VENUE International Conference Center, Waseda University, Tokyo, Japan
SCHEDULE Tuesdy , June 7, 2022 Openning Speech Room No.1 (3F) 09:50-09:55 __Speaker: Toshiki WATANABE (NAGOYA Univ.; President of SEGJ) Technical Sessions Room No.1 (3F) 10:00-15:00 Poster Core Time Room No.1 (3F) 15:20-17:20 Student Exchange Event Special Venue 17:30-18:50 Exhibition Room No.3 (3F) 11:00-17:20 Wednesday, June 8, 2022 Technical Sessions Room No.1 (3F) 10:20-12:00 Executive Sessions Room No.1 (3F) 13:00-15:00 __Chair: Keiichi SUZUKI (Kawasaki Geological Engineering Co., Ltd.; Vice-President of SEGJ) __Presentation(1): Development of 3D Geological Information in the Tokyo Metropolitan Area based on Geological Stratification Research
Tsutomu NAKAZAWA (AIST)
__Presentation(2): Latest DX for Geophysical Technicians
Kazuyoshi TAKAICHI (ITOCHU Techno-Solutions Corpration)
General Meeting Room No.1 (3F) 15:20-16:50 Exhibition Room No.3 (3F) 10:20-12:40 Thursday, June 9, 2022 Technical Sessions Room No.1 (3F) 09:40-12:00 Exhibition Room No.3 (3F) 09:40-11:30
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LIST OF EXHIBITORS Geofive Co.,Ltd.
Superconducting Sensing Technology Corporation(SUSTEC)
LIST OF ADVERTISEMENTS Geophysical Surveying Co., Ltd.(GSC)
ITOCHU Techno-Solutions Corpration(CTC)
Kawasaki Geological Engineering Co. Ltd.(KGE)
1) TEST for you internet connection to the online conference
2) Guide for Technical Session
3) DO NOT screenshot or record any part of the conference (including the audios).
|Jun.7 Room No.1 (Conference Room 1，3F)|
|Session||[Geothermal][Resource Exploration][Oil and Natural Gas]|
|Chair||Jun Matsushima (University of Tokyo)|
|Jun. 7||10:00 -
In these day, Deep learning has achieved great success in variety if research field and industrial applications. Especially, Convolutional Neural Network (CNN) has made remarkable progress in the files of image application. On the other hand, geology and geophysics, especially applied 3D seismic dataset cases are not abundant. Geng and Wang (2020) have challenged and achieved results in the application to in this filed.We also applied 3D seismic dataset for detect typical seismic events (BSR: Bottom Simulating Reflector) using CNN. And we additional tested to applied 2 different type of CNN models that are SesimicPacthNet andEfficientNet. We discuss the application results in the real seismic filed data. And we discuss how to approach the real filed data using CNN model.
|1) Feasibility analyses of applying Convolution Neural Network to reflection seismic data.|
SAKAGUCHI・Kazuyoshi TAKAICHI・Satoshi KODAMA・Yusuke SHIMONO・Tatsuro
UEMOTO・Hisako SHIMIZU(1),Shohei ISHINABE・Yoshitaka NAKAYAMA(2)
|Jun. 7||10:20 -
We analyzed the mine blast signals to map the P-wave reflection profiles at the Hishikari mine area by the autocorrelation analysis based on seismic interferometry. Because the fissure filled ore vein deposits are dominant in this area, we evaluate the potential of the autocorrelation analysis as an investigation method of the ore deposits. In autocorrelation analysis based on seismic interferometry, ambient noise or natural earthquake seismic data are commonly used. Here we used blasting of the mine as seismic events for autocorrelation instead of applying conventional used seismic events Because the blast events include high frequency and amplitude signals, using the blast events contributes to imaging efficiently the subsurface shallow structures. We successfully obtained auto-correlogram images that showed high-resolution seismic reflectors from shallow formation depths which were difficult to achieve by the conventional approach. These seismic reflection images could manifest the lithological boundaries of shallower than 500 m and possible ore vein deposit occurrence. Our simple approach using dense seismic array to acquire one optimum blast shot is inexpensive approach for higher resolution 2D and 3D lithological imaging, and useful for mineral explorations.
