云南鲁甸Ms6.5级地震罕见大峰值记录时-频反应谱分析

Time-frequency response spectrum analysis on rare large PGA record of Ludian Ms6.5 earthquake

2014年云南鲁甸Ms6.5地震龙头山台站记录到东西向峰值加速度948.50 Gal的罕见大峰值记录(简称“龙头山EW记录”),震中烈度高达Ⅸ度,而震中距大于10 km以后,峰值加速度和烈度均迅速减小。为研究这一现象,利用时-频反应谱对震中距45 km以内的6个台站记录进行了时频特性分析,发现龙头山EW记录幅值区域相对集中且谱值很大,沿持时轴连续分布两个幅值带,高频和低频成分均远大于其拓展设计反应谱,据此设计的自振周期处于0.4~0.8s的结构将遭受严重累积破坏。另外5个台站时-频反应谱值小且覆盖区域狭小,作用时间短,无论在自振周期轴方向,还是持时轴方向均远小于其拓展设计反应谱覆盖区域,结构不会发生破坏或仅发生可修复的轻微破坏。震害调查结果与时-频反应谱分析结果相符,证明鲁甸地震小震级、高烈度、大灾害的特点与龙头山EW罕见大峰值记录的时频特性有着密切关系,时-频反应谱有利于用来分析结构破坏机理,具有研究的理论意义与应用价值。

The rare large PGA 948.50gal(hereinafter referred to as Longtoushan EW record)was detected at Longtoushan observation station in Ludian Ms6.5 earthquake in 2014.The epicentral intensity reached up to nine,however,when epicentral distance was greater than 10km,both PGA and intensity rapidly decreased.To investigate this phenomenon,six seismic records with the epicentral distance less than 45km were analyzed with the time-frequency spectrum.The results showed that the amplitude area of the Longtoushan EW record was concentrated and its spectral values were very large.Along the duration axis,there were two consecutive amplitude zones and both the high-frequency and low-frequency components were much larger than its extended design response spectrum.Structures,designed by the design response spectrum above,with the natural vibration period ranging from 0.4s to 0.8s would suffer a great cumulative damage.However,the time-frequency spectrum values and the coverage areas of the other five seismic records were very small,and the action time of them was short.Along the duration axis and natural vibration period axis,spectral values were much smaller than its extended design response spectrum.Structures in this areas would not be damaged or only have repairable slight damage.Results from damage investigation coincided with those from the time-frequency spectrum analysis,which demonstrated that the features of small magnitude,high intensity and big disaster of Ludian earthquake was closely related to time-frequency characteristics of the rare large PGA of Longtoushan EW record.Time-frequency response spectrum was better for analyzing the damage mechanism of structures and had theoretical significance and application value.