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Tatsunori Ikeda Last modified dateļ¼š2024.04.26

Associate Professor / Earth Science and Technology / Department of Earth Resources Engineering / Faculty of Engineering


Papers
1. Chanmaly Chhun, Takeshi Tsuji, Tatsunori Ikeda, Potential fluid flow pathways and the geothermal structure of Kuju revealed by azimuthal anisotropic ambient noise tomography, Geothermics, https://doi.org/10.1016/j.geothermics.2024.102932, 102932, 2024.05.
2. Chammaly Chhun, Takeshi Tsuji, Tatsunori Ikeda, Potential geothermal reservoir systems in the Kenyan Great Rift Valley and volcanic region assessed by ambient noise analysis, Journal of African Earth Sciences, https://doi.org/10.1016/j.jafrearsci.2023.105161, 105161, 2024.04.
3. Hikaru Imazato, Tatsunori Ikeda, Takeshi Tsuji, Shallow S wave velocity profile from acti ve source seismic data at the Apollo 14 landing site based on virtual multichannel analysis of surface waves, Icarus, https://doi.org/10.1016/j.icarus.2023.115724, 115724, 2023.07.
4. T. Tsuji, T. Kobayashi, J. Kinoshita, T. Ikeda, T. Uchigaki, Y. Nagata, T. Kawamura, K. Ogawa, S. Tanaka, A. Araya, Lunar active seismic profiler for investigating shallow substrates of the Moon and other extraterrestrial environments, Icarus, 10.1016/j.icarus.2023.115666, 2023.11.
5. N. Bokani, T. Ikeda, T. Tsuji, Y. Iio, High-Resolution Three-dimensional Azimuthal Velocity Anisotropy of S-waves in southern-central Japan, based on Ambient Noise Tomography, Earth, Planets, and Space, 10.1186/s40623-023-01855-y, 2023.06.
6. D.A. Rezkia, T. Tsuji, T. Ikeda, S. Matsumoto, K. Kitamura, J. Nishijima, Tracking supercritical geothermal fluid distribution from continuous seismic monitoring, Scientific Reports, 10.1038/s41598-023-35159-8, 2023.05.
7. H. Nimiya, T. Ikeda, T. Tsuji, Multimodal Rayleigh and Love wave joint inversion for S-wave velocity structures in Kanto Basin, Japan, Journal of Geophysical Research Solid Earth, 10.1029/2022JB025017, 2023.01.
8. T.S. Imam, T. Ikeda, T. Tsuji, J. Uesugi, T. Nakamura, Y. Okaue , Extracting high-resolution P-wave reflectivity of the shallow subsurface by seismic interferometry based on autocorrelation of blast mining signals
, Geophysical Prospecting, 10.1111/1365-2478.13308, 2022.12.
9. Rezkia Dewi Andajani, Takeshi Tsuji, Roel Snieder, Tatsunori Ikeda, Spatial and temporal influence of sea level on inland stress based on seismic velocity monitoring, Earth, Planets and Space, 10.1186/s40623-022-01654-x, 74, 97, 2022.06.
10. Nthaba Bokani, Tatsunori Ikeda, Hiro Nimiya, Takeshi Tsuji, Yoshihisa Iio, Ambient Noise Tomography for a High-resolution 3D S-Wave Velocity Model of the Kinki Region, Southwestern Japan, using Dense Seismic Array Data, Earth, Planets and Space, 10.1186/s40623-022-01654-x, 74, 96, 2022.06.
11. Michiharu Ikeda, Kakda Kret, Takeshi Tsuji, Tatsunori Ikeda, Tomohiro Tsuji, Kozo Onishi, Naoki Nishizaka, Pore fabric anisotropy and elastic moduli of fault rocks from the Median Tectonic Line, Shikoku, southwest Japan, Tectonophysics, 10.1016/j.tecto.2022.229366, 834, 5, 229366, 2022.05.
12. Kazuki Sawayama, Tatsunori Ikeda, Takeshi Tsuji, 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, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 10.1029/2021JB022639, 127, 2, 2022.01.
13. Mohamed Mourad, Takeshi Tsuji, Tatsunori Ikeda, Kazuya Ishitsuka, Shigeki Senna, Kiyoshi Ide, Mapping Aquifer Storage Properties Using S-Wave Velocity and InSAR-Derived Surface Displacement in the Kumamoto Area, Southwest Japan, REMOTE SENSING, 10.3390/rs13214391, 13, 21, 2021.10.
