ANALYSIS ON THE CHARACTERISTICS OF DURATION AND PERIOD OF GROUND MOTION OF THE LUSHAN EARTHQUAKE BASED ON THE STATION RECORDS

Based on 60 records from the 20 stations within 100km to the epicenter of Lushan earthquake, the predominant period, period of peak response spectrum, duration of ground motion, and source duration are investigated. By the study, we conclude that within 100km to the epicenter, the scope of predominant period is 0.013~0. 275s in EW, NS and UD direction; the scope of period of peak response spectrum for 5% damping ratio is 0.03~0.65s; the scope of 90% ground motion durations is 5. 1~35. 9s; the scope of averaging source duration is 6.41 (EW), 6.05 (NS) and 5.47s (UD). Furthermore, based on the ground motion duration calculated by 20 stations dada, the predictive curve and equation of ground motion duration is regressed and compared with the recent equation of ground motion duration by Bommer (2009). We find that the ground motion durations of most stations are larger than predictively mean value by Bommer (2009), which means that the source effect of Lushan earthquake is relatively larger. Lastly, by the contour figure of ground motion duration and source duration, we conclude that the directivity character of duration is relatively apparent in NE direction. The relatively larger source duration and ground motion duration in NE direction indicate more energy release in the main shock of Lushan earthquake, which perhaps causes the relatively less aftershocks in this direction. The duration has no hanging wall effect, which perhaps results from the blind-reverse fault structure of Lushan earthquake.     

Improved evaluation of inelastic displacement demands for short‐period masonry structures

This work discusses the simplified estimation of earthquake‐induced nonlinear displacement demands as required by nonlinear static procedures, with particular attention on short‐period masonry structures. The study focuses on systems with fundamental periods between 0.1 and 0.5 s, for which inelastic amplification of the elastic displacement demand is more pronounced; hysteretic force‐displacement relationships characteristic of masonry structures are adopted, because these structures are more commonly found within the considered period range. Referring to the results of nonlinear dynamic analyses of single‐degree‐of‐freedom oscillators, some limitations of the Eurocode 8 and Italian Building Code formulations are first discussed, then an improved equation is calibrated that relates inelastic and elastic displacement demands. Numerical values of the equation parameters are obtained, considering the amount of hysteretic energy dissipation associated with various damage mechanisms observed in masonry structures. Safety factors are also calculated to determine several percentiles of the displacement demand. It is shown that the proposed equation can be extended to more dissipative systems. Finally, the same formulation is adapted to the estimation of seismic displacements when elastic analysis procedures are employed. Copyright © 2017 John Wiley & Sons, Ltd.     

黑龙江肇东痕量氢野外定点观测实验与分析

利用ATG-300H便携式测氢仪,对黑龙江省高寒地区肇东痕量氢进行野外定点连续观测,并对泰来3.3级地震震兆关系进行初步分析。结果表明:肇东痕量氢表现为高值突跳,异常幅度大,持续时间短;氢气浓度4组高值异常,表现为"先上升、后下降"趋势,具有持续性和重复性。通过对高寒地区肇东痕量氢异常特征及异常机理分析,为痕量氢资料在地震预测中的应用提供一定的观测依据。     

Effect of site amplification on inelastic seismic response

The available models for eff ective periods of site and structure are reviewed in context of frequency tuning in the inelastic seismic response of soil-structure system. The eff ect of seismic intensity and ductility demand, on the eff ective periods, is investigated, and inelastic site amplifi cation is shown to be strongly correlated to the normalized eff ective period. Two non-dimensional parameters, analogous to the conventional site amplifi cation factors in codes, are defi ned to quantify the inelastic site amplifi cation. It is shown that the inelastic site amplifi cation factor (i.e. ratio of constant ductility spectral ordinates at soil site to those at rock outcrop) is able to represent the site eff ects more clearly, as compared to the inelastic site amplifi cation ratio (i.e. ratio of inelastic spectral ordinates at soil site to the corresponding elastic spectral ordinates at rock outcrop). Further, the peak in the amplifi cation factor corresponding to the eff ective site period diminishes rapidly with increasing ductility demand.     

Long-range forecasting of suspended sediment

This study examines the employment of two methods, multiple linear regression (MLR) and an artificial neural network (ANN), for multistep ahead forecasting of suspended sediment. The autoregressive integrated moving average (ARIMA) model is considered for one-step ahead forecasting of sediment series in order to provide a comparison with the MLR and ANN methods. For one- and two-step ahead forecasting, the ANN model performance is superior to that of the MLR model. For longer ranges, MLR models provide better accuracy, but there is an important assumption violation. The Durbin-Watson statistics of the MLR models show a noticeable decrease from 1.3 to 0.5, indicating that the residuals are not dependent over time. The scatterplots of the three methods (MLR, ARIMA and ANN) for one-step ahead forecasting for the validation period illustrate close fits with the regression line, with the ANN configuration having a slightly higher R² value.     

