the same. Take Care...Don

    http://latimesblogs.latimes.com/lanow/2010/07/increased-earthquake-activity-predicted-for-california-faults.html
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    beejean

    Posts : 542
    Join date : 2010-02-20
    Location : Boston area

    Preparation Worth the Effort indeed

    Post  beejean on Sun 11 Jul 2010, 4:02 pm

    Don in Hollister wrote:... it could occur next week on any one of the faults in the area. It will occur of that there is no doubt. It is just a matter of when. Of course with all the prediction experts we have in the US they should be able to tell us, when, where and how large it will be. However if you are prepared for a major quake you don't need no one predicting it for you. The results will be nearly the same. Take Care...Don

    First there is the desire to know when, but it does not always lead to the desire to prepare. Why? Just one of life's mysteries. I'm glad you tied the two together by letting us know the probabilities. Probabilities aren't enough for some folks, but they are for me.

    Thank you for posting about this! silent Smile
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    marc / berkeley

    Posts : 41
    Join date : 2010-02-22

    Me Too...

    Post  marc / berkeley on Tue 13 Jul 2010, 3:39 am

    It's so fascinating Don!

    The Elsinore is like a waking shudder unzipping and the San Jacinto is like buttons popping, but which one will hit first.

    The links you provided sort of give a clue, at least in my mind! ( my money is on the San Jacinto giving us a show first with the grand event on or along the Elsinore.) Whittier would be the worst case, and may simultaneously trigger which would mean more 'fun' for all. A grim prospect. It's one I hadn't considered until I read your linx. (thanx for posting them by the way...)


    I think it will begin within three years, and I sure am watching this syzygy window for more clues! The ones that "report" during this time are areas where the stress is starting to give, then look for the nearby quiet spots and Bingo!

    I wish it were that simple but I know that nature is a complex woman. I also hope you and your heart will stick around for the show, even if it's beyond 7 years!

    I know the Bay Area is also likely to rumba with that time-frame, but I'll look at that potential later....heh heh, more fun to look in other backyards first(where there is a bit more action).

    The next three days have me on a chair! (watching & waiting)



    --M

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    NiteOwlSoCal

    Posts : 54
    Join date : 2010-02-17

    Re: Seismologists Are A Little Nervous

    Post  NiteOwlSoCal on Thu 15 Jul 2010, 8:10 am

    Hi, Don, hope you are well. Thanks for posting the link; it was very interesting reading.

    I have a semi-related question for you, if you happen to know the answer.

    Regarding this paragraph in that article:

    "You can actually mathematically map the transfer of stress from one fault to another after an earthquake," Rundle said. "Small earthquakes are a response to the underlying levels of stress. The higher the level of stress, the higher number of small earthquakes one typically finds. We use the patterns of small earthquakes to forecast the occurrence of larger earthquakes."

    Based on the knowledge that a higher number of small quakes is an indication of increased stress that might trigger a larger quake, wouldn't it be more informative to the public if the USGS included the microquakes (under 1.0) on their map for CA/NV? Do you have any idea why they've stopped including them?

    Don in Hollister

    Posts : 137
    Join date : 2010-02-17
    Age : 83
    Location : Hollister, California

    Re: Seismologists Are A Little Nervous

    Post  Don in Hollister on Fri 16 Jul 2010, 7:55 pm

    Hi Niteowl. USGS is using accelerometers. They cost about $1000.00 per unit. A seismometer costs about $30,000.00 per unit. They both do the same thing except the accelerometers don't record quakes very good with a magnitude below 2.0M. The other problem is that in high culture areas it is hard to see a quake below 1.0M due to traffic noise and what have you.

    When a quake is recorded below 1.0M it's hard to tell if it's a true quake or a truck going by. Also the quakes you want to see have to be around a mile from a seismometer in order for the seismometer to record it and you need 3 seismometers to record it in order to get the correct magnitude and location.

    A couple of years ago Petra and did a little test and we found we were recording more quakes on Sunday and the wee hours of the morning between 1:00 and 4:30. The culture noise is larger then the micro quakes and this covers the micro quakes making them impossible to be seen unless the seismograph is one of the newer ones that allows you to stripe away the noise until you can reach the “coda”. (The coda is composed of seismic waves which are multiply randomly scattered by 3-D inhomogeneities in the upper crust, and sample a broader swath than direct waves. As a result, path and distance corrections can take the form of average crustal properties and simple geometrical spreading relations, and source radiation patterns are washed out. After a station is calibrated for site response the correction holds for all future events. Because the coda method uses a continuum of arrivals rather than a small number of discrete direct arrivals a single station gives a much more robust measurement of $M_{w}$ than a single station MT inversion. In a densely instrumented region like Northern California coda-derived $M_{w}$ determinations can then be made over a much broader range of earthquake sizes (from $M_{w} \approx 2$ through $8$). The coda method also provides stable determinations of earthquake moment-rate spectra, which can be used to examine $E_{s}/M_{0}$ scaling in the study region. (The coda is composed of seismic waves which are multiply randomly scattered by 3-D inhomogeneities in the upper crust, and sample a broader swath than direct waves. As a result, path and distance corrections can take the form of average crustal properties and simple geometrical spreading relations, and source radiation patterns are washed out. After a station is calibrated for site response the correction holds for all future events. Because the coda method uses a continuum of arrivals rather than a small number of discrete direct arrivals a single station gives a much more robust measurement of $M_{w}$ than a single station MT inversion. In a densely instrumented region like Northern California coda-derived $M_{w}$ determinations can then be made over a much broader range of earthquake sizes (from $M_{w} \approx 2$ through $8$). The coda method also provides stable determinations of earthquake moment-rate spectra, which can be used to examine $E_{s}/M_{0}$ scaling in the study region. in the upper crust, and sample a broader swath than direct waves. As a result, path and distance corrections can take the form of average crustal properties and simple geometrical spreading relations, and source radiation patterns are washed out. After a station is calibrated for site response the correction holds for all future events. Because the coda method uses a continuum of arrivals rather than a small number of discrete direct arrivals a single station gives a much more robust measurement of $M_{w}$ than a single station MT inversion) and can be very time consuming only to find you have no quakes below 1.0M. That's not to say they didn't occur only that they weren't recorded. Take Care...Don

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    Re: Seismologists Are A Little Nervous

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