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Takeshi Tsuji received a B.S. (2002) in resources engineering from Waseda University, Japan, an M.Sc. (2004) and a Ph.D. (2007) in earth science from the University of Tokyo, Japan. From 2007 to 2012, he was an assistant professor of engineering geology group at Kyoto University. From 2010 to 2011, he stayed at rock physics department of Stanford University. From 2012 to 2016, he has been an associate professor of International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University. From 2017, he has been a professor in Department of Earth Resources Engineering, Kyushu University. He has been lead principal investigator of Multiscale Science and Engineering for Energy and the Environment Thrust of I2CNER. He also works as visiting professor of Kyoto University.
Adjoint waveform tomography, which is an emerging seismic imaging method for the crust- and global-scale problems, has gained popularity in the past and present decade. This study, for first time, applies adjoint waveform tomography to the large volume of seismic data recorded by the densely spaced, permanent monitoring network that covers the entirety of Japan. We develop a heterogeneous shear-wave velocity model of central Japan that agrees with the geology and lithology. The results reduce the time-frequency phase misfit by 18.0% in the 0.033–0.1 Hz frequency band and 1.6% in the 0.033–0.125 Hz band, respectively. We infer that some velocity anomalies resolved in this work reflect the volcanic fluids, thick sedimentary basins, and granitic rocks. The results of this study suggest the possibility of imaging heterogeneous subsurface structures around Japan island using waveform tomography with a densely distributed network of permanent seismometers.
Kota MukumotoiD; Takeshi TsujiiD. 3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island. 2021, 1 .
AMA StyleKota MukumotoiD, Takeshi TsujiiD. 3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island. . 2021; ():1.
Chicago/Turabian StyleKota MukumotoiD; Takeshi TsujiiD. 2021. "3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island." , no. : 1.
In an effort to reveal the subsurface hydraulic changes in fractures by seismic monitoring, aperture-related velocity changes need to be investigated. We developed a numerical approach for calculating changes in elastic wave velocity with fracture aperture opening by determining the internal energy of a digitized fracture model based on natural rough surfaces. The simulated local elastic energy revealed that the interaction energy converged within 1.5 mm of the mean fracture position, and was insignificant unless the fractures intersected. This energetic approach clarified the aperture–velocity relationship and reproduced the experimental results. Further calculations using digital fractures with various sizes and density demonstrated that the velocity can be accounted for by the superposition of a linear function of fracture density and quadratic function of aperture, and is insensitive to the fracture size. Although the relationship between fracture permeability and elastic wave velocity (i.e., the k-V relationship) depends on the fracture density, the offset-normalized k-V relationship shows clear linearity with the fracture density. The proposed k-V relationship as a function of the aperture and fracture density indicates that laboratory-scale fracture properties of a single fracture can be applied to multiple fractures on a larger scale. Our findings can be used to interpret temporal changes in seismic observations and to monitor fluid flow in fractures.
Kazuki SawayamaiD; Tatsunori IkedaiD; Takeshi TsujiiD; Fei Jiang; Osamu Nishizawa; Yasuhiro Fujimitsu. Elastic wave velocity changes due to the fracture aperture and density, and direct correlation with permeability: an energetic approach to mated rock fractures. 2021, 1 .
AMA StyleKazuki SawayamaiD, Tatsunori IkedaiD, Takeshi TsujiiD, Fei Jiang, Osamu Nishizawa, Yasuhiro Fujimitsu. Elastic wave velocity changes due to the fracture aperture and density, and direct correlation with permeability: an energetic approach to mated rock fractures. . 2021; ():1.
Chicago/Turabian StyleKazuki SawayamaiD; Tatsunori IkedaiD; Takeshi TsujiiD; Fei Jiang; Osamu Nishizawa; Yasuhiro Fujimitsu. 2021. "Elastic wave velocity changes due to the fracture aperture and density, and direct correlation with permeability: an energetic approach to mated rock fractures." , no. : 1.
Adjoint waveform tomography, which is an emerging seismic imaging method for the crust-and global-scale problems, has gained popularity in the past and present decade. This study, for first time, applies adjoint waveform tomography to the large volume of seismic data recorded by the densely spaced, permanent monitoring network that covers the entirety of Japan. We develop a heterogeneous shear-wave velocity model of central Japan that agrees with the geology and lithology. The results reduce the time-frequency phase misfit by 16.2% in the 0.033–0.1 Hz frequency band and 3.6% in the 0.033–0.125 Hz band, respectively. We infer that some velocity anomalies resolved in this work reflect the volcanic fluids, thick sedimentary basins, and granitic rocks. The results of this study suggest the possibility of imaging heterogeneous subsurface structures around Japan island using waveform tomography with a densely distributed network of permanent seismometers.
