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991.
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993.
A Relative Moment Tensor Inversion Technique Applied to Seismicity Induced by Mining 总被引：1，自引：0，他引：1
L. M. Linzer 《Rock Mechanics and Rock Engineering》2005,38(2):81-104
Summary. Studies of source mechanisms of mining-induced seismic events play an important role in understanding the various modes of failure observed around underground excavations and enable the geometry of likely planes of failure to be determined. These planes can be mapped using conventional techniques, for example, geological fracture mapping. However, such an approach is often problematical due to limited access to the site and/or poor exposures (if any) of the failure plane. An added difficulty is that planes of failure often do not follow faults of geological origin, but are related to the geometry of the advancing stope face. For example, the development of face-parallel shear zones ahead of deep-level stope faces. In such cases, the stresses induced by mining dominate over the geological structure in the critical region close to the stope face. Seismic methods therefore have the potential of being a practical method of studying the development of seismic shear zones underground.Slip on such a failure plane generates a three dimensional elastic wave that propagates through the rockmass, carrying a wealth of information regarding the source rupture process. The ground motions caused by the passage of the wave can be recorded by arrays of sensitive instruments called seismometers. These sets of recordings (seismograms) provide the basic data that seismologists use to study these elastic waves as they propagate through the Earth. Conventional seismic analyses provide scalar measurements of the rupture size and intensity. However, through a process known as moment tensor inversion (MTI), the seismograms recorded from a seismic event can be used to calculate a moment tensor that describes the three dimensional nature of the source mechanism. Interpretation of the moment tensor gives insight into whether the rockmass failed in tension, compression or shear and indicates the direction of movement and the failure plane.Moment tensor solutions computed using conventional MTI methods are sensitive to noise and may be biased due to systematic errors in the measurements. The primary objective of this study was to develop a robust MTI method to estimate the moment tensors of clusters of seismic events recorded in the underground environment. To achieve this, three hybrid MTI methods were developed by the author. These methods involve different iterative weighting schemes designed to enhance the accuracy of the computed moment tensors by decreasing the effect of outliers (data points whose residuals lie far from the mean or median error). The additional information required for hybrid methods is obtained by considering a spatial cluster of seismic events and assuming that the waves generated by each event in the cluster follow a similar path through the rockmass and allowing a common ray-path to be assumed. Hence the unknown effect of the heterogeneous rockmass on the waveform is similar for all the events in the cluster.The final objective was to determine whether the techniques developed could be successfully applied to real data. The hybrid MTI methods using the median and the weighted mean correction were applied to a cluster of 10 events, having remarkably similar waveforms, recorded at Oryx Gold Mine. For comparative purposes, the more conventional absolute method was also applied. The solutions computed using the hybrid MTI with a median correction displayed a distinct improvement after the iterative residual correction procedure was applied, in contrast to the solutions obtained from the absolute method. The radiation patterns and fault-plane solutions from the hybrid method showed a high degree of similarity, and were probably more accurate reflections of reality. These observations are very encouraging and point towards the potential for using the hybrid MTI method with a median correction as a standard processing tool for mine seismicity.The implications of this work are that a robust method for calculating the focal mechanisms of clusters of seismic events induced by mining activities has been developed. Regular application will lead to a better understanding of rock fracture processes and to improved safety underground. 相似文献
994.
LIU YudiState Key Laboratory of Numerical Modeling for Atmospheric Sciences Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Institute of Meteorology PLA University of Science Technology Nanjing China 《中国科学D辑(英文版)》2005,48(9):1559-1568
On variable configuration in the horizontal direction, Winninghoff[1] had some discussions in the 1960s. Subsequently, according to the thoughts of Winning- hoff, Liu Yudi[2―9] has widely and deeply studied al- most all the existing horizontal grids from the fre- quency and group velocity of inertia gravity and Rossby waves. Results show that although Arakawa C grid is the best one among all existing horizontal grids, it also has some shortcomings. For example, there is still an “average… 相似文献
995.
