Shear wave velocity structure beneath the Archaean granites around Hyderabad, inferred from receiver function analysis

Broadband receiver functions abstracted from teleseismicP waveforms recorded by a 3-component Streckeisen seismograph at Hyderabad, have been inverted to constrain the shear velocity structure of the underlying crust. Receiver functions obtained from the Hyderabad records of both shallow and intermediate focus earthquakes lying in different station-event azimuths, show a remarkable coherence in arrival times and shapes of the significant shear wave phases:Ps, PpPs, PsPs/PpSs, indicating horizontal stratification within the limits of resolution. This is also supported by the relatively small observed amplitudes of the tangential component receiver functions which are less than 10% of the corresponding radial component. Results of several hundred inversions of stacked receiver functions from closely clustered events (within 2°), show that the crust beneath the Hyderabad granites has a thickness of 36 ± 1 km, consisting of a 10 km thick top layer in which shear wave velocity is 3.54 ± 0.07 km/sec, underlain by a 26 ± 1 km thick 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/sec half space.