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

Abstract

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. © 2007 The Authors Journal compilation © 2007 RAS.