Behavior of gases from DPRI 1800 m drill core and behavior of fluid in a shallow,brittle 
                              fault zone in Nojima Fault, Japan

                                          Abstract 

       An 1800 m borehole was drilled into the Nojima Fault Zone at Ogura, AwajiIsland, Hyogo prefecture, Japan.
   The chemical compositions and isotope ratios of gases extracted from the drill core were investigated.
   Major components were carbon dioxide (CO2) and methane (CH4).
       CH4 and C2H6 formed by the thermal decomposition of organic materials at temperatures above 75°C.
   Although hydrogen (H2) and helium (He) were minor components of the gases from cores, they increased
   in quantity in the fracture zone.
       And the results of petrographical and meso- to microstructural observations of brittle fault rocks in cores
   obtained by drilling through the Nojima Fault at a drilling depth of 389.52 m.
   Fault. These observations are the basis for a model of fluid behavior along the Nojima Fault. The model
   invokes the percolation of meteoric fluids through cracks in the hanging wall fault zone during interseismic
   periods, resulting in chemical reactions in the fault gouge layer to form smectite. The low permeability
   clay-rich gouge layer sealed the footwall. The fault gouge was brecciated during coseismic or postseismic
   periods, breaking the seal and allowing fluids to readily flow into the footwall, thus causing a slight alteration.
   Chemical reactions between fluids and the fault breccia and gouge generated new fault gouge, which
   resealed the footwall, resulting in a low fluid condition in the footwall during interseismic periods.

                                                        Reference

   Takashi Arai (2001), Tamotsu Okusawa1 and Hiroaki Tsukahara . Behavior of gases in the Nojima 
   Fault Zone revealed from the chemical composition and carbon isotope ratio of gases extracted 
   from DPRI 1800 m drill core . The Island Arc . Volume 10 Issue 3-4 Page 430 – 438. 

                                          (Abstract)(Full text)

   Hidemi Tanaka (2001), Shin-Ichiro Hinoki, Kazuo Kosaka, Aiming Lin, Keiji Takemura, Akihiro
   Murata and Takao Miyata . Deformation mechanisms and fluid behavior in a shallow, brittle fault
   zone during coseismic and interseismic periods: Results from drill core penetrating the Nojima 
   Fault, Japan . The Island Arc . Volume 10 Issue 3-4 Page 381 – 391 . 

                                          (Abstract)(Full text)