Identifying multiple drivers of stratified deformation in soft deltaic deposits using integrated geosensing

Land subsidence and rebound have emerged as critical geological hazards threatening urban safety in economically developed and densely populated coastal plains and river deltas. However, conventional surface monitoring methods struggle to reveal the stratified deformation characteristics of deep Quaternary deposits and their differential responses to groundwater fluctuations, historical abstraction, and engineering disturbances. To address this, we integrated persistent scatterer interferometric synthetic aperture radar (PS-InSAR), distributed fiber optic sensing (DFOS), and fiber Bragg grating (FBG) piezometers to systematically analyze strata deformation processes under multiple driving forces in the Shengze area. PS-InSAR was initially applied to characterize the overall regional deformation field, which revealed a distinct spatial heterogeneity in land subsidence with rates ranging from -20 to -14 mm/yr in the central area. DFOS technology was then employed to investigate the depth-resolved deformation behaviour of the subsurface, enabling the identification of three distinct deformation processes: First, DFOS reveals that deformation between 2012 and 2015 was predominantly driven by delayed consolidation of deep aquitards (approximately 60-100 m), which continued to compact and contributed a cumulative displacement of 13.39 mm. Second, during 2016-2020, the primary driver shifted to seasonal groundwater fluctuations. The aquitard layers at comparable depths exhibited a synchronous periodic response, with deformation amplitudes cycling between 0 and 5 mm in accordance with seasonal hydraulic patterns. Finally, a short-term unloading effect dominated the total deformation in July 2020. DFOS captured a full-depth (0-196 m) synchronous uplift triggered by building demolition, characterized by a peak tensile strain of approximately 100 με and a surface rebound of approximately 21 mm, and this uplift signal is independently confirmed by PS-InSAR observations. This study demonstrates that strata deformation in soft soil regions is a composite result of long-term delayed consolidation, seasonal hydraulic fluctuations, and rapid engineering unloading, providing a crucial basis for assessing subsidence and rebound risks in the context of urban renewal.