9:00 AM - 9:25 AM
[AHW30-01] Case Study on Hydrogeological Structure of Accretionary Complex in Southern Nagano Prefecture
★Invited Papers
Keywords:slab-derived fluid, hydrogeological structure, accretionary complex
Hydrogeological structure is an important fundamental information in the site selection process of construction projects involving groundwater flow. Accretionary complexes are thought to be widely distributed in the subsurface of Japan, but few studies have been conducted on the hydrogeological structure of these complexes. In this study, a case study was conducted to clarify the hydrogeological structure of an accretionary complex using high-salinity groundwater (deep-seated fluid) gushing from the accretionary complex. The results of geological survey, chemical analysis of river water, and laboratory analysis of rocks in the southern part of Nagano Prefecture indicate that fractures and minor faults near geological boundary faults and pelitic schist of the Sambagawa Belt function as groundwater conduits. Based on the results of the study, we developed a conceptual model in which fractures and minor faults in the damage zone of a geological boundary fault and weathering-induced fractures in pelitic schist are groundwater conduits. The findings from this study are expected to provide reference information for the site selection process for accretionary complexes. The results of chemical analysis of river water in the study area indicate that the reaction of calcite and chlorite with groundwater and the permeability of rocks are involved in the evolution of river water chemistry. Understanding of the evolution of river water chemistry may contribute to the investigation of hydrogeological structures.