EQsimu: a 3-D finite element dynamic earthquake simulator for multicycle dynamics of geometrically complex faults governed by rate- and state-dependent friction

We develop a finite element dynamic earthquake simulator, EQsimu, to model multicycle dynamics of 3-D geometrically complex faults. The fault is governed by rate- and state-dependent friction (RSF). EQsimu integrates an existing finite element code EQdyna for the coseismic dynamic rupture phase and a newly developed finite element code EQquasi for the quasi-static phases of an earthquake cycle, including nucleation, post-seismic and interseismic processes. Both finite element codes are parallelized through Message Passing Interface to improve computational efficiency and capability. EQdyna and EQquasi are coupled through on-fault physical quantities of shear and normal stresses, slip-rates and state variables in RSF. The two-code scheme shows advantages in reconciling the computational challenges from different phases of an earthquake cycle, which include (1) handling time-steps ranging from hundredths of a second to a fraction of a year based on a variable time-stepping scheme, (2) using element size small enough to resolve the cohesive zone at rupture fronts of dynamic ruptures and (3) solving the system of equations built up by millions of hexahedral elements. EQsimu is used to model multicycle dynamics of a 3-D strike-slip fault with a bend. Complex earthquake event patterns spontaneously emerge in the simulation, and the fault demonstrates two phases in its evolution. In the first phase, there are three types of dynamic ruptures: ruptures breaking the whole fault from left to right, ruptures being halted by the bend, and ruptures breaking the whole fault from right to left. As the fault bend experiences more ruptures, the zone of stress heterogeneity near the bend widens and the earthquake sequence enters the second phase showing only repeated ruptures that break the whole fault from left to right. The two-phase behaviours of this bent fault system suggest that a 10° bend may conditionally stop dynamic ruptures at the early stage of a fault system evolution and will eventually not be able to stop ruptures as the fault system evolves. The nucleation patches are close to the velocity strengthening region. Their sizes on the two fault segments are different due to different levels of the normal stress.

[1]  G. A. Frazier,et al.  Treatment of hourglass patterns in low order finite element codes , 1978 .

[2]  J. Dieterich.  Modeling of rock friction: 1. Experimental results and constitutive equations , 1979 .

[3]  A. Ruina.  Slip instability and state variable friction laws , 1983 .

[4]  Kunihiko Shimazaki,et al.  Integration of geological and seismological data for the analysis of seismic hazard: A case study of Japan , 1984 .

[5]  John R. Rice,et al.  Crustal Earthquake Instability in Relation to the Depth Variation of Frictional Slip Properties , 1986 .

[6]  D. J. Andrews,et al.  Mechanics of fault junctions , 1989 .

[7]  C. Scholz.  The Mechanics of Earthquakes and Faulting , 1990 .

[8]  M. F. Linker,et al.  Effects of variable normal stress on rock friction: Observations and constitutive equations , 1992 .

[9]  K. Bathe.  Finite Element Procedures , 1995 .

[10]  Yehuda Ben-Zion,et al.  Dynamic simulations of slip on a smooth fault in an elastic solid , 1997 .

[11]  Steven M. Day,et al.  Dynamic 3D simulations of earthquakes on En Echelon Faults , 1999 .

[12]  J. Rice,et al.  Elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate‐ and state‐dependent friction , 2000 .

[13]  Patrick Amestoy,et al.  A Fully Asynchronous Multifrontal Solver Using Distributed Dynamic Scheduling , 2001, SIAM J. Matrix Anal. Appl..

[14]  C. Tsogka,et al.  Application of the perfectly matched absorbing layer model to the linear elastodynamic problem in anisotropic heterogeneous media , 2001 .

[15]  David D. Oglesby,et al.  Multicycle dynamics of nonplanar strike-slip faults , 2005 .

[16]  S. Day,et al.  Comparison of finite difference and boundary integral solutions to three‐dimensional spontaneous rupture , 2005 .

