Fourth-Order Staggered-Grid Finite-Difference Seismic Wavefield Estimation Using a Discontinuous Mesh Interface (WEDMI)

Shiying Nie, Daniel Roten, Kim B. Olsen, & Steven M. Day

Submitted August 15, 2017, SCEC Contribution #7794, 2017 SCEC Annual Meeting Poster #249

In a realistic geological structure with a large contrast in seismic wave speed between shallow and deep regions, simulation of seismic wave propagation using a spatially uniform grid can be computationally very demanding, due to overdiscretization of the high-speed material. The discontinuous mesh (DM) methods, operating by exchanging wavefield information between media partitions discretized with two different grids spacings, can provide a convenient way to improve such efficiency issue. However, some discontinuous mesh finite-difference methods suffer from inherent stability problems while numerically accurate. We develop a 3D fourth-order staggered-grid FD DM method (AWP-DM) to model seismic wavefield estimation using a discontinuous mesh interface (WEDMI). Benchmarks in models with realistic 3D velocity and finite-fault sources across the grid interface show great stability in addition to very good accuracy.

We implemented WEDMI in the highly efficient and scalable GPU version of AWP. AWP-GPU-DM supports an arbitrary number of different grid spacings, which further reduces oversampling in earthquake scenario simulations with realistic shear-wave velocities inside a geotechnical layer. Compared to the uniform mesh implementation of AWP-GPU, the DM version requires additional velocity and stress exchanges between subdomains to calculate the wavefield at interfaces between discontinuous grids. The size of the ghost cell region along grid interfaces is adjusted depending on the width of the smoothing window to improve the stability of the method if strong velocity contrasts are present at DM interfaces. Numerical stability in the GPU implementation of WEDMI is further improved by applying a volumetric rather than a horizontal smoothing window in the overlap zone between fine and coarse meshes. We test AWP-GPU-DM by simulating the Mw 5.1 La Habra earthquake for frequencies up to 4 Hz, using a grid spacing of 20 m in the fine grid and a minimum shear-wave velocity of 500 m/s. Synthetics obtained with the DM accurately reproduce reference solutions computed using a uniform mesh in the time and frequency domain.

Key Words
AWP, Discontinuous Mesh, GPU, La Habra earthquake

Citation
Nie, S., Roten, D., Olsen, K. B., & Day, S. M. (2017, 08). Fourth-Order Staggered-Grid Finite-Difference Seismic Wavefield Estimation Using a Discontinuous Mesh Interface (WEDMI). Poster Presentation at 2017 SCEC Annual Meeting.


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