Attenuation and dispersion ofSH waves due to scattering by randomly distributed cracks

The effect of randomly distributed cracks on the attenuation and dispersion ofSH waves is theoretically studied. If earthquake ruptures are caused by sudden coalescence of preexisting cracks, it will be crucial for earthquake prediction to monitor the temporal variation of the crack distribution. Our aim is to investigate how the property of crack distribution is reflected in the attenuation and dispersion of elastic waves.We introduce the stochastic property, in the mathematical analysis, for the distributions of crack location, crack size and crack orientation. The crack size distribution is assumed to be described by a power law probability density (p(a) a ^– fora _minaa _max according to recent seismological and experimental knowledge, wherea is a half crack length and the range 13 is assumed. The distribution of crack location is assumed to be homogeneous for the sake of mathematical simplicity, and a low crack density is assumed. The stochastic property of each crack is assumed to be independent of that of the other cracks. We assume two models, that is, the aligned crack model and the randomly oriented crack model, for the distribution of crack orientation. All cracks are assumed to be aligned in the former model. The orientation of each crack is assumed to be random in the latter model, and the homogeneous distribution is assumed for the crack orientation. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.We observe the following features common to both the aligned crack model and the randomly oriented crack model. The attenuation coefficientQ ^–1 decays in proportion tok ^–1 in the high frequency range and its growth is proportional tok ² in the low frequency range, wherek is the intrinsic wave number. This asymptotic behavior is parameter-independent, too. The attenuation coefficientQ ^–1 has a broader peak as increases and/ora _min/a _max decreases. The nondimensional peak wave numberk _p a _max at whichQ ^–1 takes the peak value is almost independent ofa _min/a _max for =1 and 2 while it considerably depends ona _min/a _max for =3. The phase velocity is almost independent ofk in the rangeka _max<1 and increases monotonically ask increases in the rangeka _max>1. While the magnitude ofQ ^–1 and the phase velocity considerably depend on the orientation of the crack in the aligned crack model, the above feature does not depend on the crack orientation.The accumulation of seismological measurements suggests thatQ ^–1 ofS waves has a peak at around 0.5 Hz. If this observation is combined with our theoretical results onk _p a _max, the probable range ofa _max of the crack distribution in the earth can be estimated for =1 or 2. If we assume 4 km/sec as theS wave velocity of the matrix medium,a _max is estimated to range from 2 to 5 km. We cannot estimatea _max in a narrow range for =3.     

A Quantitative Method of Detecting Transient Rossby Wave Phase Speed: No Evidence of Slowing Down with Global Warming

Based on the Complex Empirical Orthogonal Functions(CEOFs) of bandpass-filtered daily streamfunction fields, a quantitative method of detecting transient(synoptic) Rossby wave phase speed(RWPhS) is presented. The transient RWPhS can be objectively calculated by the distance between a high(or low) center in the real part of a CEOF mode and its counterpart in the imaginary part of the same CEOF mode divided by the time span between two adjacent peaks(or bottoms) of two principal component curves f...     

Diverse Range of Mineralization Induced by Phase Separation of Hydrothermal Fluid: Case Study of the Yonaguni Knoll IV Hydrothermal Field in the Okinawa Trough Back-Arc Basin

