Topography of the western Pacific LLSVP constrained by S -wave multipathing.

We found that SH diff phases generated by earthquakes in the Fiji–Tonga, recorded in India, are accompanied by secondary pulses. We interpreted them as a consequence of multipathing of S waves caused by the Pacific large low-shear-velocity province (LLSVP). We analysed the differential traveltimes between SH diff and the secondary pulse, together with the absolute SH diff arrival times, to constrain the thickness and velocity perturbations in the western end of the Pacific LLSVP. Our preferred model shows a lateral variation in the thickness of the LLSVP; the southern part reveals a thicker (300 km) low-velocity region compared to the northern part (200 km). However, the velocity perturbations of the LLSVP appear to be comparable (⁠|$-1.5\hbox{ per cent}$|⁠). The results are consistent with a scenario that the LLSVP is a chemically distinct pile with significant surface topography. [ABSTRACT FROM AUTHOR]