Japan Geoscience Union最新文献_第2页

The Daytime and Nighttime Mapped Whistler Plasmapause Observed by DEMETER 用DEMETER观测白天和夜间惠斯勒等离子体顶

Japan Geoscience Union

Pub Date : 2019-03-14 DOI: 10.5194/egusphere-egu2020-13485

Chao-Yen Chen, T. Liu

This paper investigates the plasmapause positions in the ionosphere by measurement of the whistler count probed by DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite in the daytime at 1030 LT (local time) and the nighttime at 2230 LT during 2005-2010. The whistler finds the plasmapause position which can be clearly allocated in both daytime and nighttime. We examine the nighttime/daytime plasmapause in various longitudes, solar activities, seasons, and geomagnetic actives. Results show that the daytime plasmapause appears in the equatorward side of the nighttime one. Both the daytime and nighttime plasmapause are sensitive to solar activity, which move equatorward form the low to high solar activity in the study period. The seasonal variation of the plasmapause are rather random and insignificant. During magnetic disturbed condition, the plasmapause tend to move equatorward.

本文利用地震带电磁发射探测卫星(DEMETER)在2005-2010年白天1030lt(当地时间)和夜间2230lt(当地时间)探测到的哨声数，研究了电离层等离子体ause的位置。哨声找到了白天和夜间都能清晰分配的浆层顶位置。我们研究了不同经度、太阳活动、季节和地磁活动的夜间/日间等离子体ause。结果表明，白天等离子体顶出现在夜间等离子体顶的赤道侧。白天和夜间的等离子体层顶对太阳活动都很敏感，在研究期间，等离子体层顶由太阳活动低峰向高峰方向向赤道方向移动。等离子体顶的季节变化是相当随机和不显著的。在磁扰动条件下，等离子体顶倾向于向赤道方向移动。

引用次数: 0

Dynamical lifetime of the Oort Cloud new comets under planetary perturbation 行星扰动下奥尔特云新彗星的动力学寿命

Japan Geoscience Union

Pub Date : 2019-03-14 DOI: 10.1002/essoar.10504761.1

Takashi Ito, A. Higuchi

引用次数: 0

Along-strike variations in protothrust zone characteristics at the Nankai Trough subduction margin 南开海槽俯冲边缘原冲断带特征的沿走向变化

Japan Geoscience Union

Pub Date : 2019-03-14 DOI: 10.1130/GES02305.1

Hannah B. Tilley, G. Moore, M. Yamashita, S. Kodaira

Protothrust zones (PTZs) are assumed to control the development of new frontal thrusts at subduction zones. PTZs are areas of incipient thrust faulting between the deformation front and the frontal thrust. However, limited resolution of previous seismic studies has hindered the study of their role in subduction accretion. New high-resolution seismic reflection surveys enabled detailed analysis of the PTZ along the Nankai Trough, SE Japan. Seventeen multichannel seismic reflection lines were collected perpendicular to the trench axis between Cape Ashizuri and Cape Muroto using a 1200m long, 192 channel hydrophone cable and a 380 in (5.24L) cluster airgun array. These lines were processed using pre-stack depth migration. PTZs only existed where a turbidite sequence was present beneath the trench wedge. The PTZs consisted of closely spaced, sub-parallel protothrusts that decreased in spacing and increased in length landward. Where the turbidites were truncated by basement topography, there was a transitional PTZ heterogeneous protothrusts and small displacement thrust faults. We hypothesize that elevated pore pressures due to the low permeability hemipelagic sediment inhibit the formation of PTZs and favor small displacement thrusts in a narrow trench wedge. Conversely, turbidite layers within the hemipelagic sediment allow drainage and reduce the pore pressure. This increases the effective stress and shear strength on faults, resulting in strain localizing protothrusts. This implies that the changes in pore pressure imposed by differences in the sediment permeability control the style of deformation in the trench wedge and consequently, the geometry of the accretionary wedge.

