To evaluate fluid, heat or chemical species transport in fractured rocks, we have to characterize hydrological properties of the medium. Generally, the fracture region plays an important role for fluid flow, whereas the matrix region works as a major storage of fluid and/or heat. Conventional well testing methods such as pressure transient/interference and tracer tests are applied to characterize fractured rocks. However, it is usually difficult to characterize separately each of the fracture and matrix regions by using these methods. Ishido and Pritchett (2003) carried out numerical simulation of electrokinetic phenomena in fractured rocks and showed that features of fractured rocks appear much more clearly in the “self-potential (SP) transients” than in the pressure transients. Combining continuous pressure and self-potential measurements is thought to therefore provide a mean for better characterizing of fractured rocks.
 In order to study this prediction experimentally, we have carried out continuous SP monitoring using multi Ag-AgCl electrodes installed within KF-1 and KF-3 wells at the Kamaishi Mine, Japan. The observed ratio of streaming potential change to the pressure change due to wellhead valve opening showed different behaviors between intact host rock and fractured rock regions. A double-porosity behavior observed in the fractured region suggests that the time required for pressure equilibrium between the fracture and matrix regions is in the range of 1000 to 2000 seconds. Fracture spacings were estimated to be 1 to 4 meters assuming 1 to 10 micro-darcies of permeability of the matrix region.

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 Kaimondake volcano is located at the southern tip of the Satsuma peninsula in Kyushu, Japan. We conducted self potential (SP) surveys on the volcano along the traverse to the summit from the northwestern coast and obtained a characteristic SP profile. A topographic effect of -3 mV/m was clearly indicated on the stratovolcano area below 400m above sea level (ASL), while the effect was unclear on the central cone of the volcano occupied above 400m ASL. Several local SP anomalies were observed around the boundary between the central cone and the 885 lava flow. In order to clarify the origin of the SP profile, we implemented VLF-MT measurements and zeta potential experiment of the sampled volcanic rocks. Although apparent resistivities of the volcano showed a small variation of 100 to 600 Ωm along the SP survey line, zeta potentials of the rock samples were measured to be -1.3 to -20.4 mV, which can be categorized into three groups corresponding to the geological units (stratovolcano area, ∼-10mV; the central cone area, ∼-1mV; 885 lava, ∼-20mV). We conducted numerical simulations of groundwater flow and SP of the electrokinetic origin within the volcano based on the results of VLF-MT survey and zeta potential experiment. The simulation results indicated (a) topographic effect (-3mV/m) on the stratovolcano area below 400m ASL and (b) unclear topographic effect on the central cone above 400m ASL. Additional simulation of the SP caused by an anomalous zeta potential distribution qualitatively explained (c) local anomalies around the boundary between the central cone and the 885 lava. These results suggest that the SP profile on Kaimondake volcano is mainly controlled by the zeta potential distribution reflecting the distribution of three geological units of the volcano.

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 To make three dimensional (3-D) soil water flows easily visible, a semi-3-D resistivity monitoring method was used based on the 2-D difference inversion technique. 2-D resistivity surveys of 4 traverse survey lines were conducted continuously at a groundwater recharge test site on the Shirasu Plateau and the resistivity change ratio distributions were derived using constrained non-linear differential tomography analysis. The resistivity distributions before the recharge test reflected the geological column at the boreholes and it was assumed that the geology of this site had a layer structure. During the recharge, resistivity changes reflected changes in the degree of soil saturation at the boreholes. This shows that 2-D difference inversions can be used to image soil water flows. Low resistivity sections spread along the secondary Shirasu layer. From this it was assumed that the soil water spread horizontally along the secondary Shirasu layer. The volumetric water content at each designated depth using a neutron moisture meter and the resistivity due to difference inversion did not change in the loam layer. This may indicate the occurrence of partial flows in the loam layer. Each survey line gave a non uniform distribution for the resistivity change ratio that reflected the fact there was no uniform filling of water in the recharge area. These results indicate that multi-line 2-D resistivity surveys make it possible to monitor easily 3-D flows of soil water in shallow geological layers compared with a 3-D survey.

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 Origin of Lake Tazawa-ko has been a geological puzzle for long time. In the past, possibilities of volcanic caldera and impact crater were suggested, but the clear evidences were not found. Recent geological surveys, however, in a view of modern volcanic sedimentology identified pyroclastic materials probably ejected from it. Magnetic survey on the lake was conducted by us in 1974-75. This data and existing aeromagnetic data were reanalyzed. Combination of both data and the reduction to the pole were effective for the interpretation. Then, we revealed a positive magnetized zone like a dike passing through under-bottom of the lake. This zone situates along a fault presumed from a marginal steep gradient zone of a remarkable negative gravity anomaly basin, which probably corresponds to an older caldera. It also overlaps a local micro-earthquake zone. A bank (Shinko-tai) in the lake seems to be a central cone related to this dike-like body. We presented an example of a physical model to match with observed magnetic anomalies.

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 There is not generally reported that a mirror image is considered as an enigmatic and a rare phenomenon which are formed between two strong reflectors or reflective targets. The mirror image is formed an apparent image below a reflector. In this report, the mirror image multiples caused between buried pipes and geological reflector are introduced using records of the stepped CW GPR exploration. The nature of the mirror image was inspected and appropriately conformed from the travel time of the reflection.

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