Combined adaptive multiple subtraction based on optimized event tracing and extended wiener filtering

The surface-related multiple elimination (SRME) method is based on feedback formulation and has become one of the most preferred multiple suppression methods used. However, some differences are apparent between the predicted multiples and those in the source seismic records, which may result in conventional adaptive multiple subtraction methods being barely able to effectively suppress multiples in actual production. This paper introduces a combined adaptive multiple attenuation method based on the optimized event tracing technique and extended Wiener filtering. The method firstly uses multiple records predicted by SRME to generate a multiple velocity spectrum, then separates the original record to an approximate primary record and an approximate multiple record by applying the optimized event tracing method and short-time window FK filtering method. After applying the extended Wiener filtering method, residual multiples in the approximate primary record can then be eliminated and the damaged primary can be restored from the approximate multiple record. This method combines the advantages of multiple elimination based on the optimized event tracing method and the extended Wiener filtering technique. It is an ideal method for suppressing typical hyperbolic and other types of multiples, with the advantage of minimizing damage of the primary. Synthetic and field data tests show that this method produces better multiple elimination results than the traditional multi-channel Wiener filter method and is more suitable for multiple elimination in complicated geological areas.     

汶川8.0级地震地表变形局部化样式与建筑物破坏特征关系初步研究

本文以汶川地震地表形变带的实地测量数据为基础,结合沿实测地震地表变形剖面建筑物破坏情况的调查与测量,分析了不同地震地表变形类型及其建筑物破坏特征,定量化地讨论了地表变形梯度与建筑物破坏程度间的关系。提出无论地震地表变形表现为何种类型的断层陡坎,地表破裂、强变形局部化在宽10~30m的地表破裂带内;建筑物受损情况最直接的影响是建筑物所处地点的地表变形梯度,地表变形梯度大于0.1的地段,建筑物均完全被摧毁;地表变形梯度在0.07~0.1间的地段,建筑物遭受严重损坏,产生倾斜及强烈变形等;地表变形梯度在0.03~0.07之间的地段,建筑物可能受到中度损坏,产生倾斜及变形等,具有抗震设防能力的构建筑物一般不会倒塌;地表变形梯度小于0.03的地段具有抗震设防能力的构建筑物一般只会受到轻的损坏或基本完好。     

龙门山断层的造山机制

龙门山断层的抬升模式过去主要有由下部地壳的流动(Lower crustal channel flow,LCCF)模式与脆性地壳的增厚(Brittle crustal thickening)的变形模式。2008年汶川地震后,一般认为它是源自在浅部由压缩性断层所导致的造山运动,这应无疑义,但深部是否为由LCCF引发的浅部压缩性断层模式或仅为薄壳构造所引起仍有待证实。     

用超长基线解算分析汶川地震动态形变特征

以远距离的IGS武汉GPS站为参考站,用超长基线双差瞬时精密定位技术,获取汶川Ms8.0地震震时震区连续GPS站1 Hz动态形变序列。同时以较近距离的雅安站为参考站解算动态形变序列,结果显示,两者的形变结果具有很好的一致性。距离断层较近的郫县、成都、绵阳、中江等站形变较大（形变最大的郫县站最大振幅达1.034 m）;位于震中南侧的邛崃、雅安等站形变较小。利用动态时序的地震波到时和震中距离估计地震波地壳平均速度为3.1 km/s。     

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新疆墨玉绿洲耕地变化及人地关系演进驱动力研究

以新疆墨玉绿洲为例,借助土地利用遥感数据和社会经济统计资料,结合多年实地调查,利用分形理论,计算了墨玉绿洲1989,1999和2006年耕地资源的分维值D、稳定性指数SI和分维变△D,并根据其值的物理意义,对耕地的动态变化进行了定量和定性分析。进而利用典型性相关分析方法,从社会经济因素进行墨玉绿洲耕地变化趋势和驱动力的研究。结果表明:人口的增长和农业生产的发展是影响耕地变化的主要经济因素;一些政策因素,如土地限制性开发、退耕还林政策等对耕地变化影响也很大。最后引进经济密度的概念,进一步验证上述结论。     

近场地震动下偏心结构的减震控制研究

本文选用远场宽频地震Kanai-Tajimi模型与近场地震He-Agrawal速度脉冲模型,对现有的典型近场地震记录进行了非线性数值拟合。通过调整脉冲分量与宽频分量的比值,得到了不同脉冲分量的地震波,分析了在合成近场地震波作用下,设置粘滞阻尼器时偏心结构的动力反应,并与未设置阻尼器时结构的地震响应进行了对比,同时也对能反映结构偏心特性的参数进行了分析研究。通过数值模拟与仿真分析,得到了一些对实际工程设计有意义的结论。     

Experimental and modeling study on Cr(VI) transfer from soil into surface runoff

With the development of modern agriculture, large amount of fertilizer and pesticide outflow from farming land causes great waste and serious pollution to surface water and groundwater, and threatens ecological environment and even human life. In this paper, laboratory experiments are conducted to simulate adsorbed Cr(VI) transfer from soil into runoff. A two-layer in-mixing analytical model is applied to analyze laboratory experimental results. A data assimilation (DA) method via the ensemble Kalman filter (EnKF) is used to update parameters and improve modeling results. In comparison with the experimental data, DA updated modeling results are much better than those without the updating. To make predictions better, the inflation method with a constant inflation factor via DA method was used to compensate the fast decrease of ensemble spread partially related to filter inbreeding. Based on the used rainfall and relevant physical principles, the updated value of the incomplete mixing coefficient γ is about 14.0 times of the value of the incomplete mixing coefficient α in experiment 1 and about 7.4 times in experiment 2, while the difference between the flow rate of runoff and infiltration is not so large even after reaching stable infiltration condition. The results indicate the loss of Cr(VI) in soil solute is mainly due to infiltration, rather than surface runoff. With the increase of mixing layer depth, soil adsorption capacity will increase and the loss of soil solute will decrease. The study results provide information for reducing and even preventing the agricultural nonpoint source pollution.     

Seismic dynamic monitoring in CO<Subscript>2</Subscript> flooding based on characterization of frequency-dependent velocity factor

The phase velocity of seismic waves varies with the propagation frequency, and thus frequency-dependent phenomena appear when CO₂ gas is injected into a reservoir. By dynamically considering these phenomena with reservoir conditions it is thus feasible to extract the frequency-dependent velocity factor with the aim of monitoring changes in the reservoir both before and after CO₂ injection. In the paper, we derive a quantitative expression for the frequency-dependent factor based on the Robinson seismic convolution model. In addition, an inversion equation with a frequency-dependent velocity factor is constructed, and a procedure is implemented using the following four processing steps: decomposition of the spectrum by generalized S transform, wavelet extraction of cross-well seismic traces, spectrum equalization processing, and an extraction method for frequency-dependent velocity factor based on the damped least-square algorithm. An attenuation layered model is then established based on changes in the Q value of the viscoelastic medium, and spectra of migration profiles from forward modeling are obtained and analyzed. Frequency-dependent factors are extracted and compared, and the effectiveness of the method is then verified using a synthetic data. The frequency-dependent velocity factor is finally applied to target processing and oil displacement monitoring based on real seismic data obtained before and after CO₂ injection in the G89 well block within Shengli oilfield. Profiles and slices of the frequency-dependent factor determine its ability to indicate differences in CO₂ flooding, and the predicting results are highly consistent with those of practical investigations within the well block.