重庆强对流短临业务评分方法

结合重庆本地实际情况,以区/县为单位对强对流中出现的短历时强降水、阵性大风及雷电进行业务质量定量评估.短历时强降水、阵性大风基于加密站观测资料采用分级的方式来评定,对雷电的评定基于ADTD系统观测到地闪资料并判断所在区/县是否有地闪出现.介绍了重庆本地强对流短临业务评分方法及开发的评分软件.从2011年的评分结果看,该评分方法在重庆本地是比较合理的,在业务应用上是可行的.     

An explanation for USGS Station 6 record, 1979 Imperial Valley earthquake: a caustic induced by a sedimentary wedge

Summary. The largest earthquake-induced acceleration yet recorded occurred at the United States Geological Survey's (USGS) Strong Motion Array Station 6 during the 1979 October 15, Imperial Valley, California earthquake. This large acceleration (1.74 g, vertical component) is anomalously strong considering the low magnitude of the event ( M = 6.4), and the fact that receivers in the immediate neighbourhood of Station 6 recorded much lower accelerations. Previous studies of the records by other investigators have suggested a number of explanations for the anomaly, several of which implicate the near-receiver geological structure.
We present a detailed time and frequency domain analysis of the acceleration records at Stations 6, 5, 7, 8 and Diff Array to suggest that the anomalous acceleration is the consequence of the focusing of the incoming body waves by the lens-like effect of the sedimentary wedge between Imperial Valley and Brawley faults. The analyses include a detailed comparison of observed particle motions between neighbouring stations. Narrow band-pass filtered particle motions at Station 6 reveal the interaction of multipath arrivals as well as the frequency-dependent interference between them. Three-dimensional ray tracing experiments confirm the fact that the faulted sedimentary wedge is capable of focusing P -waves near Station 6. The interpretation that best combines theoretical and observed results is that amplification was due to the formation of an elliptic umbilic caustic with focus near the surface.     

Equations for the Estimation of Strong Ground Motions from Shallow Crustal Earthquakes Using Data from Europe and the Middle East: Horizontal Peak Ground Acceleration and Spectral Acceleration

This article presents equations for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes with magnitudes M_w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is not large and corresponds to factors between 0.8 (normal and odd) and 1.3 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.6 over those on rock sites. Disappointingly the standard deviations associated with the derived equations are not significantly lower than those found in previous studies.     

中国大陆7级强震前地下流体前兆时空特征

对中国大陆1969年以来11次7级强震前地下流体前兆观测资料分阶段进行统计分析,并选用雷达图描述了中国大陆7级强震前地下流体前兆异常的时空特征,认为其特征主要表现在：异常出现时间上的阶段性与不均匀性,中长期趋势性异常分散,短临异常相对集中,且各占总异常比例的50％左右;震前异常集中在一定的范围内,并沿活动断裂呈现出一定的集中性;中长期趋势异常较早出现在震源区附近,并呈现出由震源区向外围扩散-收缩-扩散-收缩的过程,特别是进入短临阶段后,异常向震源区收缩的趋势更为明显;在震源区(或在距震源较近的范围内)异常所占的比例大,远离震源区所占比例小,且有由震源区向外围逐渐减小的趋势。     

An investigation of analysis of variance as a tool for exploring regional differences in strong ground motions

The statistical technique known as analysis of variance is applied to a large set of European strong-motion data to investigate whether strong ground motions show a regional dependence. This question is important when selecting strong-motion records for the derivation of ground motion prediction equations and also when choosing strong-motion records from one geographical region for design purposes in another. Five regions with much strong-motion data (the Caucasus region, central Italy, Friuli, Greece and south Iceland) are investigated here. For the magnitude and distance range where there are overlapping data from the five areas (2.50 M_s 5.50, 0 d 35 km) and consequently analysis of variance can be performed, there is little evidence for a regional dependence of ground motions. There is a lack of data from moderate and large magnitude earthquakes (M_s > 5.5) so analysis of variance cannot be performed there. Since there is uncertainty regarding scaling ground motions from small to large magnitudes whether ground motions from large earthquakes are significantly different in different parts of Europe is not known. Analysis of variance has the ability to complement other techniques for the assessment of regional dependence of ground motions.     

A simplified method for simulation of strong ground motion using finite rupture model of the earthquake source