|2) Active mine blast seismic interferometry of the P wave reflectivity to image the 3D shallow lithological boundaries|
Imam(1),Tatsunori Ikeda・Takeshi Tsuji(2),Jiro Uesugi・Takeshi
1:Kyushu University, Suez Canal University,2:Kyushu University,3:Sumitomo Metal Mining Co., Ltd ,
4:Hishikari mine, Sumitomo Metal Mining Co., Ltd
|Jun. 7||10:40 -
In 2021, we carried out DAS seismic survey in and around the Sumikawa Geothermal Power Plant in Akita, Japan. We deployed optic fiber down to 1,200 m depth in the SE-4 well, which is one of the geothermal wells. Using this optic fiber, we acquired temperature profiles and DAS seismic records in the SE-4 well. We obtained 3D velocity structure and 3D migration image. We observed reflected phases and used them to make migration records. The results show good agreements between the production and the injection zones. The reflection phases for the DAS excited by the S9 seismic source could be a granodiorite rock intrusion body.
|3) Seismic study at the Sumikawa geothermal field in Akita Pref. Japan using a geothermal well|
Hasada・Hiroshi Ohnuma(1),Hitoshi Mikada(2),Yoshihiro Fujise(3)
|Jun. 7||11:00 -
This paper shows preliminary results of Curie point depth analysis of the Japanese Islands using East / Southeast Asia magnetic anomaly map by Ishihara and the magnetic data edited from the data of GSJ and NEDO. The analysis method is Bouligand, et. al. (2009) based on fractal theory. This analysis result was combined with the geothermal gradient / heat flow data, seismic data, Moho depth, topography and bathymetry. The analysis results show 5.5km at Mt. Iwate and 6.5km at Kakkonda geothermal power plant. In the cross section, high-frequency seismic events are concentrated in a place shallower than the Curie depth. Low-frequency events are distributed vertically around Mt. Iwate at a depth of 5-10km. Low-frequency seismic events occur in the ductile zone deeper than the Curie depth, which are interpreted to be caused by fluid flow associated with volcanic activity and occur within the ductile zone. Assuming that the events are caused by magma activity, it can be interpreted that there is a magma activity at a depth of about 10 km below the eastern part of Mt. Iwate.
|4) Curie Depth Study for Geothermal Exploration, Japan|
Yamano・Kazumi Osato(1),Takayuki Ichinohe(2)
1:Geothermal Energy Research & Development,2:JOGMEC
|Jun. 7||11:20 -
The magnetotelluric (MT) method is an electromagnetic exploration method that uses natural electromagnetic field variations to estimate the resistivity structure of the subsurface based on the ratio of the electric and magnetic fields. The MT method is used not only for geothermal exploration but also for mineral resource exploration and petroleum exploration. Furthermore, the MT method's ability to probe deep subsurface has been utilized in geophysical studies of the crust and mantle. The Exploration Geophysics Laboratory of Kyushu University has been developing a small MT system for more than a decade for subsurface resource exploration and monitoring subsurface fluids. The results of this research have been recognized by the Japan Oil, Gas and Metals National Corporation (JOGMEC), which has contracted us to conduct a two-and-a-half-year research project entitled "High-efficiency High-density Exploration Technology - Advanced MT Exploration Technique Using Small and Lightweight Equipment" under the contract with JOGMEC since FY2021. The main objective of this project is to "develop a compact and lightweight MT survey device," as the research title indicates, but the project also includes many related studies. This paper describes the purpose and goals of the project and provides an overview of the project as a whole.
|5) Advancement of MT exploration techniques utilizing compact and lightweight equipment (1)： Summary of the project|
Tanaka・Koji Hashimoto(1),Shinya Onodera(2)
|Jun. 7||11:40 -
Conventional MT measurement systems are rugged and heavy for use in harsh environments. Induction coils used to measure low-frequency magnetic field variations are particularly heavy and theoretically the lower the frequency, the worse the sensitivity. To improve sensitivity in the low-frequency range and reduce size and weight, the developed prototypes used triaxial MI sensor to measure the magnetic field. In order to develop effective compact and lightweight MT measurement systems within a limited period of time, three prototypes of different configurations (A-type, B-type, and C-type) were designed and developed simultaneously. A-type prototype has both the magnetic field sensor and the wireless module all built in. B-type has the magnetic field sensor connected externally and the wireless module built in. C-type has both the magnetic field sensor and the wireless module externally connected.