原逆冲带被认为控制着俯冲带中新锋面逆冲的发育。断层带是位于变形前缘和前缘逆冲之间的早期逆冲断裂区。然而，以往地震研究的分辨率有限，阻碍了对它们在俯冲增生中的作用的研究。新的高分辨率地震反射测量能够详细分析日本东南部南开海槽沿线的PTZ。17条多通道地震反射线垂直于ashhizuri角和Muroto角之间的海沟轴线，使用1200米长、192通道的水听器电缆和380英寸(5.24L)的集束气枪阵列。这些线是用叠前深度偏移处理的。ptz只存在于海沟楔下有浊积层序的地方。PTZs由紧密间隔的亚平行原冲断层组成，原冲断层向陆地方向间距减小，长度增加。浊积岩被基底地形截断处发育过渡性PTZ非均质原冲断层和小位移逆冲断层。我们假设，低渗透半深海沉积物造成的孔隙压力升高抑制了ptz的形成，有利于狭窄海沟楔中的小位移逆冲。相反，半深海沉积物中的浊积层允许排水并降低孔隙压力。这增加了断层上的有效应力和剪切强度，导致应变局部化原始逆冲。这表明，沉积物渗透性的差异所引起的孔隙压力的变化控制了海沟楔的变形样式，从而控制了吸积楔的几何形状。

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引用次数: 3

Thermal fluid migration in the Kumano forearc basin, Nankai Trough, estimated via vitrinite reflectance measurement 南开海槽熊野弧前盆地镜质组反射率热流体运移研究

Japan Geoscience Union

Pub Date : 2018-08-15 DOI: 10.1130/2018.2534(09)

K. Kawabata, Arito Sakguchi, Y. Hamada, T. Tsuji, Y. Kitamura, S. Saito

Sediment analysis and the thermal history of the Kumano forearc basin and slope basin sediments in the Nankai Trough were studied through chemical and mineral composition analyses and the vitrinite reflectance measurement of sediments from Integrated Ocean Drilling Program Sites C0004, C0007, and C0009. The immobile component ratio (TiO2/P2O5) suggests that the depositional source of sedimentary rock underlying the Kumano forearc basin (Unit IV of Site C0009) is different from those in the Kumano forearc basin (Unit III of Site C0009). The results support that Unit IV is not a basin sediment but a part of an old accretionary prism. The source of Unit IV is similar to that of the Shikoku basin sediment currently situated in the accretionary toe and subduction input, based on mineral composition analysis. The similarity is well explained by sediment transport from the East China Sea. In the Kumano forearc basin, a paleothermal anomaly was detected at Site C0009 using vitrinite reflectance measurement. The anomaly peak is 200 m wide with a maximum temperature of 79 oC. Estimation of reflectance increase through vitrinite reaction promotion suggests that 80–100 oC thermal fluid had passed with at least 100 ky, thus causing the anomaly. The thermal fluid upwelling might relate to ancient splay fault activity near Site C0009. The thermal anomaly zone in the Kumano forearc basin at Site C0009 coincides with the currently fluid conduit zone. These results indicate that massive fluid circulation occurs spatially and temporally through a large thrust in the subduction zone.

通过对综合海洋钻探项目C0004、C0007和C0009 3个地点沉积物的化学、矿物成分分析和镜质组反射率测量，研究了南开海槽熊野弧前盆地和斜坡盆地沉积物的沉积分析和热史。固定组分比值(TiO2/P2O5)表明，熊野前弧盆地(C0009遗址第四单元)下伏沉积岩的沉积源与熊野前弧盆地(C0009遗址第三单元)下伏沉积岩的沉积源不同。结果支持第四单元不是盆地沉积物，而是一个古老的吸积棱镜的一部分。根据矿物成分分析，第四单元沉积物的来源与目前位于增生趾和俯冲输入的四国盆地沉积物相似。这种相似性很好地解释了来自东海的泥沙搬运。利用镜质组反射率测量，在熊野弧前盆地C0009测点发现了一个古温热异常。异常峰宽200 m，最高气温79℃。镜质组反应促进反射率增加估计表明，80 ~ 100℃的热流体至少通过了100天，从而导致异常。热流体上涌可能与C0009遗址附近的古展张断裂活动有关。熊野前弧盆地C0009站点的热异常带与当前流体管道带重合。这些结果表明，在空间和时间上，大量流体环流是通过俯冲带的大逆冲作用发生的。

