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]