|6) Advancement of MT exploration techniques utilizing compact and lightweight equipment (2): Hardware design and prototyping|
Mizunaga・Koji Hashimoto(1),Shinya Onodera(2)
|Session||[Civil Engineering][Disaster Prevention 1][Infrastructure Maintenance]|
|Chair||Nobuo Takai (Hokkaido University)|
|Jun. 7||13:00 -
The targets and objectives of DC electrical exploration methods are becoming increasingly diverse and complex. For example, in seafloor electrical surveys, electrodes are placed in a multilayered structure that takes seawater into account, and it is essential to calculate the potential at arbitrarily placed electrodes in a horizontal multilayered structure. A fast and stable inverse analysis is also required for, e.g., environmental and disaster monitoring. In this study, we implemented a general-purpose potential calculation code for a horizontal multilayer structure and 3D arbitrary electrode configuration using Python and verified its accuracy by comparing it with previous studies. Furthermore, we have implemented an inversion code based on nonlinear least squares with Marquardt regularization for vertical electric sounding using the Schlumberger configuration and verified that the code has fast and stable analysis performance.
|7) Numerical Methods for Layered Earth Electric Potential with 3D Electrode Configuration using Python|
Ueda(1),Daijiro Uehara・Shusuke Oji(2)
|Jun. 7||13:20 -
A vibration measurement system using 79 GHz FM-CW MIMO radar was developed, and vibration measurement tests were conducted to evaluate its performance. A MIMO radar consists of 12 Tx and 16 Rx antennas and 100 Hz or above measurement rate has been achieved. As a result of the vibration measurement test, the vibration phenomenon of the bridge was visualized on a two-dimensional InSAR image as a time variation of the interference phase, and the vibration measurement at an arbitrary measurement point was realized.
|8) Vibration measurement by 79GHz MIMO radar|
1:CNEAS, Tohoku Univ.
|Jun. 7||13:40 -
The international standard for array measurement of microtremors to estimate shear wave velocity profile (ISO 24057) has been developing since the new proposal was approved in April 2019. The current stage is DIS as of April 2022. ISO TC182/WG9 (Geotechnical aspects of geophysical methods) is responsible for developing ISO 24057. SEGJ established the committee to support the standardization activities of geophysical surveys in geotechnics. The committee is preparing a proposal to standardize the surface wave exploration for the following action after publishing ISO 24057. Standardization of the geophysical surveys is essential to disseminate and assure the quality of the result.
|9) Activities on the standardization and the internationalization of the array measurement of microtremors and the surface wave exploration|
committee of the standardization of geophysical surveys in
|Jun. 7||14:00 -
In concrete dams, cracks tend to occur on the concrete surface along the concrete joints. Therefore, early detection and evaluation of cracks are necessary. Previous studies have conducted experiments using soils that are relatively softer than concrete and have proposed empirical equations and theories of energy interception. Minami et al.(2021) used these two methods to estimate crack depths and showed their applicability to concrete. And in this paper, to extend the estimation range, crack depths between measurement lines were estimated using data incident oblique to the crack. The results showed that a wide range of crack depths could be estimated with high accuracy.
|10) Estimation of crack
depth in concrete using attenuation effect of surface wave
-Extending the estimation range using obliquely incident surface wave-
Azuma・Yoshiya Oda(1),Toru Takahashi(2),Kyosuke Onishi(3),Shinichiro
1:Tokyo Metropolitan University,2:Fukada Geological Institute,3:Public Works Research Institute
|Jun. 7||14:20 -
Quality factor (Q value) is an essential parameter for evaluating wave propagation in subsurface, especially down to a depth of about 20 meters. In order to estimate the Quality factor of the subsurface, we conducted a surface wave survey near strong motion observation station in Ukishima, Kawasaki city. Measurements were performed with multiple measurement parameters to evaluate the effect of source-receiver distance and receiver spacing on the attenuation coefficient. After converting the measured waveforms into the frequency-phase velocity domain, only the Rayleigh wave fundamental mode component was extracted, and the attenuation coefficient was calculated. The dispersion curve was calculated from the measured waveform, and the 1D velocity was also estimated. The obtained attenuation coefficient and the estimated velocity structure were used to calculate the Q-value structure. As a result, only QS was obtained up to a depth of 6m, and QP was not obtained. It was found that the attenuation coefficients could not be obtained correctly without a sufficient source-receiver distance.
|11) Estimation of shallow subsurface quality factor using Multi channel analysis of surface waves|
1:DIA Consultants,2:RTRI,3:Tokyo Tech.
