天然地震识别与震相自动拾取技术进展

震相拾取是地震数据处理过程中最基本的步骤之一。在传统的人工拾取技术不能满足庞大的地震数据处理需求的情况下,震相自动拾取技术从产生到发展至今经历了漫长的过程。本文回顾并总结了震相自动拾取技术的发展状况,重点介绍了长短时窗法、赤池准则法、模板匹配技术、基于自相关盲搜索的FAST法、S波偏振分析法、人工智能方法等,以及近年发展起来的多频率震相识别、全波形叠加、二次方自回归模型等方法,同时分析了每种方法的优势和局限性。     

Automatic modal parameter identification of high arch dams: feasibility verification

Modal parameters, including fundamental frequencies, damping ratios, and mode shapes, could be used to evaluate the health condition of structures. Automatic modal parameter identification, which plays an essential role in realtime structural health monitoring, has become a popular topic in recent years. In this study, an automatic modal parameter identification procedure for high arch dams is proposed. The proposed procedure is implemented by combining the density-based spatial clustering of applications with noise (DBSCAN) algorithm and the stochastic subspace identification (SSI). The 210-m-high Dagangshan Dam is investigated as an example to verify the feasibility of the procedure. The results show that the DBSCAN algorithm is robust enough to interpret the stabilization diagram from SSI and may avoid outline modes. This leads to the proposed procedure obtaining a better performance than the partitioned clustering and hierarchical clustering algorithms. In addition, the errors of the identified frequencies of the arch dam are within 4%, and the identified mode shapes are in agreement with those obtained from the finite element model, which implies that the proposed procedure is accurate enough to use in modal parameter identification. The procedure is feasible for online modal parameter identification and modal tracking of arch dams.

     

Geochemical characteristics and Sr‐Nd‐Hf isotope compositions of Late Triassic post‐collisional A‐type granites in Sarudik,SW Sumatra,Indonesia

Late Triassic A‐type granites are identified in this study in Sarudik, SW Sumatra. We present new data on zircon U–Pb geochronology, whole‐rock major and trace elements and Sr‐Nd‐Hf isotope geochemistry, aiming to study their petrogenesis and tectonic implications. LA‐ICP‐MS U–Pb dating of zircon separated from one biotite monzogranite sample yields a concordia age of 222.6 ±1.0 Ma, indicating a Late Triassic magmatic event. The studied granites are classified as weakly peralumious, high‐K calc‐alkaline granites. They exhibit high SiO₂, K₂O + Na₂O, FeO/(FeO + MgO) and Ga/Al ratios and low Al₂O₃, CaO, MgO, P₂O₅ and TiO₂ contents, with enrichment of Rb, Th and U and depletion of Ba, Sr, P and Eu, showing the features of A‐type granites. The granites have zircon ε_Hf(t) values from ?4.6 to ?0.4 and whole‐rock ε_Nd(t) values from ?5.51 to ?4.98, with Mesoproterozoic T_DM2 ages (1278–1544 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that the source of these A‐type granites is the Mesoproterozoic continental crust, without significant incorporation of mantle‐derived component, and their formation is controlled by subsequent fractional crystallization. The Sarudik A‐type granites are further assigned to A2‐type formed in post‐collisional environment. Combined with previous knowledge on the western SE Asia tectonic evolution, we conclude that the formation of the Late Triassic A‐type granites is related to the post‐collisional extension induced by the crustal thickening, gravitational collapse, and asthenosphere upwelling following the collision between the Sibumasu and the East Malaya Block.     

流域管理信息系统的提示界面设计

图形用户界面是当前普遍使用的软件界面设计方法,它不仅使软件易学易用,不同的软件之间保持了用户界面的一致性而且美观,赏心悦目,增加了用户的亲切感和趣味性,流域管理信息系统的界面既要保持与用户熟悉软件的一致性,又兼顾其本身的特点。界面设计是一项工程,它包括的内容很多,本文选择界面设计中最重要的一项“提示信息显示”的设计具体说明,并介绍了几种实现的方法。     

历史时期希门错湖泊沉积色素记录的古环境变化

湖泊沉积物中色素的含量,种类以及相应的参数是研究湖泊初始生产力和湖泊环境的有效手段之一。本文根据青藏高原东部希门错短柱岩芯ＸＭ９２０１沉积物的色素指标的综合判别,讨论了该地区过去２０００多年来的古环境变化过程和特点,对比分析我国东西部气候记载及冰芯研究,探讨了各气候事故表现形式的异同点。     

双轴各向异性介质多分量感应测井响应快速计算

为研究双轴各向异性介质多分量感应测井响应特征,本文基于三重傅里叶变换,推导任意方向偶极子源的谱域电磁场解析式;采用围线积分方法,自适应截断积分区间,结合谱域电磁场周期特性,实现三重傅里叶变换的精确快速积分;进而,针对双轴各向异性倾斜地层,模拟研究不同纵横向各向异性条件多分量感应测井响应特征.结果表明:利用谱域内电磁场在周向的周期特性简化解析式,可将计算速度提高4倍;自适应截断积分区间方法保证了计算精度,并极大地减少了积分节点数.对于倾斜双轴各向异性介质,倾角较大时,共面分量可反映地层横向各向异性,同轴分量可反映地层纵向各向异性;倾角较小时,同轴分量可反映地层横向各向异性,共面分量可反映地层纵向各向异性.     

