Finite-difference numerical analysis of faulting and accompanying seismicity near the Chuya and Kurai depressions, Gorny Altai, Russia

Abstract

Numerical modeling of fault zone evolution and related seismicity can provide an insight into the process of large earthquake occurrences in a complicated fault system. In this paper, we develop a three-dimensional finite-difference numerical model of stress-strain evolution in and around the Chuya and Kurai depressions of Gorny Altai, Russia, to understand the fault zone evolution and the observed distribution of earthquakes in the region. Unlike in previous studies, the process of seismo-tectonic deformations of this region is addressed in a three-dimensional formulation with an improved model of rock massif behavior. A new geometrical model is designed, which is based on the seismotectonic, paleoseismological studies, and high-resolution Space-Radar-Topography-Mission data. The mathematical model applied here represents a set of partial differential equations, which are based on the fundamental conservation laws and constitutive equations for elastic and inelastic deformations. The initial stress state of the model is due to the action of gravity forces. The model is activated by assigning different displacement fields at the model boundaries – strike-slip and GPS-based displacements. The modeling results illustrate the stages of fault zone development and are in satisfactory agreement with the field observations in the case of GPS-based boundary conditions, which has not been modeled yet. Modeled seismic process is associated with the development of a fault zone resulting from the loss of strength in the subsurface points where the inelastic strain exceeds a certain threshold. The areas of high-degree of inelastic strain localization and the modeled fault zone represent an en-echelon system of dextral strike slips and various types of shear bands. The modeled seismic process obeys the Gutenberg-Richter (frequency-magnitude) law. The number of earthquakes in the attenuation part of the rock massif fracture process follows the Omori (aftershock decay) law.