Kota MukumotoiD; Takeshi TsujiiD. 3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island. 2021, 1 .
AMA StyleKota MukumotoiD, Takeshi TsujiiD. 3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island. . 2021; ():1.
Chicago/Turabian StyleKota MukumotoiD; Takeshi TsujiiD. 2021. "3-D Crustal Shear Wave Velocity Model Derived from the Adjoint Waveform Tomography in the Central Japan Island." , no. : 1.
Pore pressure plays a key role in the generation of earthquakes in subduction zones. However, quantitative constraints for its determination are quite limited. Here, we estimate the subsurface pore pressure by analyzing the transient upwelling flow of drilling mud from borehole C0023A of the International Ocean Discovery Program (IODP) Expedition 370, in the Nankai Trough off Cape Muroto. This upward flow provided the first direct evidence of an overpressured aquifer in the underthrust sediments off Cape Muroto. To estimate the pre-drilling pore pressure in the overpressured aquifer around a depth of 950–1050 meters below sea floor, we examined the measured porosities of core samples retrieved from nearby IODP wells; we then proceeded to explain the observed time evolution of the flow rate of the upwelling flow by modeling various sized aquifers through solving a radial diffusion equation. It was observed that for a permeability of 10–13 m2, the aquifer possessed an initial excess pore pressure of ∼5 to 10 MPa above the hydrostatic pressure, with a lateral dimension of several hundred meters and thickness of several tens of meters. The overpressure estimates from the porosity-depth profile at Site C0023 differ from those at other drill sites in the region, suggesting the possible existence of multiple overpressured aquifers with a patchy distribution in the underthrust sediments of the Nankai Trough. As pore pressure is relevant in maintaining fault stability, the overpressured aquifers may be the source of slow earthquakes that have been observed around the drilling site.
T. Hirose; Y. Hamada; W. Tanikawa; N. Kamiya; Y. Yamamoto; T. Tsuji; M. Kinoshita; V. B. Heuer; F. Inagaki; Y. Morono; Y. Kubo. High Fluid‐Pressure Patches Beneath the Décollement: A Potential Source of Slow Earthquakes in the Nankai Trough off Cape Muroto. Journal of Geophysical Research: Solid Earth 2021, 126, 1 .
AMA StyleT. Hirose, Y. Hamada, W. Tanikawa, N. Kamiya, Y. Yamamoto, T. Tsuji, M. Kinoshita, V. B. Heuer, F. Inagaki, Y. Morono, Y. Kubo. High Fluid‐Pressure Patches Beneath the Décollement: A Potential Source of Slow Earthquakes in the Nankai Trough off Cape Muroto. Journal of Geophysical Research: Solid Earth. 2021; 126 (6):1.
Chicago/Turabian StyleT. Hirose; Y. Hamada; W. Tanikawa; N. Kamiya; Y. Yamamoto; T. Tsuji; M. Kinoshita; V. B. Heuer; F. Inagaki; Y. Morono; Y. Kubo. 2021. "High Fluid‐Pressure Patches Beneath the Décollement: A Potential Source of Slow Earthquakes in the Nankai Trough off Cape Muroto." Journal of Geophysical Research: Solid Earth 126, no. 6: 1.
We have developed a new continuous monitoring system based on small seismic sources and distributed acoustic sensing (DAS). The source system generates continuous waveforms with a wide frequency range. Because the signal timing is accurately controlled, stacking continuous waveforms enhances the signal-to-noise ratio, allowing the use of a small seismic source to monitor extensive areas (multi-reservoir). Our field experiments demonstrated that the monitoring signal was detected at a distance of ~80 km, and temporal variations of the monitoring signal (i.e., seismic velocity) were identified with >99.9% accuracy. Through the monitoring, we identified pore pressure variations due to geothermal operations and rains. When we used seafloor cable for DAS measurements, we identified the monitoring signals at >10 km far from the source in high-spatial resolution. This study demonstrates that multi-reservoir in an extensive area can be continuously monitored at a relatively low cost by combining our seismic source and DAS technology.
Takeshi Tsuji; Tatsunori Ikeda; Ryosuke Matsuura; Kota Mukumoto; Hutapea Lawrens; Tsunehisa Kimura; Koshun Yamaoka; Masanao Shinohara. Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs. 2021, 1 .
