Waveform inversion of broad-band body wave data for the S-velocity structure in the lowermost mantle beneath the Indian subcontinent and Tibetan Plateau

Abstract

SUMMARY We conduct waveform inversion for the radial shear velocity structure of the lowermost mantle beneath the Indian subcontinent and Tibetan Plateau using transverse component body wave waveform data obtained from the ORFEUS (Observatories and Research Facilities for European Seismology) and IRIS (Incorporated Research Institutions for Seismology) arrays in thepassband8–200s.Asthesearehigherfrequencydatathanusedbymostpreviouswaveform inversion studies, several improvements in terms of techniques were necessary. We conduct tests to confirm the robustness of the results. The average S velocity of this region is almost the same as Preliminary Reference Earth Model (PREM), but we find that the velocity is faster than PREM in the depth range 2400–2750 km and slower than PREM in the depth range 2750 km—core–mantle boundary (CMB). This suggests that the perovskite to post-perovskite phase transition occurs in the depth range 2400–2600 km. If we assume the composition of D �� is pyrolitic, the thickness of the thermal boundary layer at the CMB is about 200–300 km.