Optically stimulated luminescence (OSL) dating provides an absolute age control for marine deep-sea sediment. Optical history of target minerals such as quartz and feldspar in the sediment is critical for the OSL dating that includes not only natural processes but also artificial exposure process to the daylight during sediment coring and sampling. An onboard complete optical covered procedure for marine sediment coring from deep-sea bottom for the OSL sample was developed in order to avoid any optical exposure during the sediment sampling. The methods includes: (1) a black-colored inner tube is set up in the outer core barrel of sediment corer before sediment coring, (2) the black inner corer is carefully drawing out from outer core barrel after returning of the corer on deck, (3) both ends of section (top and bottom parts of the section) are covered by opaque caps just after sectioning of the core, (4) splitting of the whole-rounded core is carried out during the night on deck. The section is moved in the dark room and split into half-semicircle pillar-shaped core by using wire in the room, (5) split sections are pack into large opaque plastic bag and store in refrigerator (3 degree Celsius) before sampling, (6) aliquot sample for the OSL is taken from each section in the dark room and stored in small opaque plastic bag before analysis, (7) any sample preparation for the OSL is performed in the dark laboratory. By following the methods, only top and bottom parts of the section and outer rim of the sediment core may be affected by light exposure during the core processing, but the central part of the aliquot slice of the section is completely safe by exposure to daylight and available for the OSL measurement. The sediment coring in the complete dark side following the method results in fine OSL dating. The proposed procedure of this study will be a methodological standardization of optical covered sediment coring of deep-sea sediment.

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本論はコンクリートに生じた応力を推定する方法を提案する. カルサイト結晶内部の変形である双晶は, 応力によって増加する特徴がある. カルサイト双晶応力計は, カルサイトのみからなる岩石で適用されてきたが, 岩石内部の応力状態が不明瞭であったため, 多鉱岩で使われることはなかった. 個別要素法は粒状体の変形をシミュレートすることができ, 粒子にかかる平均応力が外力に比例することを明らかにした. 岩石の圧縮実験により, 多鉱岩にかかる外力に比例してカルサイト双晶が増加することが確かめられた. これらのことはカルサイト双晶応力計が多鉱岩に適用できることを示し, そしてこのテクニックはコンクリート構造物の安全評価に役立つだろう (特許公開2008-286689).

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続成から低変成度領域の地質温度計としてのビトリナイト反射率は、ISOやJISそれにASTM等でも標準化されている。しかし従来の手法では75μmより微細な粒子の判別及び測定はできなかった。しかし石炭の熱可塑性に着目した判別方法なら微細なビトリナイトであっても判別が可能である。また観察用の広視野照明装置と測定用のスポット照明装置の二つを併設した顕微測定装置は1.6μmの微小な粒子の反射率も測定できる。これにより断層周辺の局所的な温度マッピングや細粒堆積物の温度推定可能になった。

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We had developed a new particle trapping system, “TSUBUTRA”, to collect coarse grains (>67 micrometer) with measurement of grain size analyzer. Eventually, maximum 30 series of coarse grain fraction automatically collected with grain size distribution at one sequence. The system is consisted of controller unit, auto sampler unit, and trapping tubes with mesh sheets. An optical sensor generates a start trigger signal from a movement of auto sample changer of the grain size analyzer, and another optical sensor generates a stop trigger signal from the auto sampler unit, to separate individual trapped samples linked to sequential measurements of grain size distribution. Mesh sheet equipped in the auto sampler unit certainly traps >67 micrometer particles from drain of the grain size analyzer subsequently to the measurement. The TSUBUTRA enable us to observe and identify the grain composition with the size distribution.

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GEOMILL326は, 化石や岩石試料の顕微鏡レベルでのサンプリング方法である実体顕微鏡下での手作業, ミクロトームや旋盤では困難であった1/l000mm単位の正確な切削によるサンプリング技術を実現した. 本技術は, 主にサンゴ, 貝, 鍾乳石などの炭酸塩に認められるマイクロメートル単位の成長線に沿った安定同位体比分析に有効であるが, 単結晶ダイヤモンドドリルビットを用いることにより金属の切削加工も可能である. また, 切削により得られる微量の粉末状サンプル (～数十μg) の回収方法が問題であったが, 高い回収率で所定の化学分析用容器に粉末状サンプルを回収する方法を開発した. 今後, GEOMILL326は微量粉体回収装置とともに高いニーズが期待される.