AMA StyleTakeshi Tsuji, Tatsunori Ikeda, Ryosuke Matsuura, Kota Mukumoto, Hutapea Lawrens, Tsunehisa Kimura, Koshun Yamaoka, Masanao Shinohara. Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs. . 2021; ():1.
Chicago/Turabian StyleTakeshi Tsuji; Tatsunori Ikeda; Ryosuke Matsuura; Kota Mukumoto; Hutapea Lawrens; Tsunehisa Kimura; Koshun Yamaoka; Masanao Shinohara. 2021. "Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs." , no. : 1.
Carbon capture and storage has been considered as a realistic approach to reducing atmospheric CO2 concentrations. However, the cost of capturing high-purity CO2 typically used for geological storage (e.g., 98%) is high. Direct air capture (DAC), a technology that extracts CO2 of relatively low-purity from the ambient atmosphere, has been recently proposed as a means to achieve negative CO2 emissions when the product is sequestered underground. Although the CO2 produced by DAC is of low-purity, the other gaseous components (mainly nitrogen and oxygen) are not hazardous materials like NOx and SOx that must be typically dealt with by conventional projects in coal-burning plants. Here, we evaluate geological storage of the low-purity CO2 captured via advanced membrane-based DAC technology. The ubiquity of ambient air is important in reducing transport costs and ensuring social acceptance as the CO2 product can be both produced and stored at sites in remote areas, such as deserts and offshore platforms. We calculated the density of CO2–N2–O2 mixtures via molecular dynamics simulation and evaluated the cost of the low-purity CO2 storage. Our evaluation suggests that the storage of low-purity CO2 in geological formations is environmentally acceptable and economically viable. © 2021 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.
Takeshi Tsuji; Masao Sorai; Masashige Shiga; Shigenori Fujikawa; Toyoki Kunitake. Geological storage of CO 2 –N 2 –O 2 mixtures produced by membrane‐based direct air capture (DAC). Greenhouse Gases: Science and Technology 2021, 11, 610 -618.
AMA StyleTakeshi Tsuji, Masao Sorai, Masashige Shiga, Shigenori Fujikawa, Toyoki Kunitake. Geological storage of CO 2 –N 2 –O 2 mixtures produced by membrane‐based direct air capture (DAC). Greenhouse Gases: Science and Technology. 2021; 11 (4):610-618.
Chicago/Turabian StyleTakeshi Tsuji; Masao Sorai; Masashige Shiga; Shigenori Fujikawa; Toyoki Kunitake. 2021. "Geological storage of CO 2 –N 2 –O 2 mixtures produced by membrane‐based direct air capture (DAC)." Greenhouse Gases: Science and Technology 11, no. 4: 610-618.
Currently, vehicle classification in roadway-based techniques depends mainly on photos/videos collected by an over-roadway camera or on the magnetic characteristics of vehicles. However, camera-based techniques are criticized for potentially violating the privacy of vehicle occupants and exposing their identity, and vehicles can evade detection when they are obscured by larger vehicles. Here, we evaluate methods of identifying and classifying vehicles on the basis of seismic data. Vehicle identification from seismic signals is considered a difficult task because of interference by various noise. By analogy with techniques used in speech recognition, we used different artificial intelligence techniques to extract features of three, different-sized vehicles (buses, cars, motorcycles) and seismic noise. We investigated the application of a deep neural network (DNN), a convolutional neural network (CNN), and a recurrent neural network (RNN) to classify vehicles on the basis of vertical-component seismic data recorded by geophones. The neural networks were trained on 5580 unprocessed seismic records and achieved excellent training accuracy (99%). They were also tested on large datasets representing periods as long as 1 month to check their stability. We found that CNN was the most satisfactory approach, reaching 96% accuracy and detecting multiple vehicle classes at the same time at a low computational cost. Our findings show that seismic methods can be used for traffic monitoring and security purposes without violating the privacy of vehicle occupants, offering greater efficiency and lower costs than current methods. A similar approach may be useful for other types of transportation, such as vessels and airplanes.
Ahmad Ahmad; Takeshi Tsuji. Traffic Monitoring System Based on Deep Learning and Seismometer Data. Applied Sciences 2021, 11, 4590 .
AMA StyleAhmad Ahmad, Takeshi Tsuji. Traffic Monitoring System Based on Deep Learning and Seismometer Data. Applied Sciences. 2021; 11 (10):4590.
Chicago/Turabian StyleAhmad Ahmad; Takeshi Tsuji. 2021. "Traffic Monitoring System Based on Deep Learning and Seismometer Data." Applied Sciences 11, no. 10: 4590.