14. Hiro Nimiya, Tatsunori Ikeda, Takeshi Tsuji, Temporal changes in anthropogenic seismic noise levels associated with economic and leisure activities during the COVID-19 pandemic, Scientific Reports, 10.1038/s41598-021-00063-6, 11, 2021.11.
15. Takeshi Tsuji, Tatsunori Ikeda, Ryosuke Matsuura, Kota Mukumoto, Fernando Lawrens Hutapea, Tsunehisa Kimura, Koshun Yamaoka, and Masanao Shinohara, Continuous monitoring system for safe managements of CO2 storage and geothermal reservoirs, Scientific Reports, https://doi.org/10.1038/s41598-021-97881-5, 11, 2021.09.
16. Tatsunori Ikeda, Takeshi Tsuji, Chisato Konishi, and Hideki Saito, Spatial autocorrelation method for reliable measurements of two-station dispersion curves in heterogeneous ambient noise wavefields
, Geophysical Journal International, 10.1093/gji/ggab150, 226, 2, 1130-1147, 2021.08.
17. Rezkia Dewi Andajani, Takeshi Tsuji, Roel Snieder, and Tatsunori Ikeda (2021) , Spatial and temporal influence of rainfall on crustal pore pressure based on seismic velocity monitoring
, Earth, Planets and Space, 10.1186/s40623-020-01311-1, 72, 177, 2020.11.
18. Hiro Nimiya, Tatsunori Ikeda, and Takeshi Tsuji , Three-dimensional S-wave velocity structure of central Japan estimated by surface-wave tomography using ambient noise
, Journal of Geophysical Research Solid Earth, 10.1029/2019JB019043, 125, 4, e2019JB019043

, 2020.04.
19. Yudai Suemoto, Tatsunori Ikeda, Takeshi Tsuji, Yoshihisa Iio, Identification of a nascent tectonic boundary in the San-in area, southwest Japan, using a 3D S-wave velocity structure obtained by ambient noise surface wave tomography, earth, planets and space, 10.1186/s40623-020-1139-y, 72, 1, 2020.12.
20. Fernando Lawrens Hutapea, Takeshi Tsuji, Tatsunori Ikeda, Real-time crustal monitoring system of Japanese Islands based on spatio-temporal seismic velocity variation, earth, planets and space, 10.1186/s40623-020-1147-y, 72, 1, 2020.12.
21. Yudai Suemoto, Tatsunori Ikeda, Takeshi Tsuji, Temporal Variation and Frequency Dependence of Seismic Ambient Noise on Mars From Polarization Analysis, Geophysical Research Letters, 10.1029/2020GL087123, 47, 13, 2020.07.
22. Tatsunori Ikeda, Takeshi Tsuji, Two-station continuous wavelet transform cross-coherence analysis for surface-wave tomography using active-source seismic data, GEOPHYSICS, 10.1190/geo2019-0054.1, 85, 1, EN17-EN28, 2020.01.
23. Kosuke Takahashi, Takeshi Tsuji, Tatsunori Ikeda, Hiro Nimiya, Yuichiro Nagata, Yudai Suemoto, Underground structures associated with horizontal sliding at Uchinomaki hot springs, Kyushu, Japan, during the 2016 Kumamoto earthquake, earth, planets and space, 10.1186/s40623-019-1066-y, 71, 1, 2019.12.
24. Takeshi Tsuji, Tatsunori Ikeda, Fei Jiang, Evolution of hydraulic and elastic properties of reservoir rocks due to mineral precipitation in CO2geological storage, Computers and Geosciences, 10.1016/j.cageo.2019.02.005, 126, 84-95, 2019.05.
25. Rezkia Dewi Andajani, Tatsunori Ikeda, Takeshi Tsuji, Surface wave analysis for heterogeneous geological formations in geothermal fields
Effect of wave propagation direction, Exploration Geophysics, 10.1080/08123985.2019.1597497, 50, 3, 255-268, 2019.05.
26. Kakda Kret, Tatsunori Ikeda, Takeshi Tsuji, Grid-search inversion based on rock physics model for estimation of pore geometry and grain elastic moduli
Application to hydrothermal ore deposits and basalt, Exploration Geophysics, 10.1080/08123985.2018.1548605, 50, 1, 1-11, 2019.01.
27. Tatsunori Ikeda, Takeshi Tsuji, Temporal change in seismic velocity associated with an offshore MW 5.9 Off-Mie earthquake in the Nankai subduction zone from ambient noise cross-correlation, Progress in Earth and Planetary Science, 10.1186/s40645-018-0211-8, 5, 1, 2018.12.
