Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3124/segj.77.40

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.geothermics.2024.102932

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.jafrearsci.2023.105161

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.icarus.2023.115666

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1541/ieejsmas.143.331

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.icarus.2023.115724

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-023-01855-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-023-35159-8

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2022JB025017

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/1365-2478.13308

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1785/0220220049

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-022-01654-x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-022-01654-x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tecto.2022.229366

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2021JB022639

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-021-00063-6

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3124/segj.74.79

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/rs13214391

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1038/s41598-021-97881-5

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/gji/ggab150

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-020-1139-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-020-1147-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-020-01311-1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2020GL087123

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2019JB019043

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-019-1066-y

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cageo.2019.02.005

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/08123985.2019.1597497

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/08123985.2018.1548605

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40645-018-0211-8

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1190/geo2018-0084.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1071/EG17129

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1126/sciadv.1700813

Language：English   Publishing type：Research paper (other academic)  

We characterized and monitored spatial variation of the shallow subsurface at the Aquistore CO2 storage site, managed by the Petroleum Technology Research Centre, Canada. In this study, a continuous and controlled seismic source system called the ACROSS was used to enhance source repeatability and temporal resolution in the monitoring. To extract spatial variations of the surface-wave phase velocity using a fixed single source, we introduced a spatial window in surface-wave analysis. We succeeded in extracting lateral variation of phase velocities consistent with the shallow geological conditions. We also observed seasonal variation of phase velocities. Higher phase velocities observed in winter could be explained by freezing of water in shallow sediments, and their spatial variation might be related to the difference of the degree of freezing. Furthermore, we observed a mode transition between winter and warmer seasons, suggesting the importance of careful mode identification for robust monitoring. In warmer seasons, our monitoring approach showed high temporal stability, indicating the potential to identify the spatial distribution of shallow CO2 leakage.

Language：English   Publishing type：Research paper (scientific journal)  

We calculated CO₂ displacements in 3D natural sandstone (digital rock model) under various reservoir conditions using two-phase lattice Boltzmann (LB) simulations, and characterized the influence of reservoir conditions upon CO₂ - water flow. The results of LB simulations under >50 conditions were used to classify the resulting two-phase flow behaviors into typical fluid displacement patterns on the diagram of capillary number (Ca) and viscosity ratio of the CO₂ and water (M). In addition, the saturation of CO₂ (nonwetting phase) was calculated and mapped on the Ca-M diagram. These results demonstrated that CO₂ saturation is controlled by Ca and M, and the optimum CO₂ saturation scales with Ca and M. When we applied similar analysis to the different type of rock, we found that CO₂ saturation and behaviors are significantly different. These important differences could be due to the heterogeneity of pore geometry in the natural rock and differences in pore connectivity. By quantifying CO₂ behavior in the target reservoir rock under various conditions (i.e., saturation mapping on the Ca-M diagram), our approach provides useful information for investigating suitable reservoir conditions for effective CO₂ storage (e.g., high CO₂ saturation). We further calculated seismic velocity of the digital rocks with injected CO₂ under various reservoir conditions (e.g., Ca and M) using dynamic wave propagation simulation. By using the relation between seismic velocity and CO₂ saturation parameterized by reservoir conditions, we could quantify in situ CO₂ saturation in reservoir from monitoring data (seismic velocity).

DOI： 10.1016/j.egypro.2017.03.1545

Language：English   Publishing type：Research paper (scientific journal)  

Monitoring injected CO₂ is a crucial problem for reliable operation of carbon dioxide capture and storage projects. Since monitoring interval of existing seismic monitoring is limited, identifying sudden change in CO₂ storage sites is difficult. To improve temporal resolution and repeatability, we applied seismic monitoring using a continuous and controlled source, referred to as the ACROSS. In particular, we monitored shallow subsurface through surface-wave analysis to investigate the feasibility of ACROSS-based monitoring for identifying CO₂ leakage. High accuracy and temporal resolution in our monitoring results indicated the potential to identify change in surface waves associated with CO₂ leakage.

DOI： 10.1016/j.egypro.2017.03.1527

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40623-016-0487-0

Language：English   Publishing type：Research paper (other academic)  

We performed time-lapse surface-wave analysis to monitor the shallow subsurface at the Aquistore CO2 storage site, managed by the Petroleum Technology Research Centre, Canada. A continuous and controlled seismic source system called the Accurately Controlled Routinely Operated Signal System (ACROSS) is used to enhance the temporal resolution and source repeatability in the monitoring. We extracted hourly-variation of surface-wave phase velocities from continuous seismic data with 4 hour stacking. As a result, we could monitor phase velocities within 1 % accuracy during 1-9 days in the frequency range of 4.5-6 Hz. We identified 2-5 % seasonal variation of phase velocities. The high phase velocities observed in winter can be explained by the degree of freezing of partially saturated rock. Our time-lapse results contributed to improving the accuracy of monitoring deep reflections from the CO2 injection reservoir by correcting seasonal variations of near-surface velocity. The high temporal resolution and accuracy of our monitoring results have the potential to identify sudden changes such as CO2 leakage from CO2 storage sites.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1190/INT-2016-0019.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijggc.2015.11.030