Effect of source parameters on forward-directivity velocity pulse for vertical strike slip fault in half space

It has been found that the large velocity pulse is one of the most important characteristics of near-fault strong ground motions. Some statistical relationships between pulse period and the moment magnitude for near-fault strong ground motions have been established by Somerville （1998）; Alavi and Krawinkler （2000）; and Mavroeidis and Papageorgiou （2003）, where no variety of rupture velocity, fault depth, and fault distance, etc. were considered. Since near-fault ground motions are significantly influenced by the rupture process and source parameters, the effects of some source parameters on the amplitude and the period ofa forward-directivity velocity pulse in a half space are analyzed by the finite difference method combined with the kinematic source model in this paper. The study shows that the rupture velocity, fault depth, position of the initial rupture point and distribution of asperities are the most important parameters to the velocity pulse. Generally, the pulse period decreases and the pulse amplitude increases as the rupture velocity increases for shallow crustal earthquakes. In a definite region besides the fault trace, the pulse period increases as the fault depth increases. For a uniform strike slip fault, rupture initiating from one end of a fault and propagating to the other always generates a higher pulse amplitude and longer pulse period than in other cases.     

里下河古潟湖相软土基本工程特性与形成机理的关系

淮盐高速公路穿越的里下河地区,广泛分布有高含水量、高压缩性古潟湖相软土,工程性质很差,该层软土的工程性质与里下河古潟湖的形成机理密切相关。本文在对潟湖形成一般模式总结的基础上,结合苏北地区第四纪以来沉积环境及区域地质地貌变化情况,得出里下河古潟湖相软土的形成机理,并对淮沿高速公路盐线典型地段土样工程性质进行分析,根据土的工程性质的垂直变化,判断古潟湖相软土的分布情况,进而寻找古潟湖相软土工程性质与其形成机理之间的关系。     

中国近海及临近海域海浪的季节特征及其时间变化

利用1992年12月-2005年3月TOPEX卫星高度计资料,对中国近海波浪季节特征及其时间变化进行了分析。分析结果表明,冬季平均波高最大,台湾海峡、南海北部、中南半岛东南海域以及吕宋海峡外侧是冬季的大浪区;夏季平均波高最小;春、秋两季为过渡期。对冬季大浪所在区域波浪时间变化的研究表明,年变化是其主要时间变化特征,而季节内变化是该海区的另一重要特征,并且以5 a为周期的年际变化与ENSO事件有着很好的对应关系。     

上海及周边地区地闪活动特征及海陆差异

利用LS8000闪电定位系统2009—2011年的地闪观测资料对上海及周边地区(120~122.5°E,30~32°N)的地闪活动特征进行了研究。结果表明:分析区域内正地闪的比例约占8.5%,大电流地闪(电流绝对值大于50kA)的比例约为5.6%。地闪活动主要集中在6—9月,峰值出现在8月;日变化上,12:00—19:00闪电活动最为活跃,峰值出现在14:00,凌晨闪电活动最弱。从日变化上来说,正地闪和大电流地闪比例在地闪活动较强时段低于地闪活动较弱时段;在月分布上,在地闪活动最强的夏季,正地闪比例普遍在10%以下,在地闪活动较弱的春、秋、冬季,正地闪比例普遍在10%以上。以北纬31°为界,分析区域北部地闪密度基本在6~12次·km-2·a-1以上,南部基本在2.4~4.8次·km-2·a-1。同时陆地上的地闪密度要显著高于湖泊和海洋上的地闪密度,而海洋上的正地闪比例和大电流地闪比例要显著高于陆地。闪电空间分布的时间变化说明,下午地闪活动主要出现在陆地,而凌晨地闪主要出现在水体附近,其它时段则表现出过渡特征,这与下垫面的加热作用紧密相关。     

Empirical formula for fundamental vibration periods of reinforced concrete buildings in Taiwan

More than 30 buildings around Taiwan have been selected to monitor the floor responses under seismic excitation. The structural array monitoring system in each building controls at most 27 channels of accelerometers distributed in several floors. Those buildings were triggered by many events during the past five years of operation. In each building, the records at the basement can be considered as the ground excitation, and the others at the upper floors are the structural responses. The frequency transfer functions of those buildings can be identified by ARX models, and then the fundamental vibration periods are estimated. The identified fundamental vibration periods using different events are compared in order to ensure the reliability of system identification. An empirical formula in predicting the fundamental vibration period is presented through the regression analysis to the identified fundamental vibration periods of 21 reinforced concrete (RC) moment‐resisting frame (MRF) buildings. It is found that the height of a building plays an important role in predicting the fundamental vibration period, compared with the length, width, and time after completion of the building. It is also found that the RC MRF buildings in Taiwan tend to be stiffer than those in the U.S. Copyright © 2000 John Wiley & Sons, Ltd.