Dynamic rupture propagation on geometrically complex fault with along-strike variation of fault maturity: insights from the 2014 Northern Nagano earthquake

Abstract

Understanding the effect of the complex fault geometry on the dynamic rupture process and discriminating it from the complexity originating from the rheological properties of faults, is an essential subject in earthquake science. The 2014 Northern Nagano earthquake, which occurred near the end zone of a major active fault system, provided unique observations that enabled us to investigate both the detailed geometrical fault structure and surface deformation patterns as well as the temporal sequence led up from a prominent foreshock activity. We first develop a geometrical fault model with a substantial variation along strike, and a model for the regional stress field, which is well constrained by the observations. This significant along-strike variation in fault geometry probably reflects the difference of fault maturity at the end zone of the complex fault system. We used this model in order to conduct a set of dynamic rupture simulations using the highly efficient spatiotemporal boundary integral equation method. Based on our simulations, we show that the observed surface deformation can be reasonably explained as the effect of the non-planar fault geometry with a number of branch faults and bends.

Dynamic Rupture Scenarios in the Brawley Seismic Zone, Salton Trough, Southern California

“…This is illustrated by the Southern California Earthquake Center (SCEC) dynamic rupture branched‐fault benchmarks (Harris et al, ), which compare results from several codes that use various numerical techniques. For example, whereas finite‐element codes must model the behavior at each node (DeDontney et al, ), boundary‐element and discontinuous Galerkin codes can model the behavior in the interior of fault elements and therefore can sidestep the question of how the system should behave precisely at the intersection point (Pelties et al, , and Wollherr et al, ; see also Tago et al, , Pelties et al, , and Ando et al, ).…”

Landers 1992 "reloaded": Integrative dynamic earthquake rupture modeling

“…Numerical schemes such as the Boundary Integral Equation Method (BIEM) [e.g., Aochi and Fukuyama, 2002;Ando et al, 2017], Finite Element Methods (FEM) based on tetrahedral elements [e.g., Barall , 2009] -including the Discontinuous Galerkin (DG) Method [e.g., Pelties et al, 2012;Tago et al, 2012] -or numerical methods using curvilinear elements [e.g., Duru and Dunham, 2016] are able to accurately represent non-planar fault geometries. We point out that the accurate representation of fault branches is restricted to methods that do not use a traction-at-split nodes approach [Andrews, 1999;Day et al, 2005;Dalguer and Day, 2007], like BIEM and DG methods.…”

Crustal dynamics: unified understanding of geodynamic processes at different time and length scales

“…Focal mechanisms were inverted to show that the crustal stress field can generally be regarded as uniform at a scale of 1 km throughout the study region, but that strength is heterogeneous, varying over comparatively short distances (~ 100 m). Ando et al (2017) analyzed complex patterns in the wave radiation and surface displacement of the 2014 Mw 6.2 northern Nagano earthquake sequence which involved predominantly reverse slip on an irregularly segmented rupture. Observations include foreshock occurrence, large differences between the firstmotion focal mechanisms and the CMT, and along-strike variations in surface displacement.…”