云南武定地震余震近场尾波衰减的区域特征

根据地方震尾波散射理论，利用云南武定MS6.5主震后近场田心和云龙两个流动数字化台站记录的余震序列地震资料，以不同中心频率（1.5～20Ｈｚ）取样分频研究了近场尾波振幅衰减率（f ）的空间分布特征．结果表明，两个台站给出的尾波振幅衰减率（f ）存在明显的小区域范围非均匀性变化．位于主发震断层两侧的云龙台（东侧）和田心台（西侧）测得的尾波振幅衰减率（f ）值，当 f ＜6.0Ｈｚ时基本一致．相应的Qc（f ）值为66～120的低值；但在高频范围（f 6.0Ｈｚ），由于穿过主断层的近场尾波遭到断层破碎带强烈的吸收，因而云龙台测得的尾波振幅衰减率（f ）值，比不穿过主断层的田心台给出的（f ）降低30％，并讨论了产生近场尾波振幅衰减空间分布差异的原因．本文的研究结果还表明，波源因子A0（f）不仅与震源强度相关，也与频率犳相关，用1.5～20Ｈｚ求出的Ｓ波平均自由程犔在主断层东侧为30ｋｍ、西侧为40ｋｍ ，由此证实了地震波穿过主断层破碎带时有更强的散射．      

中德合作开展流动台阵近场地震观测和北京地区防震减灾研究

中国地震局和德国联邦地球科学和自然资源研究院将于2001年春季开始一项“流动台阵近场地震观测和北京地区防震减灾”的国际地震合作计划。该计划将使用由新一代数字地震仪构成的流动台阵在北京西北的延庆和中国大陆的其他地震活动区进行地震近场观测。这项计划的执行对于地震学基础研究，特别是探索地震震源过程的复杂性和首都地区的防震减灾都有重要意义。     

地基土地震液化评价方法探讨

本文对现行的“抗震设计规范”中有关地震液化评价条文进行了探讨,提出了以单元体及场地土作为评价单元,尝试引出了判别指标”场地单元体液化指数 A”。另外,对在评价过程中遇到的几个问题进行了讨论,如:贯入击数基准值的选用,软夹层的处理等。     

航天雷达遥感的作用与发展

本文论述了迄今为止唯一获得地球表面航天雷达图像的Seasat SAR、SIR-A及SIR-B三颗成象雷达系统在地球科学研究中的作用,对未来十年以ALMAZ ZAR、ERS-1 SAR、JERS-1 SAR、SIR-C、Radarsat SAR和EOS SAR为主的国际性主动微波遥感系统进行分析,指出研究过程中新的概念和趋势,展望了90年代航天雷达遥感技术发展及应用的前景.     

陕西地区地壳速度结构的层析成象研究

本文利用CT成象技术，根据陕西及邻省的地震波到时资料，反演出本区域地壳的速度结构图，并从中找出速度异常分布区。高速区为陕北地区，处于鄂尔多斯地台内；低速区为关中南部大部分区域及陕南的汉中、石泉地区。最后，对反演结果进行了讨论。     

Sequential velocity imaging and microseismic monitoring of mining-induced stress change

Sequential imaging of the temporal changes inP-wave velocity offers a practical tool to monitor a rock mass. Using established correlations between the location of seismic events and velocity structure, the temporal seismic potential characteristics of the rock may be monitored. Furthermore, the temporal velocity differences isolate the time dependent factors effecting velocity such as stress, while cancelling static factors such as lithology. Various sequential imaging techniques were compared with respect to accuracy. Differences between successive velocity images were found to have relatively high associated error estimates. However, images of velocity differences calculated from measured travel time delays between successive velocity surveys were found to have lower error estimates. In particular, travel time delays measured using cross-correlation techniques resulted in the most accurate sequential image. Two 3D sequential imaging studies were carried out at Strathcona Mine in Sudbury, Ontario, Canada. Results of the average static images indicated an association between the location of induced microseismicity and a zone of both high velocity and high gradient. Additional examples are described from the global seismology literature which also show a similar correlation between seismicity and velocity structure. We attribute this association to an interrelated stress and strength effect. The Strathcona Mine sequential images show zones of significantly decreased velocity in regions of concentrated microseismic activity, which are postulated to be indications of localized destressing and relaxation of the clamping forces resulting in the microseismicity. The zones of decreased velocity corresponded to an increase in the velocity gradient. One of the case studies also shows an increase in velocity in a zone of high static velocity, which is later the site of am _N 2.5 mining-induced seismic tremor. The increase in velocity is believed to correspond to a region of stress concentration, resulting in the subsequent seismic tremor.     

Solutions of the heat conduction equation in a non-uniform soil

A class of analytic, periodic solutions of the heat conduction equation in a non-uniform soil is derived. The class may be characterized by the fact that the speed of the temperature wave varies according to the square root of the soil diffusivity (a function of soil depth). In addition it is shown that the constant soil solution is the limiting case when the rate of change with depth of diffusivity and thermal conductivity become very small. The solutions may be regarded as general whenever temperature analysis is restricted to small values of depth or whenever the soil parameters vary slowly. For all other cases the class of solutions possess the additional property that the rate of change of conductive capacity varies directly as the product of the bulk density and specific heat of the soil. A particular temperature profile is given for the case when the diffusivity varies as the nth power of depth.