Topography of the western Pacific LLSVP constrained by S wave multipathing
Abstract
The waveforms of five deep earthquakes from the Fiji-Tonga subduction zone recorded by a seismic array in India reveal a secondary pulse just after the SHdiff phase. We obtained 51 observations for this pulse, in the distance range of 102.0° to 115.1°. The pulse is sharper on the northern part compared to the southern part of the array, with a azimuthal variation. The relative arrival time of the second pulse varies from 3.0 to 9.9 s with respect to the first pulse, with its arrival getting delayed from north to the south along the seismic array, albeit the south array being closer to the earthquake sources. We interpreted them as a consequence of multipathing of S waves caused by the Pacific Large Low Shear Velocity Province (LLSVP). We analyzed the differential travel times between SHdiff and the secondary pulse, together with the absolute SHdiff 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 of our study region revealing 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%). The results are consistent with a scenario that the LLSVP is a chemically distinct pile with significant surface topography.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMDI53A0051R
- Keywords:
-
- 1038 Mantle processes;
- GEOCHEMISTRYDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 7208 Mantle;
- SEISMOLOGYDE: 8125 Evolution of the Earth;
- TECTONOPHYSICS