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1.
Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (QP and QS) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1?10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0?500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 MW4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average vP and vS of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high vP/vS ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain QS and the near surface velocity structure. Our modeling indicates that QS is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (~10), but consistent with QS modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0?50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation. 相似文献
2.
This study focuses on the response of seismic isolated bridges subjected to near-field ground motions with distinct pulse type behavior in terms of maximum isolator displacements (MIDs) and maximum isolator forces (MIFs) transferred to the substructure. The employed isolation systems are composed of lead rubber bearings (LRBs) with bi-linear force-deformation relations that consider cycle-to-cycle deterioration in the yield strength of the LRBs due to heating of the lead core. MIDs and MIFs with due consideration of cycle-to-cycle deterioration are compared with that of non-deteriorating ones. Bounding analyses are also performed for comparison purposes. Nonlinear response history analyses are conducted with two bins of ground motions recorded at different soil conditions to investigate the effect of ground motion characteristics. Results indicate that MIDs are overestimated by lower bound analyses when seismic isolated bridges are subjected to near-field motions with high velocity pulses especially for the bearings with higher Q/W ratios. 相似文献
3.
This study develops a straightforward approximate method to estimate inelastic displacement ratio, C1 for base‐isolated structures subjected to near‐fault and far‐fault ground motions. Taking into account the inelastic behavior of isolator and superstructure, a 2 degrees of freedom model is employed. A total of 90 earthquake ground motions are selected and classified into different clusters according to the frequency content features of records represented by the peak ground acceleration to peak ground velocity ratio, Ap/Vp. A parametric study is conducted, and effective factors in C1 (i.e., fundamental vibration period of the superstructure, Ts; postyield stiffness ratio of the superstructure, αs; strength reduction ratio, R; vibration period of the isolator, Tb; strength of the isolator, Q; ratio of superstructure mass to total mass of the system, γm) are recognized. The results indicate that the practical range of C1 values could be expected for base‐isolated structures. Subsequently, effective parameters are included in simple predictive equations. Finally, the accuracy of the proposed approximate equations is evaluated and verified through error measurement, and comparisons are made in the analyses. 相似文献
4.
In this study, closed form equations as functions of the isolator, bridge and ground motion properties are formulated to calculate the optimum characteristic strength, Qd and post-elastic stiffness, kd, of the isolator to minimize the maximum isolator displacement (MID) and force (MIF) for seismic isolated bridges (SIBs). For this purpose, first, sensitivity analyses are conducted to identify the bridge, isolator and ground motion parameters that affect the optimum values of Qd and kd. Next, for the identified parameters, nonlinear time history analyses of typical SIBs are conducted to determine the optimum values of Qd and kd for a wide range of values of the parameters. Next, nonlinear regression analyses of the available data are conducted to obtain closed form equations for the optimum values of Qd and kd, to minimize the MID and MIF. The equations are then simplified for various site soil conditions. It is observed that the optimum Qd and kd are highly dependent on the site soil condition. Furthermore, the optimum Qd is found to be a linear function of the peak ground acceleration. 相似文献
5.
A comprehensive parametric study on the inelastic seismic response of seismically isolated RC frame buildings, designed for gravity loads only, is presented. Four building prototypes, with 23 m × 10 m floor plan dimensions and number of storeys ranging from 2 to 8, are considered. All the buildings present internal resistant frames in one direction only, identified as the strong direction of the building. In the orthogonal weak direction, the buildings present outer resistant frames only, with infilled masonry panels. This structural configuration is typical of many existing RC buildings, realized in Italy and other European countries in the 60s and 70s. The parametric study is based on the results of extensive nonlinear response‐time history analyses of 2‐DOF systems, using a set of seven artificial and natural seismic ground motions. In the parametric study, buildings with strength ratio (Fy/W) ranging from 0.03 to 0.15 and post‐yield stiffness ratio ranging from 0% to 6% are examined. Three different types of isolation systems are considered, that is, high damping rubber bearings, lead rubber bearings and friction pendulum bearings. The isolation systems have been designed accepting the occurrence of plastic hinges in the superstructure during the design earthquake. The nonlinear response‐time history analyses results show that structures with seismic isolation experience fewer inelastic cycles compared with fixed‐base structures. As a consequence, although limited plastic deformations can be accepted, the collapse limit state of seismically isolated structures should be based on the lateral capacity of the superstructure without significant reliance on its inherent hysteretic damping or ductility capacity. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
6.