SUMMARY The microtremor survey method (MSM) is used to estimate S-wave velocity profiles from microtremors or ambient noise. Although array-based MSM analyses are usually used for shallow exploration purposes because of their robustness, the extraction of numerous phase-velocity dispersion curves by two-station microtremor analysis is attractive because those dispersion curves can be used to construct high-resolution phase-velocity maps by solving a least-squares problem. However, in exploration studies (>1 Hz), the reliability of two-station microtremor analysis can be affected by short data acquisition times and heterogeneous noise distributions mainly caused by anthropogenic noises. In this study, we propose a new approach to estimate surface wave dispersion curves between station pairs considering a heterogeneous ambient noise distribution based on the spatial autocorrelation method. We first estimated azimuthal variations of noise energy from the complex coherencies between all station pairs in a receiver array, and then estimated dispersion curves between station pairs. Our field example demonstrates that modelling the azimuthal noise energy distribution allows us to use not only the real parts of complex coherencies, but also the imaginary parts, which are usually neglected when assuming a homogeneous noise field. The simultaneous use of the real and imaginary parts of complex coherencies improves the reliability and continuity of phase-velocity estimations between station pairs. Because the stability of phase-velocity estimations depends on the azimuths between station pairs, we carefully selected between-station azimuths that produce stable phase velocities. Selected phase velocities at 8 Hz can be used to construct high-resolution phase-velocity maps with least-squares inversion. Because our approach does not require a regular receiver interval for two-station analysis, it allows for more flexible seismic array geometries. This is particularly important for MSM analyses in urban areas, where limited space is available to install seismic stations. We conclude that our proposed approach is effective in reconstructing high-resolution shallow structures in heterogeneous ambient noise fields.
Tatsunori Ikeda; Takeshi Tsuji; Chisato Konishi; Hideki Saito. Spatial autocorrelation method for reliable measurements of two-station dispersion curves in heterogeneous ambient noise wavefields. Geophysical Journal International 2021, 226, 1130 -1147.
AMA StyleTatsunori Ikeda, Takeshi Tsuji, Chisato Konishi, Hideki Saito. Spatial autocorrelation method for reliable measurements of two-station dispersion curves in heterogeneous ambient noise wavefields. Geophysical Journal International. 2021; 226 (2):1130-1147.
Chicago/Turabian StyleTatsunori Ikeda; Takeshi Tsuji; Chisato Konishi; Hideki Saito. 2021. "Spatial autocorrelation method for reliable measurements of two-station dispersion curves in heterogeneous ambient noise wavefields." Geophysical Journal International 226, no. 2: 1130-1147.
Geothermal systems consisting of fractures in impermeable rocks are difficult to characterize by in situ methods. In an effort to link characteristics of small-scale and large-scale fractures, this study investigated possible relations between their geophysical parameters. We upscaled the relationship between fracture permeability and formation factor in a laboratory specimen to larger fracture dimensions. Microscopic flow characteristics indicate that this relationship is related to the tortuosity of flow paths. We derived an empirical formula that directly predicts changes in fracture permeability from changes in formation factor. This relation may make it possible to monitor subsurface hydraulic activities through resistivity observations.
K. Sawayama; T. Ishibashi; F. Jiang; T. Tsuji; O. Nishizawa; Y. Fujimitsu. Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces. Geothermics 2021, 94, 102065 .
AMA StyleK. Sawayama, T. Ishibashi, F. Jiang, T. Tsuji, O. Nishizawa, Y. Fujimitsu. Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces. Geothermics. 2021; 94 ():102065.
Chicago/Turabian StyleK. Sawayama; T. Ishibashi; F. Jiang; T. Tsuji; O. Nishizawa; Y. Fujimitsu. 2021. "Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces." Geothermics 94, no. : 102065.
It is important to distinguish between natural earthquakes and those induced by CO2 injection at carbon capture and storage sites. For example, the 2004 Mw 6.8 Chuetsu earthquake occurred close to the Nagaoka CO2 storage site during gas injection, but we could not quantify whether the earthquake was due to CO2 injection or not. Here, changes in pore pressure during CO2 injection at the Nagaoka site were simulated and compared with estimated natural seasonal fluctuations in pore pressure due to rainfall and snowmelt, as well as estimated pore pressure increases related to remote earthquakes. Changes in pore pressure due to CO2 injection were clearly distinguished from those due to rainfall and snowmelt. The simulated local increase in pore pressure at the seismogenic fault area was much less than the seasonal fluctuations related to precipitation and increases caused by remote earthquakes, and the lateral extent of pore pressure increase was insufficient to influence seismogenic faults. We also demonstrated that pore pressure changes due to distant earthquakes are capable of triggering slip on seismogenic faults. The approach we developed could be used to distinguish natural from injection-induced earthquakes and will be useful for that purpose at other CO2 sequestration sites.
