天津塔层风切变的研究

根据天津气象铁塔１９９０－１９９２年冬季８个月的风速、风向、温度等资料的分析，得到了天津２５０ｍ以下边界层中风切变的若干特征，如风垂直分布幂次律中指数ｐ的时空变化及频数分布，各层各时段风切变的频数分布，风切变与温度梯度、稳定度的关系。这些特征有助于对城市下垫面塔层中风垂直分布的了解。还分析了冷锋过境前后风切变及温度状 的分布情况。     

Study on the sources of some deep focus earthquakes in Northwest Pacific region

The sources for thirteen deep focus earthquakes ofm _b≥5.5 andh>400 km in Northwest Pacific region were studied using waveform fitting and shear fracture source model. The source parameters were obtained as follows: focal depth, faulting plane, slip direction, rupture velocity, rupture length, rupture direction and scalar moment tensor. It was found that all these earthquake sources can be interpreted as shear faulting and have simple source time functions. The strike direction of faulting plane for most deep focus earthquakes coincides with that of the subduction zone, especially in the deep part of the subduction zone, it results in the tendency of reducing the dip angle of the subduction zone. The multiple point source model was also used to study the source process. The waveform fitting is better than the shear fracture model, but the general rupture direction which coincides with that from unilateral shear source model can not be obtained from the multiple point source model. This study is supported by the National Science Foundation of China and the Chinese Joint Seismological Science Foundation.     

Inversion of Q value structure beneath the Tibet Plateau

A total of 11 earthquakes with 15 Rayleigh wave paths, recorded at 11 broadband digital PASSCAL seismometers installed in the Tibet Plateau by the Sino-U.S. joint research group, were used to determine the phase velocity and attenuation coefficient of surface waves in periods of 10–130 s. The average shear wave velocity and quality factor {ie271-1} structures in the crust and upper mantle were obtained in this region. The result shows the average {ie271-2} is low and there exists a high attenuation ({ie271-3}=93–141) layer in the crust. The depth range of the low {ie271-4} value layer (16–42 km) is consistent with the range of low velocity layer (21–51 km) in the crust. Below 63 km in the lower crust, {ie271-5} decreases with depth from 114 to 34 at depth of 180 km. The low shear wave velocity and low value of {ie271-6} at the same depth range in the crust indicate that the rocks in the range is probably melted or partially melted. According to the shear wave velocity structure, the average thickness of the crust is about 71 km and a clear velocity discontiniuty appears at the depth of 51 km. The low-velocity zone (4. 26 km/s) at depth of 96–180 km may be corresponding to the asthenosphere. Contribution No. 96A0047, Institute of Geophysics, SSB, China. This study was supported by the National Natural Science Foundation of China.     

Cyclic strength and deformation of crushable carbonate sand

Cyclic triaxial tests have been carried out on a skeletal carbonate sand from the west coast of Eire. Results are presented for undrained cyclic shear tests on samples with 80% of relative density consolidated under both isotropic and anisotropic conditions. Failure was defined as a 5% double amplitude cyclic strain and a 5% peak axial strain for stress-reversal and non-reversal stress conditions, respectively. Using this definition the cyclic strength for isotropically consolidated samples was affected by the confining pressure although the angular platey nature of the sand resulted in higher cyclic strengths than for a comparable silica sand. For anisotropically consolidated samples the cyclic strength increased with increasing initial static shear stress while on the other hand the cyclic strength normalised in the usual way with respect to the initial confining pressure decreased as this pressure increased.     

本溪市区剪切波速分布的初步研究

本文利用检层法、表面波法实测的波速资料。通过对实测数据的处理和回归分析,求出了本溪市区不同岩土波速与埋深的回归关系。同时收集了市区已有的钻孔资料,经分析计算,给出了本溪市区平均剪切波速的分布。     

由环境应力值寻找地震危险区的尝试

作者根据位错理论,采用二维矩形破裂模式,在导出了平均震源速度谱的基础上,导出了用地震波计算环境剪应力τ_0的公式。计算了1987—1991年中国和邻区大约1000多次4级以上中强地震的环境剪应力值τ_0,并把τ_0≥10MPa的地震看作是高剪应力值地震。自1987—1991年5年内,我国及邻区共发生M_s≥6.0的强震45次,和160余次高剪应力中强地震(M=4.0-5.0,τ_0≥10MPa),大约有1/4的强震和1/3的高应力值地震发生在台湾地区。说明台湾地区是一个高地震活动区和高应力值地区。新疆的喀什—乌恰—乌什地区也是高地震活动区和高应力值地区。我们对发生在其地区的强震,向前追溯了环境应力值τ_0的变化。发现有11个强震事件(约占全部事件80%)在震前1—5年内,在以强震为圆心,半径为200km范围内(个别略远),均有1—2个或多个高应力值地震出现。说明当高应力值地震发生时,该地区环境应力在增高,它可以作为将要发生强震的前兆。据此,推测了今后3年内大陆强震发生的可能地区是:①中印缅三国边境地区;②西藏波密地区;③青海北部到宁夏北部地区;④新疆伊宁地区;⑤纵贯新青藏90°E±2°线地带;⑥晋北忻州地区;⑦苏北及黄海地区;⑧山东长岛地区。     

衡山花岗岩体西缘韧性剪切带的特征,成因及岩体定位机制

衡山花岗岩体由南岳岩体(早期)和白石峰岩体(晚期)组成,衡山岩体西缘形成有分带明显的韧性剪切带,向西倾斜,在XZ面上呈倾向滑动剪切运动,矿物显微变形构造显示为倾向简单剪切特征。经测定,韧性剪切带形成时温度下限为343.6℃,古差应力下限为52～62MPa,应变速率下限为2.05×10~(-14)/s-3.13×10~(-14)/s,推算总位移量在13.5km左右。在花岗岩体以外没有韧性剪切变形现象,说明该韧性剪切带是衡山岩体定位过程中由白石峰岩体沿南岳岩体边缘侵位的简单剪切作用所形成。     

新城－黄陂走滑韧性剪切带的动力分异作用

本文通过对新城－黄陂断裂带中合河－殷店右行走滑韧性剪切带内糜棱岩类岩石化学成分、稀土元素及微量元素随Ｓｓ－Ｓｃ夹角和古差异应力（△δ）的变化梯度的研究，初步探讨了右行走滑韧性剪切带的动力分异作用。     

Characteristics of the Mesozoic and Cenozoic Tectonic Stress Fields of the Urumqi-Usu Region, Xinjiang

Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.