近场地震动峰值加速度及频谱衰减特性研究

计算分析了333组震中距小于40 km的欧洲及其毗邻地区的近场强震动记录的峰值加速度和3种频谱周期参数,采用回归分析方法,探讨了场地类别、震级、震中距等因素对近场地震动特性的影响特征,并统计给出了不同类别场地和震级档的近场地震动峰值加速度和频谱周期的衰减关系。结果表明:震中距是影响近场强震动峰值加速度和频谱特性的重要因素,随着震中距的增大近场强震动峰值加速度逐渐减小;特征周期参数基本上满足随着震中距增大而增大的趋势,且场地越软这一趋势越明显;因为近场地震动的复杂性,场地类别和震级对峰值加速度和特征周期有一定的影响,但具有不确定性。竖向与水平向地震动的加速度峰值比均值为0.60,但约有1/3的强地震动记录加速度峰值比大于2/3;竖向地震动的特征周期约为水平向地震动的0.8倍,且场地越软该值越小。

Attenuation characteristics of peak ground acceleration and spectrum of near-field ground motions

The peak ground acceleration and three kinds of frequency content parameters are calculated and analyzed based on 333 groups of near-field strong motion records collected from earthquakes in Europe and its adjacent areas. The epicentral distance of these strong motion records are less than 40 km. Using the regression analysis method, the influences of site, magnitude and epicentral distance on characteristics of the near-field ground motion are discussed. And the attenuation relationship of the peak ground acceleration and spectrum period of near-field ground motions at different sites and magnitudes is given. The results show that the epicentral distance is an important factor affecting the near field earthquake peak ground acceleration and spectral characteristic. With the increase of the epicentral distance, the peak ground acceleration decreases gradually but the characteristic period increases gradually. The site and magnitude factors have some influence on the peak ground acceleration and characteristic period, but with uncertainty. In the near-field, the average ratio of vertical to horizontal peak ground acceleration is 0.60, but in all records the peak acceleration ratio of about 1/3 vertical ground motion's is larger than 2/3. The characteristic period of vertical ground motion is about 0.8 times that of horizontal ground motion. The softer the site is, the smaller the value is.