S-wave velocity images of the Dead Sea Basin provided by ambient seismic noise

Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green’s functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ∼8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore.     

Probability of scour depth exceedance owing to hydrologic uncertainty

The average risk of a bridge over water in the USA collapsing from scour during its 75 years design life is estimated at 3.7×10^?3. This risk makes scour of foundations the number one cause of bridge collapse and 3 times larger than the next cause of bridge collapse, which is collisions. The current paper presents a site specific method to estimate the probability that a certain scour depth will be exceeded during the life of a bridge. The methodology is limited to some uncertainties associated with the randomness of hydrologic conditions. It does not include uncertainties associated with other input parameters, such as geometry and soil erodibility or uncertainties associated with the scour prediction model. The SRICOS–EFA method is used as the reference method to predict the scour depth. This method requires three inputs: the hydraulic parameters (e.g. velocity hydrograph), the geometry parameters (e.g. pier size) and the soil erodibility parameters (e.g. erosion function). The input is used together with the program to generate the scour depth versus time over the period of interest. The final scour depth is that reached at the end of the specified period. This paper proposes a probabilistic framework to present the final scour depth as a cumulative density function. The cumulative density function of the flow is sampled randomly to give a future hydrograph, which has the same mean and standard deviation as the original hydrograph. For this synthetic hydrograph a final scour depth is obtained by using SRICOS–EFA. Thousands of equally likely hydrographs are generated and the corresponding final scour depths are organized in a distribution. That final scour depth distribution gives the probability that a chosen scour depth will be exceeded.     

微动物探方法探测采空区

采空区探测通常采用瞬变电磁法与地震勘探方法,前者采用人工电场,后者采用人工震源,但二者施工难度大,数据采集也困难.微动探测是从台阵微动记录的垂直分量中提取瑞利波相速度频散曲线,再通过对频散曲线的反演估算地下介质S波速度,利用其低速异常解释采空区.以铜川东坡煤矿某区的探测为例,在煤层埋深50m左右、微动探测深度100m的情况下,即解释的采空区与地面电法解释的结果高度一致.     

A dimensional analysis of scaling viscosity and velocity in DEM of constant strain rate tests on asphalt

This paper presents the results from discrete element modelling (DEM) of an idealised (sand) asphalt mixture under constant strain rate (velocity) compressive loading using the Burgers viscoelastic model. Using dimensional analysis it is shown that the effect of scaling applied velocity is the same as that of scaling both viscosities in the Burgers model by the same factor. This has been shown to be the case for a bonded aggregate, and it also has been shown to be applicable even when bond breakage occurs within the sample. This scaling method will be of great benefit in modelling tests on asphalt under different constant strain rates, simply by scaling both viscosities to minimise computational time.     

地震结构爆裂理论与短临预测

在地震结构爆裂动力学理论基础上,揭示了临震前兆波的客观机制。作为储能体的地震包体,其流体压力达到覆盖岩层的断裂强度和重力之和时,在引潮力的作用下,包体发生局部破裂,裂纹发生扩张,产生破裂流和破裂波,交替发生冲击加载和垮塌卸载,同潮汐波叠加,形成地震前兆共振波,以相速度和群速度向围岩传播,其振动频率和周期表征包体的固有频率和周期。波速和周期均可以被灵敏度高和抗干扰性能强的PS100HRT地电仪在地震爆发前捕捉到,从而可用于确定地震的震中和震级。依据共振波出现后振幅随时间增加的规律,月潮规则,可以确定发震时间。地震和临震理论以及诊断技术均已经成熟,中国有望在世界上首先实现地震预报。查清地震包体,地震能可以如同油气那样供人类利用。     