We derive S-wave attenuation characteristics, earthquake source parameters and site amplification functions at seismic stations
used for earthquake early warning in the Irpinia–Basilicata region, using non-parametric spectral inversion of seismograms
from 49 local events with M
L = 1.5–3.1. We obtain relatively low Q values (Q
0 = 28 at a frequency of 1 Hz) in conjunction with a strong frequency-dependence (close to linear). The source spectra can
be satisfactorily modeled using the omega-square model, with stress drops ranging between 0.01–2 MPa, and in the narrow magnitude
range available for analysis, the source spectra seem to scale self-similarly. The local magnitude M
L shows a linear correlation with moment magnitude M
W, however with a systematic underestimation by about 0.5-magnitude units. The results obtained in this work provide important
insights into the ground-motion characteristics that are required for appropriate seismic hazard assessment and are of practical
relevance for a suite of applications, such as the calibration of ground-motion prediction equations or the correction for
site amplification in earthquake early warning and rapid calculation of shake-maps for seismic emergency management. 相似文献
7.
8.
本文采用分层粘弹性介质模型计算了汶川地震对芦山震中产生的库仑应力加载的影响,进而结合Dieterich(1994)提出的速率状态摩擦定律给出芦山附近区域6级地震累积发震概率随时间的变化。结果显示,2013年芦山7.0级地震时其累积发震概率达18%,说明汶川地震产生的应力扰动加速了芦山地震的发生。本文还计算了汶川、芦山2次地震对其间"破裂空段"处产生的累积库仑应力扰动的影响,结合背景地震发生率,给出了"破裂空段"处6级地震累积发震概率变化。虽然计算结果可能受到大邑地震、介质模型参数的选取和背景地震发生概率等因素影响而存在一定误差,但"破裂空段"在2次强震应力加载下累积发震概率是不断增大的,因此我们认为"破裂空段"处发生中强地震的紧迫性不断增强。 相似文献
9.
In the paper, we introduce Allegre＇s scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors （seismic spatial correlation length and coda Qc） associated with the earthquake （M=6.1） occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc. 相似文献
10.
内蒙古中西部地区中小地震矩震级研究 总被引：1，自引：1，他引：0
基于S震相"S窗"内的波形信号识别、品质因子Q(f)和22个台站场地响应,利用2009~2016年3月内蒙古中西部地区地震的波形资料,反演了182次中小地震的震源波谱参数,得到这些小震的零频幅值及其拐角频率,据此计算了这些地震的地震矩M_0、矩震级M_W和应力降Δσ。利用回归分析方法得到了近震震级与矩震级、矩震级与应力降的关系式。分析表明,近震震级与矩震级、矩震级与应力降呈线性关系。可见,将矩震级纳入地震的快报与正式目录中,可以丰富地震观测报告内容,更好地为地震应急和地震科研服务。 相似文献
11.
收集康定地震区及周边（99.6°~105.2°E,27.8°~33.0°N范围内）连续GPS观测站的资料求解站速度场,采用刚性-线弹性运动方程计算方法,拟合计算得到研究区域规格网格点（0.4°×0.4°）的速度值和主应变率值。基于该结果分析研究区内的运动特征和应变场变化情况,并讨论其与地震孕育发生的关系。分析结果表明,芦山7.0级地震发生前研究区呈现应变能量积累态势,而地震之后研究区呈应变能量释放调整态势,2014年康定地震的发生就是该区构造运动调整下的产物。 相似文献
12.
