基于阶跃响应在时域解析测定地震计参数

提出基于阶跃响应在时域解析测定地震计参数的方法,并对合理确定响应的时间零点提供了一种方法。对JCV1003D型便携式短周期地震计及与其配套的EDAS3M型16位地震数据采集记录仪组成的系统进行了测试。结果表明对JCV1003D短周期地震计的传递函数进行测试是可行的,对地震计的阻尼系数DC和自振周期TC的测试结果是令人满意的。

地震计阻尼和自振频率的频域测定

利用地震观测系统中的阶跃标定响应记录 ,在频域基于阶跃信号的幅频特性确定地震计的阻尼常数和自振周期。介绍了该方法的原理 。

正弦标定自动处理算法研究

由于种种原因,地震计的周期、阻尼、灵敏度等参数在仪器运行的过程中会发生变化,这些参数的变化直接影响到地震计的性能和观测数据的质量。为了掌握地震计参数的变化,通常采用定期标定的方法,对运行中仪器的参数进行跟踪监测,通过分析标定数据得到仪器的运行状态。目前,对于标定数据的处理通常采用人工分析的办法。随着台站数量的增加,对标定数据的处理工作变得日益繁重。该文介绍一种正弦标定自动处理算法,利用这种算法编写的自动处理程序,在标定数据处理过程中不需要人工干预,计算机可以自动提取有效的波形数据进行测量计算,并可以对效果不好的数据进行修复,最终给出仪器的频率响应特性。

吉林台网测震台站监测效能评估

由于种种原因,台站地震计的固有周期、阻尼、灵敏度、观测动态范围等参数和台基噪声在运行的过程中会发生变化。本文用阶跃标定和计算观测动态范围、台基噪声功率谱的方法,得到吉林测震台网各台站地震计参数和台基噪声的变化情况,掌握吉林测震台网各台站的监测能力,为以后吉林测震台网的建设和发展提出建议。

测震台网资料产出系统的开发

从系统的设计、软件的编程等方面介绍了测震台网资料快速产出系统的开发,并对数据库中相关的数据表和字段进行了简单的描述,对系统的功能与开发的意义也进行了说明。

Analytical expressions for determining the stability of cohesionless soil slope under generalized seismic conditions

In recent major earthquakes, the researchers have found the need for consideration of vertical seismic acceleration for the stability analysis of the man-made and natural slopes. However, in most past studies, the performance of slopes has been assessed by accounting only the horizontal seismic component of the ground motion, without giving due weightage to the effect of vertical component. In the present study, analytical expressions are derived to determine the factor of safety, yield seismic coefficient and consequently the seismic displacement of cohesionless soil slope under combined horizontal and vertical components of the ground motion. The derivation uses the Newmark's sliding block approach, in which the soil slope with a planar failure surface within the framework of conventional pseudo-static analysis is assumed to follow the Mohr-Coulomb failure criterion. The effects of vertical seismic coefficient on the stability of cohesionless slope have been studied through a set of graphical presentations for a specific range of soil parameters. It is observed that overlooking the effect of the vertical component of the ground motion on factor of safety and the displacement while designing the slope may be detrimental, resulting in the slope failure. The general expressions presented in this paper may be highly useful in the field of earthquake geotechnical engineering practice for designing the cohesionless soil slopes under combined horizontal and vertical seismic loads.

Analyzing the Relation Between Earthquakes and Active Faults Based on the Parameter Optimization Model

The gestation and occurrence of strong earthquakes are closely related to fault activity, which is not only revealed by abundant experimentation and seismism but also proved by modern seismology. On the Chinese mainland, the relation between earthquake activity and active faults is one of the bases for partitioning potential seismic sources, analyzing the seismotectoulcs and estimating location of strong earthquakes.Due to the nonuniformity of earth media, instability of observation systems and disturbance of the environment, etc, the variety of observational data is complicated, that is, there is no absolutely ＂normal＂ or ＂abnormal＂, and seismic anomalies can be divided into many mutually exdusive＂ abnormal states＂. In different conditions of combined time-spacestrength, determining seismic anomalies by different monomial forecast methods and its efficiency could be different due to the uncertainty of a precursor itself or complexity of the relationship between a precursor and earthquake gestation. It is very difficult to discover and dispose of this difference in actual application in a ＂two-state＂ model. But in a ＂multi-state＂ model, the difference can be easily reflected and the optimal combination of forecasting parameters for a forecast method can also be determined easily. Based on the ＂multi-state＂ precursory model and the optimization method for parameters of earthquake forecast model under the condition of optimal forecast efficiency, the relationship of the spatial location of earthquake with M ≥ 6.0 and active faults in three seismic belts are analyzed. The results demonstrate that in the Hetao Seismic Belt, seismicity is mostly concentrated in the range of 20 km along the fault, the optimization model can forecast the location of potential earthquakes of M ≥ 6.0 near the faults with a relatively high accuracy and the reliability is 0.5 ; while in the Qilian Mt. Seismic Belt, the reliability only reaches 0.14 when we use the model to estimate earthquakes within 30 km range along the faults. The ＂multi-state＂ precursory model, the efficiency-evaluating model and the parameter selection of individual earthquake forecast model based on optimal efficiency are of certain revelatory and practicable meanings for developing knowledge about precursors, investigating the laws of earthquake preparation and searching for optimal forecasting methods.

