Where it rains, it rumbles: Rainwater can help trigger earthquakes

Discussion in 'Earth Science' started by Plazma Inferno!, May 5, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

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    Rainwater and snowmelt help fuel intense earthquakes along a New Zealand tectonic fault, new research suggests.
    Tracing the source of water flowing through New Zealand’s Alpine Fault shows that more than 99 percent of it originated from precipitation. Scientists knew that underground fluids help trigger quakes, but the origins of these fluids have been uncertain. In this case, the nearby Southern Alps concentrate rainfall and meltwater on top of the Alpine Fault while the fault itself serves as an impermeable dam that traps the water.
    According to researchers, the fault essentially is promoting its own large fluid pressures that can lead to earthquakes. Identifying the fluid source will help scientists better predict the fault’s seismic cycle.

    https://www.sciencenews.org/article/rainwater-can-help-trigger-earthquakes

    Paper: http://www.sciencedirect.com/science/article/pii/S0012821X16301418
     
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  3. timojin Valued Senior Member

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    I have read long ago that the rain wate in the fault area serves as a lubricant for fault to slide and promotes earthquakes.
     
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  5. Ophiolite Valued Senior Member

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    However that is not what is being suggested here. They point to the generation of high pore pressure as the root cause.

    Frankly without reading into the matter further I am confused by their argument. With one exception all abnormally high pore pressures arise through the trapping of existing water beneath a permeability barrier. I am missing how they are getting rainfall past that permeability barrier, against a pressure gradient in order to raise the pore pressure in the region of the fault. Presumably they have thought this through, but so far I can't see how. (And the one exception - essentially an artesian explanation - does not seem obviously applicable.)
     
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I don't know, but guess the "permeability barrier" is more vertical than horizontal. A strong structure moving westward in collision with a weaker structure that is beinging thrown upward making the Southern Alps.

    I have assumed the Southern Alps are on the east side of New Zealand. If they are the west side, reverse the directions of motion stated above.

    The heavy annual rain fall runs down the Alps and "slams" into that permeability barrier. - I. e. the water does not need to get under some permeability barrier. This may be the essence of a solution to your confusion about that. I have obviously not learned much about it, but think this may be the reasons for high water pressure against a permeability barrier.
     
  8. Ophiolite Valued Senior Member

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    I see what you are getting at Billy, but high pressure is - in my experience - referenced to pressures higher than hydrostatic. There are several ways of generating these below a permeability barrier, but the only way of generating one above a barrier is through the artesian effect. That is only a pressure above hydrostatic because we are mixing two reference depths.
    This may be what is being described here, but I cannot - yet - envisage the mechanism clearly.
     
  9. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    My idea is that water could be trapped against one side of the some what vertical permeability barrier, then there would be a net force acting on the permeability barrier. Presure itself has no direction. It is the differential presure which makes the force and its direction.
     
  10. Yazata Valued Senior Member

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    Good news for us Californians, where rain doesn't seem to happen any more. (Actually we got near normal rain this winter (our rainy season) but it was a strong el nino year when floods had been predicted.)

    More seriously though, don't many/most earthquakes originate much deeper than groundwater is likely to be found?

    http://earthquake.usgs.gov/learn/topics/seismology/determining_depth.php
     
    Last edited: May 14, 2016
  11. Ophiolite Valued Senior Member

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    It depends upon how you define groundwater. (Warning: the wikipedia article on groundwater is grossly inaccurate. Whoever wrote it was not qualified to do so.)

    Pore space, and hence water, is present to considerable depths. While some faults create a permeability barrier, other are effective conduits. I have not explored current thinking on this specific issue, but based on the generalities of plate tectonic theory I would be amazed if water was not playing a significant role in fault movement at every depth.
     
  12. Write4U Valued Senior Member

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    Moreover, Robert Hazen explained that a new science is developing, which investigates deep ocean chemistry. For instance; the pressure of a large subduction of a tectonic plate creates various organic molecules *in the mantle itself*
     

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