SURFACE WAVE TOMOGRAPHY USING DISPERSION AND INVERSION FOR NORTH-EAST HIMALAYAS

Abstract

In this dissertation work, I have made an effort to observe the variation in dispersion curves characteristic of the surface waves using the local earthquake data for five stations i.e. Jorhat, Agartala, Itanagar, Dibrugarh and Kohima, all of which lie in the North-East region of the Indian Subcontinent. The seismic events chosen are within the regional distance, Shallow-depth and with a magnitude greater than 5Mb. These earthquakes are located in and around the North-east Himalayan Belt and the areas within the Central Himalayan Thrust region. Since dispersion curves give the average value along its ray path, my report focusses on observing this effect and comparing it with the different directions that the ray traversed for every station. Multiple filter technique is applied to compute the group velocities of the surface waves from the dispersion curves. The observed dispersion curves for this data set are within the period of 10-100 sec for all the five stations located in the North-East region. Group velocity is then further computed using the weighted average and best higher order polynomial fit to estimate the trend of trajectory of Love & Rayleigh waves between station and epicenters of the earthquakes. The velocity difference between the Love and Rayleigh waves at higher periods is larger for all the directions, while it is smaller for lower periods for the same. For the Multiple Filter Technique, I have used do_mft program by Robert. B. Hermann and hence computed the dispersion curves for the stations in different direction of the events.