DISCUSSING THE INFLUENCE OF MAJOR EARTHQUAKE SEQUENCE IN THE LONGMENSHAN AREA ON THE LUSHAN EARTHQUAKE FROM STRESS EVOLUTION

Calculating the coseismic static Coulomb stress change induced by an earthquake and interseismic stress change permits to explain the distribution of aftershocks, the earthquake sequence and other seismic observations. Four earthquakes greater than M7 have occurred in the Longmenshan area before the 2013 Lushan earthquake since 1900. This paper analyzes the influence of these four events on the Lushan earthquake, the stress evolution after the Lushan earthquake accompany with strong earthquake sequence on Longmenshan Fault, and the stress state of the gap between the Lushan and Wenchuan earthquakes. To address these issues would help future seismic risk assessment in the region. We construct a three dimensional finite element model based on the geological structure, the deep inversion results of density and velocity, and the GPS and the stress observation data. The simulation results show that the annual variation rate of Coulomb stress is higher on the Xianshuihe fault and southern segment of the Longmenshan fault, which is consistant with the regional seismicity. The coseismic Coulomb stresses induced by Kangding, Songpan, and Wenchuan earthquakes at the Lushan earthquake epicenter is greater than 0, implying that the three earthquakes may promote the occurrence of the Lushan earthquake, especially the Wenchuan earthquake. The viscous relaxation is remarkable which cannot be ignored in the analysis of stress evolution. From the stress evolution of this area, we can find that the gap between the Wenchuan and Lushan earthquakes is still at a relatively high stress level after the Lushan earthquake.     

Linearized amplitude variation with offset and azimuth and anisotropic poroelasticity

The normal-to-shear weakness ratio is commonly used as a fracture fluid indicator, but it depends not only on the fluid types but also on the fracture intensity and internal architecture. Amplitude variation with offset and azimuth is commonly used to perform the fluid identification and fracture characterization in fractured porous rocks. We demonstrate a direct inversion approach to utilize the observable azimuthal data to estimate the decoupled fluid (fluid/porosity term) and fracture (normal and shear weaknesses) parameters instead of the calculation of normal-to-shear weakness ratio to help reduce the uncertainties in fracture characterization and fluid identification of a gas-saturated porous medium permeated by a single set of parallel vertical fractures. Based on the anisotropic poroelasticity and perturbation theory, we first derive a linearized amplitude versus offset and azimuth approximation using the scattering function to decouple the fluid indicator and fracture parameters. Incorporating Bayes formula and convolution theory, we propose a feasible direct inversion approach in a Bayesian framework to obtain the direct estimations of model parameters, in which Cauchy and Gaussian distribution are used for the a priori information of model parameters and the likelihood function, respectively. We finally use the non-linear iteratively reweighted least squares to solve the maximum a posteriori solutions of model parameters. The synthetic examples containing a moderate noise demonstrate the feasibility of the proposed approach, and the real data illustrates the stabilities of estimated fluid indicator and dry fracture parameters in gas-saturated fractured porous rocks.     

Amplitude variation with incident angle and azimuth inversion for Young's impedance,Poisson's ratio and fracture weaknesses in shale gas reservoirs

By analogy with P- and S-wave impedances, the product of Young's modulus and density can be termed as Young's impedance, which indicates the rock lithology and brittleness of unconventional hydrocarbon reservoirs. Poisson's ratio is also an effective indicator of rock brittleness and fluid property of unconventional reservoirs, and fracture weaknesses indicate the fracture properties (fracturing intensity and fracture fillings) in fracture-induced unconventional reservoirs. We aim to simultaneously estimate the Young's impedance, Poisson's ratio and fracture weaknesses from wide-azimuth surface seismic data in a fracture-induced shale gas reservoir, and use the horizontal transversely isotropic model to characterize the fractures. First, the linearized PP-wave reflection coefficient in terms of Young's impedance, Poisson's ratio, density and fracture weaknesses is derived for the case of a weak-contrast interface separating two weakly horizontal transversely isotropic media. In addition, an orthorhombic anisotropic case is also discussed in this paper. Then a Bayesian amplitude variation with incident angle and azimuth scheme with a model constraint is used to stably estimate Young's impedance, Poisson's ratio and fracture weaknesses with only PP-wave azimuthal seismic data. The proposed approach is finally demonstrated on both synthetic and real data sets with reasonable results.