STT13-01

会場:102A

時間:5 月 27 日 14:15-14:30

グラウンドアンカーのアンカー体定着部の支持機構の解明
Numerical interpretation of anchoring mechanism by using Bonded Particles Model
水戸 義忠 1 ; 西田 昂平 1∗
MITO, Yoshitada1 ; NISHIDA, Kohei1∗1
1

京都大学大学院工学研究科
Fac. of Engineering, Kyoto University

グランドアンカーは地盤や構造物の補強手段として，多くの施工実績を数えている．アンカー体の構造形式は種々提案されているものの，その定着部におけるアンカー体および地盤の相互挙動については十分に解明されているわけではない．本研究ではアンカー支保の効果や適用限界の定量的な評価技術の向上を目指し，地盤内の亀裂の進展挙動を現実に近い形でシミュレートすることができることが知られている結合粒状体モデルを用いた個別要素法により，アンカーの引っ張り試験時におけるアンカー体定着部の力学挙動をシミュレートした．その結果，基本的な力学挙動を適切に表現することができた．
キーワード: グランドアンカー, 個別要素法, 亀裂発生・進展
Keywords: ground anchor, distinct element model, crack initiation and propagation

1/1

STT13-02

会場:102A

時間:5 月 27 日 14:30-14:45

高速電気探査装置を用いた不飽和帯浸透水の 3 次元経時モニタリング
3D Time-lapse monitoring of water infiltration in the vadose zone by means of a highspeed resistivity measurement tool
稲崎 富士 1∗ ; 今村 杉夫 2 ; 坂西 啓一郎 3
INAZAKI, Tomio1∗ ; IMAMURA, Sugio2 ; SAKANISHI, Kei’ichiro3
1
1

土木研, 2 地圏探査技術研究所, 3 モニー物探Public Works Research Institute, 2 CTGK Ltd.,, 3 Mony Ltd.,

Infiltration process of water into the surficial vadose zone of an embankment was monitored at short intervals by means ofa newly developed high-speed resistivity measurement tool. The tool can transmit 24 individual current signals and measure
24 potential responses simultaneously. A code division multiple transmission technique was adopted for the current signaltransmission. It took only 30 seconds to obtain and store a dataset composed of a total of 576 (24 by 24) potential data along withtime series waveforms. The tool enabled us to conduct high-speed time-lapse or dense 3D resistivity measurements in the field.
We monitored infiltration process of surface water into the vadose zone of an actual embankment. A total of 4 current lines and4 potential lines were set parallel on a flank of the embankment, and infused water into the vadose zone through a narrow andshallow trench dug on the crest. Electrode stakes were placed at 25 cm spacing along each line, and spacing between the lines
was set to 50 cm. A total of 6,912 (12 pairs x 576) data were acquired at 5 min intervals in the beginning and at 30 min later.
3D electrical resistivity tomography (ERT) analysis, applied to the dataset composed of a total of 40 stages during the infiltration
across two days, successfully imaged the extent of infiltrated water in the vadose zone. Consequently, our field measurements
demonstrated the usefulness of dense time-lapse 3D ERT monitoring for the characterization of dynamic unsaturated permeabilityof the vadose zone of embankments in the field.
キーワード: 比抵抗, 不飽和帯, 浸透, 経時モニタリング, 3 次元
Keywords: resistivity, vadose zone, infiltration, time-lapse monitoring, 3D

1/1

STT13-03

会場:102A

時間:5 月 27 日 14:45-15:00

Reliability of hydraulic conductivity and specific storage structures estimated by Self potential inversion.
Reliability of hydraulic conductivity and specific storage structures estimated by Self potential inversion.
尾崎 裕介 1∗ ; 三ケ田 均 1 ; 後藤 忠徳 1 ; 武川 順一 1
OZAKI, Yusuke1∗ ; MIKADA, Hitoshi1 ; GOTO, Tada-nori1 ; TAKEKAWA, Junichi1
11

京都大学工学研究科
Graduate School of Engineering, Kyoto University

The objective of this study is evaluation of reliability of estimated hydraulic conductivity and specific storage structure fromself-potential (SP) data under the realistic condition. The hydraulic conductivity and specific storage could be estimated from atransient SP inversion with the information of flux data. We have demonstrated that these parameters could be estimated withhigh resolution numerically in ideal case such that the required data is enough and artificial structure can be negligible. However,such condition is rarely satisfied in many field cases. As one of difficulties, the lack of flux data is assumed. The sampling rate of
the measurement of flux data could be too low because of the difficulty of measurement. We adopt the spline interpolation to asparse sampling data, and evaluate the reliability of estimated image using numerical tests. We calculate the SP signals following
to the fluctuated pumping rate. We use the calculated SP signals with same sampling rate as calculation as an input data in the
numerical test. The down sampled flux data is assumed to be the measured data in the test. Our numerical test shows that bothhydraulic conductivity and specific storage structure can be estimated correctly from the interpolated deficient flux data withthe trend almost same as the true variation. When the interpolated deficient flux data does not reconstruct the trend of the truevariation, only the hydraulic conductivity structure can be estimated with low resolution while the specific storage could not be
estimated at all.
In addition to the lack of flux data, the existences of artificial structures are also the obstacles for the SP inversion in a real
field. For example, a high-conductive metallic casing pipe leads the SP signal far from the SP source without decrease of theelectrical potential. Therefore, the estimated image ignoring this effect would be biased. We also evaluate this effect by numericaltests. The SP singles affected by the metal casing are used for the inversion test without considering the effect. Both hydraulicconductivity and specific storage near the metal casing in the inversion image are estimated to be a little lower than those of thetest model. In addition, the strong artifact appears in the estimated image of specific storage. From these results, we conclude
that the estimated image of hydraulic conductivity structure is robust under such unrealistic conditions. For the correct estimationof specific storage structure, the flux data with high quality is necessary.

キーワード: Self potential, Inversion, Hydraulic conductivity, Storage coefficient, Metal casing, Interpolated data
Keywords: Self potential, Inversion, Hydraulic conductivity, Storage coefficient, Metal casing, Interpolated data

1/1

STT13-04

会場:102A

時間:5 月 27 日 15:00-15:15

採石場地域における、人工震源を用いた 2 か月間の陥没モニタリング実験：震源近傍における観測An experiment of subsidence monitoring in the quarry area by a seismic source during
two months: near source observation
上村 彩 1∗ ; 笠原 順三 1 ; 藤井 直之 1 ; 牛山 素行 1
KAMIMURA, Aya1∗ ; KASAHARA, Junzo1 ; FUJII, Naoyuki1 ; USHIYAMA, Motoyuki1
1
1

静岡大学
Shizuoka Univ.

Introduction
We tested to monitor temporal changes in the subsurface at the quarry area. At this quarry, there is a subsidence warning
system to detect micro-earthquakes associated with the subsidence measured by seismometers. At the past subsidence, seismic
vibrations were repeatedly observed during several months, but the 2014 subsidence showed only four vibration events preceding
to the subsidence. It is thought that if we can observe any other temporal changes of the subsurface before the vibration, we could
help to find subsidence. Therefore we carried out ”seismic time-lapse observation”. We used a control seismic source on the
ground at fix location, and tested whether any changes of the subsurface changes during the observation period was caught ornot.
Field test
We carried out one-week experiments twice in July and August of 2014. The first and the second experiments were from 16
to 21 in July and from 21 to 25 in August, respectively. We used electro-magnetic vibrator developed by Kawasaki GeologicalEngineering Co. Ltd as the seismic source. We set 100-second sweep from 10 to 50 Hz and 5-second rest with the GPS time
accuracy and repeated 32 sweeps with 5 second rest in an hour. We operated the vibrator 12 hours consecutively at night (20:00- 08:00).
We recorded accelerations signals of reaction-mass and base-plate with desired signals, and seismic waves at east of the source,
south of the source, and near the source. Local warning system of 97 geophones also recorded these artificial seismic data.
Analysis
We carried out FFT conversions of observed data. We transformed two sweep sequences of seismic records to the frequency
domain and stacked 16 sets of data in 1 hour. We calculated source signature using the reaction-mass and the baseplate accelerations of the vibrator. The transfer functions between the source and a receiver were obtained by the division of observed spectra
by source signature. After applied window function in spectral domain, we inverse-transformed the data into a time domain.
Results
In this paper we report the characteristics near the source. When we set the amplitude of seismometer beside the source was100, that of eastern seismometer (ca. 35m east of source) was 5, and that of southern seismometer (ca. 45m south of source) was
2 (vertical axis). The transfer function of 18 and 19 of July showed a change in comparison with others periods. There were few
changes of the transfer functions during an experiment period of August.
Discussion and conclusions
We checked the weather condition during experimental periods. On July 18 03:00-04:00, 28mm/hour rainfalls measured by
the neighboring precipitation observatory, and intense thunderstorm was recorded at the test field. In other periods, such heavy
rainfalls were not observed. From these data, it is thought that the near surface layers including the water by rainfalls changed
the transfer function of the test field.
Acknowledgements
This study was supported by the Center for Integrated Research and Education of Natural Hazard, of Shizuoka University. The
field experiments was carried out by Kawasaki Geological Engineering Co., Ltd.
References
Kasahara, J., et al., Real time Imaging of CO2 storage zone by very accurate-stable-long term seismic source, Energy Precedia,
2013d.
Kasahara, J., et al., Observation of very larger temporal changes due to the near surface effects and importance on the timelapse study, Proc. Soc. #130 Exploration Geophysicists of Japan, 212-215, 2014.
Kubota, R., et al., Development of the Seismic ACROSS using electro-magnetic vibrator, Proc. ”2nd KACST-KCUST-JCCP
international workshop on Surface and Subsurface 4D Monitoring”, KAUST Feb. 2014.
Kunitomo, T., et al., Active monitoring of the Earth’s structure by the seismic ACROSS - Transmitting and receiving technolo-

