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Thread: Geology influences geomagnetic storm effects

  1. #1
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    Sep 2003
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    Geology influences geomagnetic storm effects

    Makes a huge amount of sense.

    Nationalgeographic.com

    On a regional scale, the underlying geological makeup can have a hugely significant influence on a storm’s damage potential. Sedimentary rocks tend to have pore space that contains water, which makes them electrically conductive, says Ciaran Beggan, a geophysicist with the British Geological Survey. Metamorphic and igneous rocks are denser and less porous and so are more electrically resistive.

    But during a geomagnetic storm, errant magnetic activity induces electrical currents at the planet’s surface that can mean trouble for a city built on top of metamorphic or igneous rock. Although the current can’t easily flow through these rocks, “if you’ve short-circuited the insulating part of the earth with a power grid, it flows right through it,” causing damage, Love says.

    This means when the next major geomagnetic storm strikes, “one power grid in one part of Europe might be perfectly fine, but another just a few hundred kilometers away might be seriously impacted by the same event,” says Juha-Pekka Luntama, head of the space weather for the European Space Agency's Space Situational Awareness Programme.
    Space Weather (journal)

    Abstract:
    Maps are presented of extreme‐value geoelectric field amplitude and horizontal polarization for the Northeast United States. These maps are derived from geoelectric time series calculated for sites across the Northeast by frequency‐domain multiplication (time‐domain convolution) of 172 magnetotelluric impedance tensors, acquired during a survey, with decades‐long, 1‐min resolution time series of geomagnetic variation, acquired at three magnetic observatories. The maps show that, during intense magnetic storms, high geoelectric amplitude hazards are realized across electrically resistive, igneous and metamorphic rock of the Appalachian Mountains and the New England Highlands, while low geoelectric hazards are realized across electrically conductive, sedimentary rock of the Appalachian Plateau and the Mid‐Atlantic Coastal Plain. From statistical extrapolation, once‐per‐century (100‐year) geoelectric amplitudes are highest at a site in Virginia at 25.44 V/km (followed by a site in Maine at 21.75 V/km and a site in Connecticut at 19.39 V/km); 100‐year geoelectric amplitude exceeds 10 V/km at 12 sites across the northeast; geoelectric amplitude is lowest at a site in Virginia at 0.05 V/km. Average errors for these values are estimated to be about 38%, or much less than the more than 2 orders of magnitude range seen in geoelectric amplitudes from one survey site to another across the northeast. It is noteworthy that geoelectric fields tend to be most (least) polarized at locations with high (low) geoelectric hazard. Furthermore, geoelectric fields over the Appalachians tend to be polarized southeast‐to‐northwest, or generally in a direction orthogonal to the southwest‐to‐northeast geological strike. Results reported here inform utility companies in projects for evaluating and managing the response of power grid systems to the deleterious effects of geomagnetic disturbance.
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  2. #2
    Join Date
    Jun 2002
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    1,975
    Seems to me that western Iowa, Nebraska,eastern Colorado ought to get hit hard too, with all that deep mountain runoff and silt. Likely WI, and IL to in the limestone regions.
    This does seem an obvious result. But someone needed to measure it, and probably got a PhD as a bonus.

  3. #3
    Join Date
    Feb 2005
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    11,573
    I wonder if this knowledge might allow a future Carrington type event to be harvested.

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