Anisotropic Rayleigh-wave phase velocity maps of the Sunda Plate

Abstract

We explore the Rayleigh-wave phase-velocity and shear-velocity structures beneath Sunda Plate over a broad period range of 30–150 s and 5–100 km. The two-stations technique was used to measure dispersion curves from the waveforms of 19,233 teleseismic events (1998–2018) recorded worldwide by 75 broadband seismic stations spread around the Sunda Plate. The interstation path-specific dispersion curves are then inverted for high-resolution isotropic and azimuthally anisotropic phase velocity maps in the frequency range 30–150 s as well as for shear-velocity model between 5 and 100 km. Main findings include a strong dichotomy with fast velocities located beneath the South China Sea and the Sunda Shelf compared with slow velocities found beneath the surrounding regions at short periods. Our model also exhibits very slow velocities beneath the Hainan Plume at lithospheric and asthenospheric depths. The complex anisotropy in the region at shorter periods contrasts with the pattern observed at longer periods (sampling the asthenosphere) and is consistent with the Absolute Plate Motions in the region.