Crustal Stress and Strain in the Southeastern Tibetan Plateau: Insights into Tectonic Deformation Kinematics and Dynamics

Abstract

The Southeastern Tibetan Plateau is a vital place for understanding the stress-transmitting process between the India-Eurasia collision belt and the surrounding blocks. Several geological and geodynamic models have been proposed to decipher the growth mechanisms of the Southeastern Tibetan Plateau. Yet significant discrepancies persist among these models. We perform a comprehensive analysis of the strain and stress field for the Southeastern Tibetan Plateau, employing a combination of GNSS measurements and focal mechanisms. The estimated strain generally captures the main seismotectonic characteristics, including the clockwise rotation around the Eastern Himalayan syntaxis and lateral extrusion of the crustal material from the Tibetan Plateau. Also, it provides local tectonic information, such as the Lijiang-Xiaojinhe fault accommodating most of the deformation in the Chuandian block. The comparison between the strain field and large earthquakes in the Southeastern Tibetan Plateau indicates that the India-Eurasia convergence-driven strain is not only localized around major strike-slip faults but also distributed along secondary faults or previously inactive faults. The stress inversion results in the Southeastern Tibetan Plateau exhibit spatial coherence with the regional background stress field and demonstrate uniform characteristics within measurement uncertainties at depths of 0–20 km; however, pronounced stress heterogeneity emerges at depths of 20–30 km, likely influenced by fluid activity associated with mantle upwelling or asthenospheric flow. The comparability in mechanism between the strain and stress indicators manifests that the seismic stress has a linear relationship with the geodetic strain; this also seemingly demonstrates that the surface strain could be regarded as the indicator of the stress state within the top ~ 20 km depth. Summarizing seismic stress and geodetic strain field, the main characteristics of the Southeastern Tibetan Plateau can be divided into four parts: (1) Thrust faulting regime around Eastern Himalayan syntaxis; the NE-directed push force accounts for the stress field in this region owing to the northward subduction of the Indian plate. (2) Normal faulting regime around Jinsha River Fault; the gravity potential energy, or the gravity spreading causes these regions to be in a state of extension.(3) Strike slip faulting regime along the Xianshuihe-Xiaojiang faults; as a stress transfer channel, this fault system accommodates or partitions the deformation of the plateau interior and its periphery. (4) Thrust faulting regime around the Longmen Shan Fault; this is attributed to the eastward extrusion of the Tibetan Plateau and the obstruction of the Sichuan basin. Additionally, mantle upwelling or asthenosphere flow may influence some of the normal faulting observed in the southern region. After our comprehensive analysis, we believe that the contemporary deformation of the Southeastern Tibetan Plateau could be related to the context of the India-Eurasian convergence associated with the gravity potential energy, the northeastward subduction of the Indian Plate, as well as the eastward subduction of India-Burma and slab retreat or backoff of the Burma plate.