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KAUST-IAMCS Workshop on Modeling and Simulation of Wave Propagation and Applications

Ana Ferreira, University of East Anglia (United Kingdom)
Global 3D Seismic Surface Wave Propagation: From Asymptotic to Purely Numerical Wavefield Simulations

Abstract

Long-period seismic surface waves have been extensively used for decades in studies of both the earthquake source and Earth structure. While the overall earthquake source process is well characterized by long-period surface waves, they are also key data to building detailed images of the Earth's uppermost mantle. We simulate seismic surface waves in the 3D, laterally heterogeneous Earth using both approximate and purely numerical methods. Specifically, we have implemented surface wave Full Ray Theory (FRT) to investigate long-period (T ~ 40-250 s) surface waveforms and to carry out realistic global earthquake source inversions. We validate our approach by comparing FRT calculations with purely numerical Spectral Element Method (SEM) simulations. We present results of a statistical experiment to assess the impact of source, path, and receiver effects on the fit to observed waveforms. As expected, waveforms calculated using laterally heterogeneous models match the data better than 1D Earth calculations. The improved waveform fit is mainly caused by more accurate phase predictions due to path corrections. On average, calculations using the 3D Earth models do not improve the amplitude fit compared with that for 1D Earth models, suggesting that new Earth models need to be built fully exploiting all the information in the data, particularly amplitudes. On the other hand, FRT earthquake source inversions show that that more accurate modeling of lateral heterogeneity helps constraining the earthquake source parameters, notably the seismic moment and the dip-slip components of the moment tensor. Initial comparisons between FRT and SEM waveforms suggest that FRT is well-suited to study long-period surface waves, being a useful tool for applications in global earthquake studies and waveform tomography.