Effects of complicated 3‐D rupture geometries on earthquake ground motion and their implications: a numerical study

SUMMARY We present a numerical study of the effects of geometrically complicated 3-D ruptures on near-source ground motions. In most of the kinematic and dynamic rupture modelling studies or seismic moment tensor and slip inversions the strong assumption of a perfectly planar fault is made. However, it is known from geological field studies that real fault traces are not planar but characterized by relatively strong deflections, bends and other irregularities. In this paper we, investigate the effects of such non-planar earthquake ruptures on ground motion modelling in comparison to their equivalent planar ones. For this purpose we apply the highly accurate Discontinuous Galerkin method that is capable of incorporating the geometry of complicated non-planar rupture surfaces by a set of double couple point sources that do not have to coincide with the mesh vertices. We generate a set of kinematic rupture models characterized by random spatial deflections with various correlation lengths and root mean square values. These deflections then determine the associated spatial strike and dip variations. We find that the deflected rupture models have the same seismic moment tensor as the perfectly planar one, however, with a reduced scalar moment, which we correct for. After a sound validation of our modelling approach, we present the effects of the deflections on synthetic velocity seismograms computed in the vicinity of the rupture. We observe that these geometrical irregularities do not just lead to high frequency effects but can strongly affect the synthetics in the whole frequency band. Finally, we discuss our observations in detail and conclude that the correct incorporation of the geometrical properties such as local strike and dip variations of the rupture surface is an important issue. We also discuss possible implications for some seismological fields, such as strong-motion simulations or seismic moment tensor and slip inversions, where these results might have significant consequences.

[1]  Yuehua Zeng,et al.  Fault Rupture Process of the 20 September 1999 Chi-Chi, Taiwan, Earthquake , 2004 .

[2]  John G. Anderson,et al.  Subevent rake and random scattering effects in realistic strong ground motion simulation , 1995 .

[3]  Michael Dumbser,et al.  An arbitrary high-order discontinuous Galerkin method for elastic waves on unstructured meshes - IV. Anisotropy , 2007 .

[4]  William H. K. Lee,et al.  Fine Structure of the Landers Fault Zone: Segmentation and the Rupture Process , 1994, Science.

[5]  E. Toro.  Riemann Solvers and Numerical Methods for Fluid Dynamics , 1997 .

[6]  Eleuterio F. Toro,et al.  ADER: Arbitrary High Order Godunov Approach , 2002, J. Sci. Comput..

[7]  N. Martakis,et al.  Non‐double‐couple mechanism of moderate earthquakes near Zakynthos, Greece, April 2006; explanation in terms of complexity , 2008 .

[8]  M. Dumbser,et al.  An arbitrary high-order discontinuous Galerkin method for elastic waves on unstructured meshes — II. The three-dimensional isotropic case , 2006 .

[9]  Michel Bouchon,et al.  Propagation of a shear crack on a nonplanar fault: A method of calculation , 1997, Bulletin of the Seismological Society of America.

[10]  Jean Virieux,et al.  Dynamic rupture simulation of non-planar faults with a finite-difference approach , 2004 .

[11]  J. Hardebeck.  Homogeneity of Small-Scale Earthquake Faulting, Stress, and Fault Strength , 2006 .

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

[13]  M. Bouchon.  A simple method to calculate Green's functions for elastic layered media , 1981 .

[14]  Toshimi Satoh,et al.  Empirical Frequency-Dependent Radiation Pattern of the 1998 Miyagiken-Nanbu Earthquake in Japan , 2002 .

[15]  R. Madariaga,et al.  The 1999 İzmit, Turkey, Earthquake: Nonplanar Fault Structure, Dynamic Rupture Process, and Strong Ground Motion , 2001 .

[16]  Paul Lundgren,et al.  Joint Inversion of InSAR, GPS, Teleseismic, and Strong-Motion Data for the Spatial and Temporal Distribution of Earthquake Slip: Application to the 1999 İzmit Mainshock , 2002 .

[17]  D. Wald,et al.  Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake , 1994, Bulletin of the Seismological Society of America.

[18]  F. Gallovič,et al.  On strong ground motion synthesis with k−2 slip distributions , 2004 .

[19]  R. Madariaga,et al.  Seismic Radiation from a Kink on an Antiplane Fault , 2008 .

[20]  P. Spudich.  CHAPTER 5 – Techniques for Earthquake Ground-Motion Calculation with Applications to Source Parameterization of Finite Faults , 1987 .

[21]  Kuvvet Atakan,et al.  Strong ground motion estimation in the Sea of Marmara region (Turkey) based on a scenario earthquake , 2004 .

[22]  M. Dumbser,et al.  An arbitrary high-order discontinuous Galerkin method for elastic waves on unstructured meshes - I. The two-dimensional isotropic case with external source terms , 2006 .

[23]  Kojiro Irikura,et al.  Simulation of Near-Fault Strong-Ground Motion Using Hybrid Green's Functions , 2000 .

[24]  H. Aochi,et al.  Spontaneous Rupture Propagation on a Non-planar Fault in 3-D Elastic Medium , 2000 .