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四重極型質量分析計を装備した超高真空試料真空破砕装置を実験室外に移動して分析を行うことで, 希ガスおよび共存する炭酸ガス, 水, 窒素のガス分析を機動的に行う可能性を検証した. 移動に際し装置超高真空部の封止に注意を払うことで, 移動後も実験室内での運用と同程度の10^-5 Pa台の圧力が維持された. 火山ガスを大量に含む玄武岩質ガラス6K834R4の分析において, ベースラインからの見かけ変動値は最少で, 装置内の分圧として7×10^-7 Paであった. 今回の結果により, 移送および組み立てにおいて十分な配慮があれば, 所要の電力が供給された観測船や車両において, 流体中の微量ガスのその場分析が可能であるという見通しが得られた.

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Frictional melting experiments were performed on fine grain homogeneous gabbroid with high temperatures induced by frictional heating using a high-velocity apparatus. We examined whether rapid fault movement can equilibrate fault rock gas with atmospheric components by measuring volatile gas and noble gas isotopes from a gabbroid sample using a quadrupole mass spectrometer to detect released gas from the simulated fault rock.
The anticipated rapid equilibration of volatiles during the frictional melting of rocks implies that the noble gas and volatile were released and mixed with the atmosphere during this experiment. Gases released from the sample were collected in a small aluminum tube in nitrogen atmosphere before and after the frictional melting experiment. The gas comprised carbon dioxide, water vapor, hydrogen, helium, and other noble gases. The He/Ar ratio and H₂ concentration are higher than the pre-analysis of N₂ atmosphere. This release of volatiles is consistent with the pseudotachylyte-like post experimental texture of specimen. It is also consistent with the co-seismic geochemical anomaly observed along a natural fault system.

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A two-step chemical procedure to separate Sr from whole igneous rock sample has been developed for the analysis of Sr isotopes by thermal ionization mass spectrometry (TIMS). Firstly, a Sr-bearing fraction and a REE fraction are separated from the major elements of a decomposed sample solution using H⁺ form cation-exchange chromatography. Then the Sr fraction is purified in a second column using extraction chromatography and a Sr specific resin. For small amounts of sample (< 0.1 mg) obtained by micro-milling, only the second step of column separation is applied, directly separating the Sr fraction from the decomposed sample solution. The total procedural blank of these chemical separation procedures are very low, comparable to the lowest blank levels ever reported. The purified Sr is loaded on to a single Re-filament with a Ta ionization activator and measured using TIMS in static multi-collection mode. The mean value and reproducibility for standard ⁸⁷Sr/⁸⁶Sr in NIST SRM 987 with Sr loads of 100 ng and 5 ng are 0.710240 ± 0.000012(2σ, n = 12) and 0.710248 ± 0.000022 (2σ, n = 7), respectively. These values agree well with those from previous studies. Additionally, Sr isotope ratios measured in GSJ igneous rock reference materials JB-2, JA-1 and JR-1 are within error of values from previous studies, verifying the versatility of the technique reported in this study.

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We report a procedure that separates Nd from silicate rock samples using cation exchange chromatography allowing ¹⁴³Nd/¹⁴⁴Nd ratio analyses to be performed by thermal ionization mass spectrometry (TIMS). The procedure obtains the Nd fraction using a two-step column separation. First, a rare earth element (REE) fraction is separated via a cation exchange column with HCl as the eluent. Then, Nd is separated from this REE fraction using a second cation exchange column with α-hydroxy isobutric acid (HIBA) as the eluent. The procedural Nd blanks measured for each step are very low and negligible for ¹⁴³Nd/¹⁴⁴Nd ratios in natural rock samples. The Nd yields are high, with more than 90 % of Nd recovered during each step. Repeated analysis of ¹⁴³Nd/¹⁴⁴Nd ratios in the JNdi-1 standard solution gave a mean value of 0.512096 ± 0.000014 (2 SD, n = 144, RSD % = 0.0014), which is in good agreement with those reported in previous studies. The ¹⁴³Nd/¹⁴⁴Nd ratio obtained for the corrected JNdi-1 fractions using the technique in our laboratory was 0.512094 ± 0.000011 (2 SD, n = 4). We also measured ¹⁴³Nd/¹⁴⁴Nd ratios in several geochemical igneous rock reference materials (JB-la, JB-2, JA-1, and JR-1) producing mean values consistent with available data. These results indicate that the technique for Nd isotope analysis employed at our laboratory provides reliable and accurate data for geochemical studies.

