Particle-Based Modeling of Transtensional Pull-Apart Basins

Abstract

Scaled underlapping models based on the discrete element method are used to investigate crack propagation and basin development in transtensional systems with both parallel and nonparallel master faults. The introduction of a small component of oblique divergent motion causes the crack pattern and basin geometry to become quite different. The 5° transtensional model with parallel master faults produces a much wider depression separated by a cross-basin fault, compared to pure strike slip. A single throughgoing fault that connects the two master faults forms when the obliquity of 10° is reached. For transtensional model with two nonparallel master faults, a minor change of one master fault from parallel to nonparallel with a small component of 5° causes the crack pattern to become much more diffuse. As the obliquity increases from 5° to 15°, the first cracks propagate at a higher angle relative to the master faults, the cross-basin fault forms at a lower angle clockwise to the motion direction, and the area of the first depression decreases. A single throughgoing fault linking the two master faults initiates when the obliquity of 20° is obtained. The crack patterns and basin geometries of our numerical models show many similarities to natural transtensional basins including the Cinarcik Basin and the Central Basin in the Sea of Marmara. The transtensional models with various initial fault kinematics and different obliquities lead to different fault linkages, which has implications for the possible earthquake hazards in the Sea of Marmara near Istanbul.