The purposes of this study are to elucidate the resistivity characteristics of rocks from the volcanic area by laboratory resistivity experiments using drilled core samples, and to estimate the depth distribution of porosity at the same borehole by integrating the core experiment results with log data. The target borehole is located in the Aso volcanic area in Kumamoto. In the laboratory resistivity experiments, the effects of porosity, saturation, and pore water resistivity on rock resistivity were quantitatively evaluated. The effect of each physical property on rock resistivity by this study were generally agreement with the previous study, but the m value, called the cementation factor, ranged from 2.31 to 3.22 for sedimentary rocks, which is larger than the commonly used value of 2, and smaller values (less than 2.0) with smaller porosity for volcanic rocks. In addition, the ratio of apparent formation factor to the true formation factor was compared with the pore water resistivity, indicating that at least for pore water resistivity larger than approximately 30 Ωm, the effect of surface conductivity should be taken into account even for rocks from volcanic area.

　Based on the high drilling mud resistivity (52.1 Ωm at 15.8 °C), which was inferred as the pore water resistivity in borehole wall rocks, and the experimental results in this study, we estimated the depth distribution of the porosity of the borehole by incorporating the values of surface conductivity and m of the core samples into the log data. The results of this study are consistent with the results of the estimated porosity by sonic log in the depth range of 302-562 m, indicating that porosity can be estimated from electrical log even in areas where rocks from volcanic regions are distributed and pore water resistivity is high. The estimated porosity using drilling mud resistivity of this study was larger than the core porosity and the estimated porosity by sonic log in the depth range of 562-653 m. The reason may be that the drilling mud resistivity is higher than the pore water resistivity, because penetration of drilling mud into the surrounding formation was insufficient in this depth range.

　For the purpose of site investigations of floating offshore wind farms, which will potentially become mainstream in the future, research and development of deep-sea microtremor array exploration was carried out. The applicable water depth for floating offshore wind power farm is 50 m or deeper and the current measurement method for offshore microtremor arrays, that is, measuring by dropping ocean bottom seismometers from the sea level onto the three vertices and the center of the triangular array, is not possible at deep water depths. We have developed a method for microtremor array exploration by arranging ocean bottom seismometers in a straight line (linear array) using an undersea positioning device and conducted measurement experiments. A clear dispersion curves were obtained from the acquired data. In addition, a surface wave exploration measurement experiment was also conducted in which vibration was generated by dropping a weight on the extension of the end of the linear array to actively generate surface waves. It was revealed that good data could be obtained using this method, and that in addition to the S-wave velocity structure obtained by the microtremor array survey, the velocity structure in shallower layers could also be obtained with high accuracy.

　To promptly issue seismic intensity information and earthquake warnings immediately after an earthquake occurs, it is necessary to construct and maintain an earthquake observation network and a telecommunication network, and to install seismographs that can retrieve high-quality data in an appropriate environment. In the railway field, to improve the reliability of early earthquake warning (EEW) systems, EMC standards are applied to railway seismographs that measure and record seismic motions, mainly installed in substations to reduce the influence of electromagnetic waves. However, as for seismographs that measure and record seismic motions, an investigation that the seismic motions recorded satisfy certain standards, such as the seismic intensity inspection by the Japan Meteorological Agency, has not been performed. Thus, the reliability of seismographs installed in railways has not been verified. Therefore, in this study, to comprehend the reliability of earthquake warnings in the railway field, we investigated seismic data quality affecting earthquake warnings applied to railways through temporary earthquake ground motion observation with multiple types of seismographs at the Kasama station (KSM) in the Metropolitan area maintained by the Railway Technical Research Institute.

