Summary of physical properties of rocks collected during the IODP Exp.402 in the back-arc Tyrrhenian Basin

Filina, I. Y.*; Abe, Noriaki; 25 of others*

no journal, , 

Long-term prediction of environmental fate of Cs in ocean considering migration process of Cs in a lower trophic level ecosystem

Ikenoue, Tsubasa; Nakanishi, Takahiro; Kawamura, Hideyuki

no journal, , 

The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 resulted in the release of radionuclides in the marine environment. Among the radionuclides released, since large quantities of Cs were released and Cs has a long half-life, there is concern about the impacts of Cs on marine environment. Most of Cs is dissolved in seawater, but some Cs is taken in and adsorbed on biogenic particles (phytoplankton, zooplankton, and detritus). In this study, we aim to predict the long-term fate of Cs in ocean considering migration process of Cs in a lower trophic level ecosystem. We improved an oceanic dispersion model by coupling with a lower trophic level ecosystem model and conducted the long-term simulation of Cs in ocean. This improvement enabled the long-term prediction of Cs concentrations in biogenic particles and organic seabed sediment as well as in seawater. The calculation results suggested that the adsorption process from seawater to organic sediment had a much greater impact on Cs concentration in organic seabed sediment than the sedimentation process of biogenic particles.

Host rock thermal properties on behavior of trapped charges during coseismic fault slip

Tanaka, Kiriha; Ohashi, Kiyokazu*; Muto, Jun*; Oka, Toshitaka

no journal, , 

Electron spin resonance (ESR) dating of a fault is a developing method to estimate the age of the last seismic slip assuming that trapped charges in minerals were completely released during the last coseismic slip (zeroing). However, behaviors of the trapped charges during coseismic slips are poorly understood. According to previous studies, frictional heating is a key factor in zeroing. This study investigated the effect of the rock thermal properties linked to frictional heating on the behaviors of the trapped charges during coseismic slips. To investigate the effect of the rock properties, two series of high-velocity friction (HVF) experiments were conducted on artificial quartz grains using mullite (HVF I) and titanium alloy (HVF II) host cylinders. The experiments were designed to reproduce coseismic slips in different levels of frictional power density (FPD) in HVF I and II. ESR measurements and grain characterizations were conducted for the initial quartz grains and simulated-gouges to investigate the change in the number of a fundamental trapped charge and its associated mechanism. The trapped charge was produced in all of the HVF experiments. Although the FPD ranges differed between HVF I and II, the productions decreased monotonically to a similar value with increasing FPD. On the other hand, the productions decreased with increasing the maximum temperature observed on a gouge regardless of the FPD ranges. Thermal conductivities of the mullite and titanium alloy are 4.2 and 7.5 W/m/K, respectively. Thus, mullite retains heat more easily than titanium alloy. It indicates that frictional heating could more effectively release the trapped charges in HVF I than in HVF II, resulting in the production decreases described above. This study suggests that thermal properties of a host rock can be a key factor in controlling the effect of frictional heating on trapped charges, namely, zeroing.

Effects of deposited litter on water quality and radiocesium runoff in a forested headwater basin

Nagata, Yutaro*; Onda, Yuichi*; Hiramatsu, Tsubasa*; Takahashi, Junko*; Sakakibara, Koichi*; Niizato, Tadafumi

no journal, ,