|Jun. 7||14:40 -
We conducted dense microtremor measurements in Kangori district and on the southern flank of Mt. Tsukuba, Tsukuba City, Ibaraki Prefecture. The survey covered the area about 10 square km, 3 km by 3.5 km for EW and NS direction respectively, with a total of 228 measurement points. A 3-component seismic data acquisition system (Atom-3C) was used for the microtremor measurements. Horizontal to vertical spectral ratio (HVSR) was calculated from the observed data and uploaded to an open geophysical database site named “SeisImager.com”. The peak frequencies of HVSR in the survey area varied from 0.9 to 17 Hz, and showed characteristic features as follows; namely, relatively low frequency peaks were predominant in the Kangori Lowland. Predominant frequency descended from margin to center, and from east to west. HVSRs, observed on the southern flank of Mt. Tsukuba generally had clear peaks in a relatively higher frequency zone compared to those observed in the Kangori Lowland. We estimated S-wave velocity models from the HVSR curves, and successfully imaged the basement structure of the survey site up to 1km in depth.
|12) Mapping of near surface S-wave velocity structure based on H/V spectral ratio of microtremor measurements conducted on southern flank and foot area of Mt. Tsukuba.|
|Jun.7 Core Time: Room No.1 or SpatialChat, Exhibition: Exhibition Room or Online|
|Session||[Poster Sessions: Core Time]|
|Chair||Toshiaki Tanaka (Kyushu University)|
|Jun. 7||15:20 -
It is requested to explore the underground resources in space research projects for the human space program. GPR(Ground Penetrating Rader) can identify underground resources nondestructively. Therefore, it can be useful for human space exploration. However, commercial GPRs cannot be improved in terms of using antenna and frequency. A wide range of frequencies is needed to visualize the underground resources. There are three advantages of building your own GPR transmitter. The first is that it can be used for a wide range of frequencies, the second is that it is inexpensive, and the third is that it can be used for high performance.The purpose of this research is to develop an inexpensive and high performance GPR transmitter and to realize the detection of underground structures in the meter class by using a hand-held GPR. In the experiment at the main building of Kami Campus, Kochi University of Technology, we observed the reflection waveform possibly coming from the underground structure, and it was found that the hand-held GPR could detect the underground structure.
|P-1) Trial manufacture of a simplified GPR and detection of buried objects|
1:Kochi University of Technology
|Jun. 7||15:20 -
We developed a simplified instrument for the DC resistivity survey, based on the digital multimeters. Although such geophysical instrument is expensive (higher than several thousand USD or more), our system is made from the conventional electric items obtained at DIY shop (about 120 USD). By using the self-made system, subsurface resistivity structures were obtained across an active fault (the Kuresakatoge fault, one of the Yamasaki active faults). The one-dimensional analysis of DC resistivity survey data revealed a low resistivity zone, inferred as a damage zone with a fault core. A horizontal heterogeneity of resistivity near the fault is also imaged, possibly related to dislocations along the fault.
|P-2) Development of Simplified DC-Resistivity Measurement System and Its Application to Active Fault Explorations|
Kuroda・Soma Yamamoto・Rei Amano・Sena Fujimoto・Yuki Oshima・Nagi
|Jun. 7||15:20 -
We measured the resistivity of sediment sample infiltrated with highly-viscous mud fluid, and investigated the relationship between mud fluid saturation and the resistivity. River-bed sand, mixed with gravel and fine sand, was used. As a result, the mud fluid sample indicates resistive feature at low saturated condition, higher than the samples filled by tap water. The main cause seems to be a restriction of the capillarity of mud fluid.
|P-3) Relationship between resistivity and saturation of sediments containing highly viscous pore fluids|
Kimura・Tomoki Maeda・Takaharu Yamada・Kenji Hagiya(1)
|Jun. 7||15:20 -
There are concerns that unplanned use of groundwater as a water source in the event of a major earthquake or other disaster may cause various problems such as widespread land subsidence and increased risk of flooding. A water cycle analysis system is used for planned pumping, but in order to improve the accuracy of the analysis, it is necessary to properly understand the geological structure, hydraulic structure, and groundwater level. For the purpose of efficiently and accurately ascertaining these factors, a drone airborne electromagnetic survey method has been conducted in the Seino region of Gifu Prefecture since 2019. This year, for the purpose of social implementation, ground-based D-GREATEM and airborne D-TEM were conducted twice in the Seino region of Gifu Prefecture, during the high and low rainfall seasons, and were confirmed to be effective in determining groundwater levels. By conducting the survey over a wide area, it is possible to determine the groundwater recharge rate in the study area. In this presentation, we will report the results of the two survey results obtained by the two methods.
