Thermal conductivity is one of the important parameters for accurately predicting subsurface temperature structures in various geoengineering applications, such as geothermal development and the underground disposal of radioactive wastes. Thermal conductivity varies with rock type and is anisotropic when rocks such as shale and schist are layered. Sedimentary rocks, especially sandstone and mudstone, have layer structures that are formed by consolidation and exhibit reduced porosity. Although this porosity change may be linked to the anisotropy of thermal conductivity, this relationship has not been previously investigated. In this study, we quantitatively investigated the anisotropy of the thermal conductivity of sedimentary soft rocks and then examined the relationships between porosity and the anisotropy of thermal conductivity. In addition to thermal conductivity, the anisotropy of the P-wave velocity was also examined, as it is known to correlate well with thermal conductivity. The thermal conductivity and P-wave velocity were measured both perpendicular and parallel to the bedding plane in the sample. Cubic samples of sedimentary soft rocks taken from the Boso Peninsula of central Japan, whose porosity levels ranged from approximately 37% to 55%, were used. As a result, the thermal conductivity and P-wave velocity of the samples that were parallel to the bedding plane were greater than those that were perpendicular to the bedding plane, indicating that anisotropy was observed for these physical properties in terms of the bedding plane. The degrees of anisotropy regarding to bedding plane of both physical properties were then quantitatively evaluated by two indices. The results showed that the degrees of anisotropy degrees of thermal conductivity and the P-wave velocity were linked to porosity; the degree of anisotropy in the low-porosity specimens tended to be lower than that in the high-porosity specimens.

Generally, mixing models are necessary in case of estimating thermal conductivity of an intact rock from thermal conductivity of cuttings of the same rock. However, one of the problems about this is difficulty in determining a suitable mixing model. To develop a simple method to determine the thermal conductivity of an intact rock by thermal conductivity measured using cuttings of the rock without any mixing model, we experimentally examined the relationship between the thermal conductivities of rock cuttings and core samples. We used totally 15 typical rock samples and two fused silicas, including five sedimentary rocks, nine igneous rocks, one metamorphic rock, and made two categories of cuttings size distribution: >= 2 and <4 mm and <2 mm. We then measured thermal conductivity of the water-saturated intact rock core lambda(core) and the thermal conductivity of a mixture of cuttings and water lambda(probe) by the hot disk method and using a new measurement probe for cuttings, and also investigated the relationship between the two values. As a result, we found a satisfactory linear correlation and got an empirical equation between lambda(core) and lambda(probe) as lambda(core) = 4.65 lambda(probe) - 2.38 (0.8 < lambda(probe) < 1.5 Wm(-1)K(-1)) for >= 2 and <4 mm cuttings and the average relative error (REave) of the thermal conductivity estimation based on this equation was 6.4%. In comparison between the two categories of size distributions of cuttings, the REave of >= 2 and <4 mm cuttings was smaller than that of <2 mm cuttings, and we concluded that >= 2 and <4 mm cuttings are suitable for this method. In addition, estimation by our empirical equation was more accurate than those of previous mixing models, probably this is owing to less factors of our empirical equation which effect on the estimation. Finally, we proposed this new measurement method to determine the thermal conductivity of intact rock using thermal conductivity of cuttings based on this new empirical equation without using a mixing model.

The temperature response of water-saturated rocks to stress changes is critical for understanding thermal anomalies in the crust, because most porous rocks in the shallow crust are saturated with water. Based on the adiabatic effective stress law and porothermoelasticity theory, we derived the adiabatic pressure derivative of temperature (/i = (partial derivative T/partial derivative P)s) of water-saturated rock (/iwet) in terms of that of dry rock (/idry) and water (/idry), and other measurable physical parameters. Then, we calculated the ranges of /iwet for 15 representative watersaturated rocks at background temperature (T0) between 23 and 50 degrees C. The results showed that /iwet (1.58-10.79 mK/MPa) was greater than /idry (1.52-6.15 mK/MPa) for all rocks. The ratio of /iwet to /idry is more significant for rocks with higher compressibility. For instance, for rocks with drained bulk modulus no more than 10 GPa, /iwet at 50 degrees C (10.71 mK/MPa for Berea sandstone) can be as much as twice of /idry at 23 degrees C (5.86 mK/ MPa). Also, /iwet was observed to linearly increase with the increase of T0. The theory allows us to gain understanding on the coseismic temperature responses, such as the temperature anomalies documented in boreholes drilled through seismically ruptured active faults after the Chi-Chi, Wenchuan, and Tohoku earthquakes.