The Yonaguni Knoll IV hydrothermal vent field (24°51′N, 122°42′E) is located at water depths of 1370–1385 m near the western edge of the southern Okinawa Trough. During the YK03–05 and YK04–05 expeditions using the submersible Shinkai 6500, both hydrothermal precipitates (sulfide/sulfate/carbonate) and high temperature fluids (Tmax = 328°C) presently venting from chimney‐mound structures were extensively sampled. The collected venting fluids had a wide range of chemistry (Cl concentration 376–635 mmol kg^?1), which is considered as evidence for sub‐seafloor phase separation. While the Cl‐enriched smoky black fluids were venting from two adjacent chimney‐mound structures in the hydrothermal center, the clear transparent fluids sometimes containing CO₂ droplet were found in the peripheral area of the field. This distribution pattern could be explained by migration of the vapor‐rich hydrothermal fluid within a porous sediment layer after the sub‐seafloor phase separation. The collected hydrothermal precipitates demonstrated a diverse range of mineralization, which can be classified into five groups: (i) anhydrite‐rich chimneys, immature precipitates including sulfide disseminations in anhydrite; (ii) massive Zn‐Pb‐Cu sulfides, consisting of sphalerite, wurtzite, galena, chalcopyrite, pyrite, and marcasite; (iii) Ba‐As chimneys, composed of barite with sulfide disseminations, sometimes associated with realgar and orpiment overgrowth; (iv) Mn‐rich chimneys, consisting of carbonates (calcite and magnesite) and sulfides (sphalerite, galena, chalcopyrite, alabandite, and minor amount of tennantite and enargite); and (v) pavement, silicified sediment including abundant native sulfur or barite. Sulfide/sulfate mineralization (groups i–iii) was found in the chimney–mound structure associated with vapor‐loss (Cl‐enriched) fluid venting. In contrast, the sulfide/carbonate mineralization (group iv) was specifically found in the chimneys where vapor‐rich (Cl‐depleted) fluid venting is expected, and the pavement (group v) was associated with diffusive venting from the seafloor sediment. This correspondence strongly suggests that the subseafloor phase separation plays an important role in the diverse range of mineralization in the Yonaguni IV field. The observed sulfide mineral assemblage was consistent with the sulfur fugacity calculated from the FeS content in sphalerite/wurtzite and the fluid temperature for each site, which suggests that the shift of the sulfur fugacity due to participation of volatile species during phase separation is an important factor to induce diverse mineralization. In contrast, carbonate mineralization is attributed to the significant mixing of vapor‐rich hydrothermal fluid and seawater. A submarine hydrothermal system within a back‐arc basin in the continental margin may be considered as developed in a geologic setting favorable to a diverse range of mineralization, where relatively shallow water depth induces sub‐seafloor phase separation of hydrothermal fluid, and sediment accumulation could enhance migration of the vapor‐rich hydrothermal fluid.     

新疆阿尔泰西北部白哈巴一冲乎尔一带加里东和海西两期区域变质作用的厘定

通过对新疆西北部阿尔泰白哈巴—冲乎尔一带详细的野外地质填图和综合研究,在原划分的奥陶纪、震旦—寒武纪地层中分别采获了早泥盆世双壳化石,获得了加里东期、海西期不同期次的同位素地质年龄,在浅变质岩中划分出了石英岩状结构亚带和刺状结构亚带,在区域动力热流变质岩中划分出蓝晶石带、矽线石带、铁铝榴石带、十字石带等。新的证据表明,研究区白哈巴地区发育加里东期和海西期两期区域低温动力变质,南东部发育两期区域动力热流变质,海流滩为加里东期,冲乎尔则为海西期,沿库根断裂带产生叠加。这一划分使争论了近半个世纪的该区变质类型和变质世代的问题有了新的答案。     

Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations

Precise Point Positioning (PPP) has been demonstrated to be a powerful tool in geodetic and geodynamic applications. Although its accuracy is almost comparable with network solutions, the east component of the PPP results is still to be improved by integer ambiguity fixing, which is, up to now, prevented by the presence of the uncalibrated phase delays (UPD) originating in the receivers and satellites. In this paper, it is shown that UPDs are rather stable in time and space, and can be estimated with high accuracy and reliability through a statistical analysis of the ambiguities estimated from a reference network. An approach is implemented to estimate the fractional parts of the single-difference (SD) UPDs between satellites in wide- and narrow-lane from a global reference network. By applying the obtained SD-UPDs as corrections to the SD-ambiguities at a single station, the corrected SD-ambiguities have a naturally integer feature and can therefore be fixed to integer values as usually done for the double-difference ones in the network mode. With data collected at 450 stations of the International GNSS Service (IGS) through days 106 to 119 in 2006, the efficiency of the presented ambiguity-fixing strategy is validated using IGS Final products. On average, more than 80% of the independent ambiguities could be fixed reliably, which leads to an improvement of about 27% in the repeatability and 30% in the agreement with the IGS weekly solutions for the east component of station coordinates, compared with the real-valued solutions. An erratum to this article can be found at     

雷达卫星影像中输电导线散射斑的相位时间序列稳定性分析

分析输电导线散射斑相位的几何关系,选取20幅时间跨度约为1年的TerraSAR条带模式影像,对其中两基铁塔之间6条输电导线形成的散射斑相位时间序列进行分析。文中统计分析构成导线散射斑像元的相位离散度,其标准差约为0.2弧度,表明单个散射斑相位稳定。选取铁塔顶部点的导线散射斑为参考点,与另外5个导线散射斑做差分相位时间序列分析,分析导线之间高程差的理论计算值与实际值的一致性。分析结果显示,导线散射斑差分相位序列的波动可达2弧度以上,与导线间高程差产生的相位不一致。     