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A fully-automated (FA) technique applying ²⁰⁷Pb-²⁰⁴Pb double spike (DS) to thermal ionization mass spectrometry (TIMS) has been developed (FA- DS- TIMS). A long-term baseline is measured prior to the sample measurement runs and is applied to all of the acquired sample data, avoiding sample wasting caused by frequent baseline measurements during sample runs. FA- DS- TIMS offers reliable fully automated sequential analyses of 10 samples in one batch, including 10 natural runs and 10 runs doped with a spike enriched ²⁰⁷Pb and ²⁰⁴Pb. This cuts operating labor costs, although the measurement time is longer than a conventional TIMS or an identical run using multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS).
The isotopic ratios of the ²⁰⁷Pb-²⁰⁴Pb double spike used in this study are ²⁰⁶Pb/²⁰⁴Pb = 0.10203, ²⁰⁷Pb/²⁰⁴Pb = 3.8717 and ²⁰⁸Pb/²⁰⁴Pb = 0.18865 when normalized to NIST SRM 982 ²⁰⁸Pb/²⁰⁶Pb = 1.00016. Average values for NIST SRM 981 containing 7.5 and 15 ng Pb are ²⁰⁶Pb/²⁰⁴Pb = 16.9390 ± 0.0017, ²⁰⁷Pb/²⁰⁴Pb = 15.4972 ± 0.0017, ²⁰⁸Pb/²⁰⁴Pb = 36.7213 ± 0.0045 (errors are 2SD, n = 12). These are within error of recently reported values obtained by DS-TIMS and DS-MC-ICP-MS. The reproducibility of ²⁰⁸Pb/²⁰⁴Pb in this study is 0.003% using 15 ng Pb, and 0.009% using 7.5 ng Pb. These are similar to, or better than, those reported by various other methods. The average values for JB-2 containing 20ng Pb are ²⁰⁶Pb/²⁰⁴Pb = 18. 3419 ± 0. 0027, ²⁰⁷Pb/²⁰⁴Pb = 15.5622 ± 0.0026, ²⁰⁸Pb/²⁰⁴Pb = 38.2814 ± 0.0078 (errors are 2SD, n = 5) and are comparable to those reported in recent studies. These results show that the new technique is reliable in terms of both accuracy and precision.

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海洋研究開発機構 (JAMSTEC) では, 海底下深部構造を求め地震や津波の発生メカニズムを解明するため, 1995年より制御震源による構造探査を開始した. 1997年からは海溝型巨大地震発生過程解明をめざして「かいれい」に構造探査システムを艤装, 1999年にエアガン大容量化とOBS100台化および「かいれい」「かいよう」2船体制となった. 2004年に伊豆小笠原海域等での集中的探査に対応するため, ストリーマーケーブル延長やOBS台数追加という増強を実施した. これらにより海溝型巨大地震発生過程や島弧成長過程の解明に関する重要な知見が得られた. しかし今後構造研究と掘削等による物質科学との統合をめざすため, 構造探査システムの高精度化をはかる必要がある. このような観点から, 2008年に「かいれい」のエアガンアレイチューンドアレイ化, ストリーマーケーブルの高分解能化を行い, 想定した性能を確認した. 今後も科学的要求にこたえるべく技術的更新や増強をはかる必要があると考えられる.

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Spatio-temporal distribution of temperature beneath the seafloor provides essential information on the thermal and hydrological structure and dynamics. We developed some long-term temperature monitoring systems for observation at seafloor, in a few-m-deep hole, and in deep boreholes. Measurements in a shallow hole were carried out at a hydrothermal field in the southern Mariana Trough and in the western Sagami Bay, and thermistor array system was tested in two onland boreholes in the northeastern Japan for up to 1.5 years. The thermistor elements coated with ‘Teflon’ was proved to be stable and reliable in a temperature range of 0 to 80 °C for more than one year. Shorter time scale and rather aperiodic variations in temperatures were commonly observed in boreholes. These variations would result from convection or any kind of flow within the hole. Such variation can be as large as any signal from the formation, so more careful assessment is necessary for the deep-borehole observatory that is in development at JAMSTEC.

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During the past five years, the electro magnetic (EM) team of the Japan Agency for Marine Science-Technology (JAMSTEC) has conducted many observations to investigate the crustal and mantle structure in pursuit of various scientific aims in collaboration with other universities and institutes. Around the Nankai subduction zone, we constructed a crustal and regional resistivity model, and detected the low resistivity zone with subduction. Moreover, we developed new geophysical survey tools—the small ocean bottom electro magnetometer (OBEM) and the deep-towed DC resistivity survey system—to investigate the shallow crustal structure. We also conducted an ocean bottom EM array study in the Philippine Sea and other areas to investigate the mantle structure using long-term OBEMs, thereby obtaining high-quality EM data.