|P-4) Geological survey using drone airborne electromagnetic survey method|
Shinsei・Satoshi Tomimori・Akiyo Yamaguti(1),Akira Jomori(2)
1:Oyo corporation,2:Neo Science
|Jun. 7||15:20 -
Clustering inversion is constructed by introducing a combination of Fuzzy c-me an (FCM) clustering constraint and cluster forcusing constraint in real space for the purpose of realizing geological differenceation. However, this inversi on method has a "strong parameter dependency", and it is inevitable to take me asures against it in order to apply it at the practical level. Therefore, the following modifications have been made to the inversion algorithm, (1) modific ation of the method of implementing the objective function into the optimizati on algorithm, (2) normalization of the objective function by the numbers of ob servation values, blocks, cluster centers, and (3) incorporation of the indexe s of "contribution rate" of constraints and monitoring them during the converg ence process. As a result, the parameter dependence is relaxed and the analysi s results with stable quality can be obtained. Here, we report the outline of the algorithm modification and the result of ap plying it to the airborne gravity gradiometer-magnetic data acquired in the ar ea around the Pea Ridge deposit in Missouri, USA.
|P-5) Development of clustering inversion of potential field data for geological differentation (2) Algorithm modification and application to airborne gravity gradiometer and magnetic survey data|
|Jun. 7||15:20 -
The results of seismic motion simulations are affected not only by the subsurface structure but also by the model of the ground surface geometry. In order to evaluate seismic motions accurately over a wide bandwidth, it is important to reflect both the ground structure and topography appropriately in the numerical model. We described the modification of the code as a seismic ground motion simulation tool and the extent to which the numerical modeling of both the ground surface boundary and the subsurface medium boundary of the surface soil affects the results of seismic motion simulations. These results should provide insight into the appropriate exploration density and procedures for numerical modeling and model.
|P-6) Influence of Numerical Modeling of Subsurface Structure and Microtopography on ground Motion Calculation|
1:Kochi University,2:Tokyo Institute of Technology
|Jun. 7||15:20 -
We estimated a three-dimensional (3D) S-wave velocity (Vs) model of the Napa, California, U.S. using microtremor array measurements (MAM) and horizontal to vertical spectral ratio (H/V) at approximately 100 sites. MAM was collected with seven to twenty 2 Hz geophones, and the maximum receiver spacing ranged from 30 to 1500 m. Ambient noise for MAM and H/V were collected for 20 to 120 minutes. A spatial auto-correlation (SPAC) method calculated phase velocities from the vertical component of ambient noise. Minimum frequency of dispersion curves ranged from 1 to 10 Hz. H/V was calculated from three-component (3C) seismic ambient noise using a single 3C 2Hz geophone. The peak frequency of H/V ranged from 0.25 to 10Hz. Joint inversion of a dispersion curve and H/V spectrum estimated Vs profiles to 30 to 1000 m depth. We compiled all H/V and Vs profiles, and estimated a 3D Vs model to a depth of 1000 m. The Vs30 obtained from the MAM ranged between 200 m/s and 970 m/s. Clear H/V peak frequencies of 0.25 to 0.4 Hz were consistent in the valley floor. The depth to the bedrock with Vs of 760 m/s ranged between almost surface to greater than 300 m.
|P-7) Three-Dimensional S-wave Velocity Model of Napa Velley obtained from Microtremor Array Measurements and Horizontal to Vertical Spectral Ratio|
1:OYO Corporation,2:Napa Valley College,3:Geometrics Inc.
|Jun. 7||15:20 -
The acoustic characteristics of gas are greatly affected by the effect of resonance. When the acoustic frequency approaches the resonant frequency of the bubble, the velocity and attenuation of the acoustic wave change dramatically due to the gas bubble resonance induced by acoustic wave propagation. The bubble resonance frequency significantly depends on the bubble size. Therefore, the content and size of the bubble calculated by analyzing the acoustic characteristics can predict the gas reservoir. In methodology of numerical analysis, we focus on phase velocity dispersion inversion for bubble radius. The velocity of gas-charged sediment are frequency-dependent, which is challenged for traditional method of inversion. This study proposes use deep learning to capture velocity information and predict bubble radius. From the perspective of simulation, we prove that the deep learning model can well predict the size of bubbles, and it can be used to predict the potential reservoir of seabed bubbles. Furthermore, we performed a preliminary application to ultrasonic laboratory experimental data and demonstrated the effectiveness of the proposed method.
