2013年7月22日岷县漳县6.6级地震强震记录及特征分析

Strong Mmotion Records and Its Characteristics in MinxianZhangxian M_S6.6 Earthquake on July 22,2013

2013年7月22日甘肃省定西市岷县漳县交界发生6.6级地震,国家强震动台网在甘肃、四川和陕西的64台强震仪触发并获得了主震加速度记录。本文对强震动记录进行了常规处理,统计了强震动记录数量随震中距的分布,绘制了空间地震动加速度等值线图;通过观测数据与霍俊荣和意大利新一代地震动衰减公式对比,分析了峰值加速度(PGA)及谱加速度衰减关系,发现此次地震观测数值远低于常用地震动预测值;利用渭河盆地的远场记录验证了远场地震动卓越周期变大的特点以及场地对记录的影响;参考岷县地区地质特点并通过分析宏观烈度及地震动的谱烈度,初步确定了地震震害与烈度的相关性。

The Minxian--Zhangxian Ms6. 6 earthquake occurred on July 22, 2013, at Minxian country, Gansu province （34.5°N, 104.2°E）, which had resulted in 95 persons dead and 1366 persons injured until July 24, 2013. Digital strong ground motion records of high quality have been obtained in this earthquake for the third time in China following the Wenchuan earthquake and the Lushan earthquake. 64 strong motion stations installed in Gansu, Sichuan and Shanxi province were triggered and acceleration records in the main shock were obtained. In this paper, the preliminary characteristics of these records were analyzed including the spatial locations of these stations, the number of records within different epicenter distances and PGA contours. Comparing the observed data with the attenuation relationship （ground motion prediction equa- tions： one is HUO （1989） and another one is Italy08）, it has been found that the observed PGAs and spectral accelerations are remarkably lower than the empirically predicted ones. In general, the far-field strong ground motion is much lower; however, long-period ground motion attenuates slower than the near-field ground motion due to the particular traveling path and site effect. Thereason of the amplification is that some stations located in the center of the basin have a thick o- verburden than the station located at the edge of the basin. The analysis of the far-field records obtained in Weihe Basin indicates the predominant period become longer. Housner G W proposed IH as an effective intensity measure to correlate seismic severity with structural damage to build- ings. For this reason, records and code values have also been compared in terms of IH. By analy- zing the Macro seismic intensity and Housner spectral intensity and consulting the geological characteristics of Minxian, the good correlation between the earthquake damage and seismic in- tensity has been preliminarily presented. Because of the economic backwardness, the houses in rural areas are mainly of masonry structures, of which the seismic performance is poor. Many houses are severely damaged in the earthquake, especially the houses near the epicenter in Minx- ian country. Most of them are sited in poor geological region, such as valleys, steep slopes and hills. What＇s more, the slope effect amplifies the effect, so the houses are damaged more serious- ly. The original structure of loess looses because of the ground motion, and then led to the land- slides. So the Minxian--Zhangxian earthquake was not very strong, but the earthquake also caused a lot of geological disasters. The macro intensity of China has the characteristics of inte- grated indicators. This study has an important role on ground motion characteristics and engi- neering damage investigation in the western region of China. Strong motion records in Minxian-- Zhangxian earthquake can be used in further study of ground motion characteristics by combining with that in the Wenchuan earthquake and Lushan earthquake.