High-resolution 3-D S-velocity structure in the D″ region at the western margin of the Pacific LLSVP: Evidence for small-scale plumes and paleoslabs

• Main Authors: Yuki Suzuki, Kenji Kawai, Robert J. Geller, Satoru Tanaka, Weerachai Siripunvaraporn, Songkhun Boonchaisuk, Sutthipong Noisagool, Yasushi Ishihara, Taewoon Kim
• Other Authors: The University of Tokyo
• Format: Article
• Published: 2020
• Subjects: Earth and Planetary Sciences; Physics and Astronomy
• Online Access: https://repository.li.mahidol.ac.th/handle/123456789/57860
• Institution: Mahidol University

© 2020 Elsevier B.V. Although previous tomographic studies found a large low S-velocity province (LLSVP) in the lowermost mantle beneath the Pacific, due to a lack of resolution it was unclear whether the LLSVP consists of clusters of small-scale low-velocity anomalies or large-scale anomalies. We recently deployed a seismic-array in Thailand which provides a dataset with wide azimuthal coverage of the western Pacific LLSVP. We analyze the new dataset using waveform inversion, and find high-velocity anomalies extending vertically to a height of ~400 km above the core-mantle boundary (CMB) beneath the Philippine Sea and small-scale low-velocity patches with a diameter of ~300 km at the CMB beneath New Guinea. The locations of the high-velocity anomalies are consistent with the past Izanagi-plate subduction boundary, and the low-velocity anomalies can be interpreted as a small-scale plume cluster. Hence we conclude that vertical flow (upwelling plumes and downwelling of slabs) is dominant in the lowermost mantle beneath the western Pacific region.