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

The 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. Plain Language Summary The Tianshan Mountain in the interior of the Eurasia plate was rejuvenated in the Cenozoic due to the India-Asia collision and sourced several large earthquakes, where it is ideal to do research on the structural geometry and kinematics related with intracontinental earthquakes. The 2016 Hutubi earthquake, which occurred within the northern Tianshan, China, broke the long-time quiescence in the mountain front. We constructed a 3-D model of the coseismic fault showing that it is connected to the large-scale blind Southern Junggar thrust, which sourced the 1906 Mw 8 Manas earthquake and that this event occurred on a reactivated rift-related structure. The Jurassic rifts widely developed in the northern Tianshan, so it is important to study the geometry and kinematics of such inversion structures. Sandbox modeling results suggest that the Southern Junggar thrust and related structures may be recently active and that coal beds in the rifts facilitated the transfer of fault slip and strain via the thrust wedge. In summary, this study provides a typical example for the study of the intracontinental inversion structure and its earthquake behavior.