SEGJ Technical Conference

Investigation of Salinity of groundwater at the alluvial plane near coastal area in Saijo-shi using CSAMT survey

Abstract There are about 2000 flowing wells in the Saijo plain, Saijo-shi, Ehime Prefecture. The seawater is confirmed in the area along the shore of the northern part. In order to investigate the seawater/ freshwater interface, the authors performed the CSAMT method along the survey line of approximately 3.5km distance in the inland direction from the coastal area and analyzed two-dimensional resistivity structure to 750m in depth. As a result, we can estimate the fault with vertical displacement near the boundary between the seaside groundwater basin and the landside groundwater basin. We estimated the hydro-geological structures as follows: The low resistivity zone (2-20ohmm) in the seaside area of the fault correspond to the sediments saturated by sea water. The high resistivity zone (50-150ohmm) deeper than 500m in depth in the seaside area of the fault is suggested to be the non-permeable bedrocks. The low resistivity zone (1-20ohmm) in the landside area of the fault correspond to the sediments saturated by fossil salt water. The high resistivity zone (20-500ohmm) shallower than 250m in depth near the fault is suggested to be the sediments saturated by freshwater.