JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Poster

A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW36] [JJ] Water Environment and Geology in Urban Areas

Sat. May 20, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Kei Nishida(Interdisciplinary Centre for River Basin Environment, Interdisciplinary Graduate School, University of Yamanashi), Hiroaki SUZUKI(Strategic Technology Development Dept. Research & Development Center, Nippon Koei Co., Ltd.), Asada Motoyuki(Shimizu Corporation, Institute of Technology)

[AHW36-P04] Distribution and geochemistry of gas seepage on Boso peninsula, Chiba

*yasuha Wakabayashi1, Hitoshi Tomaru1 (1.Chiba university)

Keywords:gas seepage, methane, Boso peninsula

Within the area of Southern Kanto gas field in Chiba, with methane concentration of >99%, natural gas seepage is observed widely on land in the central part of Kujukuri plain to Otaki. Such gas has been used as a fuel by local residents, however, it may cause an accidental explosion and agricultural damage. In addition, if the gas is continuously released from the subsurface environment to atmosphere through the seepage, the impacts on the local carbon cycle should be taken into account. In this research, we aim to characterize the source, migration and seep processes of these gases by analyzing their chemical and isotopic compositions. Gas samples were collected from the boundaries between alluvial mudstone and sandstone or Kazusa Group, with a methane concentration generally of >75% and trace amounts of carbon dioxide and ethane with nitrogen from atmosphere. According to the methane/ethane ratio and stable carbon isotopic composition of methane, it is suggested that the majority of methane is of biogenic origin. Together with the stable carbon isotopic composition of carbon dioxide, it is considered that the methane is produced mainly by reduction of carbon dioxide and fermentation of acetate with some contribution of methane oxidation.