Improved 3D Modeling of Complex Fault Geometries Using Poly3D, an Elastic Boundary Element Code

Recent advances in geologic mapping, aftershock location, and reflection seismology allow geoscientists to image surface and subsurface structures with greater precision. These images demonstrate that earthquake ruptures typically occur along faults or fault systems that display complex 3D geometries. Poly3D, a 3D boundary element code and user interface, enables the integration of these varied data sets to constrain fault geometry and accurately models the complex geometries, limited only by data precision and computing power. Poly3D is based on the analytical solution for the elastic boundary value problem of an angular dislocation in a half space composed of a homogeneous and isotropic linear-elastic material (Comninou & Dunders, 1975). One of the major advantages that Poly3D has over other commonly used dislocation models (e.g. based on Okada, 1985) is the use of a triangular rather than rectangular uniform dislocation patch. The triangular shape enables one to model complex 3D shapes without gaps or overlaps. A further advantage of Poly3D is the possibility of using remote strain boundary conditions to simulate tectonic deformation and traction boundary conditions to simulate stress drop on fault segments. Poly3D has been applied to numerous problems of fault interaction and earthquake deformation over the last 5 years. We present results from three recent studies that have focused on fault interaction and earthquake triggering using a variety of geologic and geophysical data sets to constrain fault geometries and deformation. 1) GPS field mapping of faults and deformed strata is used to investigate fault slip and fault interaction around a set of normal faults at Chimney Rock, Utah. 2) Large-scale geologic mapping and measured slip distributions are integrated with published geophysical data to study the interaction between the 1967 Mudurnu Valley and 1999 Kocaeli earthquakes in Turkey. 3) Aftershock triggering and the development of normal fault systems are investigated by integrating high-precision aftershock locations and published geological and geodetic data sets from the 1995 Kozani-Grevena earthquake in Greece. In each of these studies the geometric flexibility of Poly3D and the ability to integrate available data sets has led to new insights into the processes of faulting, fault interaction, and earthquake triggering.