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Regional-Scale Crustal and Mantle Structure of the Western United States From Adjoint Waveform Tomography for Improved Source Characterization

Session: Explosion Seismology Applications and Advances I

Type: Oral

Date: 4/19/2021

Presentation Time: 10:45 AM Pacific

Description: 

Recent application of moment tensor estimation promises to improve explosion monitoring. Moment tensor methods have proven effective for large magnitude and explosive yield events using average plane-layered (one-dimensional, 1D) Earth models. However, the extension of these methods to lower magnitudes and longer (regional) distances is challenging because three-dimensional (3D) Earth structure causes significant deviations in waveform Green’s functions from assumed 1D models. To address this challenge, we are using adjoint waveform tomography to obtain an improved 3D Earth model for full waveform simulations. We are focusing on the western United States (WUS) where we have ample broadband waveform data and well characterized earthquakes and explosions to test the efficacy of our model. We are inverting waveforms using the Salvus package which coordinates the workflow (e.g., forward and adjoint simulations, gradients, measurements). For the 3D starting model we used SPiRaL (Simmons et al., 2020), which is a radially anisotropic global model based on body-wave travel times and surface wave dispersion. We followed a multiscale approach starting with long-period waveforms (50-120 seconds), iteratively inverting waveforms and relaxing smoothing. As misfit reduction ceased, we then repicked windows and inverted shorter period data. Currently we have performed over 50 iterations and inverted data with periods as short as 30 seconds. We hope to reduce the minimum period further to resolve features in the crust and uppermost mantle. Results so far for the WUS are consistent with the SPiRaL starting model but show sharper features with higher amplitude wavespeed perturbations and good correlation with known crustal-scale geologic and physiographic regions. The efficacy of our new 3D model is explored in this presentation and in an accompanying presentation by Chiang et al. (2021).

Presenting Author: Arthur J. Rodgers

Student Presenter: No

Authors