We present a simplified method to simulate strong ground motion for a realistic representation of a finite earthquake source burried in a layered earth. This method is based on the stochastic simulation method of Boore (Boore, D. M., 1983, Bull. Seism. Soc. Am. 73, 1865–1894) and the Empirical Greens Function (EFG) method of Irikura (Irikura, K., 1986, Proceedings of the 7th Japan Earthquake symposium, pp. 151–156). The rupture responsible for an earthquake is represented by several subfaults. The geometry of subfaults and their number is decided by the similarity relationships. For simulation of ground motion using the stochastic simulation technique we used the shapping window based on the kinetic source model of the rupture plane. The shaping window deepens on the geometry of the earthquake source and the propagation characteristics of the energy released by various subfaults. The division of large fault into small subfaults and the method for accounting their contribution at the surface is identical to the EGF. The shapping window has been modified to take into account the effect of the transmission of energy released form the finite fault at various boundaries of the layered earth model above the source. In the present method we have applied the correction factor to adjust slip time function of small and large earthquakes. The correction factor is used to simulate strong motion records having basic spectral shape of ² source model in broad frequency range. To test this method we have used the strong motion data of the Geiyo earthquake of 24th March 2001, Japan recorded by KiK network. The source of this earthquake is modelled by a simple rectangular rupture of size 24 × 15 km, burried at a depth of 31 km in a multilayered earth model. This rupture plane is divided into 16 rectangular subfaults of size 6.0 × 3.75 km each. Strong motion records at eight selected near-field stations were simulated and compared with the observed records in terms of the acceleration and velocity records and their response spectrum. The comparison confirms the suitability of proposed rupture model responsible for this earthquake and the efficacy of the approach in predicting the strong motion scenario of earthquakes in the subduction zone. Using the same rupture model of the Geiyo earthquake, we compared the simulated records from our and the EGF techniques at one near-field station. The comparison shows that this technique gives records which matches in a wide frequency range and that too from simple and easily accessible parameters of burried rupture.     

北京北郊冬季大风过程湍流通量演变特征的分析研究

利用中国科学院大气物理研究所325 m气象观测塔1993年12月～1994年1月大气边界层实验资料, 计算分析了大风过境过程中47 m和120 m高度湍流通量演变特征及其影响因子, 以及与风速、 稳定度等参数的关系。结果表明: 大风过程对近地面层的物质能量输送有着重要影响, 大风之前出现短时间动量上传和热量下传; 大风过程中的湍流通量数值明显高于过境后, 水平方向湍流通量数值和能量增加幅度大于垂直方向; 当风速大于临界值5 m/s时, 湍流通量与风速、 湍流动能的相关迅速增大; 湍流谱特征表现为湍流能量的低频部分增加、 湍流谱曲线变宽; 大风能强烈影响近地面层的能量收支。     

一次飑线过程多普勒雷达资料分析

利用济南CINRAD/SA多普勒雷达产品,针对2006年7月5日飑线天气过程,分析回波发展演变、流场结构,讨论外流边界、强下沉气流与大风的关系,分析组合反射率因子、垂直液态含水量、中气旋产品特征.结果发现,飑线过境时风速出现两个极大值,一个出现在外流边界影响时段,另一个发生在强回波下沉气流影响时段;在横槽南下过程中,飑线后部强入流不断补充,前侧暖湿气流沿着后部入流爬升,不断产生新的单体,使得风暴得以维持发展;在垂直流场结构上表现为前侧暖湿气流倾斜上升,然后主体部分向后倾斜,后部有冷空气注入,形成下沉气流,下沉气流在地面附近辐散,与前侧入流形成低层阵风锋,是造成地面破坏性大风的主要因素.在水平流场结构上表现为低层存在气流辐合上升运动,中层有气旋性旋转气流,风暴高层为辐散气流.飑线消散阶段后期中层出现MARC,带来大风天气,而同时伴有冰雹天气的风灾产生在飑线达到最强至开始减弱的时段.当回波强度≥50dBz,且垂直液态含水量≥35kg·m-2,当有中气旋时,有利于产生冰雹和大风天气;外流边界的出现,反映了强对流回波后部下沉气流较强,是灾害性大风的前兆.     

地球系统10~(-1)年变化原因概述

我们曾论述了地球系统100～108年变化的原因[1], 唯对10-1年（月一年）的地球系统变化未指出其变化原因。经过近年的研究, 现在可以明确地指出, 地球内部有两类流体： 地外核和岩石圈裂隙中地下流体（地气）的活动是引发10-1年地球系统变化的原因。外核的上升运动会使其上部岩石圈产生上抬和压缩, 在地表层就出现3.2 m地温升高和降水减少的“干热异常”, 经过“孕震三步曲”最终引发构造地震。外核的下降运动会使其上部岩石圈产生下沉和拉张作用, 地表层表现为3.2 m地温降低, 同时降水增多的“湿冷异常”, 最终可导致发生陷落地震。外核的脉冲运动是引发岩石圈中形成地热（冷）涡的“源”。地气环流也是旋转地球上的一种流体运动, 其特征速度（地下风速）约为0.2 m/s, 据此可推得“自然气候周期”约为8个月。地气环流是使地气系统得以“流”的动力源。地热（冷）涡的“源”、 “流”相结合是使短期气候呈现纷繁复杂变化的原因。     

不同强风样本湍流特性参数的计算分析

在结构风工程中, 风湍流统计参数计算的正确与否直接影响到风荷载的计算精度。在实际风参数计算与分析中, 多选用风速较大的样本资料, 但过分强调大风可能产生不合理的计算结果。利用超声风速仪瞬时风速观测资料, 分别划分成相对强风和持续强风样本, 计算并比较其湍流统计特性参数, 发现湍流统计参数特性值 (湍流度、阵风因子、摩擦速度等) 与风速大小并不能很好匹配, 有时风速不大但其湍流特性值却很大, 反之也然。研究表明:选取的湍流风资料样本或统计方法不同, 都会影响风特性参数的计算结果, 进而影响到风荷载计算的精度。这一结果对于提高结构风工程中风参数计算与设计的科学性和合理性具有现实意义。