Taiki Kubo

Identification of linear features at geothermal field based on Segment Tracing Algorithm (STA) of the ALOS PALSAR data

Indonesia has about 40% of geothermal energy resources in the world. An area with the potential geothermal energy in Indonesia is Wayang Windu located at West Java Province. The comprehensive understanding about the geothermal system in this area is indispensable for continuing the development. A geothermal system generally associated with joints or fractures and served as the paths for the geothermal fluid migrating to the surface. The fluid paths are identified by the existence of surface manifestations such as fumaroles, solfatara and the presence of alteration minerals. Therefore the analyses of the liner features to geological structures are crucial for identifying geothermal potential. Fractures or joints in the form of geological structures are associated with the linear features in the satellite images. The Segment Tracing Algorithm (STA) was used for the basis to determine the linear features. In this study, we used satellite images of ALOS PALSAR in Ascending and Descending orbit modes. The linear features obtained by satellite images could be validated by field observations. Based on the application of STA to the ALOS PALSAR data, the general direction of extracted linear features were detected in WNW-ESE, NNE-SSW and NNW-SSE. The directions are consistent with the general direction of faults system in the field. The linear features extracted from ALOS PALSAR data based on STA were very useful to identify the fractured zones at geothermal field.

Spatial variations of tritium concentrations in groundwater collected in the southern coastal region of Fukushima, Japan, after the nuclear accident

Spatial variations in tritium concentrations in groundwater were identified in the southern part of the coastal region in Fukushima Prefecture, Japan. Higher tritium concentrations were measured at wells near the Fukushima Daiichi Nuclear Power Station (F1NPS). Mean tritium concentrations in precipitation in the 5 weeks after the F1NPS accident were estimated to be 433 and 139 TU at a distance of 25 and 50 km, respectively, from the F1NPS. The elevations of tritium concentrations in groundwater were calculated using a simple mixing model of the precipitation and groundwater. By assuming that these precipitation was mixed into groundwater with a background tritium concentration in a hypothetical well, concentrations of 13 and 7 TU at distances of 25 and 50 km from the F1NPS, respectively, were obtained. The calculated concentrations are consistent with those measured at the studied wells. Therefore, the spatial variation in tritium concentrations in groundwater was probably caused by precipitation with high tritium concentrations as a result of the F1NPS accident. However, the highest estimated tritium concentrations in precipitation for the study site were much lower than the WHO limits for drinking water, and the concentrations decreased to almost background level at the wells by mixing with groundwater.

Estimation of Regional Groundwater System in a Granitic Body by 3D Permeable Zone Modeling and Flow Simulation

Because clarifying a regional groundwater system is required for development and management of groundwater resources, it is important to evaluate the hydraulic property of a fracture system and alteration zones which act as the pass of groundwater flow in a rock body. For a case study of such hydraulic characterization, we selected an area in which the basement rock is composed of Cretaceous granite. We first constructed a 3D fracture model by a geostatistical method to simulate the regional fracture distribution by incorporating the orientation of the sampled fracture data obtained from the borehole investigations, and this model revealed the features of this fracture system in that area. We then incorporated a dataset of hydraulic conductivity obtained from single borehole hydraulic tests and rock-core tests using a N2 gas permeameter and found a positive correlation with the size of simulated fractures. Finally, a numerical simulation using MODFLOW was applied to this hydraulic conductivity model for estimating the regional groundwater flow system. Anisotropic behavior of flows near the fault was revealed by this simulation.