Dynamics of dip‐slip faulting: Explorations in two dimensions

Abstract

Abstract. Dynamic models of earthquake rupture and slip are a powerful method by which to investigate the physics of earthquakes. Owing to both conceptual and computational constraints, dynamic earthquake models have largely been limited to cases with geometrical symmetry, such as faults in unbounded media or vertical faults. However, there are both observational and theoretical reasons to believe that nonvertical dip-slip faults behave differently from faults with more symmetrical geometries. Previous observations have shown greater ground motion from thrust/reverse faults than normal faults and higher ground motion on hanging walls than on footwalls. In the present work, two-dimensional dynamic simulations of thrust/reverse and normal earthquakes show precisely these effects and also elucidate their causes. For typical nonvertical dip-slip faults the breakdown of symmetry with respect to the free surface allows radiated seismic waves to reflect off the free surface and to hit the fault again, altering the stress field on the fault. This process can lead to time-dependent normal stress and a feedback between the friction/rupture processes and seismic radiation. This interaction leads to thrust/reverse faults producing much higher fault and ground motion than normal faults with the same geometry and stress magnitudes. The asymmetric geometry also directly leads to higher motion on the hanging walls of such faults than on the footwalls. Simulations show that these effects occur for a variety of dip angles but only for faults that either intersect or closely approach the free surface. The results emphasize the strong effect that the free surface can have on the dynamics of fault rupture and slip.

Dynamic rupture simulation of the 2011 off the Pacific coast of Tohoku Earthquake: Multi-event generation within dozens of seconds

“…Also, special approaches are required to represent the time-dependent dislocations on the fault plane, such as the split-node technique (e.g. Oglesby and Archuleta, 2000;Dalguer and Day, 2007;Kaneko et al, 2011), and it is difficult to embed a low-angle dipping fault with such approaches. This is because a modification of the local coordinate system for FDM (e.g.…”

“…For the reference solutions, a finiteelement method (FEM) with split nodes on the fault plane is applied (e.g. Oglesby and Archuleta, 2000). Two different sizes of mesh layout are adapted to the fault, and the mesh sizes are, on average, 50 m and 25 m, respectively.…”

Radiation from a Finite Reverse Fault in a Half Space

“…A substantial effort to model dipslip events and the strong motion they generate has been made by OGLESBY et al (1998OGLESBY et al ( , 2000aOGLESBY et al ( , 2000b, SHI et al (1998). These works raised a number of interesting questions regarding the effect of the free surface above the shallow dipping fault that need careful study.…”

Modelling of Reverse Dip-Slip Faults Using 3D Applied Element Method

“…In this paper, it is shown that many of the observations of the near-source displacements and peak accelerations can be explained as simple consequences of the asymmetry of the dipping fault geometry. Closer to the subject of the Chi-Chi earthquake, it has been previously argued that the dynamics of dip-slip faults (especially those that intersect the free surface of the earth) are strongly affected by their fault geometry (Brune, 1996;Oglesby et al, 2000;Shi et al, 1998;Oʹ Connel et al, 2007). In particular, these studies showed that in comparison with vertical strike-slip faults, dip-slip faults exhibit many unique features associated with their asymmetrical geometry.…”