Instability of sand–silt mixtures

The instability of the sand–silt mixtures with different amount of fines contents were studied in this paper. It showed that the slope of the instability lines increases with the increasing relative densities, and it approaches the slope of the failure line (steady state line) at a high relative density. The relationship between the peak stress ratio and the intergranular void ratio can be described by a common curve for all the mixtures with fines contents less than the transitional fines content. There may also exist a unique curve for the relationship between the peak stress ratio and interfine void ratio for the mixtures with fines contents higher than the transitional fines content. If the yield strength ratio is used instead of the peak stress ratio, the relationships can be characterized in the same way.     

近源地震动峰值加速度衰减关系影响因素分析

本文收集了丰富的强震资料, 以峰值加速度为例, 采用简单且体现近场峰值加速度PGA震级饱和和距离饱和特性的衰减模型, 研究了表征震级与距离饱和效应的R0(M)的性质。R0与震级相关, 同时与震源性质、地震波频谱有关。在单个地震的R0(M)的求取中, 由于R0与系数d几乎呈线性关系, 所以要求单个地震R0的值, 必须先根据理论约束确定d的大小。在检验衰减方程的预测效果时, 不仅要判断衰减曲线是否反映了实测资料的平均变化趋势, 而且要判断实测资料是否绝大多数落在84%及16%概率水平的预测曲线之内(之间).     

利用TM遥感影像分析准噶尔盆地西南缘新构造运动与油气藏形成的关系

本文以覆盖准噶尔盆地西南缘的四景LandsatTM卫星遥感影像的地质解译为基础,结合野外实地地质考察所获取的地质资料以及盆地烃源岩的生烃、排烃模拟结果,对该区第二、三排构造带自上新世以来的新构造运动变形特征,背斜和断裂构造的形成时代以及新构造运动与油气藏的关系进行了综合分析。研究结果表明,该区第二、三排构造带的新构造运动变形非常强烈,发育于这二排构造带上的背斜构造和断裂构造的构造变形始于上新世末期,早更新世末期是新构造变形最强烈的时期,第二、三排背斜构造带在中更新世早期已基本形成。有利烃源岩---安集海河组的排烃高峰晚于背斜构造形成时期,其生成的油气很有可能聚集于这些背斜构造中。发育于背斜构造核部或北翼一侧的逆冲断裂构造,一方面为油气垂向运移提供良好的通道,另一方面也破坏了油气构造,为油气的逸散创造了条件。     

一种新的 K-Ar定年方法：峰值比较法

K-Ar法定年技术经历了体积法和稀释法等不断趋于成熟，但对于年轻火山岩进行定年时，由于同位素质量分馏的影响，上述方法都具有不可克服的缺陷。随着质谱仪稳定度和精度的提高，直接建立氩同位素含量与峰强度之间的定量关系，从而不再使用稀释剂（ 38 Ar）成为可能，这就是 K-Ar定年的新方法：峰值比较法（或无稀释剂法）。该方法可以消除质量分馏作用带来的误差，对年轻火山岩定年具有重要意义。近代火山物质都含有初始氩，且有不同程度的质量分馏，其同位素比值落在质量分馏线上，这表明质量分馏作用影响 K-Ar定年的准确性，尤其是非常年轻的样品。通过精确测定样品的 38 Ar／ 36 Ar比值，可以准确扣除样品中的初始 40 Ar，从而得到放射成因 40 Ar含量。这种测量方法可以用于较老岩石、矿物样品的年龄测定，其结果与 K-Ar稀释法以及 40 Ar－ 39 Ar法相一致；更重要的是可以用于年轻样品的年龄测定，可以测 2～5ka的岩矿样品，对富钾矿物的测量误差小于 1ka；对老于 0．1Ma的样品，相对误差不大于 1．5％。介绍了峰值比较法的基本原理和测试过程，同时还讨论它的使用条件和定年范围。     

Seismic hazard maps of Mexico, the Caribbean, and Central and South America

The growth of megacities in seismically active regions around the world often includes the construction of seismically unsafe buildings and infrastructures due to an insufficient knowledge of existing seismic hazard and/or economic constraints. Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. We have produced a suite of seismic hazard estimates for Mexico, the Caribbean, and Central and South America. One of the preliminary maps in this suite served as the basis for the Caribbean and Central and South America portion of the Global Seismic Hazard Map (GSHM) published in 1999, which depicted peak ground acceleration (pga) with a 10% chance of exceedance in 50 years for rock sites. Herein we present maps depicting pga and 0.2 and 1.0 s spectral accelerations (SA) with 50%, 10%, and 2% chances of exceedance in 50 years for rock sites. The seismicity catalog used in the generation of these maps adds 3 more years of data to those used to calculate the GSH Map. Different attenuation functions (consistent with those used to calculate the U.S. and Canadian maps) were used as well. These nine maps are designed to assist in global risk mitigation by providing a general seismic hazard framework and serving as a resource for any national or regional agency to help focus further detailed studies required for regional/local needs. The largest seismic hazard values in Mexico, the Caribbean, and Central and South America generally occur in areas that have been, or are likely to be, the sites of the largest plate boundary earthquakes. High hazard values occur in areas where shallow-to-intermediate seismicity occurs frequently.     