1/2

STT13-04

会場:102A

時間:5 月 27 日 15:00-15:15

gies of the seismic ACROSS, Proc. 1st International Workshop ”Active Monitoring in the Solid Earth Geophysics”, in Mizunami,
Japan, S4-04., 2004.
キーワード: タイムラプス, 人工震源, 陥没, 地震学的手法, 防災
Keywords: time lapse, artificial seismic sourcce, subsidence, seismic method, disaster prevention

2/2

STT13-05

会場:102A

時間:5 月 27 日 15:15-15:30

陥没地域における時間変動イメジング
Imaging of temporal changes at the surface subsidence area
笠原 順三 1 ; 藤井 直之 1∗ ; 羽佐田 葉子 2 ; 上村 彩 3 ; 牛山 素行 1
KASAHARA, Junzo1 ; FUJII, Naoyuki1∗ ; HASADA, Yoko2 ; KAMIMURA, Aya3 ; USHIYAMA, Motoyuki1
1
1

静岡大学防災総合センター, 2 大和探査技術（株）, 3 川崎地質（株）
CIRENH of Shizuoka University, 2 Daiwa Exploration and Consulting Co. Ltd., 3 Kawasaki Geological Engineering Co. Ltd.

Introduction
We have carried out seismic studies to monitor the temporal change of subsurface in CCS, EOR and oil/gas reservoirs. For
these studies, we have used ultra-stable seismic source called ACROSS (Accurately Controlled and Routinely Operated Signal
System) (Kunitomo and Kumazawa, 2004). Because ACROSS seismic source is usulally installed in heavy concreate block, it isdifficult to rellocate from one place to another. Instead, we used a conventional seismic source for this study. We carried out thetime lapse experiments at one of quarry sites in Japan.
Method and Field observation
A conventional electro-magnetic seismic source with the modification of ACROSS methodology (Kubota et al., 2014) wasused. A set of 100-second sweep from 10 to 50 Hz and 5-second rest with the GPS time accuracy was repeated 32 times in anhour. Seismic data of 97 15-Hz vertical geophones buried at 20 m depth and two 4.5-Hz borehole seismometers at 70 m and 200
m depths were sampled every 1 ms by the GPS time base too.
We repeated two observations in July and August in 2014. The first and the second one were between 16 and 21 in July andbetween 21 and 26 in August 2014, respectively. The size of the quarry is 2 km x 4.4 km. The experiments were only during thenight time from 8 PM to 8 AM.
Analysis
We used similar analysis as the ACROSS processing (Kasahara et al., 2014). Observed data (1 or 12 hours) were stacked.
Transfer functions between source and receivers are obtained by division of observed records by source signature calculated byaccelerations on reaction mass and base plate. By 210 seconds (two sweeps) data for first stage stacking, we could estimate noise
spectra. As the final stage, the residual waveforms of P portion were back-propagated by the method developed by Kasahara etal (2011).
Results
We obtained transfer functions for all datasets. By use of one hour data, we can clearly identify P arrivals up to 1.7 km distance.
The transfer functions are quite stable though the seismic source is conventional type because we kept the seismic source at thesame condition at the fixed point. However, if we compare the waveforms obtained in December 2013 with ones obtained in Julyor August 2014, we can notice large changes due to the differences of source installations.
Even within each week in July or August, the residual waveforms show changes just after P first arrivals. The P coda might bechanged by temporal change of very shallow layers. By the back-propagation, we obtained the time-lapse image of the changing
area. The changing areas are in two directions such as NW and SWW and they seem similar to the previous subsidence zone
since 2000.
Acknowledgements
This study was supported by the Center for Integrated Research and Education of Natural Hazard, of Shizuoka University.
The field experiments were carried out by Kawasaki Geological Engineering Co. Ltd.
References
Kasahara, J. et al., Imaging of ultra-long term temporal change of reservoir (s) by accurate seismic sources(s) and multireceivers, in Extended abstract of ”EAGE workshop on Permanent Reservoir Monitoring (PRM)”, 40-44, Feb.-Mar., Trondheim,
Norway, 2011.
Kasahara, J. et al., Real time Imaging of CO2 storage zone by very accurate-stable-long term seismic source, Energy Precedia,
2013.
Kasahara, J. et al., Observation of very larger temporal changes due to the near surface effects and importance on the time-lapse
study, Proc. Soc. #130 Exploration Geophysicists of Japan, 212-215, 2014.
Kubota, R. et al., Development of the Seismic ACROSS using electro-magnetic vibrator, Proc. ”2nd KACST-KCUST-JCCP
international workshop on Surface and Subsurface 4D Monitoring”, KAUST Feb. 2014.
Kunitomo, T., and Kumazawa, M., Active monitoring of the Earth’s structure by the seismic ACROSS - Transmitting andreceiving technologies of the seismic ACROSS, Proc. 1st International Workshop ”Active Monitoring in the Solid Earth Geophysics”, in Mizunami, Japan, S4-04., 2004.
1/2

STT13-05

会場:102A

時間:5 月 27 日 15:15-15:30

キーワード: タイムラプス, 地震波イメジング, 逆伝搬, 陥没, アクロス, 地震学的手法
Keywords: time lapse, seismic imaging, backpropagation, subsidence, ACROSS, seismic method

2/2

STT13-06

会場:102A

時間:5 月 27 日 15:30-15:45

数値シミュレーションに基づく微視的なシリカスケール成長に対する流体力学的影
響の検証
The Hydrodynamic effect on silicate scale growth in microscopic flow inferred from numerical simulation.
水島 諒大 1∗ ; 三ケ田 均 1 ; 後藤 忠徳 1 ; 武川 順一 1
MIZUSHIMA, Akihiro1∗ ; MIKADA, Hitoshi1 ; GOTO, Tada-nori1 ; TAKEKAWA, Junichi1
1
1

京都大学大学院工学研究科
Kyoto University, Graduate School of Engineering

Formation of inorganic sparingly-soluble salts, anhydrite and silica from brine is known as a cause of scale in pipeline systems.
Scaling is a key phenomenon to understand fluid-flow system in subsurface or sub-seafloor structure, because the scale growthstrongly affects the fluid circulation of subsurface or sub-seafloor hydrothermal systems by chocking any flow channel.
Several works (Takeno et al. 1998; Bolton et al., 1999) simulated the subsurface permeability change by the silica precipitation using the deposition rate law formulated on the basis of the simple kinetics (Rimstidt and Barnes, 1980). However it has
been reported that the predicted magnitude of the deposition rate is extremely slower than measured values in the laboratories(Malate and O’Sullivan, 1992; Weir and White, 1996). By the way, a high rate growth of scale is often observed where the flow
stagnates, so that the inhomogeneous flow could influence the deposition of the silica scale which is an alternative process ofscaling. Nevertheless, relatively little research has been undertaken to investigate hydrodynamic effect on silica scaling. The aimof this work is to investigate the kinetic of adhesion of silica particles on the wall surface based on the hydrodynamic effect using
the numerical simulation. Although we focus on the elementary (microscopic) process of the adhesion of silica particles, ourultimately goal is to help us to simulate the macroscopic flow in subsurface or sub-seafloor hydrothermal systems based on thehydrodynamic process by the feedback from this study.
We simulate the adhesion of silica particles using the lattice Boltzmann method (LBM) combined with the smoothed-particle
method (SPM) (Nakayama and Yamamoto, 2008). This method uses fixed Eulerian grids for the fluid and represents the particles
by certain smooth body forces in the Navier-Stokes equations instead of treating the particles as boundary conditions to the fluid.
The LBM is adapted to the flow in the complex geometry due to the simple treatment of the boundary condition. The LBM
combined with the SPM is the scheme having low computational cost to deal with many particles in a relatively simple manner.
We assume that the particle whose velocity reaches the threshold of the convergence is adhered and is fixed on the wall. We
use a two-dimensional parallel plate model in which flow rate and wall roughness are varied and derive the constitutive relation
between the deposition rate and flow rate and wall roughness.
A high rate of scale growth is found in areas of low flow rate and it is consistent with the observation at the experiment(Garibaldi, 1980). Therefore, we conclude that the hydrodynamic effect on the growth of silica scale is important to understandthe hydrothermal circulation.

