The 3‐D Structural Model of an Out‐of‐Sequence Earthquake in China: Implication for the Reactivation of Positive Inversion Structures Along the Northern Tianshan Fold‐and‐Thrust Belt

Abstract

AbstractThe intracontinental earthquake behavior is not well understood due to its complexity in the interior of the continent. The Tianshan Mountain is located in the interior of the Eurasian plate, which was rejuvenated in the Cenozoic due to the India‐Asia collision and sourced several large earthquakes. The 2016 Hutubi earthquake occurred within the northern Tianshan, China, during rupture of a high‐angle back‐thrust toward the hinterland, which broke the long‐time quiescence in the mountain front. The geometry, dynamics, and hazard implications of this earthquake on an out‐of‐sequence thrust fault remains unclear. The 3‐D structural model shows that the coseismic fault is connected to the large‐scale blind Southern Junggar thrust, which sourced the 1906 Mw ~8 Manas earthquake. The geometry of the coseismic fault and the occurrence of extensional tectonics in the Jurassic suggest that the Hutubi earthquake occurred on a reactivated rift‐related structure. To test this hypothesis and study the kinematics, we performed sandbox modeling, with results suggesting that coseismic fault can form during positive inversion of a preexisting Jurassic rift, and that the Southern Junggar thrust and related structures may be recently active. Coal beds facilitated the transfer of fault slip and strain from mountain to basin and from basal to roof detachment. We propose that the preexisting rift and related sedimentation controlled the subsequent structure and geomorphology of the mountain belt through thrust wedge formation. This study provides a typical example for the study of intracontinental inversion structure and its earthquake behavior.