Understanding the thermal properties of underground geological formations is crucial for geothermal energy exploration and subsurface modelling. However, data from typical volcanic regions, such as the Aso volcanic region in Japan, remain limited. This study addresses this gap by providing comprehensive measurements of thermal properties, porosity, bulk density, and elastic wave velocities of rock core samples obtained from a scientific drilling project in the Aso volcanic region. The findings reveal that thermal conductivity is significantly higher under saturated conditions than under dried conditions, underscoring the critical influence of water content on subsurface thermal behaviour. An inverse relationship between thermal conductivity and porosity was observed, with a more gradual decrease under saturated conditions due to the thermal conductivity of pore- filling fluids. Through detailed analysis, this study identifies reliable methods for estimating thermal conductivity based on porosity and compression wave velocity, particularly suited for volcanic rocks. These approaches offer practical alternatives when direct measurements, which require intact rock core samples, are not feasible. They provide satisfactory accuracy for preliminary predictions prior to conducting detailed investigations. Additionally, the evaluation of mixing models demonstrated that the geometric mean model effectively captures the influence of pore structure and mineral composition on bulk thermal conductivity, providing a reliable framework for understanding heat transfer processes in volcanic subsurface regions. By contributing valuable thermal property data and advancing predictive methodologies, this work enhances geothermal modelling and resource assessments, serving as a reference for similar volcanic regions worldwide.

ABSTRACT The frontal prism in the Japan Trench on the 2011 Tohoku‐Oki earthquake (Mw 9.0, March 11, 2011) rupture zone had been drilled during the Integrated Ocean Drilling Program (IODP) Expeditions 343 and 343 T. We investigated fossil diatoms and radiolarians to determine age constraints on the cored sediments and reveal the behavior of sediment deformation history. Although diatoms and radiolarians abundances are varied in samples from common to rare with poor to moderate preservation in studied sediments, general biostratigraphic schemes in the North Pacific are applicable and well constrain the age of those sediments, except for samples from fault clay in which fossils were barren. These results suggest that there are three large stratigraphic gaps at ~830 mbsf between the Cretaceous chert and the upper Miocene pelagic clay, at ~820 mbsf between the upper Miocene and the Pliocene –Quaternary, and at ~670 mbsf between the upper Miocene and the Pliocene –Quaternary. The former likely represents a hiatus or unconformity derived from tectonic erosion just above the incoming Pacific Plate, and the latter two correspond to an injection of late Quaternary material above the plate boundary fault due to an increase in volcanic activity in the NE Japan arc after 8 Ma. The Upper Miocene pelagic sequence below the plate boundary décollement comprises reversed stratigraphy, suggesting deformation by thrusting, slumping, folding, etc., indicating structural complexity in the frontal prism of the subduction zone most likely due to the subduction of horst‐and‐graben.

Displacement monitoring provides essential information for safe and rational tunnel excavation. The data obtained allow engineers to analyze and predict tunnel behavior, facilitating the selection of appropriate supports and the evaluation of their effectiveness. In a recent tunnelling project in the Akaishi Mountains of central Japan, displacement monitoring was intensively implemented to ensure the stability of the 4.2-km-long Hirogawara adit, excavated to a maximum depth of 832 m. Analysis revealed a strong correlation between initial and final displacements. However, the tunnel experienced occasional support deformations. To address this, the trend of 3D absolute displacements was analyzed to predict and evaluate asymmetric deformation. The effective use of 1-cycle displacement monitoring proved critical for predicting final displacements and optimizing rock supports, particularly in cases with high overburden and limited geotechnical information.