Keywords: silica scaling, hydrodynamics, particle adhesion, lattice Boltzmann method, smoothed profile method

1/1

STT13-07

会場:102A

時間:5 月 28 日 11:00-11:15

MMR 法による上部海洋地殻における比抵抗異常体の検出
Determining the three-dimensional position of the anomalous resistivity body in upper
oceanic crust using MMR method
寺岡 拓也 1∗ ; 島 伸和 1
TERAOKA, Takuya1∗ ; SEAMA, Nobukazu1
1
1

神戸大学大学院理学研究科惑星学専攻
Department of Planetology, Graduate School of Science, Kobe University

MMR 法はコントールソース法の一種であり、上部海洋地殻の比抵抗構造を推定するのに有用なツールである。この手法は、ソースとして鉛直な双極子電流、レシーバーとして海底磁力計で構成されている。1 次元の比抵抗構造は、ソース-レシーバー間距離と鉛直方向の双極子電流によって誘導される磁場の値の間の関係から容易に推定できる。しかし、3次元の比抵抗構造を見積もることは困難である。それゆえ、私たちは海洋地殻の比抵抗異常体を三次元的な位置を決定するために磁場異常マップを導入する。磁場異常は基準となる比抵抗構造 (比抵抗異常体が存在しない) で誘導される磁場と比抵抗異常体が存在する場合に発生する磁場の差と定義する。磁場異常は 1 組のソースとレシーバーに対して得られ、磁場異常の値はレシーバーに対するソースの位置でプロットされる。レシーバーに対する磁場異常図は、多くの異なるソース点での磁場異常によって作成される。私たちは、様々なパラメータ (水平方向のレシーバーと比抵抗異常体の距離、比抵抗異常体の深さなど) を持つ 10 個のモデルに対し磁場異常を 3 次元フォワードモデリンングによって計算しました。10 個の異なるモデルに対する磁場異常マップは、磁場異常と比抵抗異常体の場所に関する２つの関係を導き出すために用いました。1) 比抵抗異常体は磁場異常のピークとレシーバーの位置を結ぶ直線下に存在する。2) 比抵抗異常
体の深さは、比抵抗異常体の深さが比抵抗異常体と磁場異常のピーク間の水平距離に比例をしていることを示している
ことにより決定可能になる。これらの関係は 2 つ以上のレシーバーを設置し、磁場異常マップによってそれぞれの３次元的に比抵抗異常体の場所を推定可能にする。私たちの結果は、磁場異常マップが上部海洋地殻の比抵抗異常体の３次元的な位置を決定するのに有用であることを示し、それは MMR 法が海洋地殻の比抵抗異常体の分布を明らかにするためには、少ない台数の海底磁力計に対して多数の鉛直方向の双極子電流送信点を必要とすることを示唆している。
キーワード: 比抵抗構造, MMR 法, コントロールソース法, 海洋地殻
Keywords: resistivity structure, Magnetometric Resistivity method, controlled source method, oceanic crust

1/1

STT13-08

会場:102A

時間:5 月 28 日 11:15-11:30

港湾鋼材に対する渦電流探傷法の高精度化の研究
Improvement of eddy current testing method for sheet piles on harbor齊藤 拓也 1∗ ; 三ケ田 均 1 ; 武川 順一 1
SAITO, Takuya1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
1
1

京都大学大学院工学研究科
Graduate School of Engineering, Kyoto University

The applicability and the feasibility of eddy-current testing method for the detection of wall thinning and surface crack of steel
structure have been practically confirmed by field and laboratory experiments. Qualitative analysis of cracks has been empiricallyunderstood by analog analysis. There has, however, been a growing demand to quantitatively evaluate the cracks. We tackle thisproblem by use of time series of induced magnetic field by the cracks.
In the present study, we proposed a new digital analysis process to use the induced magnetic field waveform, and validated
the effectiveness of the method using numerical simulations. First, we developed a high-speed electromagnetic simulator using
a fictitious wave domain method to reproduce the conventional eddy current testing method for realistic sheet-piles seawatermodel. Then, we confirmed the features of the induced magnetic field waveforms by many types of cracks.
Paying attention to the residuals of the induced magnetic field waveform, we developed a novel migration procedure that has
not been used up to now in electromagnetic field. Using this, we could get crack imaging without phase lag. For the evaluationof the crack position and wall thinning of the sheet piles, we also applied attribute analysis used in the field of seismic survey.
Through the application of the digital signal processing using induced magnetic field waveform, we could be successful with
developing a high degree of accuracy of the eddy current testing method.

キーワード: 非破壊検査, 渦電流探傷法, 仮想領域法, マイグレーション処理, アトリビュート解析, 電磁気Keywords: NDT, Eddy current testing method, Fictitious wave domain method, Migration, Attribute analysis, Electromagnetic

1/1

STT13-09

会場:102A

時間:5 月 28 日 11:30-11:45

地中レーダへの位相アレイ型アンテナ適用性の研究
Applicability of Phased Array Antenna to Ground Penetrating Radar
菊地 海斗 1∗ ; 三ケ田 均 1 ; 後藤 忠徳 1 ; 武川 順一 1
KIKUCHI, Kaito1∗ ; MIKADA, Hitoshi1 ; GOTO, Tada-nori1 ; TAKEKAWA, Junichi1
11

京都大学工学研究科
Graduate School of Engineering, Kyoto University

Ground Penetrating Radar (GPR) has been widely used to detect objects in shallow subsurface. A bow-tie antenna, which isone of the major antennas, provides the clear cross sections in the shallow subsurface, especially under the survey line. On theother hand, the resolution across the survey lines depends on its interval. To overcome this problem, we tried to apply a phasedarray system to GPR. We conducted numerical simulations using a three-dimensional model composed of water, dry sand andsome small perfect conductors with cubic shape. We compared two different kinds of antenna, a dipole antenna and a phasedarray antenna. The phased array antenna has an 8 x 8 sending unit and one receiving unit at the center of the radar. Both antennas
have the length of about 0.5 meters. Our results show that the phased array antenna enhanced the noise-to-signal ratio and it
also enhanced the amplitude of a scattered wave from a perfect conductor located out of the survey line. We conclude that theapplication of the phased array system to GPR has a potential to survey with wider angle than the conventional GPR system.

1/1

STT13-10

会場:102A

時間:5 月 28 日 11:45-12:00

拡散過程を含む波動現象の新しい逆伝播手法の開発
Development of a novel backpropagation technique for waves traveling with diffusive
process
齊藤 拓也 1∗ ; 三ケ田 均 1
SAITO, Takuya1∗ ; MIKADA, Hitoshi1
11

京都大学大学院工学研究科
Graduate School of Engineering, Kyoto University

In the field of geophysics, several electromagnetic processes using waveforms, such as the full waveform inversion techniqueor the migration procedure, have been applied to visualize the subsurface structure.
While this process is very powerful and effective to interpret the subsurface structure, there are some difficulties in this process
when the phase velocity takes complex value, i.e., the propagation of waves includes diffusive process. One method to avoid
the instability due to the divergence of energy in the back propagation is to use the reciprocity to propagate from the locationsof receivers to every imaging point. However, although this method to exploit the reciprocity theorem is a powerful scheme,
amplitude attenuation and phase delay affects could be doubled due to the application of two-way forward propagation procedurein the imaging. In the conventional waveform inversion analysis, the result involves phase delay concomitantly during the backpropagate process.
Our novel electromagnetic migration process could overcome this problem. Unlike conventional back propagate process, weinvert the time of the residual waveform using forward propagation of this waveform. Then, we summed the resulting waveform
without phase delay. Although the amplitude would takes place, it is pretty important to recover the phase delay caused by theforward propagation from imaging points to receivers.
We applied this migration process for the improvement of the eddy current testing method that is one of the non-destructive
inspection techniques and confirmed this migration works well.

