RESOLVING THE THROUGH-GOING ACTIVE FAULT GEOMETRY AND FAULT STRENGTH PARAMETERS THROUGH STRESS MODELING: A STUDY OF THE NORTH ANATOLIAN FAULT (NAF)

[摘要] The North Anatolian Fault (NAF) was the source of the August 1999 M7.4 Izmit earthquake making it the focus of new research to understand its structure and processes that control earthquake ruptures. The zone of deformation (NAF system) widens westward, allowing for complications of the through-going active fault geometry of the NAF. We process simplified 2-D finite element models of possible through-going active fault geometries to develop a stress field. The stress orientations of the resulting field are compared to the maximum horizontal stress orientation as inferred from lineament analyses and focal mechanism data. The determined through-going geometry of the western NAF bifurcates into a northern and southern strand near Bolu, converging towards the Mudurnu Valley, through which they are linked. The northern strand bifurcates again in the Gulf of Izmit and bounds a principal deformation zone associated with the developing Marmara basin. It then converges as a single strand into the Gulf of Saros and the Aegean Sea. The southern strand bifurcates near Pamukova; its northern component follows the southern Marmara Sea coast to the Kapidag Peninsula, where it trends southwest across the Biga Peninsula into the Aegean Sea. The southern trace parallels the northern trace further south, and then converges on the northern trace through a linking structure. To understand fault strength and constrain ranges of static and dynamic fault parameters, modeled fault rupture times and total slip are compared against recurrence intervals, as a proxy for the time it takes stress to rupture a fault from a relaxed state, and the maximum slip following the 1999 Izmit earthquake. We constrained values of static fault parameters - static coefficient of friction (μs) and cohesion (C) - and dynamic fault parameters - kinetic coefficient of friction (μk) and slip-weakening distance (Dc) - that satisfy the geologic constraints. Given the computationally expensive processing associated with dynamic fault models, we suggest the application of statically weak fault conditions (μs≤0.2 and C=500 kPa) since they best represent laboratory experiments on the strength of fault gouge materials.

[发布机构] the University of Pittsburgh