Drone-based synthetic aperture radar (SAR) analysis offers a simple and efficient technique for acquiring observational data from various research areas. However, fundamental research on observation techniques, including the investigation of drone flight parameters, remains insufficient. This study focuses on improving the resolution of intensity images of a single-look complex (SLC) via drone-based SAR observations. By conducting experiments at different flight speeds and analysing the obtained SLC images, we demonstrated that higher drone speeds resulted in enhanced image resolution under the conditions investigated at flight speeds of <= 5 m s(-1). A comparison with satellite SAR images highlighted the superior performance of drone-based SAR in capturing topographic features. The analysis also suggested that factors including trajectory deviation and Doppler rate affected the resolution and azimuth position. The simulation results supported the experimental findings on the relationship between drone speed and resolution. Our results emphasize the potential of drone-based SAR observations for monitoring slope failures and suggest the importance of the drone flight parameter selection. In the future, drone-based SAR is expected to produce intensity images of slopes and locate slope deformations associated with blasting for mining and earthquakes.

AbstractThe physical properties of seafloor massive sulfides are crucial for interpreting sub-seafloor images from geophysical surveys, shedding light on the evolution of seafloor mineral deposits. While some studies have explored the relationship between electrical properties and the volume of conductive minerals in rocks from seafloor massive sulfide deposits, they primarily focused on artificial samples, leaving the characteristics of natural samples less understood. Moreover, there has been no comprehensive study detailing the general characteristics of electrical properties, particularly chargeability and relaxation time, in relation to the volumetric fraction of sulfides in rocks from massive sulfide mounds in typical hydrothermal areas. In this study, we employed complex conductivity measurements, elemental concentration analysis, and mineral content identification on to rock samples from the active hydrothermal zones of the Okinawa Trough in Japan. The complex conductivity observed was remarkably high, with a pronounced imaginary component and a broad frequency range. This is attributed to induced polarization extending beyond our measurement range. The rock samples were rich in conductive sulfide minerals such as pyrite, chalcopyrite, and galena. Using the Cole–Cole rock physics model, we established a correlation between rock chargeability and relaxation time coefficient with the volume fraction of conductive sulfide minerals, which deviated from previous findings. The intensity of induced polarization was notably higher than anticipated in earlier studies using artificial samples. Furthermore, we observed a distinct positive correlation between the coefficient of relaxation time and the increase in sulfide volume, likely due to the geometric characteristics of the sulfide minerals. Our findings suggest that rocks in massive sulfide mounds may generally construct sulfide clusters that lengthen the conductive path of the electrical carrier. Graphical Abstract

Research on automation and intelligent operation of tunnel boring machine (TBM) is receiving more and more attention, benefiting from the increasing construction data. However, most studies on TBM operations optimization were trained by the labels of human drivers’ decisions, which were subjective and stochastic. As a result, the control parameters suggested by these models could hardly surpass the performance of a human driver, even the possibility of subjective incorrect decisions. Considering that the geomechanical feedback to TBM under drivers’ actions is objective, in this paper, a transformer-based model called the geological response for tunnel boring machine (GRTBM), is proposed to learn the relationship between operation-adjust and TBM monitoring changes. Additionally, with the model-based offline reinforcement learning, this paper provided a novel approach to optimizing the TBM excavation operations. The decision processes, recorded in the Yin-song TBM project for a waterway tunnel in Jilin Province of China, were used for the validation of the model. By adopting an implicit perception of geological conditions in the GRTBM model, the suggested method achieved the desired state within a single action, greatly outperformed the practical adjustments where 500 s were taken, revealing the fact that the proposed model has the potential to surpass the capability of human beings.