1/1

STT13-11

会場:102A

時間:5 月 28 日 12:00-12:15

地表付近の異方性異常体による地震波動場変化の研究
Seismic wavefield distortion due to anisotropic anomalies near surface
米木 梨奈 1∗ ; 三ケ田 均 1 ; 武川 順一 1
YONEKI, Rina1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
1
1

京都大学大学院工学研究科
Graduate School of Enginnering, Kyoto University

Reservoir rocks and near surface materials are estimated to be strongly anisotropic for elastic wave propagation (e.g., Sone,2012). Therefore, it is important to take anisotropy properties into account for estimating accurate geological structure using
seismic exploration methods. There are many previous studies of elastic anisotropy, for example, azimuthal anisotropy of qP- andqSV-wave, S-wave splitting, etc. Most of these studies are based on the assumption that media is ”weakly” anisotropic (Thomsen,1986). When the anisotropy of media is not ”weak”, the assumption may not be applicable. However, the effect of ”strong”
anisotropy on the behavior of seismic wave propagation is still not well understood. In this study, we investigate the influence ofstrong anisotropy on received seismic waveforms using three-dimensional numerical models, and verified capability of detecting
subsurface anisotropy. We assumed one model that contains a block of horizontally stratified isotropic layers (transversal isotropy
with vertical axis of symmetry), while the other contains an isotropic inhomogeneity sharing the same block. We took the
difference in the received waveforms of two models to see how the anisotropy of the medium influences the wavefield basedon the orbital analysis of particle motion of the residual wavefield. Our results show that there are meaningful changes in thereceived waveform mainly due to P-wave and converted-wave (P-to-S) that might be generated by the anisotropy of the materials
as secondary seismic sources. Since the anisotropy of the material behaves as secondary sources for incoming seismic waves, weconcluded that seismic exploration method is applicable to estimate the anisotropic properties.

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STT13-12

会場:102A

時間:5 月 28 日 12:15-12:30

DONET 地震計により観測されたエアガン記録および雑振動記録を用いた南海トラ
フにおける S 波異方性構造の推定
Estimation of S-wave anisotropy in the Nankai Trough using active and passive seismic
dataset observed by DONET
木村 俊則 1∗ ; 荒木 英一郎 1 ; 三ケ田 均 2 ; 小平 秀一 1 ; 三浦 誠一 1 ; 高橋 成実 1 ; 高江洲 盛史 1 ;中野 優 1 ; 町田 祐弥 1
KIMURA, Toshinori1∗ ; ARAKI, Eiichiro1 ; MIKADA, Hitoshi2 ; KODAIRA, Shuichi1 ; MIURA, Seiichi1 ;TAKAHASHI, Narumi1 ; TAKAESU, Morifumi1 ; NAKANO, Masaru1 ; MACHIDA, Yuya1
11

独立行政法人海洋研究開発機構, 2 京都大学大学院工学研究科
JAMSTEC, 2 Graduate School of Engineering, Kyoto University

In The Nankai Trough seismogenic zone, which is formed by the subducting Philippine Sea plate beneath the Eurasian platewith rate of 4-6 cm/year, mega-thrust earthquake occurred repeatedly every 100-150 years. In this area, cabled real-time observation system, DONET (Dense Oceanfloor Network Systems for Earthquakes and Tsunamis) and IODP C0002G boreholeobservatory, have been operated to monitor seismic activity, crustal deformation and tsunami propagation since August 2011 andJanuary 2013, respectively.
For elucidating preparation and generation process of mega-thrust earthquake, which occurs repeatedly in subduction zones, it
is important to observe and monitor the stress state, a key parameter governing its fault dynamics in the vicinity of seismogenic
fault. In-situ stress analysis such as borehole breakout analysis may provide the orientation and the order of differential stressaround the borehole, but it is still challenging to drill seismogenic fault, and is even more difficult to monitor temporal changeof stress state, especially in wide area. Therefore, we have to consider another method to estimate stress state. In this study, we
performed active and passive seismic data processing to obtain seismic anisotropy using dataset acquired by three-component
seismometers installed in the DONET and IODP C0002G observatories. Seismic anisotropy can be a proxy of stress state, andby observing its temporal change is expected to identify change of stress around the seismogenic fault.
As active seismic dataset, we used airgun records observed by DONET and IODP C0002G seismometers during KR13-17
cruise conducted on November 2013. In this study, we used airgun records of eight circular shooting lines around these seismometers with radius of 3 km. In radial and transverse components computed from original horizontal records acquired by thesecircular shooting lines, P-S converted waves from bottom of shallow sediment were clearly visible. Fast symmetry axis of S-wave
was estimated by fitting simple sine curve to amplitude fluctuation with shot-receiver azimuth in radial component, and then we
obtained S-wave anisotropy in shallow sediment in the Nankai Trough wide area.
As passive data processing, we apply seismic interferometry method to ambient noise records acquired by horizontal components of each DONET and IODP C0002G seismometer. We computed zero offset 4-C ACF and CCFs (Auto-correlation function
and Cross-correlation function) comprising V11, V12, V21, and V22 from ambient noise record observed by horizontal i- andj-direction components. Vij represents impulse response which has i-direction source and j-direction receiver of each seismometer. In the ACF and CCFs calculate from long-term records for two years, several coherent events are visible. These events may
be reflected S-wave from each layer, and S-wave splitting affected by seismic anisotropy. We then applied the Alford rotationand layer stripping method to the obtained 4-C ACF and CCFs. Then S-wave anisotropy direction and amplitude beneath eachseismometer in each layer above the plate boundary were obtained.
We finally compared the obtained S-wave anisotropy from the active and passive methods. There are some differences between
the obtained results from these methods. It may result from some reasons. Airgun records have been affected by 3-D structurearound the observatory including seafloor topography and effect of undergoing P-wave anisotropy. Results from passive ambient
noise components also have causes of error. The obtained 4-C ACF and CCFs might be contaminated by surface wave component. We now evaluate above mentioned effects to obtained results. Also, we intend to obtain S-wave anisotropy in deeper partfrom active airgun dataset using weak converted waves from deeper boundaries. We now plan to conduct next airgun survey inMarch 2015 by R/V Kairei with same settings as KR13-17 cruise to detect temporal change of S-wave anisotropy.
Keywords: S-wave anistropy, Nankai Trough, DONET

1/1

STT13-13

会場:102A

時間:5 月 28 日 12:30-12:45

地域ごとの不均質特性が P 波立ち上がりに与える影響
Effect of local heterogeneous conditions on growth curves of P-wave
岡本 京祐 1∗ ; 津野 靖士 1
OKAMOTO, Kyosuke1∗ ; TSUNO, Seiji1
1
1

鉄道総合技術研究所
Railway Technical Research InstituteIn the Earthquake Early Waning (EEW) system, magnitude and epicentral location of an earthquake are estimated withinseveral seconds after P-wave arrival. According to the Odaka (2003), the equation Bt∗exp(-At) is fitted to the early portion of
P-waves. In the equation, A and B are constants and t represented time. From the B value, epicentral distances are estimatedusing an empirical relationship. The B value decreases as the epicentral distance increases due to the geometrical spreading ofseismic waves. As the amplitude of P-waves decrease by travelling through the medium, the gradient of the early portion of
P-waves also decrease. So that, the B value of a given epicentral distance marks the specific value and the epicentral distancecan be obtained from the B value. However in practice, the B values of different earthquakes having the same epicentral distanceshow quiet different values. The gap in the B values is sometimes by several hundred times. One of the causes giving major effecton the B value is seismic attenuation due to heterogeneities in subsurface. Seismic waves propagating in heterogeneous medium
attenuate due to seismic scattering and absorption. Tsukada et al. (2004) conducted a theoretical calculation on broadening of
scalar wave envelopes based on three-dimensional von Karman type random medium. They found that the gap in the B values ofdifferent earthquakes having the same epicentral distance is accountable by difference in the scattering condition.
In this study, we theoretically calculate P waves in heterogeneous medium considering the conversion waves between P and S
waves, which were ignored in the preceding studies while they give major effect on P-wave envelopes. We show that variationin condition of heterogeneities (in concrete correlation distance) changes the B value. In other word, regional conditions ofheterogeneities make the different B values of a given epicentral distance. Then we compare the theoretically calculated B value
with one calculated from earthquakes in 1996 - 2011 observed by the K-, KiK-net in Japan. We calculate a regional parameter ofheterogeneities (correlation distance) in Japan which can account the fluctuation in the observed B values. As a result, it is foundthat the spatial distribution of the correlation distance (Figure 1) shows similar tendency with that of a parameter reflecting local
heterogeneities, like coda-Q.
In this study we hypothesize that variation in the condition of heterogeneities makes the B value fluctuate significantly andverify it. If we treat the fluctuation in the B values by considering the local condition of heterogeneities, estimation on epicentral
distances becomes more accurate. It will improve accuracy of the EEW. Furthermore, B values, that is, initial curve of Pwaves can be an exploration tool for local heterogeneities. The early portion of P-wave has a strong advantage that the Born
approximation can be used. Complex heterogeneities can be treated by the simple equation.
キーワード: 不均質, ボルン近似, 早期警報, 散乱, P 波立ち上がり, B-Δ法
Keywords: heterogeneities, Born approximation, EEW, scattering, growth curve of P-wave, B-delta method

