SHEAR-WAVE VELOCITY STRUCTURE BENEATH THE ARCHEAN GRANITES AROUND HYDERABAD, INFERRED FROM RECEIVER FUNCTION-ANALYSIS

Broadband receiver functions abstracted from teleseismic P waveforms r ecorded by a S-component Streckeisen seismograph at Hyderabad, have be en inverted to constrain the,shear velocity structure of the underlyin g crust. Receiver functions obtained from the Hyderabad records of bot h shallow and intermediate focus earthquakes lying in different statio n-event azimuths, show a remarkable coherence in arrival times and sha pes of the significant shear wave phases: Ps, PpPs, PsPs/PpSs, indicat ing horizontal stratification within the limits of resolution. This is also supported by the relatively small observed amplitudes of the tan gential component receiver functions which are less than 10% of the co rresponding radial component. Results of several hundred inversions of stacked receiver functions from closely clustered events (within 2 de grees), show that the crust beneath the Hyderabad granites has a thick ness of 36+/-1km, consisting of a 10km thick top layer in which shear wave velocity is 3.54 +/- 0.07 km/sec, underlain by a 26 +/- 1 km thic k lower crust in which the shear wave velocity varies uniformly with a small gradient of 0.02 km/sec/km. The shear wave velocity at its base is 4.1 +/- 0.05 km/sec, just above the moho transition zone which is constrained to be less than 4 km thick, overlying a 4.74 +/- 0.1 km/se c half space.