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

作者：Chander Ramesh; Tomar S K^*

来源：Journal of Earth System Science, 2014, 123(7): 1729-1738.

DOI：10.1007/s12040-014-0482-4

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

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/z(2), 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 ti) 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%26apos;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.

• 出版日期2014-10