[17]  Shuo Ma,et al.  Modeling of the Perfectly Matched Layer Absorbing Boundaries and Intrinsic Attenuation in Explicit Finite-Element Methods , 2006 .

[18]  B. Duan,et al.  Heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike‐slip faults , 2006 .

[19]  Patrick Amestoy,et al.  Hybrid scheduling for the parallel solution of linear systems , 2006, Parallel Comput..

[20]  B. Duan,et al.  Nonuniform prestress from prior earthquakes and the effect on dynamics of branched fault systems , 2007 .

[21]  S. Day,et al.  Inelastic strain distribution and seismic radiation from rupture of a fault kink , 2008 .

[22]  Steven G. Wesnousky,et al.  Displacement and Geometrical Characteristics of Earthquake Surface Ruptures: Issues and Implications for Seismic-Hazard Analysis and the Process of Earthquake Rupture , 2008 .

[23]  Luis A. Dalguer,et al.  Finite difference modelling of rupture propagation with strong velocity-weakening friction , 2009 .

[24]  N. Lapusta,et al.  Three‐dimensional boundary integral modeling of spontaneous earthquake sequences and aseismic slip , 2009 .

[25]  A. Pitarka,et al.  The SCEC/USGS Dynamic Earthquake Rupture Code Verification Exercise , 2012 .

[26]  James H. Dieterich,et al.  Earthquake Recurrence in Simulated Fault Systems , 2010 .

[27]  B. Duan.  Role of initial stress rotations in rupture dynamics and ground motion: A case study with implications for the Wenchuan earthquake , 2010 .

[28]  J. Ampuero,et al.  Spectral-element simulations of long-term fault slip : effect of low-rigidity layers on earthquake-cycle dynamics , 2011 .

[29]  T. Hanks,et al.  Verifying a Computational Method for Predicting Extreme Ground Motion , 2011 .

[30]  B. Duan,et al.  Dynamic rupture of the 2011 Mw 9.0 Tohoku‐Oki earthquake: Roles of a possible subducting seamount , 2012 .

[31]  James H. Dieterich,et al.  RSQSim Earthquake Simulator , 2012 .

[32]  Matthew G. Knepley,et al.  A domain decomposition approach to implementing fault slip in finite‐element models of quasi‐static and dynamic crustal deformation , 2013, ArXiv.

[33]  N. Lapusta,et al.  Stable creeping fault segments can become destructive as a result of dynamic weakening , 2013, Nature.

[34]  S. Wesnousky,et al.  Steps and Gaps in Ground Ruptures: Empirical Bounds on Rupture Propagation , 2016 .

[35]  Nadia Lapusta,et al.  Deeper penetration of large earthquakes on seismically quiescent faults , 2016, Science.

[36]  S. Wesnousky,et al.  Bends and Ends of Surface RupturesBends and Ends of Surface Ruptures , 2017 .

[37]  B. Duan,et al.  Seismic shaking in the North China Basin expected from ruptures of a possible seismic gap , 2017 .

[38]  B. Duan,et al.  Dynamics of Nonplanar Thrust Faults Governed by Various Friction Laws , 2018, Journal of Geophysical Research: Solid Earth.

[39]  S. Somala,et al.  A Suite of Exercises for Verifying Dynamic Earthquake Rupture Codes , 2018 .

[40]  B. Duan,et al.  Scenario Earthquake and Ground‐Motion Simulations in North China: Effects of Heterogeneous Fault Stress and 3D Basin Structure , 2018, Bulletin of the Seismological Society of America.

[41]  B. Duan.  Multicycle Dynamics of the Aksay Bend Along the Altyn Tagh Fault in Northwest China: 1. A Simplified Double Bend , 2019, Tectonics.

[42]  Patrick R. Amestoy,et al.  Performance and Scalability of the Block Low-Rank Multifrontal Factorization on Multicore Architectures , 2019, ACM Trans. Math. Softw..