2013年4月20日四川芦山地震强地面运动三要素特征分析

2013年4月20日四川省芦山县境内发生MS7.0级地震，地震造成196人死亡，21人失踪，11470人受伤，震中最大烈度IX.地震发生后，中国数字强震动观测网络和成都市地震烈度速报网络分别获得了114组和63组3分量强震动记录.记录得出在近场加速度幅值较高，与汶川地震峰值相当，然而震害却不严重.本文介绍了这些记录的基本情况，分析了其地震动三要素（幅值、持时、频谱）特征以及对建筑物结构的潜在影响.分析结果表明：芦山地震PGA（地震动峰值加速度）与我国常用的霍俊荣地震动预测方程较一致，高于即将颁布的第五代区划图中使用的预测方程；PGV（地震动峰值速度）与第五代区划图中使用的预测方程基本一致；Significant持时和Bracketed持时高于全球经验预测方程，且Bracketed持时衰减显著慢于全球平均水平；典型11个幅值较大记录的5%阻尼比加速度反应谱峰值周期都在0.1~0.2 s范围内，且谱值远高于规范设计谱，但在周期0.3 s之后迅速下降至设计谱以下；芦山地震地震动PGV值较小以及对应我国中小城市和城镇主要建筑物的结构自振周期范围（0.3~1 s）内加速度反应谱远低于规范设计谱，可用于解释其震害相对较轻的原因.

The characteristics of strong ground motion of Lushan Earthquake on April 20, 2013

An M_S7.0 earthquake occurred on April 20, 2013 in Lushan Country, Sichuan Province, China with the maximum seismic intensity of IX. It caused 196 dead, 21 missing and 11470 injured. During the main shock, 114 strong motion recordings were accumulated by the National Strong Motion Observation Network System (NSMONS) of China and 63 recordings by the Local Earthquake Intensity Reporting Network of Chengdu City. There is a common question why it didn't cause heavy damage as the large ground motion is almost as the same level of Wenchuan Earthquake. The characteristics of their amplitude, duration and spectrum and the potential effect on the earthquake damage were analyzed in this paper. The results show that the PGAs of ground motion in Lushan Earthquake are in accordance with the empirical prediction equation commonly used in China, but larger than the one used in fifth-generation ground motion zonation map, while the PGVs match well;the significant durations and bracketed durations are both larger than the global empirical prediction equation, and the attenuation of bracketed duration is slower than the global level;the acceleration response spectra with 5% damping ratio of 11 typical large recordings all have the peak periods around 0.1~0.2 s where the spectral acceleration is considerably larger than the Chinese design spectra, and notably smaller when the period larger than 0.3s;the reason why the damage is relatively slight in Lushan Earthquake is inferred that the PGVs are small and the spectral acceleration is drastically smaller than the design spectra in the period range 0.3~1.0 s corresponding to the natural periods of 3~10 stories buildings mostly common in the moderate and small cities and towns of China.