1/1

STT13-14

会場:102A

時間:5 月 28 日 14:15-14:30

Development of hydraulic low frequency marine seismic vibrator
Development of hydraulic low frequency marine seismic vibrator
小笹 弘晃 1∗ ; 三ケ田 均 2 ; 佐藤 文男 1 ; 村上 文俊 3 ; 淺川 栄一 3OZASA, Hiroaki1∗ ; MIKADA, Hitoshi2 ; SATO, Fumio1 ; MURAKAMI, Fumitoshi3 ; ASAKAWA, Eiichi3
1
1

株式会社 IHI, 2 京都大学, 3 株式会社地球科学総合研究所
IHI Corporation, 2 Kyoto University, 3 JGI, Incorporated

A towed marine seismic vibrator using hydraulic servo system has been developed. We have fabricated a mock-up source witha slightly, say 60-70 %, scaled size to the real design and conducted several evaluation tests in the sea. The vibrator was towed
approximately at a depth of 250m in water. The performance such as maximum sound level, frequency characteristic, horizontal
directivity, and vertical directivity of the sound field generated from the source mock-up was examined as a field experiment.
The sound source level and the frequency characteristic were equal to or higher than the estimated specification between 3Hz
and 300Hz. The comparizon of horizontal with the vertical intensity of the generated sound fields indicate that the generated
sound field could be regarded nearly omnidirectional. Seismic survey trial using a short streamer was also conducted following
the source characteristic examination. A shot gather was acquired by several emission patterns with different frequency bands inthe trial. The results showed the performance of the mock-up to be usable as seismic source in shallow water as a vibrator sourcethat uses mechanical oscillation structure.
Keywords: seismic, vibrator, hydraulic

1/1

STT13-15

会場:102A

時間:5 月 28 日 14:30-14:45

Study of the exploration focused on shear waves generated by a dipole source
Study of the exploration focused on shear waves generated by a dipole source
永井 祐気 1∗ ; 津田 明憲 1 ; 畠中 宏明 1 ; 田上 稔 1 ; 田中 浩一郎 1 ; 佐藤 文男 1 ; 三ケ田 均 2
NAGAI, Yuki1∗ ; TSUDA, Akinori1 ; HATANAKA, Hiroaki1 ; TAGAMI, Minoru1 ; TANAKA, Koichiro1 ;SATO, Fumio1 ; MIKADA, Hitoshi2
11

株式会社 IHI, 2 京都大学大学院工学研究科
IHI Corporation, 2 Kyoto University

For the exploration and the development of the hydrocarbon fluid resources such as oil, natural gas, etc., a 3D seismic exploration method has been applied to investigate subsurface structures. In particular, the utilization of airguns and multiple streamers
have made use of 3D surveys in practice in the marine environment. Marine seismic sources are in general explosive or impulsive
so that the compressional and its mode converted waves have been used in the exploration. For further effective exploitation of
the resources, such as enhanced oil recovery, it is necessary to apply much higher exploration technologies. Shear waves are alsoa candidate to be utilized to investigate physical properties of subsurface materials. Therefore, shear waves have been of interestin research in recent years, but, unfortunately, are known as difficult to be acquired in the marine environment due to water layer
in which no shear wave travels through. The generation of shear waves without touching the seafloor is also thought impossible
in water. For efficient surveys using shear waves, we need to find an alternative way to generate shear waves.
In this paper, a feasibility study of the exploration focused on the generation of the shear wave is conducted using a dipole
source that has been used to generate shear waves in geophysical logging. We first made a scaled model of a deep-tow seismic
survey using solid material with a set of reflectors and an overlain water layer. Two dilatational sources with the opposite phaseto each other are simultaneously excited to form a point force in the water parallel to solid-water interface. The sound field
generated by the dipole in water creates a stress field tangential to the solid-water interface so that the shear wave is generated in
the solid. For the model, we performed both acoustic experiment and numerical simulations to see both compressional and shear
reflection profiles. Although the signal-to-noise ratio of the acoustic experiment is not sufficiently high, we confirmed that shear
reflection profile could be produced. It should be noted that shear waves could be produced in water using multipolar sources
fired close to the seafloor, and that some improvements to increase shear wave energy more than the compressional wave need tobe pursued for practical use of multipolar sources.

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STT13-16

会場:102A

時間:5 月 28 日 14:45-15:00

Optimal correction of data from misoriented multi-component geophysical sensors
Optimal correction of data from misoriented multi-component geophysical sensors
KRIEGER, Lars1∗ ; GRIGOLI, Francesco2
KRIEGER, Lars1∗ ; GRIGOLI, Francesco2
1

Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide (AUS), 2 Institute of Earth andEnvironmental Sciences, University of Potsdam, Potsdam (GER)
1
Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide (AUS), 2 Institute of Earth andEnvironmental Sciences, University of Potsdam, Potsdam (GER)
One of the most important problems affecting geophysical data acquisition procedures is related to the misorientation of multicomponent sensors with respect to a common reference system. Misoriented sensors affect data analysis procedures, which canlead to errors in results and interpretations. These problems generally occur in applications in which the orientation of the sensor
cannot be actively controlled and is not known a priori. Common examples are geophysical sensors deployed in borehole installations or on the seafloor. In this presentation we introduce two methods to optimally correct data sets from misaligned sensors.
Firstly, we consider two-component time-series data. These commonly result from the assumption that the vertical axis of athree-component sensor is correctly determined, and therefore the data from that respective component can be excluded from thecorrection process. This is a common approach and it is used in many applications. We show that the optimal misalignmentcorrection for such a two-component data set can be estimated in a single, non-iterative calculation step (c.f. Grigoli et al.,2012). The result is optimal with respect to the l2 norm of the overall deviation between the re-oriented and the optimal data. We
demonstrate the functionality of our method by applying it to synthetic and real data examples (seismic data; Vertical seismic
profile, Ocean bottom seismometers, Seismological array).
Although the simplification of neglecting the third sensor component is commonly applied, and the resulting deviations are
assumed to be negligible, it is still beneficial to take the full information contained in the data sets into account. Therefore,
we have developed a reorientation algorithm for multi-component geophysical sensors (i.e. two- and three-component sensors).
In the second part of this presentation, we introduce this quaternion-based method, which yields an analytical solution for the(relative) reorientation of sensors in three dimensions. We show that our method is not only fully functional, but also that it issuperior to the commonly applied approach of a grid search over the parameter space for finding optimal rotation paramters (c.f.
Krieger & Grigoli, 2015). We also demonstrate that the assumption a potential deviation of the vertical sensor component fromthe true vertical only leads to small errors in the result is not necessarily true. Hence, we conclude that it is important to rely on
an analytical estimate of reorientation paramters, and that the inclusion of all sensor components in the process of this estimation
is important. By introducing our new approach to the correction of sensor mis-alignment, we can overcome the dependency on
approximative solutions and eliminate systematic sources of errors in standard time-series data processing.

References:
Grigoli, F., Cesca, S., Dahm, T., Krieger, L. (2012); A complex linear least-squares method to derive relative and absoluteorientations of seismic sensors ; Geophysical Journal International; 188(3); 1243-1254.
Krieger, L. & Grigoli, F. (2015); Optimal reorientation of geophysical sensors: A quaternion-based analytical solution ; Geophysics; 80(2); F1-F12.

キーワード: 2D/3D sensor re-orientation, Algorithm, Quaternions, Vertical Seismic Profile, Ocean Bottom Seismometers, Array
seismology
Keywords: 2D/3D sensor re-orientation, Algorithm, Quaternions, Vertical Seismic Profile, Ocean Bottom Seismometers, Array
seismology

1/1

STT13-17

会場:102A

時間:5 月 28 日 15:00-15:15

複雑な傾斜層に対する反射法地震探査データ処理における等価オフセット・プリス
タック・マイグレーションの研究
Applicability of prestack equivalent offset migration of reflection seismic data
三ケ田 均 1 ; ジョン ダンイン 1 ; 武川 順一 1∗
MIKADA, Hitoshi1 ; JEON, Danin1 ; TAKEKAWA, Junichi1∗
1
1

京都大学
Kyoto Univ.

