HR: 1340h
AN: V13B-1342    [Abstracts]
TI: Heat Flow Distribution At A Mud Volcano In Kumano Basin, East Of Kii Peninsula, Central Japan
AU: * Goto, S
EM: s.gotou@aist.go.jp
AF: Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Yamano, M
EM: yamano@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, 113-0032, Japan
AU: Kinoshita, M
EM: masa@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Matsubayashi, O
EM: matsubayashi-osamu@aist.go.jp
AF: Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AB: Mud volcano is a surface expression of mud diapir, where over-pressured unconsolidated sediment has been intruded into the overlying sediment column, and provides information on the process of material transport and physical and chemical conditions in a deeper part without a deep drilling. Kumano Knoll No.4 (KK4) is one of the mud volcanoes in the Kumano Basin, east of Kii Peninsula, central Japan. The diameter and height above the basin floor are 800 m and 100 m, respectively. The summit area has bumpy surface with pits whose diameter are several meters. There are living and dead clam colonies in the area. In order to survey thermal and hydrological characteristics of KK4, we deployed a long-term temperature monitoring system (LTMS), which has two probes including six thermistors, at the top of the mud volcano and monitored bottom-water and sub-bottom temperatures from August 2002 to May 2003. One probe (Probe-2) was penetrated into sediment within a pit with a dead clam colony that suggests the existence of cold seepage in the past. The other (Probe-1) was installed in the outside of the pit where there was no expression of cold seepage. Measured bottom-water temperature variation (BTV) shows large amplitude variation with various periods. Measured sub-bottom temperatures show similar variation to the bottom-water temperature variation but its amplitudes decay and the phases delay with increasing sub-bottom depth. By comparing amplitude and phase of BTV and sub-bottom temperature variation, we can identify whether there is vertical fluid migration in sediment. For sub-bottom temperatures measured outside of the pit, we could explain that the effects of BTV propagated into sediment by conduction only. By correcting the effects of BTV from the sub-bottom temperatures, we estimated heat flow value as 14 mW/m². On the other hand, sub-bottom temperatures measured within the pit could be better explained by a model with upward water flow at a rate of 10^-7 m/s order, than by conduction only. Heat flow combined conduction and this upward water flow was estimated as 60 mW/m², about four times the heat flow values in the outside of the pit. Our results indicate that there was cold seepage activity at KK4. We conducted 11 heat flow measurements with small heat flow probes 60 cm in length along a survey line from west to east just before the recovery of LTMS. Using the BTV data obtained with LTMS, we removed the effects of BTV from temperature profiles measured with SAHF. The cross-section of corrected heat flow values indicates three characteristics: (1) high heat flow values higher than 70 mW/m² was measured on the base of the mud volcano, (2) low heat flow values (20-30 mW/m²) were measured on the western slope, and (3) heat flow increases to 60 mW/m² on the top of the mud volcano. Preliminary analysis by numerical computation indicates that to interpret this heat flow distribution, we need consider not only advective heat supply to KK4 but also topographic effects of KK4 on the subsurface thermal structure.
DE: 3015 Heat flow (benthic)
DE: 3021 Marine hydrogeology
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3050 Ocean observatories and experiments
DE: 8426 Mud volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting