New insights in shear wave velocity estimates through combined use of three passive techniques for tectonically active area

English Abstract:

Study area Shillong of Northeast India falls in seismic Zone V. It has experienced lot of earthquakes in recent past which are of magnitudes greater than 5. To get an insight of shear wave velocity profile of this tectonically active area, we carried out array recordings at five sites in by incorporating three passive methods, viz. SPAC, Frequency Wavenumber and Ellipticity inversion of H/V ratio. The estimated shear wave velocities out of these three methods are found to be quite consistent with each other. We observe a good convergence in the estimates by all these techniques whose methodology quite differ from each other. The computed V_s values up to depth of 30m are observed to be in the range of 275m/s to 375m/s, indicating a low velocity region in most of the sites. This has been found to be in good agreement with local geology. Additionally, the profiles exhibit a rising tendency of V_P and V_S values with increase in depth.