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981.
Fei Li Tao Xu Minghui Zhang Zhenbo Wu Chenglong Wu Zhongjie Zhang Jiwen Teng 《地震科学(英文版)》2014,27(2):127-136
Seismic traveltime tomographic inversion has played an important role in detecting the internal structure of the solid earth. We use a set of blocks to approximate geologically complex media that cannot be well described by layered models or cells. The geological body is described as an aggregate of arbitrarily shaped blocks, which are separated by triangulated interfaces. We can describe the media as homogenous or heterogeneous in each block. We define the velocities at the given rectangle grid points for each block, and the heterogeneous velocities in each block can be calculated by a linear interpolation algorithm. The parameters of the velocity grid positions are independent of the model parameterization, which is advantageous in the joint inversion of the velocities and the node depths of an interface. We implement a segmentally iterative ray tracer to calculate traveltimes in the 3D heterogeneous block models. The damped least squares method is employed in seismic traveltime inversion, which includes the partial derivatives of traveltime with respect to the depths of nodes in the triangulated interfaces and velocities defined in rectangular grids. The numerical tests indicate that the node depths of a triangulated interface and homogeneous velocity distributions can be well inverted in a stratified model. 相似文献
982.
Seismic inversion with generalized Radon transform based on local second-order approximation of scattered field in acoustic media 下载免费PDF全文
Sound velocity inversion problem based on scattering theory is formulated in terms of a nonlinear integral equation associated with scattered field. Because of its nonlinearity, in practice, linearization algorisms (Born/single scattering approximation) are widely used to obtain an approximate inversion solution. However, the linearized strategy is not congruent with seismic wave propagation mechanics in strong perturbation (heterogeneous) medium. In order to partially dispense with the weak perturbation assumption of the Born approximation, we present a new approach from the following two steps: firstly, to handle the forward scattering by taking into account the second-order Born approximation, which is related to generalized Radon transform (GRT) about quadratic scattering potential; then to derive a nonlinear quadratic inversion formula by resorting to inverse GRT. In our formulation, there is a significant quadratic term regarding scattering potential, and it can provide an amplitude correction for inversion results beyond standard linear inversion. The numerical experiments demonstrate that the linear single scattering inversion is only good in amplitude for relative velocity perturbation ( \( \delta_{c}/c_{0} \) ) of background media up to 10 %, and its inversion errors are unacceptable for the perturbation beyond 10 %. In contrast, the quadratic inversion can give more accurate amplitude-preserved recovery for the perturbation up to 40 %. Our inversion scheme is able to manage double scattering effects by estimating a transmission factor from an integral over a small area, and therefore, only a small portion of computational time is added to the original linear migration/inversion process. 相似文献
983.
Holocene slip rate and paleoearthquake records of the Salt Lake segment of the Northern Zhongtiaoshan Fault,Shanxi Province 总被引:1,自引:0,他引:1
The Northern Zhongtiaoshan Fault is a major deep fault at the southern margin of the Yuncheng Basin. There have been few studies on the fault, and the historical earthquakes are few and weak. However, the intensity of activity on the fault should never be underestimated. Through interpretations of aerial images, topography measurements and excavation of trenches, this paper studied the fault distribution, the surface deformation and the activity of the normal fault south of Salt Lake near the city of Yuncheng. By tracing faults in the three trenches, it was found that there had been at least three large paleoseismic events, at 1–3.5, 3.6–4.4 and 7.4–8.8 ka BP. Employing 14 C dating, we determined the same gravel layers in the uplifted side and downthrown side. Making differential Global Positioning System measurements of the vertical difference and topographic profile, we obtained the mean slip rate of the Northern Zhongtiaoshan Fault since 24.7 ka BP(0.75±0.05 mm/a). Using the results of relevant studies, we calculated the possible vertical fault displacement of one earthquake(2.35 m) and obtained the recurrence interval of characteristic earthquakes as 2940–3360 a after dividing the displacement by the mean slip rate. 相似文献
984.
Fapeng Li Zongxue Xu Wenfeng Liu Yongqiang Zhang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):517-526
The Tibetan Plateau (TP) is the “water tower of Asia” and it plays a key role on both hydrology and climate for southern and eastern Asia. It is critical to explore the impact of climate change on runoff for better water resources management in the TP. However, few studies pay attention to the runoff response to climate change in large river systems on the TP, especially in data-sparse upstream area. To complement the current body of work, this study uses two rainfall-runoff models (SIMHYD and GR4J) to simulate the monthly and annual runoff in the upstream catchments of the Yarlung Tsangpo River basin (YTR) under historical (1962–2002) and future (2046–2065 A1B scenario) climate conditions. The future climate series are downscaled from a global climate model (MIROC3.2_hires) by a high resolution regional climate model (RegCM3). The two rainfall-runoff models successfully simulate the historical runoff for the eight catchments in the YTR basin, with median monthly runoff Nash–Sutcliffe Efficiency of 0.86 for SIMHYD and 0.83 for GR4J. The mean annual future temperature in eight catchments show significant increase with the median of +3.8 °C. However, the mean annual future precipitation shows decrease with the median of ?5.8 % except in Lhatse (+2.0 %). The two models show similar modeling results that the mean annual future runoff in most of catchments (seven in eight) shows decrease with the median of ?13.9 % from SIMHYD and ?15.2 % from GR4J. The results achieved in this study are not only helpful for local water resources management, but also for future water utilization planning in the lower reaches region of the Brahmaputra. 相似文献
985.
986.
Jie Liu Yunpeng Li Rehan Sadiq Yong Deng 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(6):1323-1331
Many researches have been conducted on the health influence of Particle Matter with diameters less than 2.5 microns (PM \(_{2.5}\) ). There are also some researches on the cause of PM \(_{2.5}\) . However, such research generally focuses on the economic and political aspect of the environment issue. In this paper, a data-analysis approach of the PM \(_{2.5}\) issue is raised to offer a new viewpoint of this problem. The applied method extracts the relations of air quality system record as a relation map, which illustrates the influence among the parameters in a graph. The method successfully fitted the weather record, and derived from it the influencers of PM \(_{2.5}\) . The result shows that the average temperature, average barometric pressure and concentration of Ozone are all factors that have an influence on the concentration of PM \(_{2.5}.\) A short justification of it is also provided. 相似文献
987.
988.
随着人类的活动,地电阻率和地电场观测受到更多干扰。介绍浙江省长兴深井地电台建设过程,并讨论建设中存在的问题,初步分析地电观测资料,证明井下地电阻率和地电场观测在一定程度上可以屏蔽干扰,由此可见建设深井地电台的重要性。 相似文献
989.
990.
The dynamic equations of motion of asymmetric offshore platforms under three different environmental conditions:seismic action,wave action and their combination are established in this paper. In establishing these motion equations,three typical eccentricity types including mass eccentricity,rigidity eccentricity and their combination were considered,as are eccentricities that occur un-idirectionally and bi-directionally. The effects of the eccentricity type,the dynamic characteristics and the environmental conditions on the torsional coupling response of platforms are investigated and compared. An effort has also been made to analyze the inffluence of accidental eccentricity on asymmetric platforms with different eccentricity in two horizontally orthogonal directions. The results are given in terms of non-dimensional parameters,accounting for the uncoupled torsional to lateral frequency ratio. Numerical results reveal that the eccentricity type has a great inffluence on the torsionally coupled response under different environmental conditions. Therefore,it is necessary to consider the combination of earthquake and wave action in the seismic response analysis of some offshore platforms. 相似文献