Spatiotemporal analysis of late Pleistocene to Holocene deposits using a borehole database to evaluate land surface deformation in a tectonically subsiding area: Echigo Plain, central Japan

The Echigo Plain in central Japan is an actively subsiding sedimentary basin influenced by tectonic subsidence and anthropogenic activity. In this study, late Pleistocene to Holocene sequences were analyzed using high-density borehole data from geological databases and radiocarbon dates obtained in previous studies to estimate spatiotemporal variations in subsurface geological distribution and paleo-water depths, as well as to understand the trend of subsidence. The results showed that paleowater depths were shallow in the early stages of sea-level rise, but continued rise caused the sea to expand inland, deepening the paleowater depths near the mouth of the present river. Paleo-water depths were estimated to be shallower in areas with barriers, lagoons, and delta systems that developed during the transgression and maximum sea-level periods. The relationships between local land subsidence zones identified from leveling surveys and GNSS observations and the spatiotemporal distribution of surface geology were compared. In areas where marine or lagoon deposits are thickly distributed; a temporarily low water table may cause plastic compaction of clay layers adjacent to aquifer layers composed of river and dune deposits. However, even under similar depositional conditions, significant land subsidence areas were identified that cannot be explained by local geology and local tectonics alone; other factors, such as the effects of human activities and deformation of deeper geology, need to be considered. These findings provide important insights for future regional development and groundwater use.