COMPARISON OF ON-LINE COUPLED AND CONSTANT TRANSFER SIMULATION METHODS FOR DIRECT RADIATIVE FORCING OF ANTHROPOGENIC SULFATE

1 INTRODUCTIONOf three main methods for studying the radiativeforcing of anthropogenic sulfate and climatic responseon the regional scale, the first is, with given rates fortransforming SO2 to sulfate, converting actuallyreleased SO2 into sulfate and acqu…     

基本气流的垂直切变作用下的低纬低频波

在低纬地区,风速的垂直切变也是很明显的,作者解释了这些纬向气流的垂直切变对低纬长波性质以及对不同模态的相互作用的影响,并且发现切变对低纬波动的影响具有明显的选择性.     

土-地铁车站结构动力相互作用大型振动台模型试验研究

以南京地铁为背景,开展了深厚软弱场地土-地铁地下结构动力相互作用的大型振动台模型试验研究。在试验中获得的主要数据有:模型体系的加速度反应时程、模型结构的应力反应时程和结构表面的土压力时程等。本文对试验反映的地铁车站结构的动力反应规律及其周围模型地基的地震反应规律进行了分析。结果表明:车站结构的中柱应变反应明显大于别的构件,同时,深厚软弱地基上车站结构侧墙底部的应变反应也明显大于侧墙顶部的反应,其中,车站结构顶板、中间层楼板和底板的应变反应都很小;输入地震动的频谱特性对车站结构应变反应的影响是不同的,在同一加载情况下,在台面输入傅氏谱频宽最大的南京人工波时车站结构应变反应最大。     

Assessment of liquefaction potential based on peak ground motion parameters

Conventionally, evaluation of liquefaction potential of loose saturated cohesionless deposits as specified in Japanese design codes employs peak ground acceleration (PGA). However, recent large-scale earthquakes in Japan revealed that liquefaction at some sites did not occur even though large PGAs were recorded at or near these sites. As an alternative approach, an evaluation procedure based on peak ground motion parameters, i.e. incorporating both PGA and the peak ground velocity (PGV), is proposed. By performing parametric studies using one-dimensional seismic response analysis and formulating regression models, seismic-induced shear stresses within the deposit are expressed in terms of peak ground motion parameters at the surface, and these are used to calculate the factor of safety against liquefaction. Application to case histories in Japan indicates that the proposed two-parameter equation can adequately account for the occurrence and non-occurrence of liquefaction at various sites as compared to the conventional PGA-based approach. Moreover, analyses of several strong motion records at various sites show that liquefaction may occur when PGA≥150 gal and PGV≥20 kine, indicating that these values can serve as thresholds in assessing the possible occurrence of liquefaction.     

苍山地震与新沂台前兆异常

根据新沂台前兆资料，运用加卸载响应比、差分法对地磁场Z分量进行分析；运用滑动平均对短水准资料进行分析；运用速率法对视电阻率进行分析；结果表明：在苍山地震前，新沂台前兆资料具有良好的中、短期异常，并有进入临震的异常标志。     

Influence of the ground profile on the reduction of earthquake motion at the filled man-made islands in the Kobe harbor during the 1995 Hyogoken Nambu earthquake

During the 1995 Hyogoken Nambu earthquake in Kobe, the ground motion at the filled man-made islands in the Kobe harbor was not as severe as that at the mainland. The building damage was also less compared to that on the mainland. It was found by comparative study of earthquake records that the magnitude of acceleration response on the ground surface decreases at the islands as opposed to the mainland. One dimensional effective stress analysis is adopted in this study. Input data has been generated from test results, e.g. the SPT N-value by standard penetration test and shear wave velocity V_s by PS logging. Results obtained by the analyses showed good agreement with the observed records, which is an indication of the suitability of the adopted analysis procedure. From this study, the followings are concluded. By the increase of SPT N-value of the filled layers, liquefaction near ground surface is restrained and damage modes such as ejection of water and soil can be prevented. Since the ground profile at the islands is that considerably soft filled layer and marine clay layers, etc. are present and the thickness of the surface layer is large, the initial natural period of the ground is above 1 s and the natural period is elongated further under the earthquake excitation, which is deemed to be the principal reason for the reduction of the earthquake motion at the ground surface.     