This research was published in “Sustainability”, https://doi.org/10.3390/su12229723.
Keywords: pore pressure; CO2 injection; induced earthquakes; seasonal earthquakes; remote earthquakes; seismogenic faults.
Chanmaly Chhun; Takeshi Tsuji. Natural and artificial pore pressure variation for distinguishing earthquakes induced by CO2 injection from natural earthquakes. 2021, 1 .
AMA StyleChanmaly Chhun, Takeshi Tsuji. Natural and artificial pore pressure variation for distinguishing earthquakes induced by CO2 injection from natural earthquakes. . 2021; ():1.
Chicago/Turabian StyleChanmaly Chhun; Takeshi Tsuji. 2021. "Natural and artificial pore pressure variation for distinguishing earthquakes induced by CO2 injection from natural earthquakes." , no. : 1.
Monitoring the hydraulic properties within subsurface fractures is vitally important in the contexts of geoengineering developments and earthquakes. Geophysical observations are promising tools for remote determination of subsurface hydraulic properties; however, quantitative interpretations are hampered by the paucity of relevant geophysical data for fractured rock masses. This study explored simultaneous changes in hydraulic and geophysical properties of natural rock fractures with increasing normal stress and correlated these property changes through coupling experiments and digital fracture simulations. We show that electrical resistivity is linked with permeability and flow area regardless of fracture roughness, whereas elastic wave velocity is roughness dependent. We also are able to categorize fracture flow patterns as aperture-dependent, aperture-independent, or disconnected flows, with transitions at specific stress levels. Elastic wave velocity offers potential for detecting the transition between aperture-dependent flow and aperture-independent flow, and resistivity is sensitive to detect the connection/disconnection of the fracture flow.
Kazuki Sawayama; Takuya Ishibashi; Fei Jiang; Takeshi Tsuji; Yasuhiro Fujimitsu. Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. 2021, 1 .
AMA StyleKazuki Sawayama, Takuya Ishibashi, Fei Jiang, Takeshi Tsuji, Yasuhiro Fujimitsu. Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. . 2021; ():1.
Chicago/Turabian StyleKazuki Sawayama; Takuya Ishibashi; Fei Jiang; Takeshi Tsuji; Yasuhiro Fujimitsu. 2021. "Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow." , no. : 1.
Monitoring the hydraulic properties within subsurface fractures is vitally important in the contexts of geoengineering developments and earthquakes. Geophysical observations are promising tools for remote determination of subsurface hydraulic properties; however, quantitative interpretations are hampered by the paucity of relevant geophysical data for fractured rock masses. This study explored simultaneous changes in hydraulic and geophysical properties of natural rock fractures with increasing normal stress and correlated these property changes through coupling experiments and digital fracture simulations. We show that electrical resistivity is linked with permeability and flow area regardless of fracture roughness, whereas elastic wave velocity is roughness dependent. We also are able to categorize fracture flow patterns as aperture-dependent, aperture-independent, or disconnected flows, with transitions at specific stress levels. Elastic wave velocity offers potential for detecting the transition between aperture-dependent flow and aperture-independent flow, and resistivity is sensitive to detect the connection/disconnection of the fracture flow.
Kazuki Sawayama; Takuya Ishibashi; Fei Jiang; Takeshi Tsuji; Yasuhiro Fujimitsu. Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. 2021, 1 .
AMA StyleKazuki Sawayama, Takuya Ishibashi, Fei Jiang, Takeshi Tsuji, Yasuhiro Fujimitsu. Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. . 2021; ():1.
Chicago/Turabian StyleKazuki Sawayama; Takuya Ishibashi; Fei Jiang; Takeshi Tsuji; Yasuhiro Fujimitsu. 2021. "Relating Hydraulic-Electrical-Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow." , no. : 1.
