Seismic Risk Evaluation in Densely Populated Area

1.人口密集区地面脉动测量在人口密集区，以25-50 m的空间间隔采集了周期小于1 s的地面三分量脉动。获得了每个点的H/V谱，并评估了地下土壤的自然周期分布。结果表明，地面的自振周期在北方地区变短，而在南方地区变长。最短周期小于0.2 s，最长周期大于0.5 s.建筑物自振周期的估算为了获得该地区建筑物的自振周期，对27栋RC/S/SRC建筑物的顶层进行了地脉动测量。由实测值估算的建筑物的自然周期与根据建筑物的自然周期与建筑物高度的经验关系预测的周期具有良好的相关性，说明该地区建筑物的自然周期可以由建筑物的高度来预测.房屋层数和结构类型的实地调查通过实地调查，对该地区9520栋房屋的层数和结构类型进行了评估，结果表明，70%的房屋为2层木结构房屋.根据建筑物的自振周期分布和单自由度体系的频率响应曲线，对建筑物的各自振周期进行了地震危险性评估。结果表明，自振周期为0.5s的建筑物在车站南侧的地震危险性较高，而0.3s的建筑物在车站北侧的地震危险性较高。前者的结果与1854年和1923年地震中建筑物的破坏分布相一致。

1. Microtremor measurements on the ground in densely populated areaIn the densely populated area concerned herein, three-component microtremors on the ground in the period range shorter than 1 sec were collected with spatial intervals of 25-50 m. H/V spectra were obtained for each points and the distribution of natural period of subsurface soils were evaluated. The results showed that the natural period of the ground was shorter in the northern area whereas the period becomes longer in the southern area. The shortest period is less than 0.2 s and the longest period is longer than0.5 s.2. Evaluation of natural periods of buildingsIn order to obtain natural period of the buildings in the area, microtremor measurements were conducted on the top floor of 27 RC/S/SRC buildings. The natural periods evaluated form the measurements were correlated well with the periods predicted from empirical relationships between natural periods and building heights demonstrating that natural periods of buildings in the area can be predicted form buildings heights.3. Field survey of the number of stories and structural types of buildingsThe numbers of stories and structural types of 9520 buildings in the area were evaluated through field survey showing that 70% of buildings were 2 story-wooden houses.4. Evaluation seismic risk map of the areaFrom the distribution of the natural period and a frequency-response curve of SDOF system, a seismic risk map of buildings is evaluated for each natural period of buildings. The results show that seismic risk for buildings with the natural period of 0.5 sec is high in the south of the station while the risk for 0.3 sec is high in the north of the station. The former result is consistent with the distribution of damage to buildings in the 1854 and 1923 events.