A. V. Klyuchevskii 《Journal of Volcanology and Seismology》2010,4(4):274-283
The numerical modeling of actually observed events contained in the Baikal earthquake catalog allowed the production of synthetic
catalogs. These catalogs reflect real situations that can give rise to heterogeneities in earthquake catalogs acquired by
seismological monitoring. For each of the resulting 65 catalogs we calculated the slope γ and seismic activity (so-called
in Russian; it is the seismicity rate or the constant term in the frequency-size relation) A
10 in the recurrence relation. We also investigated the effects of changes in estimates of earthquake energy class on the parameters
of the recurrence relation. It was shown that the slope γ is not very sensitive, but that the seismic activity A
10 is sensitive, to changes in earthquake energy class and can be used to test an earthquake catalog for heterogeneity. Formulas
were derived to relate the parameters of recurrence relations and the scaling factors of two energy scales, which can yield
recurrence parameters for one of the scales, provided we know the ratio of the respective scaling factors and the recurrence
parameters based on the other scale. 相似文献
13.
Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake 
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下载免费PDF全文 Nonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake. 相似文献
14.
The convex model approach is applied to derive the robust seismic fragility curves of a five-span isolated continuous girder bridge with lead rubber bearings (LRB) in China. The uncertainty of structure parameters (the yield force and the post-yield stiffness of LRB, the yield strength of steel bars, etc.) are considered in the convex model, and the uncertainty of earthquake ground motions is also taken into account by selecting 40 earthquake excitations of peak ground acceleration magnitudes ranging from 0.125 to 1.126 g. A 3-D finite element model is employed using the software package OpenSees by considering the nonlinearity in the bridge piers and the isolation bearings. Section ductility of piers and shearing strain isolation bearings are treated as damage indices. The cloud method and convex model approach are used to construct the seismic fragility curves of the bridge components (LRB and bridge piers) and the bridge system, respectively. The numerical results indicate that seismic fragility of the bridge system and bridge components will be underestimated without considering the uncertainty of structural parameters. Therefore, the failure probability P f,max had better be served as the seismic fragility, especially, the fragility of the bridge system is largely dictated by the fragility of LRB. Finally, the probabilistic seismic performance evaluation of the bridge is carried out according to the structural seismic risk estimate method. 相似文献
15.
A method for determining medium quality factor is developed on the basis of analyzing the attenuation dispersion of the arrived
first period P wave. In order to enhance signal to noise ratio, improve the resolution in measurement and reduce systematic
error we applied the data resampling technique. The group velocity delay of P wave was derived by using an improved multi-filtering
method. Based on a linear viscoelastic relaxation model we deduced the medium quality factor Q
m, and associated error with 95% confidence level. Applying the method to the seismic record of the Xiuyan M=5.4 earthquake sequences we obtained the following result: (1) High Q
m started to appear from Nov. 9, 1999. The events giving the deduced high Q
m value clustered in a region with their epicenter distances being between 32 and 46 km to the Yingkou station. This Q
m
versus distance observation obviously deviates from the normal trend of Q
m linearly increasing with distance. (2) The average Q
m before the 29 Dec. 1999 M=5.4 earthquake is 460, while the average Q
m between the M=5.4 event and the 12 Jan. 2000 M=5.1 earthquake is 391, and the average Q
m after the M=5.1 event is 204.
Foundation item: State Key Project of Science and Technology during the Tenth Five-year Plan (2004BA601B01-03-01). 相似文献
16.