Monitoring the hydraulic properties within subsurface fractures is vitally important in the contexts of geoengineering developments and seismicity. Geophysical observations are promising tools for remote determination of subsurface hydraulic properties; however, quantitative interpretations are hampered by the paucity of relevant geophysical data for fractured rock masses. This study explores simultaneous changes in hydraulic and geophysical properties of natural rock fractures with increasing normal stress and correlates these property changes through coupling experiments and digital fracture simulations. Our lattice Boltzmann simulation reveals transitions in three-dimensional flow paths, and finite-element modeling enables us to investigate the corresponding evolution of geophysical properties. We show that electrical resistivity is linked with permeability and flow area regardless of fracture roughness, whereas elastic wave velocity is roughness-dependent. This discrepancy arises from the different sensitivities of these quantities to microstructure: velocity is sensitive to the spatial distribution of asperity contacts, whereas permeability and resistivity are insensitive to contact distribution, but instead are controlled by fluid connectivity. We also are able to categorize fracture flow patterns as aperture-dependent, aperture-independent, or disconnected flows, with transitions at specific stress levels. Elastic wave velocity offers potential for detecting the transition between aperture-dependent flow and aperture-independent flow, and resistivity is sensitive to the state of connection of the fracture flow. The hydraulic-electrical-elastic relationships reported here may be beneficial for improving geophysical interpretations and may find applications in studies of seismogenic zones and geothermal reservoirs.
K. Sawayama; T. Ishibashi; F. Jiang; Takeshi Tsuji; Y. Fujimitsu. Relating Hydraulic–Electrical–Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. Rock Mechanics and Rock Engineering 2021, 54, 2145 -2164.
AMA StyleK. Sawayama, T. Ishibashi, F. Jiang, Takeshi Tsuji, Y. Fujimitsu. Relating Hydraulic–Electrical–Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow. Rock Mechanics and Rock Engineering. 2021; 54 (5):2145-2164.
Chicago/Turabian StyleK. Sawayama; T. Ishibashi; F. Jiang; Takeshi Tsuji; Y. Fujimitsu. 2021. "Relating Hydraulic–Electrical–Elastic Properties of Natural Rock Fractures at Elevated Stress and Associated Transient Changes of Fracture Flow." Rock Mechanics and Rock Engineering 54, no. 5: 2145-2164.
Episodes of tectonic tremor are observed in the Nankai accretionary prism close to the trough axis; however, their non-impulsive signals and the distortion of seismic signals in the accretionary prism make it challenging to accurately estimate their locations. Reliable tremor locations would help to characterize geological conditions favourable for tremor generation and could offer insights into the up-dip limit of coseismic ruptures. Here we report a new approach to pinpoint tremor locations based on seismic phase polarization. The estimated epicentres of tremor distribution mostly coincide with low-velocity shear zone or thick underthrust sediments where high pore pressures are inferred, and the distribution of tremor appears to be controlled by characteristics of the shear zone. A tremor episode occurred a couple days after the off-Mie earthquake clearly shows migration at a velocity similar to that of very low frequency earthquakes. Migration of tremor initiated around the outer ridge where the estimated pore pressure is greatest. The spatio-temporal tremor distribution indicates that pore pressure relaxation could trigger the tremor migration. The occurrence of tremor thus may indicate a weak shallow plate interface that is prone to slip following large earthquakes. Based on the information of tremor migration, the permeability along the fault can be estimated as 3.7×10−12 m2.
Andri Hendriyana; Takeshi Tsuji. Influence of structure and pore pressure of plate interface on tectonic tremor in the Nankai subduction zone, Japan. Earth and Planetary Science Letters 2021, 558, 116742 .
AMA StyleAndri Hendriyana, Takeshi Tsuji. Influence of structure and pore pressure of plate interface on tectonic tremor in the Nankai subduction zone, Japan. Earth and Planetary Science Letters. 2021; 558 ():116742.
Chicago/Turabian StyleAndri Hendriyana; Takeshi Tsuji. 2021. "Influence of structure and pore pressure of plate interface on tectonic tremor in the Nankai subduction zone, Japan." Earth and Planetary Science Letters 558, no. : 116742.
Geothermal systems consisting of fractures in impermeable rocks are difficult to characterize by in situ methods. In an effort to link characteristics of small-scale and large-scale fractures, this study investigated possible relations between their geophysical parameters. We upscaled the relationship between fracture permeability and formation factor in a laboratory specimen to larger fracture dimensions. Microscopic flow characteristics indicate that this relationship is related to the tortuosity of flow paths. We derived an empirical formula that directly predicts changes in fracture permeability from changes in formation factor. This relation may make it possible to monitor subsurface hydraulic activities through resistivity observations.
Kazuki SawayamaiD; Takuya IshibashiiD; Fei Jiang; Takeshi TsujiiD; Osamu Nishizawa; Yasuhiro Fujimitsu. Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces. 2020, 1 .