28. Tatsunori Ikeda, Takeshi Tsuji, Masashi Nakatsukasa, Hideaki Ban, Ayato Kato, Kyle Worth, Don White, Brian Roberts, Imaging and monitoring of the shallow subsurface using spatially windowed surface-wave analysis with a single permanent seismic source, GEOPHYSICS, 10.1190/geo2018-0084.1, 83, 6, EN23-EN38, 2018.11.
29. Chandoeun Eng, Tatsunori Ikeda, Takeshi Tsuji, Study of the Nankai seismogenic fault using dynamic wave propagation modelling of digital rock from the Nobeoka Fault, Exploration Geophysics, 10.1071/EG17129, 49, 1, 11-20, 2018.01.
30. Hiro Nimiya, Tatsunori Ikeda, Takeshi Tsuji, Spatial and temporal seismic velocity changes on Kyushu Island during the 2016 Kumamoto earthquake, Science advances, 10.1126/sciadv.1700813, 3, 11, 2017.11.
31. Tatsunori Ikeda, Takeshi Tsuji, Masashi Nakatsukasa, Hideaki Ban, Ayato Kato, Kyle Worth, Donald White, Brian Roberts, Shallow characterization and monitoring of the Aquistore CO2 storage site from spatially windowed surface-wave analysis with a permanent seismic source, SEG Technical Program Expanded Abstracts 2017, 5465-5470, 2017.08, 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..
32. Tatsunori Ikeda, Takeshi Tsuji, Mamoru Takanashi, Isao Kurosawa, Masashi Nakatsukasa, Ayato Kato, Kyle Worth, Don White, Brian Roberts, Temporal variation of the shallow subsurface at the Aquistore CO2 storage site associated with environmental influences using a continuous and controlled seismic source, Journal of Geophysical Research: Solid Earth, 10.1002/2016JB013691, 122, 4, 2859-2872, 2017.04.
33. Takeshi Tsuji, Tatsunori Ikeda, Fei Jiang, Hydrologic and Elastic Properties of CO2 Injected Rock at Various Reservoir Conditions
Insights into Quantitative Monitoring of Injected CO2, 13th International Conference on Greenhouse Gas Control Technologies, GHGT 2016 Energy Procedia, 10.1016/j.egypro.2017.03.1545, 114, 4047-4055, 2017.01, 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)..
34. Tatsunori Ikeda, Takeshi Tsuji, Robust Subsurface Monitoring Using a Continuous and Controlled Seismic Source, 13th International Conference on Greenhouse Gas Control Technologies, GHGT 2016 Energy Procedia, 10.1016/j.egypro.2017.03.1527, 114, 3956-3960, 2017.01, 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..
35. Tatsunori Ikeda, Takeshi Tsuji, Surface wave attenuation in the shallow subsurface from multichannel-multishot seismic data
A new approach for detecting fractures and lithological discontinuities, earth, planets and space, 10.1186/s40623-016-0487-0, 68, 1, 2016.12.
36. Tatsunori Ikeda, Takeshi Tsuji, Mamoru Takanashi, Isao Kurosawa, Masashi Nakatsukasa, Donald White, Kyle Worth, Brian Roberts, Time-lapse monitoring of shallow subsurface in the Aquistore CO2 storage site from surface-wave analysis using a continuous and controlled seismic source, SEG Technical Program Expanded Abstracts 2016, 5479-5484, 2016.09, 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..
37. Takeshi Tsuji, Tatsunori Ikeda, Tor Arne Johansen, Bent Ole Ruud, Using seismic noise derived from fluid injection well for continuous reservoir monitoring, Interpretation, 10.1190/INT-2016-0019.1, 4, 4, SQ1-SQ11, 2016.03.
38. Tatsunori Ikeda, Takeshi Tsuji, Toshiki Watanabe, Koshun Yamaoka, Development of surface-wave monitoring system for leaked CO2 using a continuous and controlled seismic source, International Journal of Greenhouse Gas Control, 10.1016/j.ijggc.2015.11.030, 45, 94-105, 2016.02.
39. Tatsunori Ikeda, Toshifumi Matsuoka, Takeshi Tsuji, Toru Nakayama, Characteristics of the horizontal component of Rayleigh waves in multimode analysis of surface waves, GEOPHYSICS, 10.1190/GEO2014-0018.1, 80, 1, EN1-EN11, 2015.12.
