3D Finite‐Element Modeling of Earthquake Interaction and Stress Accumulation on Main Active Faults around the Northeastern Tibetan Plateau Edge in the Past ∼100 Years

Abstract

The northeastern Tibetan plateau edge is an active tectonic region with crustal deformation featured mainly by thrust and strike‐slip faults. In the past ∼100 years, several strong earthquakes have occurred around this region. Associated with regional tectonic loading, these strong earthquakes altered the stress buildup of active faults; this in turn should affect the potential hazard of seismicity around the northeastern Tibetan plateau. Here, we developed a 3D viscoelastic finite‐element model to explore the stress accumulation along the main active faults during the past ∼100 years. In this model, rheological contrast of the crust and upper mantle between the Tibetan plateau and its surrounding regions is approximated, and regional tectonic loading is simplified from dense Global Positioning System measurements. Results show that after the 1920 M ∼8.7 Haiyuan earthquake, the succeeding ruptures, both of thrusting and strike‐slipping events, had received positive changes of Coulomb failure stress—among which the coseismic and the postseismic deformations from previous earthquake(s) contributed 36%–80%. This means that significant mechanical interactions existed between the active faults around northeastern Tibet during the earthquake process even though they were separated by hundreds of kilometers. Numerical results also suggest that the 1954 M ∼7.2 Shandan earthquake and the 1990 M ∼6.2 Tianzhu earthquake could have been triggered because the Coulomb failure stress received from coseismic and postseismic deformation of previous earthquakes around the epicenter of these two events reached ∼0.02–0.3 MPa. After about 100 years of regional tectonic loading—coseismic and postseismic deformations of past large earthquakes—the Coulomb failure stress along the northeastern segment of the Altyn Tagh fault, the Tianzhu segment of the Haiyuan fault, and the Gulang fault has accumulated to 0.005–0.2 MPa. Therefore, as previous studies mentioned for the Tianzhu seismic gap, these active faults should be carefully studied because of their potential earthquake hazard. Online Material: Snapshots of Coulomb failure stress changes.