AMA StyleKazuki SawayamaiD, Takuya IshibashiiD, Fei Jiang, Takeshi TsujiiD, Osamu Nishizawa, Yasuhiro Fujimitsu. Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces. . 2020; ():1.
Chicago/Turabian StyleKazuki SawayamaiD; Takuya IshibashiiD; Fei Jiang; Takeshi TsujiiD; Osamu Nishizawa; Yasuhiro Fujimitsu. 2020. "Scale-independent relationship between permeability and resistivity in mated fractures with natural rough surfaces." , no. : 1.
Crustal pore pressure, which controls the activities of earthquakes and volcanoes, varies in response to rainfall. The status of pore pressure can be inferred from observed changes in seismic velocity. In this study, we investigate the response of crustal pore pressure to rainfall in southwestern Japan based on time series of seismic velocity derived from ambient noise seismic interferometry. To consider the heterogeneity of the area, rainfall and seismic velocity obtained at each location were directly compared. We used a band-pass filter to distinguish the rainfall variability from sea level and atmospheric pressure, and then calculated the cross-correlation between rainfall and variations in S-wave velocity (Vs). A mostly negative correlation between rainfall and Vs changes indicates groundwater recharge by rainfall, which increases pore pressure. The correlations differ between locations, where most of the observation stations with clear negative cross-correlations were located in areas of granite. On the other hand, we could not observe clear correlations in steep mountain areas, possibly because water flows through river without percolation. This finding suggests that geographical features contribute to the imprint of rainfall on deep formation pore pressure. We further modelled pore pressure change due to rainfall based on diffusion mechanism. A strong negative correlation between pore pressure estimated from rainfall and Vs indicates that the Vs variations are triggered by pore pressure diffusion in the deep formation. Our modelling results show a spatial variation of diffusion parameter which controls the pore pressure in deep formation. By linking the variations in seismic velocity and crustal pore pressure spatially, this study shows that seismic monitoring may be useful in evaluating earthquake triggering processes or volcanic activity.
Rezkia Dewi Andajani; Takeshi Tsuji; Roel Snieder; Tatsunori Ikeda. Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring. Earth, Planets and Space 2020, 72, 1 -17.
AMA StyleRezkia Dewi Andajani, Takeshi Tsuji, Roel Snieder, Tatsunori Ikeda. Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring. Earth, Planets and Space. 2020; 72 (1):1-17.
Chicago/Turabian StyleRezkia Dewi Andajani; Takeshi Tsuji; Roel Snieder; Tatsunori Ikeda. 2020. "Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring." Earth, Planets and Space 72, no. 1: 1-17.
It is important to distinguish between natural earthquakes and those induced by CO2 injection at carbon capture and storage sites. For example, the 2004 Mw 6.8 Chuetsu earthquake occurred close to the Nagaoka CO2 storage site during gas injection, but we could not quantify whether the earthquake was due to CO2 injection or not. Here, changes in pore pressure during CO2 injection at the Nagaoka site were simulated and compared with estimated natural seasonal fluctuations in pore pressure due to rainfall and snowmelt, as well as estimated pore pressure increases related to remote earthquakes. Changes in pore pressure due to CO2 injection were clearly distinguished from those due to rainfall and snowmelt. The simulated local increase in pore pressure at the seismogenic fault area was much less than the seasonal fluctuations related to precipitation and increases caused by remote earthquakes, and the lateral extent of pore pressure increase was insufficient to influence seismogenic faults. We also demonstrated that pore pressure changes due to distant earthquakes are capable of triggering slip on seismogenic faults. The approach we developed could be used to distinguish natural from injection-induced earthquakes and will be useful for that purpose at other CO2 sequestration sites.
Chanmaly Chhun; Takeshi Tsuji. Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes. Sustainability 2020, 12, 9723 .
AMA StyleChanmaly Chhun, Takeshi Tsuji. Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes. Sustainability. 2020; 12 (22):9723.
Chicago/Turabian StyleChanmaly Chhun; Takeshi Tsuji. 2020. "Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes." Sustainability 12, no. 22: 9723.
