首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 93 毫秒
1.
使用超宽频带JCZ-1型地震计记录到的不同震中距、不同类型的地震波形,通过对这些典型地震波形的分析,得到JCZ-1型地震计除震中距1 000 km的特大地震不能很好记录外,均能够较好记录不同震中距及不同类型的地震波形.  相似文献   

2.
针对目前城市和村镇地区采用统一抗震设防标准的现状,将村镇建筑分为农村、乡镇、县城3个层次,制定基于性态抗震设防标准并开展相应的地震易损性分析,进而计算典型砌体结构的离散化震害矩阵。通过考虑不同地区地震危险性特征的差异来计算地震危险性曲线,并分析不同层次村镇结构在将来地震中的可能经济损失,确定相应地震保险费率。通过对不同层次、不同设防标准的典型砌体结构地震保险费率的对比,验证了将村镇地区分3个层次并考虑不同地区地震危险性差异来研究地震保险费率的合理性。  相似文献   

3.
研究了新疆中强震前地震活动空间演化过程。结果表明:①新疆发生7级地震的主要地震活动特征是震前2年新疆4级地震增强,震前1年新疆4级地震平静;②新疆发生6级地震的主要地震活动特征是,在不同时段的增强背景下,构造带4级地震活动经历增强—平静过程,不同构造区震前3个月震源区的活动具有各自的特点;③对强震而言,地震活动不同阶段所表现出的特征与构造有较好的关联。4~5级地震的孕震影响范围远低于7级地震,地震活动的强弱更多的与所处的构造带相关,反映了区域应力场对不同量级地震的影响。  相似文献   

4.
关于结构系统地震输入模式问题的讨论   总被引:4,自引:2,他引:2  
通过具有不同自振频率的单自由度系统地震响应的数值计算,讨论了基于运动学和动力学关系所形成的不同地震动时程输入模式对计算结构地震响应的影响.数值结果表明,不同地震输入模式对计算结构地震响应是有较大的影响,要慎重应用地震位移输入模式.  相似文献   

5.
中国地震震源机制测定结果的比较   总被引:10,自引:1,他引:10  
在搜集了 1 988年以来 ,地震学家用不同方法和不同资料测定的中国地震震源机制结果 ,包括用地震波形反演得到的地震矩张量、P波初动解和用地形变观测反演的震源参数的基础上 ,计算了同一地震的不同反演结果的滑动矢量之间的夹角、不同反演结果 P,T轴之间的夹角和不同的反演结果给出的地震矩之间的差别 ;并与哈佛 CMT的结果进行比较。结果表明 ,同一地震不同测定结果的滑动矢量之间的夹角分布较分散 ,但优势分布在 2 0°左右 ;不同测定结果的地震矩一般不超过 1倍 ,对应的震级差约为 0 .2 ;中国地震矩张量的测定结果与哈佛矩心矩张量测定结果滑动矢量之间的夹角集中在 0°~ 1 0°。以丽江地震为例 ,讨论了地震震源参数的不同结果对地震“应力触发”中库仑破裂应力计算结果的影响。  相似文献   

6.
通过倾斜矢量法和垂直形变剖面图分析法,对安庆Ms4.8地震前肥东短水准数据进行了分析,结果显示肥东台短水准数据在安庆地震前出现异常变化.对比分析了安庆地震与九江地震前肥东短水准异常形态的差异,认为安庆地震和九江地震的震源机制不同,震前应力积累在肥东台附近的不同类型可能是两次地震前肥东短水准异常形态不同的主要原因.  相似文献   

7.
井下地震计方位角检测技术应用研究   总被引:8,自引:0,他引:8       下载免费PDF全文
本文利用波形相关分析法对井下地震计方位角检测精度及一致性进行分析研究.研究中在地表布设地震计进行不同距离、不同频带多套地震计方位角检测对比测试,并在四川泸州、宁夏灵武、陶乐、河南安阳、清丰、陕西定边等6个分别安装井下甚宽频带、宽频带、短周期地震计的台站,进行地表同台址不同频带多套地震计与井下地震计方位角检测及一致性对比测试.根据全球噪声模型1~10s之间存在明显的噪声峰值的特点,对测试数据进行0.2~0.3Hz带通滤波和仿真处理,通过分析得出,对于不同地震计组合,测试地震计方位角检测结果一致性较好,根据地表不同距离、不同频带地震计组合的检测精度和地脉动记录的特点,认为井下地震计方位角检测精度优于4°.  相似文献   