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1190/GEO2014-0018.1

Language：English   Publishing type：Research paper (other academic)  

We propose an approach for detecting localized heterogeneities from surface-wave phase-velocity and attenuation using conventional multichannel seismic data. In most surface-wave analysis, only phase information of seismic data is used to obtain near-surface S-wave velocity profiles. However, we further utilize surface-wave attenuation extracted from amplitude information of seismic data. We focus on the sensitivity difference between local phase velocities and attenuation coefficients to localized heterogeneities such as lithological boundaries and localized fractures. To characterize such heterogeneities from lateral variation of attenuation coefficients and phase velocities, we perform numerical experiments for laterally heterogeneous models with a lithological boundary and a fracture zone. We observe lateral variation of attenuation coefficients near the lateral heterogeneities. As a result, the lithological boundary can be characterized by lateral variations of local phase velocities and attenuation coefficients near the boundary. On the other hand, the fracture zone can be characterized by low lateral variation in phase velocities and increase of attenuation coefficients near the fracture. Therefore, our propose method has the possibility to distinguish lithological boundaries from localized fractures. In fluid-injection experiments (e.g., CO2 geological storage), our approach has high potential in evaluating possible existence of localized fractures, which may serve as leakage path of injected fluid.

Language：English   Publishing type：Research paper (other academic)  

To construct a reliable and cost-effective monitoring system for injected CO2 in Carbon Capture and Storage (CCS) projects, we have developed a seismic monitoring technique using ambient noise. The passive seismic interferometry can continuously monitor the injected CO2, allowing us to detect accidental incident associated with CO2 injection (e.g., CO2 leakage from reservoir). Here we used seismic interferometry approaches for construction of virtual seismic data. By applying these methods to the passive seismometer data acquired during fluid-injection experiment in Svalbard in the Norwegian Arctic, we estimated variations of reflection amplitude. The reflectors around the reservoir can be identified on the common mid-point (CMP) gather constructed via seismic interferometry, and they enable us to estimate seismic velocity. Therefore, the technique we have developed in this study can extract subsurface structures around the water-injection field and provide its time-lapse information. On the time-lapse seismic profiles derived from seismic interferometry, the injected water can be imaged as a number of bright reflections within the reservoir. The amplitude anomaly appeared just after fluid injection. The amplitude variation extracted from our analysis has clear relation with pressure. Therefore the variation of reflection amplitude may be induced by pore pressure variation due to fluid injection. This low-cost approach is particularly attractive for long-term, continuous monitoring of CCS projects. We further applied surface-wave analysis for the ambient noise data and estimated variation of S-wave velocity structure in the shallow formation. This information enables us to evaluate the influence of shallow formation on the monitoring results of deep reservoir.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014JB011567

Language：English   Publishing type：Research paper (other academic)  

Multimode inversion of surface waves improves S-wave velocity estimations. In surface wave analysis, only vertical components of the P-SV wavefield have been conventionally used to extract multimode Rayleigh waves. In this study, horizontal components of the P-SV waves were analyzed to extract additional mode information of Rayleigh waves. First, we extracted Rayleigh waves from vertical and horizontal components of the numerically synthesized P-SV waves. Additional mode information of Rayleigh waves could be obtained from horizontal component data. We then estimated S-wave velocity structures by multimode inversion using a genetic algorithm. Inclusion of dispersion curves from horizontal component data improved the investigation depth of Swave velocity estimation. Next, multimode Rayleigh waves were extracted from three-component seismic data acquired in Alberta, Canada. By including dispersion curves from horizontal component data, which have different mode information from those from vertical component data, the inverted S-wave velocity structures agreed well with logging data for deeper layer. Therefore, inclusion of horizontal component data of the P-SV wavefield makes it possible to extract additional mode information of Rayleigh waves, thus eliminating ambiguity from S-wave velocity estimations in multimode inversions.