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海底に近い場所で地磁気を測ると, 高分解能地磁気異常が得られ, 海洋地殻の詳細な磁化構造や, 海洋地殻に記された古地磁気変動を調べることに役立つ. 潜水調査船を利用した地磁気調査では, 磁力計のシステムが簡便である, 海底の画像や採取試料等の他の観測情報が同時に入手できる等の長所がある. 潜水船は海底直上を移動できるので, 数mの分解能が期待できる. 「しんかい6500」に深海磁力計を搭載しての地磁気観測が幾度か行われてきた. それらにより観測経験の蓄積,研究成果が積み重ねられてきた. 一方で, 計測に関しての問題点も次第に浮き彫りにされてきている. 潜水船は地質観察優先の高度, 航行をすること, センサーの設置位置, 短い測線長などの制約により, 地磁気測定に適したオペレーションを実現し難い. 地磁気データのキャリブレーション法, オペレーション法には改善の余地が十分にあり, 今後の検討が肝要である. 潜水調査船で海底に近づいて観測することならではの長所を生かした地磁気観測は, 潜水船観測の幅を拡げ, 海洋底調査研究に非常に大きな効力を発揮することができると期待される.

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深海底堆積物の採取によって連続的な地球科学的情報を得る事ができる. その手法としてピストン式採泥器 (通常のピストンコアラーやIntegrated Ocean Drilling ProgramにおけるAdvanced Piston Core Systemといったピストンコアラー) が使われている. これらのピストン式採泥器はグラビティー式コアラーに比べ, ピストンが作る負圧の効果で長い堆積物コアを採取することができる. しかし, ピストン式採泥器は, ピストンの作用が適切でないと, 堆積物コアを変形させ, 基本的な研究データに影響を与える可能性がある. こうした変形は残留磁化方位 (古地磁気方位) あるいは帯磁率異方性(磁気ファブッリク) によって推定する事ができる.

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海底に設置された地震計は, 0.1Hzより低い周波数帯域において海底底層流の影響を受けることが知られている. 底層流による低周波ノイズを低減するためには, 地震計と海底面とのカップリングを向上させる必要がある. 本研究では, 自由落下で地震計を設置する海底地震観測において低周波ノイズを低減するため, 異なる形状のおもりを用いた比較実験を行った. 従来の井型おもりと, 新しく考案した平板おもりをそれぞれ装着した2台の海底地震計を, 紀伊半島沖熊野灘に2007年12月末から2008年2月初旬の約2ケ月間設置した. 実験の結果, 水平動成分に関しては両者のノイズレベルは変わらなかった. しかし, 上下動成分に関しては, 平板おもりを装着した地震計は従来の井型おもりに比べて0.01Hzより低い周波数帯域においてノイズレベルの低減がみられた.

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深海用微差圧計 (DPG) は非常に感度の高い圧力計で水晶水圧計と比べ低いノイズを持つため10mHzから1Hzの帯域での地震や音響現象の観測に適している. DPGの周波数レスポンスは, 設置される場所の温度や圧力環境に依存する. 海底および実験室でDPGに長周期の小さな圧力変化を与えParoscientific社の水晶水圧計と比較することによりDPGの周波数レスポンスを校正する方法を開発した. これらの校正方法を用いることにより, DPGの周波数レスポンスおよび感度を正確に校正することが実現される.

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The existence of fluid in seismogenic zones plays a key role in great earthquakes. Data on electrical conductivity structures obtained by electromagnetic surveys across the great earthquake zones show that the seismically locked zones correspond to low conductive zones. This low conductivity is possibly interpreted as relatively low fluid content in rock or sediment. For more discussion on the role of fluid in earthquake occurrence, we have recently started an electromagnetic and seismological monitoring project using long submarine cables off Toyohashi, in the southwest part of Japan's main island. The cables are located on the Tokai seismogenic zone, where both slow-slipping and locked zones are obvious by GPS observation. We constructed a seafloor observatory at the tip of the western cable, including a seismometer, pressure gauges, a magnetometer, voltmeters, and thermometers. These sensors measure and transfer data on the seafloor environment in real time. The data will be used for passive and active monitoring below the seafloor, including in the Tokai seismogenic zone.

