• S K TOMAR

      Articles written in Journal of Earth System Science

    • On a model simulating lack of hydraulic connection between a man-made reservoir and the volume of poroelastic rock hosting the focus of a post-impoundment earthquake

      Ramesh Chander S K Tomar

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      The idea that a direct hydraulic connection between a man-made reservoir and the foci of postimpoundment earthquakes may not exist at all sites is eminently credible on geological grounds. Our aim is to provide a simple earth model and related theory for use during investigations of earthquakes near new man-made reservoirs. We consider a uniform circular reservoir which rests on the top surface of a no-hydraulic-connection earth model (NHCEM). The model comprises a top elastic (E) layer, an intermediate poroelastic (P) layer, and a bottom elastic half space. The focus of a potential earthquake in the P layer is located directly under the reservoir. The E layer disrupts the hydraulic connection between the reservoir and the focus. Depth of water in the reservoir varies as H'+h cos(ωt). Expressions for reservoir-induced stresses and pore pressure in different layers of the NHCEM are obtained by solving the boundary-value problem invoking full coupling between mean normal stress and pore pressure in the P layer. As an application of the derived mathematical results, we have examined and found that earthquakes on 60° normal faults may occur in the P-layer of a selected NHCEM at epochs of low reservoir level if the reservoir lies mostly in the footwall of the fault. The exercise was motivated by observations of such earthquakes under the man-made Lake Mead after it was impounded

    • On assessing the inCuence of a newly impounded reservoir on a nearby normal fault using a simple three-dimensional model of subsurface geological heterogeneity

      RAMESH CHANDER S K TOMAR

      More Details Abstract Fulltext PDF

      We assume that the subsurface at the site of a newly impounded reservoir has a small volume of rock with porous-elastic properties significantly different from those of the other rocks in the area. A normal fault passes through this rock volume. We adopt the following implications to quantify reservoir influence at different points of the fault in such a case. The reservoir is circular and of uniform depth. The small rock volume is spherical in shape and embedded in an otherwise homogeneous half space with values of porous-elastic properties in the range normally observed through laboratory measurements on rocks. We infer from calculated results that the reservoir will promote slip at low water level at points of the fault lying within the small rock volume if its diffusivity, and undrained and drained Poisson’s ratios are significantly lower than those of the other rocks at the site. The reservoir will promote slip on the normal fault at points outside the small rock volume at high water level.

      $\bf{Highlights}$

      $\bullet$ A 3D model for reservoir promoted slip on a subsurface normal fault at low water is investigated.

      $\bullet$ The reservoir is circular. The fault cuts a porous-elastic (PE) sphere in a PE half-space.

      $\bullet$ The fault slips at low water at points in the sphere if PE half-space has nominal properties.

      $\bullet$ PE sphere has low diffusivity and low undrained and drained Poisson’s ratios.

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