Response of the Tarzana strong motion site during the 1994 Northridge earthquake

Exceptionally high ground motions (horizontal peak ground acceleration (PGA) of 1.82g) were recorded at the Tarzana Station during the main shock of the 1994 Northridge earthquake (moment magnitude 6.7 at an epicentral distance of 6 km). At the time of the main shock, the instrument was located near the edge of a 21 m-high ridge with side slopes ranging from 3H:1V to 15H:1V. The ridge is underlain by shallow fill and soft rocks of Medelo Formation.

The objectives of this study were to (1) identify the relative contributions of various factors such as local geology, topography, source mechanism, and travel path on the large ground motions recorded at Tarzana Station and (2) develop an analytical model that could adequately predict observed ground motions at the Tarzana site during the Northridge earthquake and at similar sites during future earthquakes. This study is an integral part of a series of inter-related studies referred to as the ROSRINE research (Resolution of Site Response Issues during Northridge Earthquake) project.

The PGA at the surface of competent bedrock (1 km/s shear wave velocity found about 100 m below ground surface) is estimated by Silva [ROSRINE Study (2000)] at 0.46 gravity (g). To identify the source of ground motion amplification, one-dimensional ( ), two-dimensional (TELDYN and SASSI), and three-dimensional (SASSI) analyses were conducted using both recorded aftershock data and an estimated ground acceleration time histories at a 100 m depth.

The results of the analyses indicate that (1) local geology and topography could only partially account for the observed ground motion amplification, and (2) the PGA and response spectra at a point near the edge of the ridge (the location of the instrument at the time of the main shock) is in good agreement with recorded values when the angle of incident of shear waves (SV waves) at 100 m depth is assumed at 30° from vertical. Considering the local geology and variation of shear wave velocity with depth, the 30° incident angle at 100 m depth corresponds to an 8° incident angle of shear waves at the ground surface. This observation is, in general, consistent with the incident angles of shear waves reported from study of the recorded aftershock data.     

Centrifuge modeling of seismic behavior of a slope in liquefiable soil

Two centrifuge tests were designed to improve the understanding the response of liquefied sandy slopes beyond initial liquefaction. A distinctive dilative behavior of the soil was observed near the slope where static shear stresses are present. The corresponding drops in the piezometric records and simultaneous negative upslope spikes in the acceleration records were measured in the transducer raw data. This dilative response became stronger as the input acceleration increased and tends to limit the downslope accumulation and thus reducing the permanent lateral displacements. Therefore, the maximum permanent displacement was smaller in the model with the larger input motion, because it developed a stronger dilative response. The dilative response was not observed away from the slope, where no static shear stresses are present.     

条形荷载作用下梯度饱和土的动力响应分析

根据Biot波动理论,研究了条形均布荷载作用下非均匀饱和土地基的动力响应问题。利用Fourier积分变换,通过Helmholtz矢量分解原理,建立了饱和土层在动荷载作用下的回传射线矩阵法计算列式,考虑饱和土的物理力学性质沿深度方向按幂函数连续变化,采用数值Fourier逆变换获得了饱和土地基的位移、应力和孔隙压力等物理量的数值解。分析讨论了材料非均匀性对饱和土介质动力特性的影响。结果表明,非均匀饱和土的动力行为与均匀饱和土有着明显的不同,当土体的非均匀程度越高,条形荷载中点下流体压力和应力幅值越大,而位移、流体压力以及应力等物理量在水平方向的振动频率均随着土体非均匀变化程度的增强而增大。