Large aftershocks triggering by Coulomb failure stress following the 2001<Emphasis Type="Italic">M</Emphasis><Subscript>S</Subscript>=8.1 great Kunlun earthquake

The great Kunlun earthquake occurred on Nov. 14, 2001 in Qinghai Province, China. Five large aftershocks with magnitude larger than 5.0 occurred near the Kunlun fault after main shock. Calculations of the change in Coulomb failure stress reveal that 4 of 5 large aftershocks occurred in areas with Δσ_f>0 (10^?2–10^?1 MPa) and one aftershock occurred in an area with Δσ_f=?0.56 MPa. It is concluded that the permanent fault displacement due to the main shock is the main cause of activity of large aftershocks, but not the whole cause.     

鄂尔多斯盆地北部黄土沙漠区隐蔽薄气层预测

长庆油田公司针对黄土沙漠区低孔、低渗、薄气藏的地震目标处理,经过多年的探索与实践,已形成了一套适合该类气藏特点的储层横向预测技术。在榆林、乌审旗、苏里格庙和神木等地区的上古生界天然气勘探、开发阶段取得了显著效果,使长庆油田上古生界天然气储量连续八年保持稳定增长。本文详细剖析了该技术的应用效果及经验。     

Electron microscopy study of the sakhaite from endogenous borate deposit in Hunan, China

Sakhaite was first discovered by Ostrovskaya, Pertsev and Nikitina at Siberia in the former Soviet Union. By using the X-ray diffraction technique, they proved that the crystal system of sakhaite was cubic (a = 1.464 nm), its possible space groups were Fm3m, F432, F43m, Fm3, F23, and its crystal chemical for-mula was Ca48Mg16(CO3)16(BO3)28Cl4(OH)8 4H2O[1]. Chichagov, Simonov and Belov studied the crystal structure of synthetic sakhaite and determined that its space group was F4132, …     

Study of charge structure and radiation characteristic of intracloud discharge in thunderstorms of Qinghai-Tibet Plateau

The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges. A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection.     

Application of the Wavelet Packet Method in Discrimination Between Nuclear Explosion and Earthquake

Although the CTBT (Comprehensive Nuclear Test-Ban Treaty) was passed in 1996, it is still necessary to develop new and highly efficient methods (Wu Zhongliang, Chen Yuntai, et al.,1993 ; Xu Shaoxie, et al. 1994; Richard L. Garwin, 1994) to monitor possible events. Many discrimination criteria (Xu Shaoxie, et al., 1994 ; Institute of Geophysics, Chinese Academy of Sciences, 1976; Richard L. Garwin, 1994) have been put forward since the 1950s. The results show that each of the existing criteria has its own limitation, but the seismological method is an important and efficient method in the discrimination between nuclear explosion and earthquake. Especially in recent years, because of the little and little equivalent as well as the increasing hiding steps used in the test, a number of more efficient seismological methods have been worked out. In this paper, a new discrimination method, the Wavelet Packet Component Ratio (WPCR) method, is put forward. This method makes full use of the difference in variation with time between the spectra of nuclear explosions and earthquakes. Its discrimination efficiency is rather high.     

The Activity of Major Faults and the Hydrothermal Alteration Zone at Tianchi Volcano of Changbaishan

It is found by field investigation that the near horizontal top surface of the brown or brick-red hydrothermai alteration zone varies obviously in elevation at different sections of the same layer on the caldera‘s inner wall of Tianchi, with that at the north section near the Tianwen Peak about 110 m higher than that at the south near the Jiangjun Peak in Korea. The top surface of the hydrothermai alteration zone can be taken as key horizon to tectonic movement. The difference indicates that the total uplift height of the NW wall of the Liudaogou-Tianchi-Jingfengshan fault, the principal fault trending NE at Tianchi, is bigger than that of the SE wall ever since the occurrence of hydrothermal alteration. This also explains why the topography in the northwest side of Tianchi is steeper and with more developed river system than in the southeast. The uplifting of the northeastern wall is bigger than that of the southwest along the principal NW-trend fault, namely, the Baishanzhen-Tianchi-Jince fault. It is observed from characters of hydrothermal alteration and the palaeoresiduum, that the recent vertical movement rate along the principal NE-trend fault is larger than that of the principal NW-trend fault. The two faults intersect at Tianchi, dividing the volcano into 4 blocks, with the uplift magnitudes decreasing successively in the order of the north, the west, the east and the south block. The biggest uplift of the north block corresponds well to the shallow magma batch in the north of Tianchi observed by DSS and telluric electromagnetic sounding, and etc. and they may be related with the causes.     

