STRESS ORIENTATION USING FOCAL MECHANISM FOR UTTARKASHI REGION

Abstract

When attempting to comprehend tectonic processes, earthquake mechanics, and seismic hazard assessment, it is essential to consider the orientation of stress inside the Earth's crust. With the help of focal mechanism solutions produced from seismic data, this study intends to analyze the process for identifying stress orientation in Uttarkashi region of Garhwal Himalayan area of Uttarakhand, India. The fault plane solutions are established by carefully analyzing the polarities, amplitudes, and arrival times of the first arriving P wave from 29 local earthquake occurred between the year 2019-2022, recorded at 18 station VSAT-based local seismological network set up by the Department of Earthquake Engineering, IIT Roorkee in the region surrounding the Tehri dam. In order to compute focal mechanism, computer program FOCMEC has been used. This program forms a part of SEISAN program. The result of fault plane solution shows 10 events exhibited normal faulting, with a component of normal left lateral, 10 events showed reverse faulting and reverse faulting with left lateral component while 5 events showed pure dip slip reverse and 4 events showed left lateral strike slip.Within the focal mechanism, the orientations of the P-axis (which represents the highest compressional stress) and T-axis (which represents the maximum extensional stress) are examined in respect to the orientation of the fault plane. The results of this study help us to understand the stress orientations in seismic regions and how they affect local tectonic processes. It emphasizes how crucial it is to consider various fault plane solutions and their consistency in order to determine the stress direction accurately. For finding stress orientation WIN TENSOR program has been used. The inversion of earthquake focal mechanism is indicating a predominant compressional stress regime which has been represented by NE-SW trending mechanism.