40. Tatsunori Ikeda, Takeshi Tsuji, Characterization of near-surface heterogeneity by integrating surface-wave phase velocity and attenuation, Proceedings of the 12th SEGJ International Symposium, 34-37, 2015.11, 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..
41. Tatsunori Ikeda, Takeshi Tsuji, Advanced surface-wave analysis for 3D ocean bottom cable data to detect localized heterogeneity in shallow geological formation of a CO2 storage site, International Journal of Greenhouse Gas Control, 10.1016/j.ijggc.2015.04.020, 39, 107-118, 2015.08.
42. Takeshi Tsuji, Tatsunori Ikeda, Tor Arne Johansen, Bent Ole Ruud, Time-lapse seismic profiles derived from passive seismic interferometry in fluid-injection experiments, SEG Technical Program Expanded Abstracts 2015, 2412-2418, 2015.08, 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..
43. Tatsunori Ikeda, Takeshi Tsuji, Azimuthal anisotropy of Rayleigh waves in the crust in southern Tohoku area, Japan, Journal of Geophysical Research: Solid Earth, 10.1002/2014JB011567, 119, 12, 8964-8975, 2014.01.
44. Tatsunori Ikeda, Takeshi Tsuji, Toshifumi Matsuoka, Window-controlled CMP crosscorrelation analysis for surface waves in laterally heterogeneous media, GEOPHYSICS, 10.1190/geo2013-0010.1, 78, 6, EN95-EN105, 2013.11.
45. Tatsunori Ikeda, Toshifumi Matsuoka, Takeshi Tsuji, Toru Nakayama, Multimode inversion of Rayleigh waves using vertical and horizontal component data, SEG Technical Program Expanded Abstracts 2013, 1782-1787, 2013.09, 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..
46. Tatsunori Ikeda, Toshifumi Matsuoka, Computation of Rayleigh waves on transversely isotropic media by the reduced delta matrix method, Bulletin of the Seismological Society of America, 10.1785/0120120207, 103, 3, 2083-2093, 2013.06.
47. Tatsunori Ikeda, Takeshi Tsuji, Toru Nakayama, Multimode inversion of Rayleigh waves using vertical and horizontal component data, SEG Houston 2013 Annual Meeting, SEG 2013 SEG Technical Program Expanded Abstracts, 10.1190/segam2013-0200.1, 32, 1782-1787, 2013, 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..
48. Tatsunori Ikeda, Toshifumi Matsuoka, Takeshi Tsuji, Koichi Hayashi, Multimode inversion with amplitude response of surface waves in the spatial autocorrelation method, Geophysical Journal International, 10.1111/j.1365-246X.2012.05496.x, 190, 1, 541-552, 2012.07.
49. Takeshi Tsuji, Tor Arne Johansen, Bent Ole Ruud, Tatsunori Ikeda, Toshifumi Matsuoka, Surface-wave analysis for identifying unfrozen zones in subglacial sediments, GEOPHYSICS, 10.1190/geo2011-0222.1, 77, 3, EN17-EN27, 2012.05.
50. Tatsunori Ikeda, Toshifumi Matsuoka, Takeshi Tsuji, Koichi Hayashi, Evaluation of vibration characteristics at improved soft ground by surface wave method, 24th Symposium on the Application of Geophysics to Engineering and Environmental Problems 2011, SAGEEP 2011 24th Symposium on the Application of Geophysics to Engineering and Environmental Problems 2011, SAGEEP 2011, 10.4133/1.3614263, 121-130, 2011.01, 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..
51. Takeshi Tsuji, Tor Arne Johansen, Bent Ole Ruud, Tatsunori Ikeda, Toshifumi Matsuoka, Surface wave analysis for studying elastic properties of glacier bed sediments, SEG Technical Program Expanded Abstracts, 10.1190/1.3627455, 30, 1, 1358-1362, 2011.01, 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..
52. Takeshi Tsuji, Tor Arne Johansen, Bent Ole Ruud, Tatsunori Ikeda, Toshifumi Matsuoka, Surface wave analysis for studying elastic properties of glacier bed sediments, Society of Exploration Geophysicists International Exposition and 81st Annual Meeting 2011, SEG 2011 Society of Exploration Geophysicists International Exposition and 81st Annual Meeting 2011, SEG 2011, 1358-1362, 2011.01, 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..
53. Tatsunori Ikeda, Toshifumi Matsuoka, Takeshi Tsuji, Higher modes of surface waves in microtremor analysis, Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010 Society of Exploration Geophysicists International Exposition and 80th Annual Meeting 2010, SEG 2010, 2034-2038, 2010.01, 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..


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