福岡市西区・九州大学伊都キャンパス地区の岩脈年代と地下水の化学組成

概要

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Within the Ito Campus and surrounding area, subsurface investigations with several borings had been conducted by the Kyushu University. Core samples obtained by the boring and groundwater samples collected from the boring wells provide important information on understanding geological and geochemical features of this area. Age determination of a lamprophyre dike in the Itoshima Granitoid using K-Ar technique provided age of around 90.7±1.2 Ma, which is in accordance with the reported age for main body of the granitoid. This result would be one of constraints for discussion on igneous activities in the northern Kyushu. The groundwater collected from this area can be classified into four types based on the chemical and isotopic compositions. The relationship between water chemistry and water elevation can be explained as a snap shot of groundwater evolution from meteoric water to the Ca-HCO3 type groundwater accompanying weathering of granitic rocks. Within the alluvial sediments in the east of the Ito Campus, the Na-Cl type groundwater is widely distributed, which is attributed to the influence of seawater intrusion. The natural flow which is associated with the West Off Fukuoka Earthquake on March 20, 2005 is explained as a result of rising of the freshwater-seawater boundary.
2007-02-15