8.
根据重庆台网建设的时间阶段性,在对不同震级下限地震频度时间特征分析的基础上,研究了重庆地区不同时段的G-R关系和震级分布特征,并运用z检验方法对不同时段地震目录差异的显著性进行了分析,进而评估了重庆地区1970年以来不同时段的地震目录完整性,为区域地震活动性研究中地震目录的合理运用提供参考依据。  相似文献   

9.
在对构造运动差异较大的柯坪块体和天山中部地区地震活动研究基础上,深入分析了这两个不同构造单元的中强地震活动对整体新疆地震形势的影响。不同构造环境下不同构造单元地震活动差异性很大。柯坪块体内构造运动强烈,它是新疆6级地震主要活动区之一。6级地震发生后的1年内,天山地震带是中强地震的主要响应区,在时间上具有短期预测意义。位于特殊构造环境的中天山地区地震少,地震强度低。4次5级地震后的1~3年,新疆地震活动呈明显增强趋势,中天山地区中强地震活动对周边地区中强地震活动会产生触发作用。  相似文献   

10.
用F-K方法确定腾冲火山区震源机制*   总被引:2,自引:0,他引:2  
介绍了计算理论地震图的 F- K方法在不同深度 ,不同震中距 ,不同震源类型的情况 ,表明这种方法在高频区和多层水平层状模型计算效果较好 ,适用于研究中小地震的震源机制。采用 F- K方法得到了发生在腾冲火山区的 3个地震的震源机制 ,结果表明地震 1和地震 2是走滑断裂 ,地震 3是逆断层。 3个地震的主压应力轴基本呈北西向 ,与云南地区主压应力轴方向基本吻合 ,因此 ,推断这 3个地震是构造地震。  相似文献   

11.
利用GPS技术监测城市地面沉降,监测基准的合理选取对获得真实的形变结果至关重要.本文详细分析了城市沉降监测网基准的特点,针对传统基准模型的局限性提出了顾及板块运动、基准点稳定性以及其他系统误差影响的拟稳基准模型.该模型考虑了基准点自身的稳定性以及板块运动对高程形变的影响,同时采用系统参数统一各期基线框架以及区域拟稳基准,有效解决了因基准点不稳定性和基线框架不一致对形变结果造成的误差,确保正确形变信息的获取.最后通过六期西安市地面沉降监测网数据试验,验证了该方案的合理性和可靠性.  相似文献   

12.
Construction works related to large cities, engineering projects and communication systems in loess regions influence and charge natural conditions in the loess. This results in collapse, settlement and other deformations of terrains, geodetic benchmarks and engineering constructions. On this background, the paper examines crustal movements and expedient schemes of geodetic networks, methods, fundamental and control benchmarks and the character of deformations at construction sites on the basis of concrete examples.  相似文献   

13.
Ensemble Kalman filter, EnKF, as a Monte Carlo sequential data assimilation method has emerged promisingly for subsurface media characterization during past decade. Due to high computational cost of large ensemble size, EnKF is limited to small ensemble set in practice. This results in appearance of spurious correlation in covariance structure leading to incorrect or probable divergence of updated realizations. In this paper, a universal/adaptive thresholding method is presented to remove and/or mitigate spurious correlation problem in the forecast covariance matrix. This method is, then, extended to regularize Kalman gain directly. Four different thresholding functions have been considered to threshold forecast covariance and gain matrices. These include hard, soft, lasso and Smoothly Clipped Absolute Deviation (SCAD) functions. Three benchmarks are used to evaluate the performances of these methods. These benchmarks include a small 1D linear model and two 2D water flooding (in petroleum reservoirs) cases whose levels of heterogeneity/nonlinearity are different. It should be noted that beside the adaptive thresholding, the standard distance dependant localization and bootstrap Kalman gain are also implemented for comparison purposes. We assessed each setup with different ensemble sets to investigate the sensitivity of each method on ensemble size. The results indicate that thresholding of forecast covariance yields more reliable performance than Kalman gain. Among thresholding function, SCAD is more robust for both covariance and gain estimation. Our analyses emphasize that not all assimilation cycles do require thresholding and it should be performed wisely during the early assimilation cycles. The proposed scheme of adaptive thresholding outperforms other methods for subsurface characterization of underlying benchmarks.  相似文献   

