https://insu.hal.science/insu-03748871Konishi, KensukeKensukeKonishiFuji, NobuakiNobuakiFujiIPGP - Institut de Physique du Globe de Paris - INSU - CNRS - Institut national des sciences de l'Univers - UPD7 - Université Paris Diderot - Paris 7 - UR - Université de La Réunion - IPG Paris - Institut de Physique du Globe de Paris - CNRS - Centre National de la Recherche ScientifiqueDeschamps, FrédéricFrédéricDeschampsElastic and anelastic structure of the lowermost mantle beneath the Western Pacific from waveform inversionHAL CCSD2017Inverse theoryElasticity and anelasticityBody wavesSeismic attenuationSeismic tomographyPacific Ocean[SDU] Sciences of the Universe [physics][SDU.STU] Sciences of the Universe [physics]/Earth SciencesPOTHIER, Nathalie2022-08-10 09:53:582023-07-29 20:52:252022-08-10 09:54:00enJournal articleshttps://insu.hal.science/insu-03748871/document10.1093/gji/ggw450application/pdf1We investigate the elastic and anelastic structure of the lowermost mantle at the western edge of the Pacific large low shear velocity province (LLSVP) by inverting a collection of S and ScS waveforms. The transverse component data were obtained from F-net for 31 deep earthquakes beneath Tonga and Fiji, filtered between 12.5 and 200 s. We observe a regional variation of S and ScS arrival times and amplitude ratios, according to which we divide our region of interest into three subregions. For each of these subregions, we then perform 1-D (depth-dependent) waveform inversions simultaneously for radial profiles of shear wave velocity (V<SUB>S</SUB>) and seismic quality factor (Q). Models for all three subregions show low V<SUB>S</SUB> and low Q structures from 2000 km depth down to the core-mantle boundary. We further find that V<SUB>S</SUB> and Q in the central subregion, sampling the Caroline plume, are substantially lower than in the surrounding regions, whatever the depth. In the central subregion, V<SUB>S</SUB>-anomalies with respect to PREM (dV<SUB>S</SUB>) and Q are about -2.5 per cent and 216 at a depth of 2850 km, and -0.6 per cent and 263 at a depth of 2000 km. By contrast, in the two other regions, dV<SUB>S</SUB> and Q are -2.2 per cent and 261 at a depth of 2850 km, and -0.3 per cent and 291 at a depth of 2000 km. At depths greater than ∼2500 km, these differences may indicate lateral variations in temperature of ∼100 K within the Pacific LLSVP. At shallower depths, they may be due to the temperature difference between the Caroline plume and its surroundings, and possibly to a small fraction of iron-rich material entrained by the plume.