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引用次数: 3

Estimation of azimuthal angle of S-wave anisotropy using virtual cross-dipole data generated by the Virtual Source Method 利用虚源法生成的虚交叉偶极子数据估计横波各向异性方位角

Japan Geoscience Union

Pub Date : 2018-05-24 DOI: 10.3997/2352-8265.20140236

Yusuke Watanabe, H. Mikada, J. Takekawa

A novel scheme we proposed for analyzing S-wave azimuthal anisotropic angle in the subsurface below the seafloor has been applied to a tilted transversally isotropic medium of horizontal axis of symmetry (HTI). The proposed method utilizes the virtual source method to acquired data set with single ocean bottom seismometer and an air-gun array. To evaluate the effectiveness of our scheme, we conducted the numerical experiments for 3D model with a tilted anisotropic target. We applied this method to the synthetic data to make the virtual cross-dipole data at each shot location. Finally we applied the Alford rotation to estimate an azimuthal angle of the anisotropy of the target layer. Our numerical results show the limitations of the Alford rotation. Especially, the Alford rotation assumes that a dipole signal in one direction has an amplitude equivalent to the other dipole to the other normal direction in the cross dipole measurements. Since our approach could not assume the equality of the amplitudes for each of the cross dipole signals, we conclude that a strategy using full waveforms needs to be taken into consideration for estimating azimuthal angle of tilted targets.

我们提出了一种分析海底以下地下s波方位各向异性角的新方案，并将其应用于倾斜的横向各向同性水平对称轴介质中。该方法采用虚拟源方法，利用单个海底地震仪和气枪阵列采集数据集。为了验证该方案的有效性，我们对具有倾斜各向异性目标的三维模型进行了数值实验。我们将该方法应用于合成数据，在每个拍摄位置制作虚拟交叉偶极子数据。最后，我们应用Alford旋转来估计目标层各向异性的方位角。我们的数值结果显示了阿尔福德旋转的局限性。特别是，Alford旋转假设在交叉偶极子测量中，一个方向上的偶极子信号具有与另一个偶极子到另一个法向的振幅相等的振幅。由于我们的方法不能假设每个交叉偶极子信号的振幅相等，因此我们得出结论，需要考虑使用全波形的策略来估计倾斜目标的方位角。

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引用次数: 0

Numerical study on the interaction of solid grains with fluid in the production of natural resources 自然资源生产中固体颗粒与流体相互作用的数值研究

Japan Geoscience Union

Pub Date : 2018-05-24 DOI: 10.3997/2352-8265.20140234

N. Tanimoto, H. Mikada, J. Takekawa

The sanding is recognized as one of the main problems in producing hydrocarbon resources. Although it is important to predict the occurrence of the sanding during production, the prediction or countermeasure still remains to be established. In this study, we conduct numerical simulation of fluid-solid multi-phase flow in order to investigate the factors which affect the occurrence of the sanding. Our numerical model is a fluid path consists of a set of planar plates of a finite length filled by fluid and a mound of small solid grains. A fluid flow is produced by the pressure gradient with different magnitudes between the both end of the path. We found that a few small grains leave the mound with a high pressure gradient whereas no floating grains were observed with a low pressure gradient. We also observed a reasonable change in the flow velocity and relative permeability when the floating of small grains occurs. This result indicates that the sanding can be detected by observing the time variation of flow rate during production.