|P-8) Phase velocity dispersion estimation in gas-charged sediments by deep learning inversion|
1:Univ. of Tokyo
|Jun.8 Room No.1 (Conference Room 1，3F)|
|Session||[Buried Objects][Groundwater][Disaster Prevention 2]|
|Chair||Chisato Konishi (OYO Corporation)|
|Jun. 8||10:20 -
Elastic wave velocity is a composite parameter of density and elastic constant, and it is difficult to separate them by elastic wave exploration alone. However, by separating both parameters, it is expected that the uncertainty in the interpretation of the underground structure will be reduced. In order to separate both parameters, a joint inversion method using muon tomography, which is a density estimation method using cosmic ray muons, and elastic wave exploration was considered. In this study, a joint inversion method using FCM clustering was examined. Numerical calculations for a simple model suggest that the joint inversion method using FCM clustering may improve the estimation results of density and elastic wave velocity.
|13) Study on the joint inversion of muography and elastic wave exploration|
Yokota(1),Jun Matsushima(2),Hiroyuki Tanaka(3),Tadahiro Kin・Naoya
1:AIST,2:The Univ. of Tokyo, GSFS,3:The Univ. of Tokyo, ERI,4:Kyushu Univ.
|Jun. 8||10:40 -
A new ground penetrating radar (GPR) system that can measure the full-polarimetric scattering matrix with phase information was completed. It has orthogonal pairs of transmit and receive antennas and can measure two orthogonal polarizations at the same position. GPR images at any orientation angle of the antenna alignment can be reproduced by the mathematical polarization basis transformation from a measured data. We demonstrated that we can measure buried objects independent of the measurement polarization direction.
|14) Development of a Full-polarimetric MIMO GPR System|
|Jun. 8||11:00 -
By 2011 Typhoon Talas, many deep-seated landslides occurred in the Kii mountainous area and caused great damage. In future measures against the landslides, it is important to properly evaluate the risk of the landslides. We focused on geophysical exploration technology as one of the risk assessment methods. We conducted the helicopter airborne electromagnetic survey, the drone airborne transient electromagnetic measurements, and the electrical prospecting on the slopes of the Tochio district in Tenkawa Village, Nara Prefecture. The resistivity distributions from these geophysical explorations were compared with the boring survey and groundwater level data. The helicopter airborne electromagnetic survey and the electrical prospecting were conducted during the dry season in November 2012 and December 2021, respectively. the drone airborne transient electromagnetic measurements were conducted in two periods, October (flooding period) and December (dry period), 2021 for the purpose of investigating the effect of faults on the movement of groundwater. The geophysical exploration was found to be effective in assessing the risk of the landslides. It was also found that the risk level can be evaluated more accurately by conducting multiple geophysical surveys.
|15) Identification of slopes at very high risk of deep-seated landslides in the Kii mountainous area through a helicopter airborne electromagnetic survey and drone airborne transient electromagnetic measurements|
Kitamoto(2),Takao Yamakoshi・Hiroaki Nakaya(1),Katsushi Kawato・Minoru
Okumura・Kentaro Kanayama・Hiroshi Baba(3),Akira Jomori(4)
1:National Institute for Land and Infrastructure Management,2:Sediment Disaster Prevention Technology Center,3:NIPPON ENGINEERING CONSULTANTS CO.,LTD.,4:NEOSCIENCE CO.LTD.
|Jun. 8||11:20 -
In 2012-2013, The National Institute of Advanced Industrial Science and Technology (AIST) conducted geophysical surveys using frequency-domain airborne electromagnetic (AEM) exploration and ground time-domain electromagnetic (TDEM) survey to investigate the infiltration of tsunami saltwater into the ground and the distribution of saline aquifers in the Southern Sendai Plane Coastal Region, which was inundated by the 311 tsunami. In the previous study by AIST, commercial inversion software, based on the nonlinear least-squares method (NL- LSM), was adopted for estimating the subsurface geoelectrical model for TDEM data interpretation. However, NL-LSM inversions often exhibit instability and depend on the initial model. In this study, we aim to overcome this problem, implement a novel approach of regularized gradient type inversion called re-weighted regularized conjugate gradient (RRCG) by Zhdanov (2015), and applied developed methods for field TDEM data acquired by AIST. Then, we have integrated the lateral constraint (LC) into the RRCG code. This algorithm, named LC-RRCG, can obtain a smooth geoelectrical model with horizontal continuity by inversion of multiple observed locations at a time. The results of LC-RRCG revealed the effectiveness of the lateral constraint in all survey lines of Tohoku coastal TDEM data. Therefore, LC-RRCG, combining the two methods, such as RRCG and lateral constraint, can be a powerful tool for practical TDEM inversion.