Application of fuzzy theory on earthquake damage rate estimation of buildings

Variations between earthquakes result in many factors that influence post-earthquake building damage(e.g.,ground motion parameters,building structure,site information,and quality of construction).Consequently,it is necessary to develop an appropriate building damage-rate estimation model.The building damage survey data were recorded and constructed into files by the Architecture and Building Research Institute(ABRI),Taiwan for the 1999 Chi-Chi earthquake in the Nantou region as a basis for developing a building damage rate estimation model by applying fuzzy theory to express the fragility curves of buildings as a membership function.Empirical verification was performed using post-earthquake building damage data in the Taichung city that suffered relatively severe damage.Results indicate that fuzzy theory can be applied to predict building damage rates and that the estimated results are similar to actual disaster figures.Prediction of disaster damage using building damage rates can provide a reference for immediate disaster response during earthquakes and for regular disaster prevention and rescue planning.

Seismic response of a typical fixed platform foundation under earthquake loading

Offshore platforms in seismically active areas should be designed to service severe earthquake excitations with no global structural failure. This paper summarizes the dynamic analysis of a typical fixed platform under the earthquake loading in the seismically active area. The dynamic analysis includes interpretation of dynamic design parameters based on the available site-specific data,together with foundation design recommendations for earthquake loading conditions,which include free-field site response analyses,liquefaction analyses and soil-pile interaction analyses.

Study on the Seismic Fortification Criteria of Offshore Platforms in the Bohai Sea

This paper analyzes the seismicity and seismic risk distribution in the Bohai Sea. Based on the seismic design parameters of 46 platforms in the Bohai Sea, a statistic analysis is made on the ratios of the peak accelerations for different probability levels. In accordance with the two-stage design method, a scheme of two design seismic levels is proposed, and two fortification goals are established respectively for strength level earthquakes and ductility level earthquakes. Through analogy and comparison to the Chinese seismic code for buildings, it is proposed that the probability level for the strength and ductility level earthquakes takes return periods of 200a and 1000～2500a respectively, and we further expounded on its rationality. Finally, the fortification parameters in the sub-regions of Bohai Sea area are given in the light of seismic risk zonation and ground motion division. This article is a summary of experiences from many years of offshore platform seismic fortification work, and an exploratory study on the seismic fortification standards of offshore platforms in China, which may provide some references for the establishment of the standard.

A statistically refined Bouc-Wen model for the identification of structures under tri-directional seismic excitations

This paper presents a statistically refined Bouc-Wen model of tri-axial interactions for the identification of structural systems under tri-directional seismic excitations. Through limited vibration measurements in the National Center for Research on Earthquake Engineering in Taiwan conducting model-based experiments, the 3-D Bouc-Wen model has been statistically and repetitively refined using the 95% confidence interval of the estimated structural parameters to determine their statistical significance in a multiple regression setting. When the parameters＇ confidence interval covers the ＂null＂ value, it is statistically sustainable to truncate such parameters. The remaining parameters will repetitively undergo such parameter sifting process for model refinement until all the parameters＇ statistical significance cannot be further improved. The effectiveness of the refined model has been shown considering the effects of sampling errors, of coupled restoring forces in tri-directions, and of the under-over-parameterization of structural systems. Sifted and estimated parameters such as the stiffness, and its corresponding natural frequency, resulting from the identification methodology developed in this study are carefully observed for system vibration control.

Statistical Analysis of the Dynamic Parameters of Silty Clay in the Beijing Area

Soil dynamic parameters,including dynamic shear modulus ratio and damping ratio,have important effects on the results of layered soil earthquake response. In this paper,the mean parameter values of silty clay in different depths are obtained after statistical analysis of the experimental soil dynamic data from 20 recent site seismic safety evaluation reports in the Beijing area. Furthermore,based on two typical engineering sites,the influence of four different soil dynamic parameters,the statistic mean values,experimental values, values recommended by Yuan Xiaoming,and the values recommended in the code for seismic safety evaluation of engineering sites( DB001-94) are analyzed. The result shows that mean statistical values are applicable to seismic safety evaluation work in the Beijing area,especially for some inter-layered silty clays whose undisturbed soil samples are hard to obtain.

Identification of flexible buildings with bending deformation and the unmeasured earthquake ground motion

It is important to explore efficient algorithms for the identification of both structural parameters and unmeasured earthquake ground motion.Recently,the authors proposed an algorithm for the identification of shear-type buildings and unknown earthquake excitation.In this paper,it is extended to the investigation of the identification of flexible buildings with bending deformation and the unmeasured earthquake ground motion.In the absolute co-ordinate system,the unmeasured ground motion can be treated as an unknown translational force and a bending moment at the 1st floor level of a flexible building.Structural unknown parameters above the 1st story of the building can be identified by the extended Kalman estimator and the 1st story stiffness and the unmeasured ground motion are subsequently estimated based on the least-squares estimation.The proposed algorithm is further extended to the identification of tall bending-type buildings based on substructure approach.Inter-connection effect between sub-buildings is treated as‘additional unknown inputs’to sub-buildings,which are estimated by the extended Kalman estimator without the measurements of rotational responses.Numerical examples demonstrate the identification of a multi-story,tall bending-type building and its unmeasured earthquake ground motions using only partial measurements of structural absolute responses.