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Fluid pressure and earthquakes

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Abstract

During 1961, a deep well was drilled at the Rocky Mountain Arsenal northeast of Denver, Colorado, to dispose of contaminated waste water. The well is bottomed in 75 feet of vertically fractured Precambrian gneiss. In November 1965, I proposed [Evans, 1966] that injection of waste water into the fractured rocks beneath the well was related to a series of 710 small earthquakes recorded in the area from 1962 through 1965. I proposed that Hubbert and Rubey [1959] had devised a mechanism that explained how fluid pressure could trigger crustal movement (and earthquakes) beneath Denver. This was a simple and an adequate means of reducing the frictional resistance to the sliding of large overthrust blocks down very gentle slopes. The weight of such a block is jointly supported by solid stresses and pressure of interstitial fluids. As fluid approaches lithostatic pressure, the sheer stress required to move the block approaches zero.

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