|16) 1D Layered Tikhonov Regularized Conjugate Gradient Inversion and Application of Horizontal Constraint for Onshore TDEM Data observed at Southern Sendai Plane Coastal Region|
1:Waseda Univ.,2:GSJ, AIST
|Jun. 8||11:40 -
It has been pointed out that groundwater with high NO3- concentrations originating from adjacent grazing and cultivation lands may be gushing into forested streams beyond the watershed boundary determined from the topography in forests located on the Konsen Plateau, Eastern Hokkaido. Since the topographic and subsurface watersheds may not coincide with each other, we have evaluated the subsurface watersheds of forests on the Konsen Plateau, Eastern Hokkaido using microtremor array surveys. As the result, the watershed based on subsurface structure would be located east side of topographically determined watershed. We also discussed the applicability of the microtremor array survey to the forest area. As a result, the usefulness of the microtremor array survey was demonstrated in areas with dense vegetation such as forests and swamps.
|17) Evaluation of the watershed boundary of forests on the Konsen Plateau, Eastern Hokkaido, using microtremor array survey.|
Oda(1),Keitaro Fukushima・Koki Nagasawa(2),Hikaru Ota(1)
1:Tokyo Metropolitan Univ.,2:Kyoto Univ.
|Chair||Keiichi Suzuki (Kawasaki Geological Engineering Co., Ltd.)|
|Jun. 8||13:00 - 14:00||Tsutomu Nakazawa (AIST)|
|Jun. 8||14:00 - 15:00||Kazuyoshi Takaichi (ITOCHU Techno-Solutions Corporation (CTC))|
|Jun.9 Room No.1 (Conference Room 1，3F)|
|Session||[Earthquake][Disaster Prevention 3]|
|Chair||Nobuyuki Yamada (Kochi University)|
|Jun. 9||9:40 -
A 2D microtremor array survey was conducted in Taihaku Ward, Sendai City, for estimation of the shallow S-wave velocity structural model across the Nagamachi-Rifu line fault zone. The S-wave velocity structure and peak frequency of H/V spectral ratio changed slightly east of the main fault at the leading edge based on topographic interpretation.
|18) 2D microtremor array measurements for estimation of shallow subsurface structural model in Nagamachi-Rifu line fault zone.|
Haruhiko(1),TAKAHASHI Naoya・YOSHIMI Yoko・NAKAMURA Tomoki・NORIMATSU
Kimie(2),MATSUYAMA Hisanori(1),TODA Shinji(2)
|Jun. 9||10:00 -
In the central part of Yahaba Town, where site amplification factors in the J-SHIS has been revised significantly, we conducted simultaneous microtremor array observations with a radius of 0.6 m and ones with a radius of about 10 m to obtain the S-wave velocity structure down to 30 m below a surface and evaluated the distribution of site amplification factors. The average S-wave velocity calculated from the estimated S-wave velocity structure was 193 - 409 m/s, which was small on the west side and large on the east side. Furthermore, the amplification factor calculated from the estimated S-wave velocity structure was 0.98 - 1.86. On the east side of Yahaba Station, the observed factor was about 1.5 and the that of J-SHIS was about 1.9, and the observed value along National Route 4 was about 1.3 and that of J-SHIS was about 1.5, which were relatively close. However, the observed value on the west side of Yahaba Station was about 1.8, while that of J-SHIS was about 1.0, showing a large difference. A comparison of the seismic intensities in the questionnaire with the amplification factors obtained from the microtremor observations were good agreement with those on the west side of Yahaba Station.
|19) Site amplification characteristics in central Yahaba Town, Iwate Prefecture by using dense microtremor array surveys|
|Jun. 9||10:20 -
The Shonai Plain has no detailed subsurface structure estimated, and is required to be modeled for earthquake countermeasures. In this study, microtremor array method was used to estimate the engineering bedrock shape, which is important for ground modeling. In addition, the elevation of the engineering bedrock was estimated using various methods, including the S-wave velocity structure, the equation relating N-value to S-wave velocity, and the H/V spectral ratio. As a result, the elevation of the engineering bedrock was found to be almost monotonically lower from east to west, with the contour line overhanging to the east in some places. Also, the elevation of the engineering bedrock estimated from the S-wave velocity structure of 3 or 4 layers were consistent with the engineering bedrock elevation obtained from borehole logs.
