2025年1月7日定日MS6.8地震诱发的液化大变形特征及其成因机制OA

[Objective]In liquefaction-susceptible geological settings,the spatial superimposition of earthquake-induced liquefaction and coseismic fault rupture renders the genetic attribution of surface deformation highly ambiguous,yet systematic field diagnostic criteria and a unified geomechanical framework remain elusive.[Methods]Integrating field emergency surveys,high-resolution remote sensing image interpretation,unmanned aerial vehicle(UAV)photogrammetry,and borehole-trench investigations with regional geological and hydrogeological context,this study systematically characterizes the spatial distribution and controlling mechanisms of large-scale surface deformation triggered by the 7 January 2025 MS 6.8 Dingri,Tibet earthquake.[Results]Our results show that the extensive surface deformation along the eastern shore of Dengmecuo Lake to the Pengqu River is dominated by liquefaction-induced lateral spreading rather than coseismic tectonic surface rupture;small-scale coseismic surface ruptures occur locally along the eastern lake shore;and north of Nixiacuo,coseismic surface rupture predominates,with superimposed liquefaction deformation.The spatial extent of liquefaction-induced lateral spreading is governed by two topographic configurations:free-face conditions in river valleys,and gently sloping ground on low-gradient alluvial-lacustrine plains.Earthquake-induced liquefaction substantially reduces the shear strength of water-saturated sandy sediments and,driven by the combined effects of seismic inertia and gravity,triggers lateral spreading that generates lateral compressive forces and horizontal displacement.At the trailing edge of the deformation zone,tensional ground cracks and graben-like subsidence develop,whereas the leading edge is characterized by pressure ridges and shallow thrust structures formed by lateral compression.Tensile fissures generated by lateral spreading further provide conduits for the upward injection of liquefied sand from depth,giving rise to abundant sand volcanoes.The systematic coexistence of trailing-edge extension,leading-edge compression,and sand volcanoes constitutes a diagnostic deformation assemblage of liquefaction-induced lateral spreading,which is fundamentally distinct in geometry and kinematics from tectonic coseismic surface ruptures.The development of liquefaction deformation is jointly controlled by seismic intensity,micro-topography,the spatial distribution of liquefiable sand layers,and the depth of the shallow groundwater table.Importantly,lateral spreading can impose additional displacement onto active fault zones,and compressional liquefaction deformation may overprint fault traces,systematically biasing the identification of the geometry and kinematics of coseismic surface ruptures.Accordingly,we propose three field criteria for identifying liquefaction-induced deformation:(1)macroscopic plastic flow or fluid-like deformation features;(2)highly consistent deformation patterns along watercourses across both fault and non-fault zones under comparable depositional conditions;and(3)systematic spatial association with liquefaction indicators such as sand volcanoes.[Conclusions]We conclude that the large-scale deformation triggered by the 2025 Dingri earthquake should not be classified as coseismic surface rupture;rather,trailing-edge extension,leading-edge compression,and sand boils together constitute a unified lateral spreading system.Liquefaction-induced deformation exerts a pronounced overprinting effect on coseismic surface ruptures,and rigorously distinguishing the two in liquefaction-prone seismotectonic settings is essential for accurately assessing fault activity.[Significance]This study provides the first systematic mechanistic framework for liquefaction-induced large-scale deformation associated with the Dingri earthquake,and the field criteria and conceptual model established herein offer a scientific basis for seismic hazard assessment,post-earthquake reconstruction,and major engineering siting in the southern Tibetan rift system.