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    Bay Area Dialational Strain


    Don in Hollister

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

    Bay Area Dialational Strain

    Post  Don in Hollister on Sun 03 Jul 2011, 3:50 am

    Hi All. I think its time to sit back, put your heels up and wait and see what happens next.

    There is an indication of dialational strain showing at for locations in the East Bay. It all started very close to the same time on 06/28/2011. There has also been an acceleration in creep at the Fremont site which sits in the middle of the strain meters.

    This is something new for me. I have seen an increase in strain at only one site in the past, but never 4 sites at the same time. 3 of the sites are close together with the 4th one somewhat removed.

    If the indications of strain is good then we could be in for a felt event larger then were use to. Take Care...Don

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

    the geysers - a place you've visited

    Post  beejean on Sun 03 Jul 2011, 5:01 pm

    Don in Hollister wrote:Hi All. I think its time to sit back, put your heels up and wait and see what happens next.

    There is an indication of dialational strain showing at for locations in the East Bay.

    I certainly found plenty of evidence to support your assessment of the risks facing Bay residents on the USGS site after I went looking. I'm beginning to think that Japan was just a linchpin that is failing on one side of the ocean, and as it goes, the other side just finds its moorings pulled apart.

    I heard that song about putting my heels up, titled "Don't Worry, Beee happy", but now I see on the strain map that you're not exaggerating about there being some strain, so I know you were speaking of putting you heels up like the writer of Ecclesiastes in your consideration of bothersome worry as a vanity only since what will be, will be.

    Now, although colors have come into disfavor as warning symbols, I still think, "red is red". cherry bom Area looks very strained as reported at the link for the stress map linked to a recent quake near "the Geysers" area

    Stress map - near one of about 50 EQ's at Geysers cherry bom

    Geysers geologic problems study
    Quote from this source is given below:
    "The closest active fault zone to the Fulton Substation site is the Rodgers Creek Fault Zone, located approximately 1.3 miles northeast of the site. The fault is capable of generating a magnitude 7 earthquake (WGCEP) 1990, Toppozada et al. 1994). The likelihood of such an event occurring in the period between 1990 and 2020 is 22 percent. An earthquake of this magnitude on the Rodgers Creek Fault Zone would generate very strong seismic shaking of Modified Mercalli Intensity (MMI) VIII at the Fulton site."

    "Other fault zones could produce moderate to strong ground shaking that could potentially affect the project area. These include the San Andreas and the Maacama Fault Zones. The Maacama Fault Zone is the closest major fault to the Eagle Rock Substation. Located approximately eight miles to the west, the Maacama Fault Zone could generate a magnitude 7 earthquake. The probability of this event has not yet been calculated. The Big Valley and Collayomi Faults are smaller active faults in the Clear Lake Highlands. The Geysers site experiences microseismicity (magnitudes of less than 1 to 3) on a daily basis related to the natural movement of molten rock below the surface as well as effects of geothermal energy production activities."

    "Estimates of the peak ground acceleration in an earthquake have been made for the project area based on probabilistic models that account for multiple seismic sources. Under these models, consideration of the probability of expected seismic events is incorporated into the determination of the level of ground shaking at a particular location. The expected peak horizontal acceleration generated by any of the seismic sources potentially affecting the area, including the project site, is estimated by the California Division of Mines and Geology at greater than 0.7g (g = gravitational acceleration). The expected peak acceleration at the Geysers site would be 0.5 to 0.6g."

    The facilities at the Geysers site would experience moderate ground shaking from a seismic event within the Rodgers Creek Fault Zone; however, the facility is not expected to sustain significant damage. PG&E power poles and lines are not anticipated to be damaged from ground shaking. Although local surface failures can cause collapse of poles, evidence of unstable soils or slopes were not identified at the proposed pole locations. "

    From Wikipedia, don't know if you agree with them, but on another note, I saw that after the Kobe Japan quake Japanese scientists carefully documented uneven Japanese related fault stresses some higher and some lower per fault but not entirely predictable. Wikipedia writers discuss the Hayward fault area and Rodgers Creek at the same time in the following quote. i bet you have a more informed opinion, but I think the "big picture" is that there is a big uptick in the area lately :

    "The estimated probability of a major earthquake on the Hayward within the next thirty years was estimated at nearly 30 percent, compared to about 20 percent for the San Andreas Fault, which can have larger earthquakes but farther away from a significant portion of the urbanized parts of the Bay Area. Recent (January 2008) assessments[15] suggest that the Hayward, Rodgers Creek, and Calaveras faults may be more likely to fail in the next few decades than previously thought."hayward fault wiki comments

    Last edited by beejean on Mon 04 Jul 2011, 1:10 am; edited 1 time in total (Reason for editing : decided to expand on the reason for my concerrn about the area 50-80 miles N of San Fran based on the comments that Don feels are groundless, but I think jury is out)

      Current date/time is Mon 18 Jun 2018, 2:13 am