In the current global energy crisis, ensuring a stable supply of energy resources is an extremely important challenge; however, future prospects are shrouded in deep uncertainty. This article aims to grasp recent trends in energy and resource dynamics, clarify the role of geophysical exploration technologies, and discuss the direction of necessary technological advancements. While there have been continuous innovations of data acquisition and analysis technologies in geophysical exploration, there has been less focus on innovation in interpreting exploration results. We discuss the potential for breakthroughs in interpretation of exploration results, particularly addressing the multifaceted nature of uncertainty and the significance of human subjectivity within it. Emphasizing the distinction between the concepts of risk and uncertainty, I point out that human subjectivity in the interpretation of exploration results is not a cause of uncertainty but, rather, plays a vital role in reducing uncertainty. Through focusing on boldly formulating hypotheses and validating them, it is expected to reduce uncertainty, suggesting that extracting beneficial subjective elements from human cognition is an important direction for reducing exploration risks.

　This paper describes the effectiveness of geophysical surveys for the study and protection of archaeological site investigations. The study and protection of underground archaeological sites are problematic because most of them are buried and cannot be seen, and their existence and contents cannot be assumed. Site exploration, which is the visualization of human activities in the ground using geophysical methods, is an important method not only for obtaining information on human history, but also for responding to the social need to preserve and record the traces of the human past. In this paper, we discuss the importance of this method and its effectiveness based on the status of archaeological preservation activities in recent years, as well as the results and direction of this method to date.

　We report on the overview of the environmental session at the 75th anniversary symposium of the Society of Exploration Geophysicists of Japan (SEGJ) which was held in 2023. In this session, we discussed the social importance of recent environmental issues in the geosphere, and discussed soil contamination, groundwater conservation, geological disposal projects for high-level radioactive waste (HLW), and geological storage projects for carbon dioxide in Japan. In the session, we had reports on related laws and governmental plans, the roles of geophysical exploration technology, and application examples. As examples of specific applications for soil contamination and groundwater conservation in the session, there were reports on investigating the integrity of tailings dams installed for mine developments and the impact evaluation of civil engineering work on nearby well water (hot spring water). Regarding the geological disposal of HLW projects, there was the report on the status of each related organization's efforts for the research and development of geophysical exploration techniques and an example of investigations of freshwater groundwater beneath the seabed in coastal shallow waters. In terms of geological storage projects for carbon dioxide, there was a report on the status of efforts of each related organization and the application of monitoring using a seismic method of subsurface carbon dioxide migration.

　This article discusses the topic of "geophysical exploration from space and the air (remote sensing and drone geophysical exploration)."

　First, in terms of trends in satellite remote sensing, the rise of small commercial satellites, the construction of satellite constellations, and satellite-related programs in Japan is discussed. This is due to the development of small optical and SAR (Synthetic Aperture Radar) satellites, and the construction of satellite constellations. These advancements indicate that in the near future, constant observation of the entire world will be possible. Next, as examples of remote sensing applications, we introduce SAR applications in the fields of disaster prevention and civil engineering. These technologies enable the quick extraction of inundation information during flooding events, the possibility of detecting landslide disasters in advance, and the enhancement of efficiency in the maintenance and management of road structures.

　Drone geophysical surveying is particularly utilized in the civil engineering field, supported by the Ministry of Land, Infrastructure, Transport, and Tourism's i-Construction initiative. While there are many examples of UAV surveying (LiDAR and LP) in the civil engineering field, airborne electromagnetic surveying is common in the geophysical exploration community. Drones are also employed in underwater exploration as Autonomous underwater vehicles (AUVs). As examples of drone geophysical survey applications, we introduce an investigation of the collapse mechanism of a collapsed slope caused by a typhoon using airborne electromagnetic survey by a drone, and a river patrol demonstration experiment using a VTOL aircraft.

　Looking ahead, satellite remote sensing is expected to feature higher resolution sensors, more frequent observations by satellite constellations, and improved real-time data provision. Drone geophysical surveys are expected to be applied to various geophysical survey methods as the technological development of observation equipment progresses. These advancements are expected to be useful for rapid response to disasters and infrastructure monitoring during peacetime.

　Remarks related to various types of Prestack Depth Migration (PreSDM) supported by Madagascar have been pointed out and such methods have been compared through application to the synthetic Sigsbee2a model, which was simulated for complicated subsurface with dominant salt structure. Excellent software and script for PreSDM based on ray theory and wave theory with one-way approach have been published and supported by Madagascar so far. In addition to such tools, efficient script for Reverse Time Migration (RTM) based on wave theory with two-way approach created newly by CWP consortium has been used for the current evaluation. RTM has been considered and adopted as the best tool for imaging complex subsurface structure. Nevertheless, it has been recognized that clear image can be obtained by the current PreSDM based on the latest ray theory and revised wave theory with one-way approach. Regarding RTM, it has been desired that low frequency noise should be efficiently suppressed, and expensive calculation time should be significantly reduced. Smoothed correct velocity model included in Madagascar has been used in each PreSDM shown in this article.