A Preliminary Analysis of Relations Between Tectonic Deformation of Sedimentary Cover and Basement in Kuqa Depression

Study of seismic activity in the Kuqa area enables us to infer some possible active faults in basement from the epicentral distribution on different profiles. The relations between active faults in the basement and surface structures are analyzed and the difference between sedimentary cover and basement in their deformation characteristics and the genesis are discussed. The following conclusions have been drawn : ( 1 ) the epicentral distribution indicates that, the east Qiulitag and south and north Qiulitag deep faults in the basement correspond to the east and west Qiulitag anticlines, respectively. Moreover, deep faults also exist beneath the Yiqiklik and Yaken anticlines. It indicates that the formation of surface structures is controlled by deep structures; (2) A NE-trending strike-slip fault develops along the line from the western termination of Yiqiklik structure to Dongqiu Well 5 and a NW-trending active fault on the western side of Baicbeng. The two active faults across the tectonic strike are the main causes for tectonic segmentation of the Kuqa depression and possibly the cause for the middle segment (Kuqa-Baicheng) of the depression to be more shortened than both its eastern and western terminations; (3) The difference between the sedimentary cover and basement in their deformation characteristics depends mainly on the different properties of media between them.The lithospheric strength of the basement in the basin is fairly high, which determines the basement deformation to be mainly of brittle fracture seismic activity. While the strength of sedimentary cover is low, where there exist weak thin layers, such as coal and gyps. Under the effect of strong tectonic compression, the sedimentary rocks may undergo strong viscous or plastic flow deformation; meanwhile, an aseismic detachment may take place along the weak layers.     

Dynamic response of partially sealed circular tunnel in viscoelastic saturated soil

Based on Biot's wave equation, dynamic response of a circular tunnel with partially sealed liner in viscoelastic saturated soil is investigated. By introducing two scalar potential functions, the analytical solutions of stresses, displacements and pore pressure induced by axisymmetric gradually applied step load are derived in Laplace transform domain. Numerical results are obtained by inverting Laplace transform presented by Durbin and used to analyze the influences of partial permeable property of boundary and viscoelastic damping coefficient of soil on dynamic response of the tunnel. It is shown that the attenuation of radial displacement appeared with the increase of viscoelastic damping coefficient of soil, and relative rigidity of liner and soil, and the influence of partial sealing property of boundary on stresses, displacements and pore pressure is remarkable. The available solutions of permeable and impermeable boundary conditions are only two extreme cases of this paper.     

山东省气候变化及其对冬小麦生产潜力的影响

利用全省 2 7个台站 1 96 1～ 1 998年的温度、降水、日照等基本气象要素资料 ,对山东省气候变化特点进行了分析 ,并对冬小麦生产潜力进行了计算、分析。结果表明 ,山东省年、季平均气温呈波动性增暖趋势 ,降水量呈减少趋势。气候变暖有利于生产潜力的提高 ,冬小麦气候生产潜力总的变化趋势是波动性的上升 ,但较光温生产潜力倾向率小 ,反映了小麦生育期内光、温、水的综合影响。     

兰州市城区大气烟尘污染的变化与气象条件分析

利用1961-2001年有烟日观测资料，统计分析了41年中，兰州市城区大气受烟尘污染的变化。结果表明：1961～1984年污染日在119-201天问徘徊；1985-1988年是污染“严重期”，年平均污染日达224天；1996-2001年为显著“好转期”，年平均污染日66天。一年中主要污染段是1月和11、12月，污染日占全年的49％。在污染日，大气水平能见度具有明显的日变化，能见度最差，污染最严重的时间是11～14时。