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SASSY21: A 3D Seismic Structural Model of the Lithosphere and Underlying Mantle Beneath Southeast Asia from Multi-scale Adjoint Waveform Tomography

We present the first large-scale seismic structural model of the lithosphere and underlying mantle beneath Southeast Asia obtained from adjoint waveform tomography (often referred to as full-waveform inversion or FWI), using seismic data filtered at periods from 20 - 150 s. By simulating the 3-D wavefield, FWI can account for the true physics of seismic wave propagation and is thus especially suitable for strongly heterogeneous regions such as Southeast Asia. Based on > 3,000 h of analyzed waveform data gathered from ~13,000 unique source-receiver pairs, we image isotropic P-wave velocity, radially anisotropic S-wave velocity and density via an iterative non-linear inversion that begins from a 1-D reference model. At each iteration, the full 3-D wavefield is determined through an anelastic Earth using the spectral-element solver Salvus, accommodating effects of topography, bathymetry and ocean load. Our data selection aims to maximize sensitivity to deep structure by accounting for body-wave arrivals separately.

SASSY21, our final model after 87 L-BFGS iterations across seven period bands, reveals detailed anomalies down to the mantle transition zone. The most prominent feature is the Australian plate descending beneath Indonesia, which is imaged as one continuous slab along the 180-degree curvature of the Banda Arc. Furthermore, the tomography confirms the existence of a hole in the slab beneath Mount Tambora and locates a high S-wave velocity zone beneath northern Borneo that may be associated with subduction termination in the mid-late Miocene. A previously undiscovered high-velocity feature beneath the east coast of Borneo is also revealed, which may be a signature of post-subduction processes, delamination or underthrusting from the formation of Sulawesi.

Session: Adjoint Waveform Tomography: Methods and Applications I

Type: Oral

Room: Grand B

Date: 4/22/2022

Presentation Time: 02:30 PM Pacific

Presenting Author: Deborah Wehner

Student Presenter: Yes

Additional Authors