提出了一个新的水平跳点网格（LE网格），这种网格将h放置在格点上，u,v同时放置在x方向和y方向格点中间.并采用一种推导频散关系的通用方法，研究在该LE网格上与Arakawa A E网格上描述Rossby波产生误差的情况，分可分辨和不可分辨两种情况.采用二阶中央差或四阶紧致差分格式从频率和群速度两个方面进行对比分析，结果表明不论在可分辨或不可分辨情况下，还是采用二阶中央差或四阶紧致差分格式，在频率和群速度两方面，LE网格在描述Rossby波产生的误差均较Arakawa A E网格要小，同时也表明不论在可分辨还是不可分辨的情况下，采用高精度的四阶紧致差分格式，LE网格和Arakawa A_E网格在描述Rossby波时产生的频率误差和x、y方向群速度误差并非必然减少. 相似文献
996.
共反射面元（Common Reflection Surface）叠加是一种独立于宏观速度模型的零偏移距成像方法，该方法属于典型的克希霍夫型成像方法. 根据成像方式的不同，克希霍夫型成像方法可以分为两大类：输出道成像方式和输入道成像方式. 考察共反射面元叠加方法，它属于输入道成像方式. 本文基于理论模型数据，实现了输出道成缘方式的CRS叠加方法. 相比传统的输入道成像方式，它具有能够保证大偏移距反射信息的成像精度和计算效率较高的优点，而且更加容易推广到三维情形. 相似文献
997.
Piñon (Pinus edulis)-juniper (Juniperus monosperma)-ecosystems increased substantially in the western USA during the 20th century. Sustainability of these ecosystems primarily depends on soil quality and water availability. This study was undertaken with the objective of assessing the effect of tree species on soil physical quality in a semi-arid region in the western part of Sugarite Canyon, northeast of Raton, Colfax County, NM (37°56′32″N and 104°23′00″W) USA. Three cores and three bulk soil samples were obtained from the site under the canopy of three juniper, Gambel oak (Quercus gambelii) and piñon trees for 0–10 and 10–20 cm depths. These samples were analyzed for particle size distribution, soil bulk density (ρb), water stable aggregation (WSA), mean weight diameter (MWD) of aggregates, pH, electrical conductivity (EC) and soil organic carbon (SOC) and total nitrogen (TN) concentrations and stocks. Sand content was greater under juniper (48%) than oak (32%), whereas clay content followed the opposite trend. The ρb, WSA, MWD, pH and EC were similar under juniper, piñon, oak canopies for both depths. Estimated (from Philip and Green and Ampt infiltration models) and measured water infiltration parameters did not vary among these sites and were in accord with the values for ρb, WSA and MWD. The SOC concentrations and stocks were greater under oak (43.1 Mg ha−1 for 0–10 and 37.5 Mg ha−1 for 10–20 cm depths) than piñon (23.3 Mg ha−1 for 0–10 and 18.5 Mg ha−1 for 10–20 cm depths). The TN concentrations were greater under oak (3.4 g kg−1) than piñon (1.7 g kg−1) for the 0–10 cm depth only. Accumulation of detritus material under tree canopies reduced soil compaction and crusting caused by raindrop impact and increased SOC, and TN concentrations, and water infiltration. Coefficients of variation ranged from low to moderate for most soil properties except infiltration rate at 2.5 h, which was highly variable. Overall, soil quality for each site was good and soil aggregation, water infiltration and SOC concentrations were high, and soil ρb was low. 相似文献
998.
999.
某校体育运动场边坡因场地平整引起多次滑坡。经勘查,分析了其中的滑坡特征及滑坡形成的机理,提出治理方案。实践证明该方案达到了预期的目的。 相似文献
1000.
黑河流域额济纳绿洲生态保护措施及其效应分析 总被引：3，自引：0，他引：3
讨论黑河流域水资源开发利用以及引起的生态环境问题,分析额济纳绿洲生态保护措施及其效应。流域调水等治理措施使下游天然绿洲萎缩和生态退化的趋势得到一定程度的遏制;拟建的正义峡水库和输水渠道等水利工程可保护额济纳绿洲核心地带生态,但带来外围天然生态植被的退化,需要进行大时空尺度的生态影响分析论证。提出中游地区地表水和地下水联合开发利用,以提高水资源利用率,同时修建山区水库是提高水资源利用效率的理想方式;下游地区实施生态移民安置工程。 相似文献