　Several regions in Japan, including the Kakkonda geothermal field in Iwate Prefecture, have been identified where magma-derived fluids rise to shallow depths (several kilometers deep), forming supercritical geothermal reservoirs (non-conventional geothermal reservoir composed of magma-derived geothermal fluids). This makes it a promising candidate for supercritical geothermal development. However, despite the high likelihood of the existence of supercritical geothermal reservoirs based on geological and geochemical considerations, direct evidence from geophysical exploration other than MT surveys has not been found. In this study, attempts were made to image the supercritical geothermal reservoir based on microseismic observations and seismic reflection surveys using natural earthquakes and vibrator sources in the Kakkonda geothermal field. In addition, numerical calculations (ray tracing) based on models that simulate the actual seismic sources, receivers, and obtained reflection structures were conducted. In the numerical calculations, synthetic reflection records were calculated, and the effects of artifacts potentially caused by P-wave multiple reflections, P-S converted waves, etc. were evaluated to assess the reliability of the obtained reflection structures. As a result, it is likely that, for the first time in Japan, successful detection of reflectors corresponding to the upper boundary of the supercritical geothermal reservoir was achieved through seismic reflection imaging.

　Using distributed acoustic sensing (DAS), we can obtain seismic data from optical fibers. Compared to conventional seismometers, DAS is cost-effective because it is easy to observe seismic data in high spatial resolution. Furthermore, once optical fibers are installed, seismic data can be easily obtained many times. In this study, we applied autocorrelation analysis with spectral whitening to natural seismic data obtained from DAS observations using optical fibers installed off the Sanriku coast and estimated the subsurface structure beneath the seafloor by producing a seismic reflection profile. To increase signal-to-noise ratio, we performed a stacking process of autocorrelation functions from 23 earthquakes. Typically, extracting shallow reflection surface using autocorrelation analysis is difficult because the resulting seismic reflection profile has high amplitude close to 0 second in travel time. Therefore, we calculated a moving average of every 5 km along the fiber from the autocorrelation function obtained at each observation point and suppressed the apparent shallow reflective surfaces by calculating their difference from the original autocorrelation function. The resulting autocorrelations show the basement structure at some of the observation locations in this study. The results also show a disturbance in the reflected wave affected by a fault and reflections affected by a shallow reflective surface, which had not appeared in the previous study using ambient noise. This is probably because natural earthquakes have strong energy over a wide range of frequencies, and S-waves reflected from fault surfaces reach the ground surface and can be observed by the DAS. This study shows that DAS observations can provide high-resolution subsurface structure.

　Understanding pathways of volcanic hydrothermal fluids or non-volcanic slab-related fluids by means of investigations from the surface is effective for preventing the loss of the function as a natural barrier in the geological disposal system of high-level radioactive waste (HLW). There are few long active faults and is no record of remarkable groundwater discharge in the Miyazaki Plain and its adjacent areas located in the fore-arc region of Kyushu, Japan. However, previous studies on seismic wave velocity and resistivity structures suggest the existence of the zones of slab-related fluids derived from the Philippine Sea Plate in the crust. Moreover, it is reported that the partial distribution of groundwater indicates the influence of upwelling slab-related fluids. To associate pathways of such crustal fluids in the fore-arc region of Kyushu with distribution and properties of cracks, we applied a shear wave splitting analysis to waveform data of earthquakes at depths shallower than 20 km in this region. In the inland part of Kyushu, the orientation of the faster polarized shear wave (φ) is subparallel to the axes of the maximum horizontal compressional stress derived from focal mechanism solutions, which can attribute the shear wave polarization anisotropy mainly to the distributions of cracks aligned along the crustal stress. The faster polarized shear wave at the seismic stations in the coastal area of Hyuganada Sea shows the orientation of NNE-SSW~NE-SW or NNW-SSE~NW-SE different from that of the crustal stress. The average intensity of anisotropy over the ray-path length from hypocenters to each seismic station is also calculated. As a result, a few ray paths acquired at the seismic station TAKAZA to the east of Kirishima Volcano show larger anisotropic intensity, 5.6 - 7.0%. There is no denying the possibility that these ray paths reflect the pathways of the hydrothermal fluids. In the coastal area of Hyuganada Sea, however, it is confirmed that we do not obtain the ray paths that indicate continuous fluid pathways extending from hypocenters to each seismic station because the anisotropic intensity over the ray-path length is less than 5%.