|20) Estimation of the Engineering Bedrock Shape in the Shonai Plain Using Microtremor Array Survey|
Oda(1),Tsutomu Ochiai・Takahisa Enomoto(2),Hiroyuki Azuma(1),Kazuya
1:Tokyo Metropolitan Univ.,2:Kanagawa Univ.,3:Yamagata Univ.,4:NIED
|Jun. 9||10:40 -
We carried out the surface wave exploration by multi-channel active source and microtremor array measurements in Kitami city of the cold region to understand the seasonal variation of the shallow underground structures. We set the artificial irregularity by being sand backfilled to know the detection performance for irregularity and the effect of underground water level. We observed the surface wave method with short interval geophones and array measurement with a short radius to grasp the shallow surface seasonal variation and irregularity. We can see that the recorded waveforms are changed by several seasons. We analyzed F-K spectra from these waveforms to get the phase velocity of the Rayleigh waves. From these results, we grasped the phase velocity variation from October to February. The wave packets are simple in the cold season. The phase velocities of the cold season are higher than those of the other seasons.
|21) Study on the Seasonal Variations of the Surface Underground Structure in Kitami City using High-Density Multi-Channel Surface Wave Exploration Method|
Nakagawa・Momoko Iwazaki(1),Jun Horita・Shingo Nomoto・Tetsunori
Kishikawa(2),Michiko Shigefuji(3),Shunzo Kawajiri(4),Seiji Tsuno(5),Hiroaki
1:Hokkaido Univ.,2:Geotechnical Research,3:Kyushu Univ.,4:Kyushu Tech.,5:RTRI,6:Tokyo Tech.
|Jun. 9||11:00 -
To evaluate the effects of seasonal variation in the irregularly layered media due to the freezing in the cold region, we carried out continuous seismic observations including a shallow borehole and weight-drop measurement at a site with a softly change of soil materials, in Kitami city. In this paper, we reported the outline of the observations and measurements, and we showed the results of initial analysis by weight-drop excitation data in a linear array.
|22) Study on the site amplification characteristics of irregularly layered media in the cold region by the weight-drop excitation data and borehole seismic data at Kitami city|
Yamanaka(2),Nobuo Takai(3),Shunzo Kawajiri(4),Naofumi Nakagawa(3),Michiko
Shigefuji(5),Akinobu Ogasawara(6),Shingo Nomoto・Tetsuhiro Kishikawa・Jun
1:RTRI,2:Tokyo Tech.,3:Hokkaido Univ.,4:Kyushu Tech.,5:Kyushu Univ.,6:Toyota College,7:Geotech.
|Jun. 9||11:20 -
We applied seismic reflection imaging based on reverse-time migration (RTM) to teleseismic records to reveal the crustal-scale structures. RTM imaging calculates the wavefield in the forward and the backward direction in time and then applies the imaging condition to construct reflection images. First, we performed numerical simulations and examined the advantages of the use of teleseismic records. The effect of receiver density on imaging was examined using different receiver alignments. Then, we conducted seismic imaging of teleseismic records observed using both temporal observations and seismic networks in the Kinki region from 2005 to 2009. The reflection image shows the land Moho and reflective structures in the crust, which are consistent with the receiver function analysis, seismic tomography, and the reflection survey conducted near the survey lines. The structure of the subducting Philippine Sea plate was not well imaged. The reasons for this may include the effects of the inhomogeneous and scattering nature of the crust and the effects of waves from outside the cross-section as well as the effects of the density and arrangement of seismic stations and the effects of velocity structure.
|23) Application of reverse-time seismic reflection imaging to teleseismic records|
Watanabe(1),Kazuya Shiraishi(2),Takuo Shibutani(3)
1:Nagoya Univ.,2:JAMSTEC,3:Kyoto Univ.
|Jun. 9||11:40 -
The Exploration Geophysics Laboratory of Tokyo Metropolitan University conducted temporary seismic observation on Hachijojima in 2019 and 2021. The purpose is to detect earthquakes and to determine the subsurface structure using seismic wave propagation. It is necessary to detect as many earthquakes as possible to improve the accuracy of the subsurface structure. We have applied several deep learning methods to detect earthquakes from continuous observation records. The use of deep learning has the effect of reducing labor and potential to detect earthquakes that are difficult for humans to find. This paper focuses on these deep learning “methods” and provides a more detailed description of those methods.
|24) Seismic wave detection method by deep Learning applied to temporary seismic observation data at Hachijojima Island|
Kunimasa・Ryohei Tottori・Yoshiya Oda(1)
1:Tokyo Metropolitan University