出砂是油气资源开发中的主要问题之一。虽然在生产过程中对出砂的发生进行预测是很重要的，但预测或对策仍有待建立。在本研究中，我们对流固多相流动进行了数值模拟，以探讨影响砂化发生的因素。我们的数值模型是由一组由流体填充的有限长度的平面板和一堆小固体颗粒组成的流体路径。流体流动是由路径两端不同大小的压力梯度产生的。我们发现少量小颗粒在高压梯度下离开土丘，而在低压梯度下没有观察到漂浮颗粒。我们还观察到，当小颗粒发生漂浮时，流速和相对渗透率也发生了合理的变化。结果表明，可以通过观察生产过程中流量的时间变化来检测出出砂。

引用次数: 0

Checkerboard resolution test for natural earthquake tomography of volcanic islands in Tokyo 东京火山岛自然地震层析成像的棋盘解析度测试

Japan Geoscience Union

Pub Date : 2018-05-24 DOI: 10.3997/2352-8265.20140230

Kentaro Omori, Y. Oda

In natural earthquake tomography targeting a single volcano, temporary seismic observation is carried out in order to improve resolution in general. However, since the number of observation points and observation period are limited, it is important to grasp the presumable resolution in advance. Therefore, we conducted to examine how much resolution we can estimate the underground velocity structure by performing temporary seismic observation with how many observation points and observation period (the number of earthquakes), when carrying out natural seismic tomography on Hachijojima, Kozushima and Niijima of volcanic islands in Tokyo by using numerical experiments, a checkerboard resolution test (CRT). CRT is one of the reasonable tests to show the resolution of the natural earthquake tomography and to evaluate the influence of parameters with good resolution (a pair of grid point spacing, observation points and number of earthquakes) on the resolution. As the results of parametric study using CRT, we have found that in every island I have researched, when setting a pair of some grid point spacing, some number of observation points and some number of earthquakes, they were possible to image with a resolution of some degree. Considering that temporary seismic observation will be carried out in volcanic islands, Tokyo, in the future, the data obtained in this study will be very important for establishing the observation plan.

在以单一火山为目标的自然地震层析成像中，一般采用临时地震观测来提高分辨率。但是，由于观测点数量和观测周期有限，因此提前掌握假定分辨率非常重要。因此，在对东京火山岛八丈岛、小竹岛和新岛进行自然地震层析成像时，采用棋盘分辨率试验(CRT)的数值实验方法，考察了通过临时地震观测，以多少个观测点和观测周期(地震次数)估算地下速度结构的分辨率。CRT是显示自然地震层析成像分辨率和评价分辨率较好的参数(一对网格点间距、观测点和地震次数)对分辨率影响的合理方法之一。使用CRT进行参数化研究的结果发现，在我所研究的每一个岛屿上，当设置一对一定的网格点间距、一定数量的观测点和一定数量的地震时，它们都可以以一定的分辨率成像。考虑到未来将在东京火山岛进行临时地震观测，本研究获得的数据对于制定观测计划非常重要。

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引用次数: 0

Unexpected Consequences of Transverse Isotropy 横向各向同性的意外后果

Japan Geoscience Union

Pub Date : 2018-03-14 DOI: 10.1785/0120200205

H. Kawakatsu

In a series of papers, Kawakatsu et al. (2015) and Kawakatsu (2016a, b, 2017) introduced and discussed a new parameter, ηκ, that characterizes the incidence angle dependence (relative to the symmetry axis) of seismic body wave velocities in a transverse isotropy (TI) system. With the properly defined new set of parameters, Kawakatsu (2016b) further demonstrated that sensitivities of those parameters to Rayleigh wave phase velocity made much more sense and thus they were useful for long-period seismology. More recently, Kawakatsu (2017) showed how the reflection and transmission coefficients behaved in terms of ηκ. During the course of these exercises, several nontrivial consequences of transverse isotropy are realized and summarized as follow: (1) a trade-off exists between ηκ and Vp/Vs-ratio if assumed for isotropy; (2) P-wave velocity (anisotropy) strongly influences the conversion efficiency of P-to-S and S-to-P, as much as S-wave velocity perturbation does; (3) Rayleigh wave phase velocity has substantially sensitivity to P-wave anisotropy near the surface. These findings, especially the last two, might deserve careful attention in interpretation of results of popular seismic analysis methods, such as receiver function analyses and ambient noise Rayleigh wave dispersion measurements. Especially, the strong influence of P-wave anisotropy to P-to-S and S-to-P conversion may be essential to the receiver function analysis, because, for isotropic media, we typically attribute the primary receiver function signals to S-wave velocity changes. Considering that the receiver function analysis has become a popular and powerful tool to investigate the crustal and upper mantle structures, it seems important to fully investigate to what extent and under what circumstances the effect might be significant.