14.
A 17-benchmark geodetic network in the volcanic area of the Teide Caldera, Canary Islands has been utilised several times since 1982 to detect crustal movements associated with volcanic activity within the network, as well as a procedure for solving configuration problems. The network is located on the mid-western side of the Caldera, where there are two different morphological zones that both have benchmarks. The authors performed a sensitivity test of this geodetic network for volcano monitoring purposes. To do so, we use a deformation model to calculate surface displacement caused by a dike intrusion in a homogenous half space. The depth and location of dike are changed to study the variation of the effects produced (displacements). The size and location of the intruded dike are found to play a major role in determining both the displacement pattern and magnitude. When the dike is close to the surface, there is an inversion of the surface displacement pattern and very large surface displacement at certain benchmarks. Such phenomena can serve as precursors of such dike eruptions. Our study show a clear need to extend the existing geodetic network to cover the full island for volcano monitoring purposes.  相似文献   

15.
The geological and non-geological influences on the velocity of vertical movements of benchmarks along lines of relevelling have been examined and determined. Those parts of anthropogenic, technogenic, subrosive, halokinetic, and faulting-tectonic origin have been eliminated. The remaining part of endogenic recent vertical movements has been used in calculating and drawing the isobases of a new map of recent vertical crustal movements.  相似文献   

16.
We present elevations between long-term benchmarks in the Tolbachik Geodynamic Test Site as directly measured by second-order leveling in 1976–2011. These raw data are very important for future researchers, since the measurements can be repeated between surviving benchmarks using any more accurate techniques for comparisons with past results. We show that the greatest ground subsidence occurred at the base of Cone II, at the North Vent eruption center during the 1975–1976 Great Tolbachik Fissure Eruption, with the subsidence reaching 2.33 m for the past 35 years. The subsidence nearly decays at a distance of 7 km. Assuming that subsidences propagate symmetrically, we found an approximate volume for this subsidence, which is 0.12 km3. To make a comparison, we mention that the volume of all the three cones is 0.254 km3. We adduce data showing that a ground uplift of 4–5 cm over an extensive area in the southeastern sector from Cone VIII after the eruption at the South Vent came to an end. We hypothesize that the uplift was caused by lateral emplacements of magma at depths of 0–5 km along numerous southeasterly directions without coming to the surface.  相似文献   

17.
Modern ecological assessments of running waters are based on the a priori definition of ecological benchmarks, given by reference-quality sites. Such benchmarks are established at the level of ecoregions, typologies, or site. Yet, in highly disturbed regions, such as coastal areas of European countries, the assessment of streams’ water quality based on the reference condition concept is very difficult, due to the lack of undisturbed sites. Among others, the reduced number of reference sites may have as a consequence the definition of imprecise ecological benchmarks. Here we tested the hypotheses that (1) the increase in the number of potential reference sites (2) the definition of more precise abiotic thresholds using the least disturbed condition approach (LDC), and (3) the use of diatom assemblages, as the most ubiquitous element in lowland areas, would result in refinement and eventual sub-division of existing river types of a highly disturbed area, such as the Portuguese centre-western region. For this purpose, abiotic data characterising natural conditions of 55 sites from a littoral highly disturbed region were used in a hierarchical classification analysis that revealed the existence of three different sub-groups. In addition, a three-step approach was used to define thresholds for the pressure variables in LDC. Based on these new thresholds, sites in LDC were selected. A hierarchical classification performed to the LDC diatom spring assemblages revealed the existence of two sub-groups, concordant with two of the abiotic sub-groups. Several species contributed to the dissimilarity between the two sub-groups (e.g., Achnanthidium minutissimum and Karayevia oblongella). Differences between the sub-groups were also found in the trait proportions of stalked species. New benchmark values for these two sub-groups, based on the scores of the official diatom index, the Indice de Polluosensibilité Spécifique (IPS), were different from the previous reference value used. Yet, no biological benchmark values were established for one of the groups due to the absence of sites in the LDC. Our study suggests that streambed substrate is an important characterisation variable in the river type definition and highlights that, in spite of the potential refinement in reference conditions and typology obtained, an alternative approach that does not require the use of reference sites should be explored in the future.  相似文献   