Language：English   Publishing type：Research paper (scientific journal)  

Multimode inversion of surface waves improves S-wave velocity estimations. In surface wave analysis, only vertical components of the P-SV wavefield have been conventionally used to extract multimode Rayleigh waves. In this study, horizontal components of the P-SV waves were analyzed to extract additional mode information of Rayleigh waves. First, we extracted Rayleigh waves from vertical and horizontal components of the numerically synthesized P-SV waves. Additional mode information of Rayleigh waves could be obtained from horizontal component data. We then estimated S-wave velocity structures by multimode inversion using a genetic algorithm. Inclusion of dispersion curves from horizontal component data improved the investigation depth of Swave velocity estimation. Next, multimode Rayleigh waves were extracted from three-component seismic data acquired in Alberta, Canada. By including dispersion curves from horizontal component data, which have different mode information from those from vertical component data, the inverted S-wave velocity structures agreed well with logging data for deeper layer. Therefore, inclusion of horizontal component data of the P-SV wavefield makes it possible to extract additional mode information of Rayleigh waves, thus eliminating ambiguity from S-wave velocity estimations in multimode inversions.

DOI： 10.1190/segam2013-0200.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/j.1365-246X.2012.05496.x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1190/geo2011-0222.1

Language：English   Publishing type：Research paper (other academic)  

For soil improvement, the rigid bodies are cast into the soft ground at periodic distance. It is important to estimate macroscopic rigidity (S-wave velocity) of this improved ground for the construction of a building. Here we propose a new approach combining surface wave method and homogenization method in order to evaluate the vibration characteristics of improved soft ground. The homogenization method provides a microscopic equivalent homogeneous medium of improved soft ground. This medium is considered as a theoretical macroscopic model. As a result of simulation study, it is concluded that macroscopic S-wave velocity structure can be estimated from surface wave method by the restriction of the ratio between the wavelength of surface waves and the intervals of cast rigid bodies.

DOI： 10.4133/1.3614263

Language：English   Publishing type：Research paper (other academic)  

To reveal if glacier bed sediments are unfrozen, we apply multi-channel analysis of surface waves (MASW) on seismic data acquired across a glacier at the southern central Spitsbergen in the Norwegian Arctic. The S-wave velocity varies significantly with the degree of freezing of the pore fluids. We clearly observe the offset of the dispersion curves at the transition of predominant modes. These higher modes may indicate a velocity reversal beneath the glacier (or interface between glacier and sediment). Based on simulation studies, we find that the offset observed on the dispersion curve seems to be related to the glacier thickness when the velocity structure beneath the glacier is similar. Therefore, we can roughly estimate the geometry of the surface of the sediment (sharp velocity contrast) only from the transition of predominant mode on the dispersion curve. We then estimate the S-wave velocity distribution via Genetic Algorithm (GA) inversion, using information of ice thickness derived from Ground Penetrating Rader (GPR) data. The estimated S-wave velocity structure clearly represents the velocity reversal beneath the glacier.

Language：English   Publishing type：Research paper (scientific journal)  

To reveal if glacier bed sediments are unfrozen, we apply multi-channel analysis of surface waves MASW on seismic data acquired across a glacier at the southern central Spitsbergen in the Norwegian Arctic. The S-wave velocity varies significantly with the degree of freezing of the pore fluids. We clearly observe the offset of the dispersion curves at the transition of predominant modes. These higher modes may indicate a velocity reversal beneath the glacier or interface between glacier and sediment. Based on simulation studies, we find that the offset observed on the dispersion curve seems to be related to the glacier thickness when the velocity structure beneath the glacier is similar. Therefore, we can roughly estimate the geometry of the surface of the sediment sharp velocity contrast only from the transition of predominant mode on the dispersion curve. We then estimate the S-wave velocity distribution via Genetic Algorithm GA inversion, using information of ice thickness derived from Ground Penetrating Rader GPR data. The estimated S-wave velocity structure clearly represents the velocity reversal beneath the glacier.

DOI： 10.1190/1.3627455

Language：English   Publishing type：Research paper (other academic)  

We usually analyzed microtremors using a fundamental mode only. However, recent studies demonstrated that higher modes should be considered in SPAC method. In order to investigate this theoretically, we simulate microtremors numerically and applied the proposed method using higher modes. Also we applied this method to field data. In this method, we calculated apparent phase velocity from phase velocity and amplitude of higher modes, and compare the apparent velocity with the observed phase velocity. Since the phase velocity obtained from simulated data and field microtremor data is well consistent with the apparent phase velocity, the analysis method using the apparent velocity works well in S-wave velocity estimation.

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：United States  

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：United States  

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.6

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.5 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.5 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2022.5 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Event date： 2021.10

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.5 - 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2021.3 - 2021.7

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Event date： 2020.9

Language：English   Presentation type：Oral presentation (general)  

Event date： 2020.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.5

Language：English   Presentation type：Oral presentation (general)  

Country：Austria  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：United Arab Emirates  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：United Arab Emirates  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：3

Number of peer-reviewed articles in Japanese journals：1

Proceedings of International Conference Number of peer-reviewed papers：2

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：1

Proceedings of International Conference Number of peer-reviewed papers：2

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：3

Number of peer-reviewed articles in Japanese journals：1

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Number of peer-reviewed articles in Japanese journals：1

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：1