Preliminary Results on the 3-dimensional Seismic Structure of the Lithosphere under the USGS Central California Seismic Array

About 1500 readings of teleseismic P -time residuals obtained from the US Geological Survey seismograph network in central California have been used to obtain a three-dimensional image of seismic velocity anomalies for this area by the method of Aki, Christoffersson & Husebye We found that the California network is less suitable than the LASA and NORSAR arrays for this kind of studies because of its greater proportion of peripheral blocks in which the resolution is very poor for the stochastic inverse solution and the random error effect is severe for the generalized inverse solution. Nevertheless, the resultant velocity anomalies show a remarkable correlation with the San Andreas fault zone to a depth of 75 km. The anomaly pattern changes drastically as the depth exceeds 75 km, suggesting that the asthenosphere has been reached.     

Shear Velocity Structure of Jordan From Explosion Seismic Data

Summary. Combined analysis of P - and S -wave data from seismic refraction lines in Jordan has led to the derivation of a Poisson's ratio model for the crust. This model shows that the upper crust, including the sediments, has an average Poisson's ratio of around 0.25, except beneath NW Jordan where the sediments have a high ratio of around 0.32. However, the lower crust below about 20 km depth has high Poisson's ratios ranging from 0.29 to 0.32. These high Poisson's ratios may be interpreted mineralogically in terms of high feldspar and low quartz content in the rocks (e.g. gneiss, amphibolite) of the lower crust or fluid phases in the form of separated penny-shaped inclusions.     

Seismic anisotropy as measured under high-pressure, high-temperature conditions

Summary. Four types of crustal and upper-mantle rocks have been used for the investigation of seismic P -wave velocities in three mutually perpendicular directions. Hydrostatic pressure, up to 6 kbar and temperatures up to 500°C were applied to the samples. Measurements of the ultrasonic P -wave travel times and velocities were carried out along two geotherms. All rock types show an anisotropic behaviour which is caused by the orientation of certain minerals. The anisotropy is not dependent on temperature and pressure. Gneiss and peridotite have 5–6 per cent anisotropy whereas granite and a metagabbro show values of only 2–3 per cent. The smallest velocity is always in the z direction, perpendicular to a schistocity or foliation. It is shown that the data agree with those of field observation. We conclude that anisotropy caused by preferred orientation of minerals must be expected in the whole lithosphere. Additional effects of layering, of cracks, and of nonhydrostatic stresses are estimated.     

The Structure of Atmospheric Turbulence and its Application to the Design of Pipe Arrays

Summary Turbulent boundary layers at the surface of the Earth limit the detection of infrasonic waves with periods greater than 1 s. Pipe arrays designed to improve the signal-to-noise ratios of infrasonic waves usually assume that the background noise due to this turbulent boundary layer is incoherent between the array inlets. The power at various points on a surface was measured; coherences between these points were determined and they were found to be significant in the period range 1–100 s. Such coherent noise must be considered when pipe arrays are designed.     

地震作用下边坡稳定性分析的坐标转换法

在地震作用下边坡稳定性分析中,拟静力法是将地震作用简化为水平方向或垂直方向的不变加速度作用.此加速度产生作用于不稳定体质心的地震力,根据极限平衡理论,将所有作用于潜在滑动体上的力沿滑动面进行分解,得出沿滑动面的安全系数.在拟静力法的基础上,提出一种坐标转换法,通过坐标旋转,将地震力与重力的合力转变为垂直向下的力,从而使边坡地震稳定性问题等效为经过边坡几何形态和土体容重修正后的一般静力稳定性问题,再利用比较成熟、简便的静力分析方法进行边坡稳定性分析.利用此方法可以克服传统拟静力分析的不足,并且用于水下边坡分析,将滨水边坡的拟静力分析模型转换为相应的静力分析模型,考虑地下水的流动来模拟水对边坡的动力作用.此方法对于分析水库边坡体和堰塞湖坝体的抗震稳定性问题具有一定的应用价值.     

The Acoustics of Pipe Arrays

Summary A theoretical analysis is given for the acoustical behaviour of the pipe-microbarograph systems used to detect acoustic gravity waves and other modes of infrasound. It is shown how to compute the response of the microbarograph to a fluctuating pressure at any one inlet port of the pipe and how the results of such computations may be used to calculate the response to a plane sound wave traversing the system.
The analysis is illustrated by numerical examples obtained by means of a computer program. These examples confirm that the tapered tube modelled after Daniels' line microphone has very good characteristics, but that good results may also be obtained using pipes of uniform bore. The work leans heavily on Benade's calculations of sound propagation in a circular conduit.     

试论新经济发展条件下城市产业结构演进与空间结构变迁

新经济是以知识和信息为基本生产要素．以智力资本创新为核心．以信息网络为基本生产工具的新经济形态。基于对新经济产业及其空间分布特征的探讨,认为在新经济发展条件下．城市产业结构有着螺旋式上升的轻型化发展趋势,城市空间结构在整体扩散的同时．中心城区蕴含着聚集产业和人口的引力,并从宏观、中观、微观三个层面给出对城市规划的启示。