ESTIMATION OF SOURCE, PATH AND SITE PARAMETERS FOR THE GARHWAL HIMALAYA USING LOCAL EARTHQUAKES

Abstract

The ground motion recorded in the form of seismic waves produced during occurrence of earthquakes is mainly combination of the three factors, source, path and site. The earthquake source describes how the size and nature of earthquakes source mechanism controls the generation of seismic waves and the path effect describes the change in the amplitude and frequency contents of seismic waves by the earth’s medium when the seismic waves travel from earthquake source to the recording station. The site effect describes the modification of ground motion due to the composition and configuration of local geological structure below the recording station. It mainly depends on earthquake generation source, the propagation path of seismic waves and site characteristics of the local geological features beneath the recording station. Earthquake source parameters are important for understanding the kinematic and dynamic properties of earthquake source processes, simulating strong ground motion, investigating the characteristics of seismicity precursors for earthquake prediction research, discriminating nuclear explosions from earthquake, demarcating plate boundaries, to infer the direction of relative plate motions and major fault systems, to estimate relative velocity between plates and mapping of temporal and spatial variation of tectonic stress. Source parameters such as stress drop, corner frequency and fmax find applications in the estimation of strong motion simulation. The stochastic approach requires knowledge of spectral parameters (e.g., corner frequency) and source parameters (e.g., stress drop) of study region for simulating strong ground motion. Study of path provides the information about the medium characteristics as well as level of inhomogeneities present in the medium. This is important for understanding the seismotectonics and also plays a significant role in the estimation of seismic hazard for a given region. Its knowledge is also required for the precise estimation of earthquake source parameters and for the prediction of strong ground motion at a site due to probable earthquake source zones identified in the region.