Recently equivalent offset migration (EOM) has been applied to image the subsurface structure in seismic surveys. In thepresent study, we investigate the effectiveness of EOM for complex geological structures with inclined layers using numericalsimulations. In our experiments, the geological boundaries have different dipping angles. We estimate the underground structureusing EOM, and compare the result with that from dip moveout (DMO) which is a popular method for the dipping structures.
The result of EOM achieve similar resolution to DMO whereas the computational cost of EOM is fifth part of that of DMO. Our
result indicates that EOM has advantage over DMO.
キーワード: 等価オフセットプリスタックマイグレーション, 共通散乱点
Keywords: Prestack equivalent offset migration, Common scattering point

1/1

STT13-18

会場:102A

時間:5 月 28 日 15:15-15:30

音波検層における全波形インバージョン適用可能性の研究
Applicability of Full Waveform Inversion in Sonic Logging
石倉 一樹 1∗ ; 三ケ田 均 1 ; 武川 順一 1
ISHIKURA, Kazuki1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
11

京都大学工学研究科
Graduate school of Engineering, Kyoto University

Sonic logging has been widely used for many years to acquire physical properties of hydrocarbon reservoirs, and then, velocity
analysis is performed by detection of first break or slowness time coherence (STC) method.
The estimation of velocity and quality factors is important for the identification of fluid contacts, e.g. oil-water contact.
But the resolution of existing methods is restricted to 6 inch by receiver distance of logging tool.In sonic logging, highresolution imaging and detection of oil-water contact (OWC) are recognized as urgent issues.On the other hand, many studies inseismic reflection survey focus on full-waveform inversion (FWI) as an innovative technique to acquire high resolution velocity
structure in the subsurface.However, the applicability of FWI to the sonic logging has not been revealed yet.So, we examined theapplicability of FWI using some numerical experiments.
Our results show that gas-oil contact and OWC can be detected with higher resolution than the conventional methods whose
resolution is 6 inch.Therefore, we conclude that we could apply FWI to sonic logging with high resolution imaging.
Keywords: FWI, OWC, GOC

1/1

STT13-19

会場:102A

時間:5 月 28 日 15:30-15:45

フルウェーブを用いた坑井間トモグラフィーによる密度定数推定法の研究
Density parameter estimation in full waveform well-to-well tomography
寺西 慶裕 1∗ ; 三ケ田 均 1 ; 武川 順一 1
TERANISHI, Keisuke1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
1
1

京都大学大学院工学研究科
Kyoto university

The importance using the full waveform is widely recognized in seismic explorations. Especially, seismic full waveform
inversion (FWI) can detect the high-resolution physical properties in the subsurface. Since the seismic wave propagation cannot
be controlled by not only P-wave and S-wave velocities but the density of the medium, it is necessary to include all threeparameters in the modeling and inversion (Vireux and Operto, 2009). However, multi-parameter FWI is a challenging problem
because parameters are coupled with each other, and the coupling effects prevent from the appropriate estimation of the elastic
parameters. Especially, the estimation of density is a very difficult issue because plural elastic parameters including density
increases the dimension of the solution space, so that any minimization could be easily trapped in local minima. Therefore, thedensity is typically estimated using an empirical formula such as the well-known Gardner’s relationship (Gardner et al., 1974) or
is fixed to a constant value. Since the density parameter is directly included in the elastic wave equation, it is necessary to check
whether it is possible to estimate density value exactly or not. Moreover, the Gardner’s relationship is an empirical equationand could not always show the proper relation between Vp and density(e.g., in the salt dome). Pre-salt exploration conducted inrecent decades could accordingly be influenced.
The objective of this study is to investigate the feasibility of the estimation of density structure when the density is invertedwith the other elastic parameters and to assess if density is separable from the other parameters. We perform 2D numericalsimulations in order to investigate the most important factor in the inversion of density structure as well as Vp and Vs. We
conducted four numerical experiments with different inversion strategies; i.e. we invert 1) Vp and density simultaneously, 2) Vs
and density simultaneously, 3) Vp, Vs and density simultaneously, and 4) only density. Considering these results, the density
inversion results are affected by the other parameters and inversion results are worse than the result of inverting solely density.
Compared with the other parameters, the density has a little influence on the waveform, and it is likely to be ignored in the
inversion. Moreover, we conducted grid analysis of misfit function (Gholami et al., 2013) to estimate the contribution of eachparameter to misfit function. These results suggest that solely inversion of density is the most effective to estimate the reliablevalue, on the other hand to estimate density with the other parameters is captured in the local minima.

キーワード: 全波形逆解析, 密度
Keywords: full waveform inversion, density

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STT13-20

会場:102A

時間:5 月 28 日 15:45-16:00

Full waveform inversion for subsurface exploration using vertical cable seismic data
Full waveform inversion for subsurface exploration using vertical cable seismic data
JAMALI HONDORI, Ehsan1∗ ; MIKADA, Hitoshi2 ; ASAKAWA, Eiichi1 ; MIZOHATA, Shigeharu1
JAMALI HONDORI, Ehsan1∗ ; MIKADA, Hitoshi2 ; ASAKAWA, Eiichi1 ; MIZOHATA, Shigeharu1
1
1

JGI, Inc., 2 Kyoto University
JGI, Inc., 2 Kyoto University

Subsurface exploration for natural resources is mainly conducted by surface seismic experiments which use receiver arrays on
the surface to record the propagated energy from seismic sources and produce an image of the earth after processing. Sources
and receivers could be placed on the ground, i.e. land acquisition, or towed in the sea by a vessel, i.e. marine acquisition, inorder to cover the desired area of the imaging. This requires appropriate data acquisition geometry and optimized data processing
flows for reliable subsurface images. However, when the target is a small area in the marine environment with certain obstacles
like platforms or buoys, in the deep sea conditions, or in the geologically complex areas the surface seismic exploration fails
to deliver a high resolution image either because of the restrictions in the data acquisition or inefficiency of the data processing
algorithms. Instead, a Vertical Cable Seismic (VCS) experiment provides a high resolution image for the investigation of thenatural resources below sea floor. In the VCS configuration vertical arrays of hydrophones are deployed near the sea floor andare kept in the vertical situation by using an anchor in the bottom and a buoy at the top of the cable. Seismic source is towed
by the vessel and the data is recorded for every shot point, then processing and Pre-Stack Depth Migration (PSDM) of the data
yields an image of the structures. However, a good PSDM section is achieved only if accurate wave velocity model is available
for the migration. Full Waveform Inversion (FWI) of the seismic data is a reliable tool to reconstruct the subsurface properties
by using pre-stack recorded data. We use full waveform inversion of the acoustic data recorded by a VCS simulated experiment
to develop P wave velocity model.
In the FWI workflow acoustic wave equation is solved using 2D finite difference method to produce waveforms using an
initial model. Then, misfit between recorded and simulated waveforms is minimized via a local optimization algorithm, e.g.
preconditioned conjugate gradient, to update the model. This process is iterated until a convergence criteria is satisfied or the
maximum number of FWI iterations is reached. Because of the nonlinearity of the problem, a good initial model which is closeenough to the exact solution is necessary. For the simulated experiment, we considered a marine environment with water depthof 900 m and lateral extension of 5000 m. We used four vertical cables located near the sea floor in the middle of the modelarea. Each vertical cable has 8 hydrophones spaced every 10 m and the deepest hydrophone is 10 m above the sea floor. Seismic
sources are located 10 m beneath sea level and 500 shots at every 10 m are used for the VCS experiment. VCS experimentshowed reliable results to prove that it is very useful for high resolution imaging of a small area in the subsurface, which is notpractically resolvable by using surface seismic experiments.

キーワード: full waveform inversion, vertical cable seismic, acoustic
Keywords: full waveform inversion, vertical cable seismic, acoustic

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STT13-21

会場:102A

時間:5 月 28 日 16:15-16:30

メッシュフリー差分法を用いた解像度可変型フルウェーブフォームインバージョン
An adaptive resolution FWI using a mesh-free finite-difference method
武川 順一 1∗ ; 三ケ田 均 1
TAKEKAWA, Junichi1∗ ; MIKADA, Hitoshi1
1
1

京都大学
Kyoto Univ.

