DETERMINING STATIC COEFFICIENT OF FRICTION AND COHESION FOR THE WESTERN PORTION OF THE NORTH ANATOLIAN FAULT (NAF) THROUGH THE USE OF NUMERICAL SIMULATIONS

Plate tectonic boundaries source the majority of earthquakes and deformation at the Earth’s surface, so understanding the strength of faults and the processes that control earthquake rupture – particularly at plate boundaries – is crucial. The strength of a fault is best described by the parameters which define when it will fail: static coefficient of friction (μ_s) and cohesive strength (C). Tectonic faults are thought to be weak, with low friction coefficients (μ≤0.25) and cohesion. Most studies ignore cohesive strength, and as a result, there has been no consensus on the impact of cohesive strength along tectonic faults from fault gouge material. Assuming no cohesive strength further assumes a rough, clean discontinuity surface with rock-to-rock contact and no infilling; however, cohesion can be developed on fault planes in many conditions, and even a low cohesion value could have a significant effect on the strength of a fault. To determine µ_s and C for a fault, two approaches are typically used: rock friction experiments in a laboratory, and numerical modeling of the fault system. Two of the most intensively studied plate boundary strike-slip faults are the San Andreas Fault (SAF) in the United States and the North Anatolian Fault (NAF) in Turkey. Previous numerical and experimental work on these two large tectonic faults have not evaluated the impact of cohesion on fault strength, nor have they arrived at a consensus regarding the acceptable ranges of μ_s acting upon the interface. To better constrain the fault strength parameters acting along a tectonic fault (NAF), we employ a viscoelastic finite element analysis.

Our methodology considers that strength parameters acting on a fault exert control on stress and strain accumulation, thus affecting the velocity field of fault-bound blocks. We attempt to evaluate the acceptable ranges of fault strength parameters for the NAF from numerical simulations by comparing the velocity and orientation of fault-bound blocks in our model to their known GPS velocity field. In addition to providing a range of acceptable fault strength parameters, we will show the value of cohesion as a parameter when modeling tectonic faults, such as the NAF. While we only consider a tectonic strike-slip fault, the methodology and implications are applicable to other types of faults.