Earthquake source model using strong motion displacement as response of finite elastic media

The strong motion displacement records available during an earthquake can b e treated as the response of the earth as the a structural system to unknow n forces acting at unknown locations. Thus, if the part of the earth partic ipating in ground motion is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an ear thquake as an inverse problem in structural dynamics. Based on this analogy , a simple model for the basic earthquake source is proposed. The unknown s ource is assumed to be a sequence of impulses acting at locations yet to be found. These unknown impulses and their locations are found using the norm al mode expansion along with a minimization of mean square error. The mediu m is assumed to be finite, elastic, homogeneous, layered and horizontal wit h a specific set of boundary conditions. Detailed results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure clo sely associated with the causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceler ation time histories are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations.