10:45 AM - 11:00 AM
[SCG45-16] Dynamic earthquake ruptures and its radiations with off-fault fracture network in various spatial resolutions
Keywords:Off-fault damage, Dynamic rupture modeling, High-frequency radiation, Radiated energy
The high-resolution geological observations show the fracture network in the off-fault medium on a broad length scale, part of which is co-seismically activated during the dynamic earthquake ruptures. The effect of the minimum length scale of off-fault fractures, i.e., the spatial resolution of the off-fault fracture network, on the characteristics of earthquake sources is of great interest to unravel the earthquake source mechanisms. We thus conducted a case study of different sizes of mesh discretization to identify its role in the earthquake source processes.
We modeled a finite planer fault using the combined finite-discrete element method (FDEM). We used the FDEM-based software tool, the hybrid optimization software suite (HOSS) educational version, developed by LANL. In this numerical framework, the minimum length scale of off-fault fractures is determined by the size of the edges of mesh elements. We thus conducted the dynamic earthquake rupture modeling using three different meshes with 1/10, 1/15, and 1/20 of the static process zone size associated with the main fault. Our focus here is not on the common analysis of numerical mesh convergence but on investigating the effect of the length scale of the off-fault fracture network in the rupture dynamics.
The spatial fracture pattern varied due to the topology with different mesh resolutions, while the total seismic moment M0 and the radiated energy ER, which is contributed from both the main fault and the off-fault fractures, were comparable. We then estimated the power spectrum density of the time series of velocity magnitude in the off-fault medium to evaluate the spatial distribution of the radiation field with different frequency ranges. The radiation field associated with the low-frequency range, corresponding to the rupture on the main fault, was similar with different mesh resolutions. We found even the radiation of the middle-frequency range, which involves some contributions from the off-fault fracture network, could be averaged with distance from the damage zone although the location of the localized spot of the peak velocity varies with the pattern of the off-fault fracture network.
Overall, the macroscopic characteristics such as the seismic moment and overall radiated energy can be resolved with standard criteria of mesh size associated with the main fault, while the localized peak of the high-frequency radiation depends on the relations between the mesh-dependent fracture patterns and the location of stations. These analyses will help evaluate the radiation patterns from the earthquake sources with co-seismic off-fault damage in various spatial resolutions.
We modeled a finite planer fault using the combined finite-discrete element method (FDEM). We used the FDEM-based software tool, the hybrid optimization software suite (HOSS) educational version, developed by LANL. In this numerical framework, the minimum length scale of off-fault fractures is determined by the size of the edges of mesh elements. We thus conducted the dynamic earthquake rupture modeling using three different meshes with 1/10, 1/15, and 1/20 of the static process zone size associated with the main fault. Our focus here is not on the common analysis of numerical mesh convergence but on investigating the effect of the length scale of the off-fault fracture network in the rupture dynamics.
The spatial fracture pattern varied due to the topology with different mesh resolutions, while the total seismic moment M0 and the radiated energy ER, which is contributed from both the main fault and the off-fault fractures, were comparable. We then estimated the power spectrum density of the time series of velocity magnitude in the off-fault medium to evaluate the spatial distribution of the radiation field with different frequency ranges. The radiation field associated with the low-frequency range, corresponding to the rupture on the main fault, was similar with different mesh resolutions. We found even the radiation of the middle-frequency range, which involves some contributions from the off-fault fracture network, could be averaged with distance from the damage zone although the location of the localized spot of the peak velocity varies with the pattern of the off-fault fracture network.
Overall, the macroscopic characteristics such as the seismic moment and overall radiated energy can be resolved with standard criteria of mesh size associated with the main fault, while the localized peak of the high-frequency radiation depends on the relations between the mesh-dependent fracture patterns and the location of stations. These analyses will help evaluate the radiation patterns from the earthquake sources with co-seismic off-fault damage in various spatial resolutions.