Crustal pore pressure, which controls the activities of earthquakes and volcanoes, varies in response to rainfall. The status of pore pressure can be inferred from observed changes in seismic velocity. In this study, we investigate the response of crustal pore pressure to rainfall in southwestern Japan based on time series of seismic velocity derived from ambient noise seismic interferometry. To consider the heterogeneity of the area, rainfall and seismic velocity obtained at each location were directly compared. We used a band-pass filter to distinguish the rainfall variability from sea level and atmospheric pressure, and then calculated the cross-correlation between rainfall and variations in S-wave velocity (Vs). A mostly negative correlation between rainfall and Vs changes indicates groundwater recharge by rainfall, which increases pore pressure. The correlations differ between locations, where most of the observation stations with clear negative cross-correlations were located in areas of granite. On the other hand, we could not observe clear correlations in steep mountain areas, possibly because water flows through river without percolation. This finding suggests that geographical features contribute to the imprint of rainfall on deep formation pore pressure. We further modelled pore pressure change due to rainfall based on diffusion mechanism. A strong negative correlation between pore pressure estimated from rainfall and Vs indicates that the Vs variations are triggered by pore pressure diffusion in the deep formation. Our modelling results show a spatial variation of diffusion parameter which controls the pore pressure in deep formation. By linking the variations in seismic velocity and crustal pore pressure spatially, this study shows that seismic monitoring may be useful in evaluating earthquake triggering processes or volcanic activity.
Rezkia Dewi Andajani; Takeshi Tsuji; Roel Snieder; Tatsunori Ikeda. Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring. 2020, 1 .
AMA StyleRezkia Dewi Andajani, Takeshi Tsuji, Roel Snieder, Tatsunori Ikeda. Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring. . 2020; ():1.
Chicago/Turabian StyleRezkia Dewi Andajani; Takeshi Tsuji; Roel Snieder; Tatsunori Ikeda. 2020. "Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring." , no. : 1.
It is important to distinguish between natural earthquakes and those induced by CO2 injection at carbon capture and storage sites. For example, the 2004 Mw 6.8 Chuetsu earthquake occurred close to the Nagaoka CO2 storage site during gas injection, but we could not quantify whether the earthquake was due to CO2 injection or not. Here we simulated changes of pore pressure during CO2 injection at the Nagaoka site and compared them with estimated natural seasonal fluctuations of pore pressure due to rainfall and snowmelt as well as estimated pore pressure increases related to remote earthquakes. We clearly distinguished changes of pore pressure due to CO2 injection from those due to rainfall and snowmelt. The simulated local increase in pore pressure at seismogenic fault area was much less than the seasonal fluctuations related to precipitation and increases caused by remote earthquakes, and the lateral extent of pore pressure increase was insufficient to influence seismogenic faults. We also demonstrated that pore pressure changes due to distant earthquakes are capable of triggering slip on seismogenic faults. The approach we developed could be used to distinguish natural from injection-induced earthquakes and will be useful for that purpose at other CO2 sequestration sites.
Chanmaly Chhun; Takeshi Tsuji. Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes. 2020, 1 .
AMA StyleChanmaly Chhun, Takeshi Tsuji. Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes. . 2020; ():1.
Chicago/Turabian StyleChanmaly Chhun; Takeshi Tsuji. 2020. "Pore Pressure Analysis for Distinguishing Earthquakes Induced by CO2 Injection from Natural Earthquakes." , no. : 1.
Short term outcomes of the COVID-19 pandemic have included improved air quality and reduced carbon dioxide (CO2) and other greenhouse gas emissions, while long term repercussions may include a disruption to joint international research efforts, the creation of silos, and the potential for internalizing efforts toward national rather than global goals. In this study, we identified the impacts of reduced mobility on pollutants and emissions, the emergence of nationalist approaches and effects on international cooperation, and how these issues will affect the achievement of global carbon targets and the Sustainable Development Goals (SDGs). COVID-19 presents a global short-term crisis and there is a demonstrated global desire and effort to develop a vaccine and effective treatments. Similarly, climate change is also a near future issue, and as a result we need to reduce CO2 emissions rapidly. This review highlights potential policy interventions, which capitalize on learnings from COVID-19, while identifying SDGs 10, 13, and 17 as critical to engendering a successful, cooperative transition toward sustainability. The recognition of the earth as a closed system, demonstrated by the shared impacts of the COVID-19 crisis, may encourage positive future effects on cooperative approaches toward mitigating climate change, another looming crisis for humanity.
Andrew Chapman; Takeshi Tsuji. Impacts of COVID-19 on a Transitioning Energy System, Society, and International Cooperation. Sustainability 2020, 12, 8232 .
AMA StyleAndrew Chapman, Takeshi Tsuji. Impacts of COVID-19 on a Transitioning Energy System, Society, and International Cooperation. Sustainability. 2020; 12 (19):8232.
Chicago/Turabian StyleAndrew Chapman; Takeshi Tsuji. 2020. "Impacts of COVID-19 on a Transitioning Energy System, Society, and International Cooperation." Sustainability 12, no. 19: 8232.