Complex structures with different stress regimes pose challenges in tectonic studies and have implications for the oil and gas industry. The analysis of in-situ stress state and natural fractures in the Dezful Embayment, the southwestern part of the Zagros fold and thrust belt (ZFTB) in Iran, and their implications for tectonic and oil field development are poorly understood. This study analyzes stress orientations, natural fractures, pore pressure (Pp), and stress regime in two oil fields located in the Zagros foothills. The study utilized various data types, including image logs and conventional logs, to determine the in-situ stresses and their implications for energy field development. The results show that the mean orientations of the maximum horizontal stress SH in Field A and Field B are N32°E and N55°E, respectively. The analysis of natural fractures indicates that most tensional fractures are subparallel to the orientation of the maximum horizontal stresses, and the present stress state is responsible for these fractures. The analysis of stress magnitudes demonstrates that the stress regime in Field A changes from thrust faulting toward strike-slip faulting in deeper intervals below water-oil contact. The findings provide valuable insights into the region's reservoir development plans and seismic activities. The orientation of natural fractures suggests that horizontal wells drilled parallel to the orientation of SH can optimize wellbore stability. In addition, the stress variations and complexities observed in Field A are attributed to factors such as folding degree, lateral deformability contrasts, and geological structures like faults. The stress regime analysis indicates the influence of regional tectonic forces and the proximity to the collision boundary. This study will provide valuable insights into the exploration, development, and management of hydrocarbon resources in complex structure regions such as the Dezful Embayment, and it may contribute to understanding stress variations and distribution patterns in similar geological settings elsewhere.

Deep learning has gained attention as a potentially powerful technique for modeling natural-state geothermal systems; however, its physical validity and prediction inaccuracy at extrapolation ranges are limiting. This study proposes the use of transfer learning in physics-informed neural networks to leverage prior expert knowledge at the target site and satisfy conservation laws for predicting natural-state quantities such as temperature, pressure, and permeability. A neural network pre-trained with multiple numerical datasets of natural-state geothermal systems was generated using numerical reservoir simulations based on uncertainties of the permeabilities, sizes, and locations of geological units. Observed well logs were then used for tuning by transfer learning of the network. Two synthetic datasets were examined using the proposed framework. Our results demonstrate that the use of transfer learning significantly improves the prediction accuracy in extrapolation regions with no observed wells.

Sedimentary soft rocks are one of the foundations of large and important constructions. Because the mechanical properties of the soft rocks control the behavior of the foundations, it is necessary to understand the consolidation characteristics of the sedimentary soft rocks. Particularly, the anisotropy of mechanical property is important, therefore, the relationship between these properties to bedding planes and the stress environment should be considered. In this study, consolidation tests were conducted in three directions using four block samples of Neogene to Quaternary sedimentary soft rocks from the western part of the Boso peninsula, central Japan: orthogonal to the bedding plane (σ3direction) and two directions within the bedding plane defined by paleo-stresses (σ1 and σ2). In comparison with other fundamental physical properties, elastic wave velocity measurements and tensile strength tests were also conducted to investigate their anisotropy. The results show that the consolidation yield stresses in the three directions are almost the same or larger in the past principal stress direction than others, suggesting that they reflect the tectonic stress history experienced in the past. In addition, the anisotropic degree of consolidation yield stress is almost the same as that of tensile strength and higher than that of P-wave velocity. As the degree of anisotropy of consolidation yield stress increases, tensile strength increases negatively. Anisotropy of the internal structure due to lateral compressive stress increases with the action of lateral compressive stress, while anisotropy of the internal structure due to the sedimentation process decreases.

Porosity of rocks is one of the most fundamental physical properties and is required to quantitatively evaluate the characteristics of rocks in fault zone drilling projects. In the drilling project of Futagawa fault, which ruptured during the 2016 Kumamoto earthquake mainshock, although porosities of intact rock core samples were measured, there was not a continuous porosity profile because core samples could not be obtained in fractured zones. Therefore, we estimated a vertical, continuous porosity profile for a depth interval of about 300–660 m except 383–399 m in the borehole FDB-1 of the project using sonic log data. First, we tested several different empirical equations proposed in previous studies for both sedimentary and volcanic rocks and proposed a new equation considering the effects of compaction and lithology for sedimentary rocks. Second, we compared the estimated porosities with the core porosities at the depths of the measured core samples. As a result, our new equation showed better estimations for sedimentary rocks, but a previous one called Li et al.’s equation gave closer estimations for volcanic rocks. The porosities estimated by our new equation for sedimentary rocks were approximately 50% at the depths of about 300–330 m and approximately 20–40% at about 330–350 m and 510–660 m. The porosities by Li et al.’s equation were approximately 15% for volcanic rocks (massive lava) at the depths of about 380–460 m, and approximately 30–40% for volcanic rocks (autobrecciated lava) of about 350–380 m and 460–510 m. Obviously, the porosity derived from a sonic log of volcanic rocks was higher than those measured using intact core samples due to fracture porosity existing and alteration. Therefore, the derived porosity profile might reflect a reasonable in-situ state in the borehole of the Futagawa fault drilling project.