安徽闪电与雷达资料的相关分析以及机理初探

WSR-98D多普勒天气雷达和新型闪电定位仪是监测灾害性天气十分有效的手段,利用合肥多普勒天气雷达的物理量产品和中国科技大学研制的新型闪电定位仪资料,对2001年7月24日、2002年5月27日、2004年4月6日发生在安徽省的冰雹和强降水的3次天气过程的闪电与雷达回波特征做相关性分析和机理初探,发现一些有意义的统计规律：（1） 闪电发生的数目和变化与回波顶高（ET）有较好的对应关系, 而与垂直含水量积分（VIL）对应关系不明显;（2） 强对流天气的云地闪中正地闪与负地闪发生频次相当,甚至超过负地闪,但正地闪比较分散,负地闪比较集中,闪电发生的位置与强回波位置不一致,云下一般存在一个次正电荷层;（3） 强降水天气的负地闪占优势,闪电发生的位置比较集中并且与强回波位置一致,云下没有正电荷层;（4） 垂直累积液态水含量（VIL）和回波顶（ET）很小处出现的闪电是由云砧和对流云分裂的碎云产生的.     

雷达资料在云南一次强降水过程中的三维变分同化试验

鉴于云南观测信息相对不足、局地强降水突出的现状,利用WRF(Weather Research and Forecasting)模式及其变分同化系统进行雷达反射率因子和反演风场的三维变分同化试验。通过对2012年9月12日00:00—13日00:00发生在云南的一次强降水过程进行数值模拟和对比分析,结果表明,同时同化雷达反演风场和基本反射率因子,对区域模式同化系统中风矢量、相对湿度、位势高度几个基本分析量都有明显影响。雷达资料的同化,有利于区域模式初始场中强降水区域的上游中低层空气湿度增加、水汽输送增强和强降水发生区域的风场辐合加强,从而改善区域模式对强降水落区、强度的预报质量。对于切变线等天气尺度系统影响下的强降水过程,雷达资料的同化持续时间选取3 h、同化间隔为1 h较适宜。另外,雷达反演风场和基本反射率因子的同化均对降水预报改善有明显贡献,且多种资料的同化效果好于单一资料同化。     

门源6.4级、共和7.0级地震前后波速比变化特征

通过来用门源台、湟源台所记录的地震资料，对1986年门源6．4级地震、1990年共和7．0级地震前后进行波速比-时空分析，发现两次地震前后其时间分布形态为持续低值-恢复-发震的现象，空间分布为圆形、椭圆形的异常区，震后异常区消失。     

Experimental Study Optimizing Hole Cleaning-Cuttings Transport in Oil Drilling Engineering

With a clear understanding of the drilling fluid techniques and the cutting-taking mechanism, a new advanced model is set up for analyzing field data and quantitative forecast of cutting-taking mechanism. Therefore, a number of values affecting the drilling rate and the hole cleaning are studied over a wide range of parameters. Drilling data obtained under high-borehole-pressure conditions are analyzed to determine the causes of the reduction in rate of penetration (ROP) as the borehole pressure increases, which in some cases is caused by the buildup of rock debris under the bit. The theoretical achievement and testing conclusions can be very instructional for horizontal well drilling. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. Highviscosity muds are observed to provide better transport than low-viscosity muds.     

Influence of the ground profile on the reduction of earthquake motion at the filled man-made islands in the Kobe harbor during the 1995 Hyogoken Nambu earthquake

During the 1995 Hyogoken Nambu earthquake in Kobe, the ground motion at the filled man-made islands in the Kobe harbor was not as severe as that at the mainland. The building damage was also less compared to that on the mainland. It was found by comparative study of earthquake records that the magnitude of acceleration response on the ground surface decreases at the islands as opposed to the mainland. One dimensional effective stress analysis is adopted in this study. Input data has been generated from test results, e.g. the SPT N-value by standard penetration test and shear wave velocity V_s by PS logging. Results obtained by the analyses showed good agreement with the observed records, which is an indication of the suitability of the adopted analysis procedure. From this study, the followings are concluded. By the increase of SPT N-value of the filled layers, liquefaction near ground surface is restrained and damage modes such as ejection of water and soil can be prevented. Since the ground profile at the islands is that considerably soft filled layer and marine clay layers, etc. are present and the thickness of the surface layer is large, the initial natural period of the ground is above 1 s and the natural period is elongated further under the earthquake excitation, which is deemed to be the principal reason for the reduction of the earthquake motion at the ground surface.