不同型号GNSS接收机短基线检定实验研究

全球卫星导航系统(GNSS)以其全天候、操作简便、高精度等优点在测绘、航空、地质勘察、环境监测与保护等领域得到了广泛应用。为提高GNSS接收机检定设备的利用率和检定工作的效率,也为测量工作中提高GNSS接收机的使用效率提供可靠依据,文中设计了不同型号的GNSS接收机与相同型号GNSS接收机联合检测和联合数据处理的实验。实验证明,不同型号GNSS接收机联合检测具有可行性。     

InSAR干涉图滤波方法对比

针对不同滤波算法在InSAR数据处理中去噪效果的差异,该文从滤波理论出发,采用模拟和真实干涉数据进行实验。在各种滤波算法中,均值滤波(多视处理)、Goldstein滤波及其变种滤波应用广泛,本文对4种滤波方法进行了系统分析,深入探讨了经典InSAR滤波和国内外学者算法的优缺点。实验表明:4种滤波均能有效抑制噪声,提升干涉图质量。其中,Goldstein滤波以及两种改进的滤波效果要明显优于均值滤波,且具有更好的自适应性或条纹保持能力,较经典Goldstein滤波而言,变种滤波方法不仅保持了Goldstein滤波的优点,在边缘信息和细节保持能力方面优势更加显著。     

利用时序InSAR技术分析北京及河北廊坊地面沉降

利用带大气估计模型的时序InSAR方法对24幅覆盖北京及河北廊坊的Envisat-ASAR影像数据进行了时序分析,获取了该地区2007年4月—2010年9月的地面沉降速率及均方差。发现了以北京朝阳区和通州区交界处为中心和以河北廊坊城区为中心的两个沉降区域,中心区平均沉降速率分别为35mm/a与22mm/a。研究区域形变速率均方差1.5mm/a。研究结果表明:利用时序InSAR技术进行城市地表沉降监测具有较好的精度及稳定性;产生该沉降的可能原因为地下水的开采、城市基础建设的发展及工业用地量、人为活动的增加。     

Extrinsic and intrinsic mode of hydrogen occurrence in natural olivines: FTIR and TEM investigation

Olivine crystals from two mantle nodules in kimberlites (pipe Udachnaya and pipe Obnazennaya, Yakutiya, Siberia) were investigated using EMP, TEM, AEM and FTIR techniques to determine the mode of hydrogen occurrence in olivine. Olivine contains three types of nanometer-sized inclusions: “large” inclusions of hexagonal-like shape up to several hundred nm in size (1), lamellar defects (2) and small inclusions of hexagon-like shape up to several 10?nm in size (3). Lamellar defects and small inclusions are considered to be a “hydrous” olivine. All three types of inclusions contain OH^? or water, but they are different with respect to their phase composition. In “large” inclusions (1) hydrous magnesium silicates, such as serpentine?+?talc (“kerolite”?) and 10-Å phase?+?talc were identified. Lamellar defects (2) and small inclusions (3) are depleted in Mg and Fe compared to the olivine matrix, while the silica content is the same as that of olivine. Modulations in the periodicity of the olivine structure are observed in SAED patterns and HREM images of (2) and (3). The superperiodicity can be referred to OH^?-bearing point defect ordering in the olivine structure. If this is the case, the material of both lamellar defects and small inclusions can be assumed to be a “hydrous olivine” Mg_{2– x} v _x SiO₄H_{2 x} with a cation-deficient olivine crystal structure. Thus, both an extrinsic mode of hydrogen occurrence in olivine, such as nanometer-sized inclusions of OH^?-bearing magnesium silicates, and an intrinsic mode of hydrogen incorporation into the olivine structure, such as “hydrous olivine” in itself, were found. The data obtained here show that the OH absorption bands observed in olivine spectra at 3704(3717) and 3683(3688) cm^?1 can be unambiguously identified with serpentine; the band at 3677(3676) cm^?1 can be associated with talc. The absorption bands observed at 3591 and 3660?cm^?1 in olivine match those of the 10-Å phase at 3594, 3662 and 3666?cm^?1.