Characterization of forward-directivity ground motions in the near-fault region

Ground motions close to a ruptured fault resulting from forward-directivity are significantly different than other ground motions. These pulse-type motions can place severe demands on structures in the near-fault region. To aid in the characterization of these special type of ground motions, a simplified parameterization is proposed based on a representative amplitude, pulse period, and number of significant pulses in the velocity–time history. Empirical relationships were developed for estimating the peak ground velocity (PGV) and period of the velocity pulse (T_v) of available forward-directivity motions. PGV in the near-fault region varies significantly with magnitude and distance. Additionally, the PGV for soil sites are systematically larger than those at rocks sites. T_v is a function of moment magnitude and site conditions with most of the energy being concentrated within a narrow-period band centered on the pulse period. Hence, lower magnitude events, which produce lower pulse periods, might produce more damaging ground motions for the stiff structures more common in urban areas.     

Assessment of liquefaction-inducing peak ground velocity and frequency of horizontal ground shaking at onset of phenomenon

It is recognized that soil improvement techniques are not economically feasible for mitigation of liquefaction-induced lifeline damages because of the large areas served. Instead, it is more practical to execute an emergency action immediately after an earthquake in order to prevent or minimize possible lifeline failures caused by the soil liquefaction. Essential element in the implementation of such a plan is the real-time identification of liquefied sites, which can be successfully achieved by analyzing surface strong motion records. In this paper, the thresholds of two ground motion parameters—the peak surface velocity and horizontal shaking frequency of the ground—that are associated with the soil liquefaction are assessed utilizing the theory of one-dimensional wave propagation in linearly elastic medium. Obtained simple expressions for both parameters are used to estimate their ranges and are examined against several case histories. Minimum level of peak ground velocity (PGV) is verified by experimental data from shaking-table test. Linear relationships between amplitude ground motion parameters at liquefied-soil sites are also developed. Results suggest that liquefaction is likely to take place when PGV exceeds 0.10 m/s and that the upper bound of horizontal ground vibration frequency after liquefaction occurrence is 1.3–2.3 Hz.     

CALCULATION OF THE VOLUME METHODOF DETENTION POND

1INTRODUCTIONDuetotiledecreaseoflandcoverandtheincreaseofwaterproofareasinurbandevelopment,itisclearthattherainwaterinfiltrationratewillreduceandtherunoft'volumewillincrease.Increasedrunoft'maycausetyequentfloodingandseveresedimentwashoutdownstream.Toavoidsuchadversedownstreameffects,storm-waterrunoft'andsedimentouttlowratemustbecontrolledusingdetentiontbcilitiesinInanynewcommunities.ThemainfunctionsofdetelltionpondsaretoreducepeakflowandcontrolthestreamlineandsedimentOutflowrate.Inperfo…     

珠穆朗玛峰重力值的推估──兼论推估方法的基本原理

在山区 ,尤其是在有全球第三极之称的喜马拉雅山区 ,当相邻点间距不大时 ,如何利用这些点上的重力与地形 (高程 )数据推估待求点的重力值 ,这对难以攀登和不能用仪器观测的山峰很有意义。研究指出 ,在地形负荷的波长很短时 ,具有一定强度的地壳足以能够支撑这种负荷 ,因此 ,不能用Airy Heiskanen和Pratt Hayford局部补偿模型作重力推估 ;由于空间异常主要受地形起伏制约 ,因此借助于邻近重力点的地形 (高程 )作推估会得到满意的结果。基于这一思路 ,我们采用了 4种有关公式 ,有效地推估了第三极之巅珠穆朗玛峰顶上的重力值 ,该值为(976 970± 7)× 1 0 - 5m·s- 2 。这一结果为精确推求珠峰大地水准面和正高提供了必要的数据 ,若用均衡的方法来推估 ,则可能相差近 1 0 0× 1 0 - 5m·s- 2 。     

Application of the microtremor measurements to a site effect study

Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about0.1–1 microns. Microtremor measurement is fast, applicable, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplification factor were calculated for all microtremor stations.According to the analysis, the peak frequency varies from0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor observations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.