Kawakatsu et al.(2015)和Kawakatsu (2016a, b, 2017)在一系列论文中引入并讨论了一个新的参数ηκ，该参数表征了横向各向同性(TI)系统中地震体波速度的入射角依赖性(相对于对称轴)。Kawakatsu (2016b)进一步证明了这些参数对瑞利波相速度的敏感性更有意义，因此它们对长周期地震学很有用。最近，Kawakatsu(2017)展示了反射系数和透射系数在ηκ方面的表现。在这些练习过程中，实现了横向各向同性的几个重要后果，并总结如下:(1)如果假设各向同性存在ηκ和Vp/Vs-ratio之间的权衡;(2)纵波速度(各向异性)对p - s和s - p转换效率的影响与横波速度扰动的影响相同;(3)瑞利波相速度对近地表纵波各向异性有较强的敏感性。这些发现，尤其是最后两个发现，在解释流行的地震分析方法(如接收函数分析和环境噪声瑞利波色散测量)的结果时可能值得仔细注意。特别是，纵波各向异性对p - s和s - p转换的强烈影响可能对接收函数分析至关重要，因为对于各向同性介质，我们通常将主要接收函数信号归因于s波速度变化。考虑到接收函数分析已经成为研究地壳和上地幔结构的一种流行而有力的工具，充分研究在什么程度上和在什么情况下这种影响可能是显著的，似乎很重要。

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引用次数: 1

Impact of mid-glacial ice sheets on the recovery time of the AMOC: Implications on the frequent DO cycles during the mid-glacial period 中冰期冰盖对AMOC恢复时间的影响:对中冰期频繁DO旋回的影响

Japan Geoscience Union

Pub Date : 2018-03-14 DOI: 10.5194/egusphere-egu2020-7844

S. Sherriff-Tadano, A. Abe‐Ouchi

Paleo reconstructions such as ice cores have revealed that the glacial period experienced frequent climate shifts between warm interstadials and cold stadials. The duration of these climate modes varied during glacial periods, and that both the interstadials and stadials were shorter during mid-glacial compared with early glacial period. Recent studies showed that the duration of the interstdials was controlled by the Antarctic temperature through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, similar relation was not found for the stadials, suggesting that other climate factors (e.g., differences in ice sheet size, greenhouse gases and insolation) might have played a role. In this study, we investigate the role of glacial ice sheets on the duration of stadials. For this purpose, freshwater hosing experiments are conducted with an atmosphere-ocean general circulation model MIROC4m under early-glacial and mid-glacial conditions. Then, a sensitivity experiment is conducted modifying only the configuration of the ice sheets. The impact of mid-glacial ice sheets on the duration of the stadials is evaluated by comparing the recovery time of the AMOC after the cessation of the freshwater forcing. We find that the expansion of glacial ice sheets during mid-glacial shortens the recovery time of the AMOC. Partially coupled experiments, which switch the surface winds between the two experiments, show that the differences in the surface wind cause the shorter recovery time under mid-glacial ice sheet. The wind shortens the recovery time by increasing the surface salinity and decreasing the sea ice at the deepwater formation region. Thus the results suggest that differences in the surface wind between mid-glacial and early glacial ice sheets play an important role in causing shorter stadials during mid-glacial period.