　First, we investigated the self-noise of seismographs by the calibration test for microtremors. We showed that the seismographs need to measure the power spectral density of microtremors of about －120 dB in the frequency range of more than 0.12 Hz, to properly record microtremors at KSM on the rock site. In addition, the average power of microtremors recorded by all seismographs was less than 10^-4 cm²/s⁴, indicating no particular problems with data accuracy when measuring vibrations with an amplitude of 0.01 cm/s² or more. Second, we investigated seismic data quality affecting two types of earthquake warnings applied to railways (the threshold method and the C－Δ method). As for the threshold method, the variability can be seen in the case of values of 10.1 to 10.7 cm/s² exceeding 10 cm/s² for all seismographs (average: 10.4 cm/s², standard deviation: 0.2 cm/s²). It is revealed that the timing of exceeding the threshold varies by a few tenths of a second among the seismographs in this observation data. And, the residual average ± the standard deviation with the unified earthquake catalog of Japan Meteorological Agency (JMA) of the epicentral distance estimation by the C－Δ method were within the range of 0.05 to 0.6 km (Common logarithm), and the impact of this observation data affecting the C－Δ method to estimate the epicentral distance was not very large. On the other hand, the residual average ± the standard deviation with the unified earthquake catalog of JMA of the epicentral direction estimation by the C－Δ method were within the range of －90° to 90°, and the impact affecting the C－Δ method to estimate the epicentral direction was relatively large compared to the epicentral distance estimation.

　Seismic observation was conducted on Hachijojima Island, the second largest volcanic island among the Izu Islands, Japan. This temporary observation took place twice, with each session occurring within a 7-months period in 2019 and 2021. We have densely installed 46 temporary stations across the island, in addition to 9 permanent stations, to collect seismic data. In this paper, our primary focus is to describe the seismic observation and establish an earthquake catalog, with initial evaluation of seismicity in relation to the magmatic system and tectonic setting. The arrival times of P- and S- wave were manually picked using WIN System, a processing system that handles multi-channel seismic waveform data. Subsequently, the hypocenters of the local earthquakes were located directly during manual pick using the ‘hypomh’ program within WIN System. A total of 179 local earthquakes were localized where 119 took place in 2019 and the remaining 60 occurred in 2021. It was observed that most earthquake events' hypocenters were situated primarily in the northwestern region of the island, located at the northern edge of the rift margin. These earthquake events appear to be associated with the long-distance lateral magma transport in the middle to lower crust at depths of 10-20 km, which is driven by the regional tectonic conditions within the deeper crust. The catalogue obtained from this study can be utilized for investigating the subsurface structure around Hachijojima Island.

　We propose a method to automatically estimate regression lines indicating the average depths of the causative layers and their wavenumber ranges from the power spectrum of potential fields, such as gravity anomalies or magnetic anomalies, by setting the adjusted coefficient of determination (R²_adj) as the indicator. In the proposed method, the data in all wavenumber zones are set as the initial data, and the regression line indicating the depth of the deepest layer is then estimated. The regression lines are estimated by sequentially reducing the data from the higher- wavenumber side, and R²_adj is calculated each time the regression line is estimated. When R²_adj of one line assumes the highest value, this line is considered the optimum regression line. The same process is then applied to the residual data (high- wavenumber side), resulting in a regression line indicating the second deepest layer. By repeating these processes, the number of causative layers is automatically determined, and the regression lines are obtained, indicating the layer depths and wavenumber ranges. In numerical tests, we confirmed that our method could estimate the model parameters correctly using L₁ and L₂ norm minimisation. We applied our method to the spectrum analysis of the Bouguer anomaly in central Kyushu, Japan, and obtained the following results as the average depth of causative layers: 8.9 km, 2.2 km, 0.6 km by L₁ norm minimizations and 9.2 km, 2.2 km, 0.6 km by L₂ norm minimizations. There were no significant differences among the results estimated by L₁ and L₂ norm minimisation and no differences in the wavenumber range for each regression line estimated by each minimisation.

　Permeability is an important rock physical property for understanding geological phenomena and for resource assessment. However, it is not feasible to measure permeability compared to other rock physical properties (e.g., porosity, elastic wave velocity, and electrical resistivity), especially for impermeable rocks. This study developed an experimental system that can measure permeability rapidly and simply using only inexpensive commercial products (less than 500,000 yen in total). In this system, a sample holder is placed in an acrylic pressure vessel and a water pressure pump is used to simultaneously pressurize the confining and pore pressure. This makes it possible to measure permeability under relatively high water pressure gradient (0.3 MPa) and near atmospheric pressure conditions. The constant water pressure method is adopted as the measurement method. Test measurements using sandstone, granite, and 3D printed sample showed that the results were consistent with those obtained using a syringe pump and with literature values. Our results under near-atmospheric conditions makes it possible to compare with other physical properties (e.g., porosity, elastic wave velocity, and electrical resistivity) under ambient pressure. The measurement range of permeability verified by this system is ~10^-10－10^-15 m², or smaller when increasing the measurement time or extending the measurement method.