• An integral-free expression for short-term changes in fault stability due to pore pressure induced when a point load is placed on the pervious boundary of a porous elastic half space containing a fault

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    • Keywords


      Rock mechanics; geomechanics; poroelasticity; pore pressure; half space, point load; faults; fault stability; earthquakes; seismic hazard.

    • Abstract


      A concentrated load with step-function time behaviour is placed normal to the planar, pervious boundary of a porous elastic half space (PEHS) with compressible constituents. A planar fault exists in the PEHS in such a way that the poroelastic behaviour of the medium is unhindered. We derive an approximate but integral-free expression for CFSCPP, i.e., changes in fault stability due to changes in pore pressure, at a point not too far off the line along which the load acts. But, in the interest of simplicity, the main discussion is focussed on a consideration of CFSCPP at a point 𝑃 located on the fault at depth 𝑧 directly beneath the load. It is convenient to introduce dimensionless time $t_D$ directly proportional to real time 𝑡. The constant of proportionality is 4c/z2, where 𝑐 is hydraulic diffusivity. The derived approximate expression gives results with an accuracy of greater than 99% for limited values of $t_D$ after the load is imposed. We learn from the derived expression that, for a given 𝑧, fault stability undergoes an initial sudden decrease commensurate with the undrained pore pressure induced in the PEHS. This is followed by a more gradual decrease in fault stability with increasing $t_D$ until a minimum is reached. The real time 𝑡 to minimum fault stability increases with 𝑧. The magnitude of CFSCPP decreases with 𝑧 as $z^{−2}$ for a given $t_D$ in the permissible range. The derived expression and the inferences based on it should be useful during earth science investigations of the possible hazards due to reactivation of a pre-existing shallow fault when a civil engineering project involving imposition of a heavy load on the earth’s surface is to be executed nearby. They should be useful also for investigations if a shallow earthquake occurs near such a project soon after its execution.

    • Author Affiliations


      Ramesh Chander1 S K Tomar2

      1. #290 Sector - 4, Mansa Devi Complex, Panchkula 134 114, Haryana, India.
      2. Department of Mathematics, Panjab University, Chandigarh 160 014, India.
    • Dates

  • Journal of Earth System Science | News

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      Posted on July 25, 2019

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