Large-scale earthquake sequence simulations on 3-D non-planar faults using the boundary element method accelerated by lattice H-matrices

• Published in: Geophysical journal international Vol. 232; no. 3; pp. 1471 - 1481
• Main Authors: Ozawa, So, Ida, Akihiro, Hoshino, Tetsuya, Ando, Ryosuke
• Format: Journal Article
• Language: English
• Published: Oxford University Press 09.11.2023
• Subjects: Rheology and friction of fault zones; Computational seismology; Dynamics and mechanics of faulting; H-matrices; Seismic cycle; Numerical modelling; Boundary element method
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1093/gji/ggac386

SUMMARY Large-scale earthquake sequence simulations using the boundary element method (BEM) incur extreme computational costs through multiplying a dense matrix with a slip rate vector. Hierarchical matrices (H-matrices) have often been used to accelerate this multiplication. However, the complexity of the structures of the H-matrices and the communication costs between processors limit their scalability, and they therefore cannot be used efficiently in distributed memory computer systems. Lattice H-matrices have recently been proposed as a tool to improve the parallel scalability of H-matrices. In this study, we developed a method for earthquake sequence simulations applicable to 3-D non-planar faults with lattice H-matrices. We present a simulation example and verify the mesh convergence of our method for a 3-D non-planar thrust fault using rectangular and triangular discretizations. We also performed performance and scalability analyses of our code. Our simulations, using over ${10}^5$ degrees of freedom, demonstrated a parallel acceleration beyond ${10}^4$ MPI processors and a > 10-fold acceleration over the best performance when the normal H-matrices are used. Using this code, we can perform unprecedented large-scale earthquake sequence simulations on geometrically complex faults with supercomputers. The software is made an open-source and freely available.