We developed an adaptive resolution full-waveform inversion (FWI) using a mesh-free finite-difference method (MF-FDM).
The conventional finite-different methods (FDMs) have been widely used to calculate full-waveform synthetic traces in FWI.
Most of FDMs are based on the assumption of the regular alignment of computational grids. This causes the computationalburdens if the analysis model includes large velocity contrast, e.g. salt dome model. We propose a strategy to use MF-FDM
for reducing computational cost in simple and seamless manners. Since MF-FDM calculates full-waveform synthetic trace withirregular distribution of nodes, our strategy can arranges adaptive resolution nodes depend on the velocity structure, i.e. fine nodes
are used only around low velocity zones. We investigate the effectiveness of the method using some numerical experiments. Our
results indicate that the method can successfully reduce the computational cost in simple and seamless manners.
キーワード: フルウェーブフォームインバージョン, メッシュフリー差分法, 数値シミュレーション
Keywords: full-waveform inversion, mesh-free finite-difference method, numerical simulation

1/1

STT13-22

会場:102A

時間:5 月 28 日 16:30-16:45

亀裂性岩盤を対象とした水圧破砕法における破砕流体の粘性が及ぼす影響
Influence of pre-existing fracture and viscosity of injected fluid on effective hydraulicfracturing
長曽 真弥 1∗ ; 三ケ田 均 1 ; 武川 順一 1
NAGASO, Masaya1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
11

京都大学工学研究科
Graduate School of Engineering, Kyoto University

Hydraulic fracturing has been applied for enhanced recovery of hydrocarbon reservoirs and enhanced geothermal systems.
In this technique, rock mass is fractured by applying fluid pressure on borehole wall. For the estimation of the propagationof hydraulically induced fractures, the strike of pre-existing fractures and the viscosity of injected fluid should be taken into
consideration. Although theoretical solution shows that hydraulically induced fracture propagates in the direction of maximum
principle stress in a homogeneous medium, the propagation direction in real field does not always correspond to the expected
direction from the regional stress due to pre-existing fractures. The viscosity of injected fluid also influences the behavior ofhydraulic fractures. The injection of high viscous fluid could improve the permeability of rock and enhance the effectivenessof the hydraulic fracturing. In order to examine the influence of pre-existing fractures and of injected fluid viscosity on the
propagation of hydraulic fractures, we performed a series of numerical simulations for hydraulic fracturing in naturally fractured
rock by using a 2D flow-coupled discrete element method. In our simulations, fluid pressure is applied to a borehole wall,and hydraulically induced fracture would intersect with an inclined pre-existing fracture adjacent to the borehole. We perform
simulations with three different strike angles of the pre-existing fracture, using two different viscosity of fluid. As a result,hydraulic fracture propagates beyond the pre-existing fracture when high viscous fluid is injected, while it is trapped by the preexisting fracture in the low viscous fluid injection. This is caused by the strong fluid pressure on the borehole wall and the surfaceof the pre-existing fracture in the high viscosity case. The results also show that the higher the intersection angle of hydraulicfracture and pre-existing fracture is, the more hydraulic fracture propagation is retarded. We conclude that high viscous fluid
could be recommended for effective hydraulic fracturing when the hydraulic fracture has high intersection angle to pre-existing
fracture.
キーワード: 水圧破砕法, 個別要素法, 粘性, 既存亀裂
Keywords: Hydraulic Fracturing, Discrete Element Method, Viscosity, Pre-existing Fracture

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STT13-23

会場:102A

時間:5 月 28 日 16:45-17:00

地域応力場を考慮した水圧破砕による亀裂進展
Fracture propagation stimulated by hydraulic injection under in-situ stress field
大久保 蔵馬 1∗ ; 三ケ田 均 1 ; 武川 順一 1
OKUBO, Kurama1∗ ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1
1
1

京都大学大学院工学研究科
Kyoto University

Hydraulic fracturing is a major scheme for improving the production of non-conventional energy resource as well as horizontal
well. It increases the permeability of reservoirs which is usually tight and low permeability by making fracture net in thereservoirs. Acoustic Emittion (AE) is observed on the ground surface or in observation wells to monitor the expansion of thefracture net by fluid injection. Laboratory experiments indicate that hydraulic fractures would propagate in the direction of
the maximum principal stress around the fractures. Hence it is assumed that in-situ stress could play an important role for the
behavior of hydraulic fracture propagation in the field scale. It is, however, difficult to observe the fracture propagation directly
due to the depth of the reservoir layer (>2km generally). Therefore, the ratio of tensile crack to shear one induced by the fluid
injection has not been revealed yet.
Distinct element method (DEM) has often been applied to the simulation of the hydraulic fracturing, which shows the fracturing
mechanism around the injection well, while it has a limit of analytical area around the borehole due to the computational cost.
It is, therefore, challenging to simulate hydraulic fracturing in the real scale (>10m). In this study, we adopted the extended
finite element method (X-FEM) and add a new degree of freedom for the effects of the fluid inside the fracture (Chen 2013). We
optimized this scheme to simulate the fracture propagation in the large scale under in-situ stress field. The advantages of thisscheme are following. a) Fractures are defined independent of the mesh, which could reduce the computational cost due to there-meshing process. b) It maintains the continuity of displacement at each node on the elements. It would bring stable stress field
and fracture simulations. We developed the hydraulic fracturing simulation tools with this scheme and explored the mechanismof fracture propagation triggered by the fluid injection.
For the evaluation of the fracture propagation, we made a simulation model in real scale and put external forces as in-situ
stress. The aim of this simulation is to investigate the influence of the in-situ stress on the fracture propagation and fracturing
mechanics. To understand the effect of the stress field around the fracture tip, we also created a heterogeneous model of P-wave
velocity. We conducted two simulations with the homogeneous and heterogeneous models, and obtained the characteristics ofthe fracture propagation in the geological formation.
The first result, using the homogeneous model, shows that fracture propagates with not only tensile but also shear stresscomponents even if the injected fluid inside the fracture presses outward. It suggests that hydraulic fractures could generate
mixed-mode crack. The second result from the heterogeneous model simulations indicates that the in-situ stress field could be
disturbed by the heterogeneity and the fractures no longer propagate simply in the direction to the maximum principal stress fromfar field. It indicates that while fractures propagate in a linear fashion in the homogeneous model, they propagate in a turbulent
manner in the heterogeneous model.
We investigated the influence of the in-situ stress field on the hydraulic fracture propagations in the geological layer. It issuggested that the hydraulic fractures would propagate with both tensile and shear crack that is mixed-mode cracks. In addition,
the macroscopic heterogeneity in the subsurface could affect the behavior of the microscopic fracture propagation. These results
might help to estimate the radiation of the AE and evaluate the fractured reservoir in the real field.

キーワード: 水圧破砕, 拡張有限要素法, 原位置地圧, 亀裂進展
Keywords: Hydraulic Fracturing, X-FEM, In-situ stress, Fracture propagation

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STT13-P01

会場:コンベンションホール

時間:5 月 27 日 18:15-19:30

地表磁場成分を用いた電磁マイグレーションによる地下構造可視化の研究
Subsurface imaging with EM migration of magnetic fields
兵藤 大祐 1 ; 後藤 忠徳 1 ; 三ケ田 均 1 ; 武川 順一 1∗
HYODO, Daisuke1 ; GOTO, Tada-nori1 ; MIKADA, Hitoshi1 ; TAKEKAWA, Junichi1∗11

京都大学大学院工学研究科
Graduate school of Engineering, Kyoto University

The underground impedance data is estimated by observing and analyzing both electric and magnetic components in themagnetotelluric (MT) method. Although this method is often used in fault surveys or geothermal prospecting, it has the two
problems caused by the observation of electric components. One is that the static shift effect bias the apparent resistivity at thesurface, and the other is that it is difficult to secure broad places for the observation of electric fields. Furthermore the analysis
of electromagnetic data is also challenging because of its high computational costs, especially in three-dimensional cases. This
causes barriers to application to large amounts of field data. So, a new technology which can estimate the subsurface information
simpler and faster is needed.
In this study, we suggest the new method to use magnetic components at the surface in order to overcome these problems. The
static shift effect can be controlled and the great mobility of magnetometers makes it possible to obtain data at a lot of sites, if
magnetic fields are used as analysis data. Magnetic components are applied to not inversion method but migration method, whichis generally the visualization method in seismic data processing to save computational cost. We adopted the PSPI (Phase-Shift
Plus Interpolation) method (Gazdag and Sguazzero, 1984) and applied this method to the magnetic fields at the surface. In thecase of applying the migration technique to the electromagnetic data, it is very important to select the correct frequency band toprevent the multiple reflection and attenuation of the electromagnetic waves.
Through the numerical calculation analyses and the analysis of field data, it was confirmed that applying migration method tomagnetic components is the effective. In this migration method, the large value of reflection intensity is estimated around thearea if the proper resistivity structure is assigned to the migration. This means that the resistivity structures in the subsurface
have an effect on the migration results. In the analysis of the real field data around an active fault, large reflection intensity wasestimated beneath the active fault. We discussed the results of the estimated apparent resistivity cross section and the migration
results with the geological structure of the area and a previous 2D MT inversion result.
In conclusion, our method can estimate the underground resistivity structure simpler and faster. The combination of thiselectromagnetic migration method and inversion has possibility to reveal more detailed subsurface resistivity structure.
Keywords: electromagnetic migration, magnetic fields

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STT13-P02

会場:コンベンションホール

時間:5 月 27 日 18:15-19:30

Pareto-optimal Joint Inversion Modelling and Data Set Compatibility Analysis
Pareto-optimal Joint Inversion Modelling and Data Set Compatibility Analysis
SCHNAIDT, Sebastian1 ; KRIEGER, Lars1∗ ; HEINSON, Graham1
SCHNAIDT, Sebastian1 ; KRIEGER, Lars1∗ ; HEINSON, Graham1
1
1

Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide (AUS)
Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide (AUS)

In the process of modelling geophysical properties, jointly inverting different data sets can greatly improve the results. In order
to conduct a joint inversion modelling, a relationship between the different data sets has to be established, which can be either beof analytical or structural nature. Classically, the joint inversion problem is then expressed as a scalar objective function, which
combines the misfit functions of all involved data sets combined with a joint term accounting for the assumed connection between
the data sets. This method bears two major disadvantages. Firstly, a weighting of the data sets is enforced by aggregating all
misfit terms. Secondly, the data sets cannot be assessed with respect to their compatibility. Data sets are compatible if they aresensitive to similar physical features, and the joint interpretation of incompatible data sets can lead to incorrect resulting models.
In order to generate unbiased joint inversion models, it is important to mitigate the influence of weighting and to analyse thecompatibility of data sets. Therefore, we have developed a new approach to the joint inversion modelling of geophysical data. We
present MOJO , a Pareto-optimal multi-objective joint inversion algorithm. It is based on an advanced genetic algorithm, hence
it does not only calculate a single optimised model, but a distribution of possible models as final result. In contrast to common
approaches, MOJO treats data sets as a separate objectives, which avoids spurious weighting. Additionally, we use the output
of MOJO to calculate and evaluate curves of the trade-off between the different objectives. The shapes and evolutions of thesecurves yield a measure for the compatibility of the used data sets. Furthermore, the evaluation of the resulting model distribution
provides valuable uncertainty estimates.