18.
In the context of developing a real‐time seismic damage assessment technique, this paper proposes a simplified model that accounts for abutment stoppers, focusing on the transverse direction. Detailed 3D finite element models of 4 bridges of the Attiki Odos motorway are developed and used as benchmarks to assess its efficiency. The selected bridges vary in length, pier typologies, clearances, and pier‐deck connections. The simplified model entails a SDOF system of a pier, with assemblies of gap elements, lateral and rotational springs, and dashpots (top and bottom), representing the deck, the bearings, the abutment stoppers, and the foundation. The effect of stoppers is initially studied, focusing on the response of the abutment‐embankment system. To shed more light on the role of abutment stoppers, a parametric study is conducted, considering a wide range of clearances. Subsequently, the effect of variabilities in span length and pier height is examined. The simplified method is extended to nonideally symmetric systems and verified against the 3D benchmarks. Finally, the model is modified to account for multicolumn piers. The extended simplified model offers a reasonable prediction of the seismic damage state, reducing significantly the computational cost, and allowing detailed parametric studies. The latter are used to develop nonlinear regression model equations correlating a selected damage index with statistically significant intensity measures. Such equations offer a viable alternative for network‐wide seismic damage assessment as part of a real‐time emergency response framework. A pilot implementation is presented, illustrating the applicability of the proposed methodology.  相似文献   

19.
The seismic activity of the Guardamar-Torrevieja zone (Eastern Betic Cordillera, SE Spain) can be associated with the Bajo Segura fault zone, an E-W reverse blind fault with secondary NW-SE dextral faults. A high-precision levelling profile 30 kilometers long was set up and levelled in 1997 to monitor the vertical displacement of this active fault zone. This profile runs parallel to an older high-precision levelling line included in the Spanish first order levelling network measured by the Instituto Geográfico Nacional (IGN) in two different campaigns (1934 and 1976). The 1997 line was relevelled in 2003 and 10 new benchmarks were set up, both to increase benchmark density and to restore some of the 1997 benchmarks that had been destroyed. We have used the 1976 IGN and the 2003 measurement to construct a recent vertical movements profile with a significant time difference (27 years). This recent vertical movements profile shows that the vertical movements are very small, nearly equal to the error bars, with a 0.2 mm/year rise in the town of Guardamar, and a 0.2 mm/year subsidence of the southern part of the profile (Punta Prima) respect to the town of Torrevieja. These movements could be related to the activity of the Bajo Segura and the San Miguel faults respectively. Using geological markers we have deduced uplift rates of 0.1 mm/year during the last 3 million years. Therefore, these preliminary results indicate that geodetically (short-term deformation) determined uplift rates are similar to those estimated from geological markers (long term deformation).  相似文献   

20.
In 1982, the Central Laboratory for Geodesy (CLG) started a long-term study of the recent crustal movements in a local test area in a mobile region located southwards of Sofia.The recent geodynamic conditions and the deep structure of the Earth's crust in this region are described.Data on the local network of precise leveling are given-the scheme and characteristics of the loops, benchmarks and their monumentation. A first geodynamic analysis of the results of the first and third cycles of measurements is made, a map of the module of horizontal gradient of vertical velocity has been elaborated. The results obtained corroborate the reasons for the selection of this geodynamic test area.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号