&lt;p&gt;Temperature is one of the important parameters to understand complex dynamics, because temperature of the crust is changed by some events such as volcanic activities and a passage of high temperature fluid, which affects physical property, chemical cycle and also microbiosphere. Therefore, information about temperature allow us to understand the dynamics of the active subduction zone.&lt;/p&gt;&lt;p&gt;IODP Site C0023, located at the tip of subduction zone in the Muroto transect of the Nankai Trough, was drilled by IODP Expedition 370. There, we measured the vitrinite reflectance which is an index of the maximum temperature experienced by the sediments. Comparing the measured reflectance and the model values calculated by assuming the past heat flow, it was found that Site C0023 experienced a higher heat flow than the present, which was approximately 160 mW/m&lt;sup&gt;2&lt;/sup&gt;. However, the vitrinite reflectance is significantly higher than that in the above model just below the d&amp;#233;collement, which suggested that another thermal anomaly originated directly under the d&amp;#233;collement in addition to the high heat flow from the basement. With assumptions on the temperature of the heat source and the duration of heating below the d&amp;#233;collement, we calculated the vitrinite reflectance in different models.&lt;/p&gt;&lt;p&gt;As a result, it was found that heat source temperature of 200&amp;#730;C and heat generation duration of 500-1000 years are required just below the d&amp;#233;collement to explain the depth distribution of the measured values. At Site C0023, a high pore pressure zone is distributed just below the d&amp;#233;collement, which can serve as a path for fluids from deeper part. Considering that the temperature at the depth corresponding to the seismogenic zone in the Muroto area of the Nankai Trough is approximately 200&amp;#730;C, and that a specific high temperature has not been confirmed just below the d&amp;#233;collement of C0023 at present, the origin of the high-temperature fluid would be the deep seismogenic zone. Furthermore, the advection of high-temperature fluids is thought to be intermittent. In other words, the high reflectance just below the d&amp;#233;collement is considered to indicate the advection of the high-temperature fluid from deep to shallow areas at the time of past earthquakes.&lt;/p&gt;

The frictional characteristics of sediments control the development of landslides in submarine landslide areas. They are the basic parameters for the evaluation of submarine slope stability, and the study of the geothermal-pressure field evolution, and the law of gas hydrate hosting during the landslide process. The continental slope areas of the northern South China Sea are not only rich in gas hydrate resources, but also have many landslides in geological history. They are still potential submarine landslide areas. In order to understand the in situ frictional characteristics of the sediments in the landslide areas of the northern South China Sea as much as possible, we carried out the triaxial quasi-static frictional sliding experiments for four sediment collected from the Shenhu Canyons, under the conditions of confining pressure P-c = 20 MPa, pore pressure P-p =10 MPa and temperature T approximate to 20 degrees C. The experimental results show that: (1) all the four shallow sediments show the characteristics of velocity strengthening and displacement strengthening. (2) The maximum static friction coefficient (mu(max)) and steady-state friction coefficient (mu(ss)) of these four sediments range from 0. 460 to 0. 510, and from 0. 455 to 0. 554, respectively. Moreover, there is a positive relationship between mu(max) and mu(ss). (3) The ranges of cohesion (c) and friction angle (phi) are 0. 30 similar to 0. 57 MPa and 24. 5 degrees similar to 27. 0 degrees, respectively. In fact, the topographic slope usually lower than 6. 8 degrees in the Shenhu Canyons. It means that the unstable slip could not be induced only by the sediments weight in this area. In addition, based on the multi-stage landslide characteristics of the Shenhu Conyons, the spatial distribution relationship between the landslide bodies and the bottom boundaries of the hydrate stability domain which usually overlap with the bottom simulating reflectors (BSRs), gas chimneys and other structures, we infer that the landslides are predominantly caused by the increase of pore pressure which reduces the formation strength near the BSRs. The increase of pore pressure may be caused by the accumulation of the thermogenic free gas from deep, or/and the hydrate decomposition near the BSRs due to the disturbance of geothermal-pressure fields after the sudden geological events, such as earthquakes.