キーワード: Multi-objective optimisation, Joint-inversion, Data set compatibility, Model uncertainty, Magnetotellurics
Keywords: Multi-objective optimisation, Joint-inversion, Data set compatibility, Model uncertainty, Magnetotellurics

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STT13-P03

会場:コンベンションホール

時間:5 月 27 日 18:15-19:30

Interferometric location of microseismic events induced by gas storage operations
Interferometric location of microseismic events induced by gas storage operations
GRIGOLI, Francesco1∗ ; CESCA, Simone2
GRIGOLI, Francesco1∗ ; CESCA, Simone2
1

Institute of Earth and Environmental Sciences, University of Potsdam, Germany, 2 GFZ German Research Centre for Geoscience, Section 2.1 Earthquake and Volcano physics, Germany
1
Institute of Earth and Environmental Sciences, University of Potsdam, Germany, 2 GFZ German Research Centre for Geoscience, Section 2.1 Earthquake and Volcano physics, Germany
Underground gas storage is a common industrial operation that consist in the injection of natural gas in aquifers, undergroundcavities or depleted hydrocarbon reservoirs. Gas is seasonally injected or extracted to meet the market demand. Although these
operations rarely stimulated seismicity, a recent case at the Castor platform in the offshore Spain was accompanied by a significant seismic sequence, culminated with a magnitude Mw 4.3 earthquake (Cesca et al. 2014). Ad hoc microseismic monitoring
networks are nowadays extensively used to analyse the induced microseismicity generated by these industrial operations. However, in many cases, the lack of local microseismic monitoring networks limits the performance of the standard data analysis
procedures. In such cases, non conventional methods need to be established. Within this context, we extend here the analysisof triggered seismicity related to gas injection at the Castor platform, in September-October 2013, where standard location procedures failed for magnitudes below Ml 2. In this work we relocate these low magnitude events using an interferometry based
location method (Snieder and Vrijlandt, 2005). This technique exploits slight changes in the coda waves between two seismic
events within a cluster. We proof that microseismic events can be classified in different families by combining a waveform correlation analysis and a clustering technique. Clustered events are characterized by a high similarity of waveforms, which implies asimilarity in both source mechanism and location. In these conditions, the analysis of seismic coda recorded at a single receivercan be used to infer a measure of the spatial separation between two seismic sources. Coda waves are radiated in all directions
with a radiation pattern determined by the source mechanism and a small change in the source position affects the interference
pattern of the scattered waves that constitute the coda. This change in the coda waves is used to constrain the interevent distancefor each events pair. Absolute locations can be then retrieved by considering all interevent distances, a procedure which requires
at least three reference locations. We discuss the potential of the coda interferometry location approach to monitor triggered andinduced seismicity, by relocating about 1000 seismic events of the September-October 2013 seismic sequence offshore Spain,
close to the Castor project injection platform. Results are used to discuss the possible proposed faults scenarios.
References:
Cesca, S. et al. 2014, The 2013 September?October seismic sequence offshore Spain: a case of seismicity triggered by gas
injection?, Geophys, Jour. Int., doi: 10.1093/gji/ggu172
Snieder, R., and Vrijlandt, M., 2005. Constraining the source separation with coda wave interferometry: Theory and application to earthquake doublets in the Hayward fault, California, J. Geophys. Res., doi:10.1029/2004JB003317

キーワード: Induced seismicity, Microseismic monitoring, Seismic event location, Seismic interferometry
Keywords: Induced seismicity, Microseismic monitoring, Seismic event location, Seismic interferometry

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STT13-P04

会場:コンベンションホール

時間:5 月 27 日 18:15-19:30

Retrieving Focal Mechanism using Double Couple - Tensile Constrained Inversion : Method
and Synthetic Tests
Retrieving Focal Mechanism using Double Couple - Tensile Constrained Inversion : Method
and Synthetic Tests
飯田 周平 1∗ ; 金 亜伊 1
IIDA, Shuhei1∗ ; KIM, Ahyi111

横浜市立大学
Yokohama City University

Understanding the source characteristics of hydraulic fracturing induced microearthquakes is expected to provide better understanding of both the fracturing process and the influence of pre-existing structures on the distribution of events. However, detailsof the source characteristics of the microearthquakes remain largely unknown. One controversial issue is whether a significant
volumetric change occurs because of the stimulation. Answering this question is important to provide the insight of the future
effective and safer hydraulic fracturing. Although the moment tensor inversion is one of the best approaches for studying source
mechanisms, it is often biased due to uncertainty of geologic model, sparse receiver coverage and low signal to noise ratio forthis types of induced earthquake analyses. So it is necessary to quantify the factors which bias the solution. Herein, to address
this question, we modified the double couple focal mechanism inversion method using the body-wave amplitude ratio and polarities developed by Snoke (2003) for stimulation induced microearthquake analysis. Since our goal is to figure out whether it
is possible to identify volumetric change with limited receiver azimuthal coverage, it is necessary to incorporate the non-double
couple mechanism in the inversion. Since the mechanism of the microearthquakes can be considered as 1) shear slip along thepre-existing fracture surface, 2) an tensile displacement which increase the porosity, or 3) a combination of these mechanisms,
we added tensile crack component to the original method. In this manner, we have smaller degree of freedom to stabilize theinversion than that of full moment tensor case. In this study we will examine the performance of the method with synthetic tests
under various conditions.
キーワード: 誘発地震, 水圧破砕, 震源メカニズム, テンサイルクラック
Keywords: induced seismicity, hydraulic fracturing, focal mechanism, tensile crack

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STT13-P05

会場:コンベンションホール

時間:5 月 27 日 18:15-19:30

Extraction of body waves from seismic ambient noise
Extraction of body waves from seismic ambient noise
Kim Eun Mi1∗ ; KANG Tae seob1 ; KIM Tae sung2 ; KIM Min wook1
KIM, Eun mi1∗ ; KANG, Tae seob1 ; KIM, Tae sung2 ; KIM, Min wook1
1
1

Pukyong National University, 2 Korea Institute of Geoscience and Mineral Resources
Pukyong National University, 2 Korea Institute of Geoscience and Mineral Resources

Ambient noise cross-correlation is used in seismology to obtain the part of the surface waves and applied to the theoreticalresearches and various experiments. Obtaining the part of body waves from the ambient noise correlation is difficult to recognize
because of the feature decreasing body waves along the travel path. However, the travel times of body waves detected from
temporal and spacial events occurrence involve uncertainty of the epicenter and accompany temporal-spacial restriction. On theother hand, ambient noise is always occurred and is obtained at the all stations. So it can be applied to research of the internal
earth when the case of extracting the body waves using the cross-correlation is possible. This study shows that body waves
can be observed by analyzing the ambient noise recorded seismic data in South Korea. Using 42 broad-band three components
stations located on the South Korea. The data removed the mean and trend are filtered high-frequency band(0.5-2Hz). The noisecorrelations were calculated for all combinations of radial, transverse and veltical components, which required rotation of thehorizontal components for each station pair according to the azimuth at each station of the greatcircle between the two stations.
Removing the part of broad-band signals effected by occurring event, the part of standard deviations more than three times are
removed. And it applied spectral whitening to reduce effects of the surface waves. After data processing, all ambient noise
signals are cross-correlated and temporal stacked. We found the signals propagating from one station to another station, thissignals can be interpreted as the body waves distinguished surface travel-time in high-frequency band. From this analysis, we
can extract the body waves using ambient noise cross correlation of continuous data at the stations.
キーワード: ambient noise, cross correlation
Keywords: ambient noise, cross correlation

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