OBZHIROV, ANATOLIY, Pacific Oceanological Institute, Vladivostok; ERWIN SUESS and STEPHAN LAMMERS, GEOMAR, Kiel

Abstract: Tectonic Activation of Methane Seepage from the Sakhalin Shear Zone: Results from Long-Term Monitoring

The change of carbon dioxide and methane in the atmosphere is a major factor in the current debate about global change. Over the past 100 years methane in the atmosphere increased by about 100%, the main source of which is believed to be anthropogenic. It is a simplification to attribute these changes solely to anthropogenic activity, because natural gases continually escape to the surface at changing rates. We contend that activation of tectonic processes, largely along existing and newly formed fault zones, promotes escape of gases from depths to the surface and that these fluxes are modulated by tectonics.

We have observed long-term changes between 1984 and 1998 in methane emission at the North Sakhalin slope in the Sea of Okhotsk. The region contains active submarine gas vents whose methane emissions appear to be affected by the earthquake. The area registered an earthquake near Nefte-gorsk of magnitude 7.5 in May 1995. Prior to this ethane showed a sharp increase in concentration in early 1988 which persisted at least through 1993; concentration increased 100-1000 times over background values. Between 1995 and 1997 methane monitoring was discontinued but in 1998 showed a decrease relative to 1993, roughly by a factor of 10. We content that methane emissions were activated over several years before the earthquake, reaching their maximum sometime between 1993-1995, and are now decreasing.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California