近断层竖向地震动峰值特征

Peak amplitude characteristics of vertical seismic ground motions in near-fault regions

为了研究近断层区域竖向地震动的加速度峰值衰减特征和竖向与水平加速度峰值比特征，为进行近断层区域结构抗震设计和地震危险性分析等提供基础数据参考，根据1952—1999年世界范围内震级在M5．4-M7．6之间的18次地震的地震动记录提出一种同时考虑断层距和震级影响的竖向峰值加速度衰减关系，并与其他学者提出的衰减关系进行了对比分析。然后初步统计分析了竖向与水平峰值加速度比值、竖向地震动PGV／PGA比值的特征。研究结果表明，本文提出的加速度峰值衰减关系形式比较简单而且能较好地体现地震动加速度峰值的衰减变化关系；断层距在0—40km范围内相当一部分竖向与水平向峰值加速度比值大于一般抗震设计规范中规定的比值即0．65；至少对于竖向地震动而言，只将PGV／PGA〉0．2s作为识别近断层脉冲型地震动的强度指标是不够的。

The characteristics of peak value attenuation relationship of vertical ground motions and its ratio to horizontal ones in near-fault regions will be investigated to provide the basic data reference for seismic design and seismic hazard analyses in the vicinity of fault rupture. A peak acceleration attenuation relationship with the consideration of distance to fault rupture and magnitude was proposed according to 18 worldwide earthquakes of M5. 4 -M7. 6 during 1952 - 1999, and the comparative analysis was performed with other attenuation relationships. Furthermore, vertical to horizontal acceleration ratios, PGV/PGA, were statistically analyzed. It is concluded that the proposed peak acceleration attenuation relationship can represent the attenuation of peak acceleration and also have comparatively simple representation; a good many vertical-to-horizontal peak acceleration ratios within the region of 0 - 40kin have exceeded 0.65 prescribed in many seismic provisions. It is not enough to use PGV/PGA 〉 0.2s only as the determinant factor for the near-fauh condition.