North China as a mechanical bridge linking Pacific subduction and extrusion of the Tibetan Plateau

Abstract

North China, one of the most populated regions in the world, is exposed to elevated seismic hazards and has experienced multiple M ≥ 8 earthquakes in the past 1,000 years. The recent 1976 Ms 7.8 Tangshan earthquake constitutes a vivid reminder of the tectonic activity. Yet, the tectonic origin of the regional seismic unrest remains poorly understood. Here, we use geodetic data to construct a kinematic model encompassing the North China Block (NCB) and its neighboring Amurian Block (AB) and the South China Block (SCB) to illuminate the link between lithospheric strain accumulation and seismic activity. Our analysis illuminates two east-west oriented left-lateral shear zones that decouple the AB from the NCB, the latter representing a collage of the North China Plain (NCP) and the Ordos Block (OB). Bookshelf faulting slices the NCP through a series of NNE-trending right-lateral and conjugate WNW-trending left-lateral shear zones. These shear zones drive historical and instrumental seismic activities. The NCB serves as a mechanical bridge accommodating the relative motion of the surrounding mobile tectonic units. In the far field, Pacific subduction at the Japan Trench, extrusion of the Tibetan plateau, and retreat at the Ryukyu trench cause internal strain within the NCB, leading to the frequent occurrences of destructive earthquakes.