冰芯等古重建表明，冰期经历了温暖间冰期和寒冷间冰期之间频繁的气候变化。这些气候模态的持续时间在不同冰期有所不同，中冰期间冰期和间冰期均较早冰期短。最近的研究表明，间隙期的持续时间是由南极温度通过其对大西洋经向翻转环流(AMOC)的影响而控制的。然而，在冰川上没有发现类似的关系，这表明其他气候因素(如冰盖大小、温室气体和日照的差异)可能起了作用。在这项研究中，我们研究了冰川冰盖对冰期持续时间的作用。为此，在早冰期和中冰期条件下，利用大气-海洋环流模式MIROC4m进行了淡水冲洗试验。然后，只修改冰盖的结构进行灵敏度实验。通过比较淡水强迫停止后AMOC的恢复时间来评估中冰原对冰期持续时间的影响。研究发现，中冰期冰盖的扩张缩短了AMOC的恢复时间。部分耦合实验在两个实验之间切换地表风，结果表明地表风的差异导致中冰期冰盖下的恢复时间更短。在深水地层区，风通过增加地表盐度和减少海冰来缩短恢复时间。结果表明，中冰期和早冰期地表风的差异是造成中冰期冰碛物较短的重要原因。

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引用次数: 0

DEM-SJM combined 2D-hydraulic fracturing simulation for consideration of the influence of differential stress DEM-SJM结合二维水力压裂模拟，考虑差应力影响

Japan Geoscience Union

Pub Date : 2018-03-14 DOI: 10.3997/2352-8265.20140228

H. Ohtani, H. Mikada, J. Takekawa

For improving the production of conventional oil and shale gas, the practice of hydraulic fracturing has been increasing in recent years. In addition, hydraulic fracturing is used for the development of geothermal energy known as hot dry rock (HDR) geothermal power, and enhanced geothermal system (EGS), and for measuring the rock failure strength and the orientation of principal stress direction, etc. On the other hand, hydraulic fracturing has some environmental impact, such as pollution caused by chemical substances in injected proppant or fluid, induced seismicity, etc. Since it is necessary to minimize the environmental impact, techniques to predict propagating directions and distances of fractures to be generated hydraulically, which are known still very difficult, have been waited for. In this paper, we demonstrate the influence of differential stress and the anisotropy using numerical experiments based on distinct element method (DEM) combined with smooth joint model (SJM). Hydraulic fractures in general propagate in the direction of maximum principal stress on large differential stress conditions. As the differential stress decreased, the propagating directions hydraulic fractures curves to the direction of bedding plane, i.e., anisotropic direction of weak rock strength, and sometimes fractures branch to plural directions. These results suggest that the behavior and propagating direction of hydraulic fractures are strongly influenced by both the differential stress and the rock strength anisotropy in the underground shallow layer.

为了提高常规石油和页岩气的产量，近年来水力压裂的实践越来越多。此外，水力压裂还用于地热能源的开发，即热干岩地热发电(HDR)和增强型地热系统(EGS)，以及岩石破坏强度和主应力方向的测定等。另一方面，水力压裂有一定的环境影响，如注入支撑剂或流体中的化学物质造成污染，诱发地震活动等。由于有必要将对环境的影响降至最低，因此人们一直在等待水力压裂技术来预测裂缝的传播方向和距离，而这一技术目前仍然非常困难。本文采用离散元法(DEM)和光滑节理模型(SJM)相结合的数值实验方法，论证了不同应力和各向异性的影响。在大差应力条件下，水力裂缝一般沿最大主应力方向扩展。随着差应力的减小，水力裂缝的扩展方向向顺层面方向，即弱岩石强度的各向异性方向弯曲，有时裂缝会向多个方向分支。这些结果表明，地下浅层水力裂缝的行为和扩展方向受到差应力和岩石强度各向异性的强烈影响。

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引用次数: 0