This study proposed and evaluated a method of measuring the thermal conductivity (TC) of drill cuttings from several igneous and pyroclastic rocks using the transient plane source principle, which allows quick and reliable measurements. The estimated bulk TCs of rocks were within an error of <10%, and suitable models were found. Measurements were applied to drill cuttings obtained along a well in the Hachimantai geothermal field, Japan, and TCs were obtained at similar to 25 m intervals to a depth of 1700 m. Our analysis of the temperature profile using estimated TCs suggest the possible presence of fluid-flow zones in the well.

Predicting the temperature, pressure, and permeability at depth is crucial for understanding natural-state geothermal systems. As direct observations of these quantities are limited to well locations, a reliable methodology that predicts the spatial distribution of the quantities from well observations is required. In this study, we developed a physics-informed neural network (PINN), which constrains predictions to satisfy conservation of mass and energy, for predicting spatial distributions of temperature, pressure, and permeability of natural-state hydrothermal systems. We assessed the characteristics of the proposed method by applying it to 2D synthetic models of geothermal systems. Our results showed that the PINN outperformed the conventional neural network in terms of prediction accuracy. Among the PINN-predicted quantities, the errors in the predicted temperatures in the unexplored regions were significantly reduced. Furthermore, we confirmed that the predictions decreased the loss of the conservation laws. Thus, our PINN approach guarantees physical plausibility, which has been impossible using existing machine learning approaches. As permeability investigations in geothermal wells are often limited, we also demonstrate that the resistivity model obtained using the magnetotelluric method is effective in supplementing permeability observations and improving its prediction accuracy. This study demonstrated for the first time the usefulness of the PINN to a geothermal energy problem.

Correlations between surface displacements and groundwater level changes have been widely used to understand aquifer properties and their site characteristics; however, the underlying mechanisms of various correlation types and the influence of earthquakes have not been fully investigated. In this study, we examine correlations between surface displacements from interferometric synthetic aperture radar analyses and groundwater level monitoring data in Osaka and Kyoto, Japan, over 4 years, a period including the 18 June 2018 Mw 5.6 northern Osaka earthquake. Both positive and negative correlations between the seasonal groundwater level changes and the seasonal surface displacements are identified. Based on the observations of the effects of the earthquake, a new conceptual aquifer dynamical model driving the relationship between the surface displacements and the groundwater level changes is proposed. We further reveal that sites with negative correlations increased after the earthquake, suggesting that the earthquake increased the groundwater recharge rate as a result of increases in aquifer transportation properties such as permeability and porosity.

For a comprehensive understanding of the Nankai Trough seismogenic zone, the Integrated Ocean Drilling Program/International Ocean Discovery Program (IODP) conducted a deep ocean drilling project referred to as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) from 2007 to 2019 off the Kii Peninsula, Japan. To investigate the subduction zone's physical properties and reveal the sediments' compressive strength, we carried out consolidated-undrained triaxial compression tests with pore water pressure measurements on NanTroSEIZE core samples. The core samples used were retrieved from depths of approximately 400 m below the seafloor at sites C0006 and C0007 with <^>4000 m water depths. The rocks are Pliocene siltstones with a porosity of <^>50%, classified as sedimentary soft rocks. As a result of the triaxial compression tests, the cohesion ccu and internal frictional angle & curren;cu derived from the total stress analyses ranged in 1.8-1.9 MPa and 15-17 degrees, respectively. In addition, the cohesion c lambda and internal frictional angle & curren;lambda determined by the effective stress analyses were within 1.6-2.2 MPa and 18-28 degrees, respectively. All the specimens tested caused brittle failure and formed clear shear fractures. In the case of these brittle failures, we found that post-failure specimen area correction when calculating differential stress in post-failure might cause a nonnegligible underestimation of the differential stresses. Therefore, we suggest that the area correction for undrained triaxial compressive tests of soft rocks should be conducted until reaching their peak strength if brittle failure occurs. [doi:10.2320/matertrans.MT-Z2023007]