Seismic Structure Beneath Western Pacific and Adjacent Regions from Seismic Full-Waveform Inversion

Summary A comprehensive full-waveform inversion model of the seismic velocity, covering nearly the entire tectonic domain of the western Pacific (FWP24) is developed using an optimized many-core version of SPECFEM3D_GLOBE on the New Generation Sunway supercomputer. Taking the global adjoint tomography model GLAD-M25 as the initial model, the three-component seismograms from 1 228 earthquakes recorded at 3 687 stations are employed in iterative gradient-based inversions for three period bands: 40-100 s, 17-40 s, and 10-60 s. A total of 36 iterations are carried out using the conjugate gradient method to update the velocities of horizontally and vertically polarized P-waves and S-waves (Vph, Vpv, Vsh, and Vsv) in the FWP24 model. This process systematically reduces the phase difference between the synthetic and observed seismograms within the phase measurements. Compared with existing region inversion results, the FWP24 model realizes a wider, more continuous, and higher-resolution inversion range, including all subduction zones in the western Pacific (e.g. Kurile-Japan, Izu-Bonin-Mariana, New-Britain-Solomon, New-Hebrides, and Tonga-Kermadec). Furthermore, compared to the initial model, FWP24 reveals more detailed structures particularly in oceanic regions around the Philippine Sea Plate, the Caroline Sea Plate and the Ontong-Java Plateau by applying more seismic data.