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我々はより精度・分解能の高い地震波トモグラフィーモデルを得るために, 特に観測点密度が低い太平洋地域に焦点を当て, 様々な地震観測網で得られた地震波形記録から地震波走時を精度よく測定し, 地震波走時データベースの作成を行った. 測定としてはハンドピッキング法によるP, PcP, S相などの絶対走時の測定, 波形相関によるPP-P, S-P走時差測定, 同じく波形相関によるP波の2観測点間の相対走時測定を行った. グローバルに展開されている広帯域地震計, 日本全土に展開されている短周期地震計をはじめ, 広帯域海底地震計, 短周期海底地震計のデータも使用し, 15万個に及ぶ地震波走時データを得た.

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We have developed a new system to visualize observation data obtained in JAMSTEC research vessels. We use Google Earth as a data browser. Google Earth supports an XML-based language, called KML (Keyhole Markup Language), to plot data on Google Earth. We have developed a program, called KML generator, to convert the original data to KML. Our KML generator accepts the research data such as navigation data, sea water salinity and temperature data (CTD data), geomagnetic field data, and bathymetry data obtained in research vessels. The KML generator enables us to visualize those data on Google Earth quickly and compare with other data easily. It would become a powerful tool to interpret these research data and to get insights toward Earth's dynamical processes.

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Real-time monitoring of broadband seismographs through the Internet enables us to discover various technical troubles of broadband seismic observation system of Pacific21 and to take measures to solve them at the next field maintenance occasions. This paper summarizes the characteristics and the countermeasures of four typical troubles that we discovered from real-time monitoring or encountered in our maintenance work. One trouble was a deviation of seismometer's response owing to insufficient insulation of its connector. It was very effective to protect the connectors from moisture as a preventive measure. Another trouble was that spike-like noise was generated in the seismometer's output when some equipment demanded high current from the power supply. In order to remove the noises, we have two solutions: to disconnect extra impedance from the grounding line for power return, and to improve the power supply. A third was high frequency noise from one-sided connection of differential signaling. It is important to check the waveforms diligently to find this trouble as soon as possible. The other was that the data logger's dedicated hard disk often stopped for a maximum of several hours. The frequency of bard disk's shutdown seems to depend on its firmware version. For this trouble, we learned that we should operate equipment with various firmware versions for some time before installation.

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グローバル地震観測は地球内部ダイナミクス研究のための有力な手段のひとつである. IFREEは西太平洋域を中心に広帯域地震観測網を展開, 運用をおこなっている. 良質なデータを得るためには高い稼動率を維持することが必須である. 当グループは収録システムの更新と通信回線の整備によって, 常時データの取得と観測点の状況を監視するシステムを構築した. その結果, 観測点の稼動状況が飛躍的に改善し, 且つデータの伝送, 保管の多重化によって欠測の少ない連続的なデータセットの取得が実現された.

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This paper briefly explains a recently developed numerical technique called PDS-FEM and its dynamic extension. PDS-FEM is a simple and efficient numerical technique for modeling propagation crack in brittle materials. The discretization scheme used in this new numerical technique is called particle discretization scheme (PDS). PDS uses characteristic functions of Voronoi and Delaunay tessellations to discretize function and its derivatives, respectively. The uses of non-overlapping shape functions facilitate simple and numerically efficient failure treatment. We considered the dynamic extension of PDS-FEM and simulated several real life experiments, to illustrate the potential of simulating dynamic crack propagation of problems requiring fine domain discretizations.

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海洋研究開発機構(JAMSTEC), 地球内部変動研究センター (IFREE), 地殻ダイナミクス研究グループで開発された高速個別要素法コードHiDEM (Hyper Intelligent Discrete Element Method) のアルゴリズムと高速プログラミングについての概要を説明する. また, HiDEMの科学と産業に対する貢献を幾つかの例を紹介しながら説明する.

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屈折法・広角反射法構造探査データを用いた走時解析は, リソスフェアの地震波速度構造の不均質性をイメージングする効果的な手段である. しかし, 構造解析は非線形性が強い問題であることもあり, 伝統的に試行錯誤的, 主観的な解析アプローチを取らざるを得ず, 客観的なモデルを得ることが難しかった. 近年の観測の大規模化, 高密度化により得られる大量のデータのお陰で, 主観的な作業を大輻に減らした解析アプローチが採用できるようになり, 客観的で信頼性の高い構造モデリングが可能になってきた. 本論文では, 大規模探査データを用いた構造モデリング手法の概要について, 海洋研究開発機構が開発・採用している解析手法やソフトウェアを中心にして紹介する.

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