Japan Geoscience Union Meeting 2023

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG45] Science of slow-to-fast earthquakes

Thu. May 25, 2023 10:45 AM - 12:15 PM International Conference Room (IC) (International Conference Hall, Makuhari Messe)

convener:Aitaro Kato(Earthquake Research Institute, the University of Tokyo), Asuka Yamaguchi(Atomosphere and Ocean Research Institute, The University of Tokyo), Yohei Hamada(Japan Agency for Marine-Earth Science and Technology Kochi Institute for Core Sample Research), Yihe Huang(University of Michigan Ann Arbor), Chairperson:Takanori Matsuzawa(National Research Institute for Earth Science and Disaster Resilience), Kurama Okubo(National Research Institute for Earth Science and Disaster Resilience)

10:45 AM - 11:00 AM

[SCG45-16] Dynamic earthquake ruptures and its radiations with off-fault fracture network in various spatial resolutions

*Kurama Okubo1, Carlos Villafuerte2, Esteban Rougier3, Harsha S. Bhat2 (1.National Research Institute for Earth Science and Disaster Resilience, 2.École Normale Supérieure, 3.Los Alamos National Laboratory)

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.