利用山东台网记录的长岛震群2017年2月14日—9月1日期间的波形与震相资料研究长岛地区非弹性衰减系数,得到该地区介质平均Q值与频率f的关系式为Q(f)=363.9f1.374 1。采用Moya等[1]提出的利用遗传算法联合反演得到长岛周边台站的场地响应,根据Brune模型震源参数计算公式求解长岛震群序列地震震源参数。结果显示,各个震源参数之间均存在一定的相关关系,地震矩随ML震级的增大而增加,地震矩与破裂半径R之间存在半对数关系,拐角频率fc随地震矩的增大而减少;长岛地震序列的应力降数值普遍偏小,最大不超过0.9MPa,这意味着长岛震源区整体构造应力较低,也可能指示长岛震群为低摩擦应力的断层作用;震源参数随时间的变化方面,整体而言,长岛震群地震应力降变化起伏很大,在M4.1地震发生前,拐角频率与应力降均发生快速下降后随即翻转上升的现象,证明在M4.1地震发生前震源区整体应力的挤压逐渐增强。 相似文献
17.
对临夏地震台的YRY-4分量应变仪、水位仪和地震仪记录数据分析后发现:2008年5月12日汶川MW7.9地震前,在3种不同学科的观测记录上,在相近时间段内均记录到了预滑震相Xp和震颤震相Tp。总结Xp震相和Tp震相记录特征的基础上,试图用实验室做的小尺度黏滑实验结果来佐证和解释所记录到的临震预滑和震颤震相的物理机制。结果表明:临震前的2008年4月18日和5月6日,临夏台所处的地块发生了2次较大幅度的预滑错动,在预滑发生前后还伴有N次震颤现象发生。临震前这2次较大幅度的预滑错动有可能引发了汶川MW7.9地震。 相似文献
18.
The physical implication of coda amplitude ratio is discussed in term of energy ratio. The digitized data recorded at the
station of Beijing Telemetered Seismograph Network between 1989 and 1990 are used to calculate amplitude ratios of coda to
direct S wave, and energy ratios. The spectral energy ratios are used to estimate the coda Q and mean free path l in the Beijing area, as well as the two quality factors Q
i and Q
S separately due to intrinsic absorption and scattering attenuation. The decay of seismic waves in their propagation seems
mainly resulted from the intrinsic absorption in Beijing region. The temporal variations of amplitude ratio and energy ratio
at Changli station during the above two years are inspected; some of them largely depart from their mean value. It may reflect
the seismogenic process, but using the data lasting longer time with more case histories needs further study.
This study is sponsored by the Key Project of State Science and Technology of China, No. 96-918. 相似文献
19.
通过测量介质品质因子来开展大同窗附近测震台站记录P波衰减频散特征的研究,并分析大同窗近场区和外围区震例前后的变化。对山自皂台记录的2001年以来大同窗地震序列的研究结果表明,近场区3次和外围区6次地震前,介质品质因子显示超出1倍均方差的高值变化特征,震后逐渐恢复到背景起伏状态;与大同窗传统的频次指标相比,介质品质因子的映震效果更好;阳原台的结果表明,仅近场区1次和外围区2次地震前,介质品质因子显示超出1倍均方差的高值变化特征,且有虚报、漏报。所处地质构造位置不同、传播路径介质差异可能是引起上述两个台站附近介质品质因子的地震对应效果明显不同的原因。 相似文献
20.
Dispersion attenuation structure of the crust around the Weifang-Jiashan segment of the Tanlu fault zone in North China 下载免费PDF全文
下载免费PDF全文 On the condition that the velocity ratio of compressive wave to shear wave is stable during the propagating process of seismic wave, this paper develops an estimation method for medium quality factor based on single station's travel time difference between direct S and P waves and the first period signal of direct P wave. 8 774 high SNR wave data altogether recorded by 75 stations are analyzed. The results show that: (1) under the normal regional stress field, the quality factors QmSP in the stable tectonic area are higher than that in the active tectonic area around the Weifang-Jiashan section and its surrounding area in the Tanlu fault zone; (2) in the Juxian-Tancheng section the seismic wave attenuation is relatively quick, and the media is relatively broken, suggesting no tectonic stress accumulation; (3) the Xinyi-Sihong section is currently locking and in accumulating elastic strain energy stage, which has the deep environment and conditions of strong earthquake generation similar to those of the 1668 M8.5 Tancheng strong earthquake. 相似文献