2013年甘肃岷县MS6.6地震区域地震波传播模拟与地面运动特征研究

Regional seismic wave propagation modeling and ground motion characteristics of the 2013 M S6.6 Minxian Earthquake in Gansu

2013年7月22日,甘肃省定西市岷县发生MS6.6地震,造成了严重的人员伤亡和经济损失.地震发生于青藏高原东北部边缘与甘肃东南部地区的交界处,是该区域一百多年以来发生的最大地震.分析本次地震观测数据显示,岷县M S6.6地震产生的地震地面运动呈现出明显的区域变化特征.为了研究这种区域变化特征,本文使用全球CRUST1.0和SRTM30模型数据建立了甘肃岷县及周边地区的地下三维传播介质模型,使用并行的三维有限差分方法进行了岷县地震的区域地震波传播模拟,并与研究区内数字地震台网记录的地震观测资料进行对比.通过分析地面运动的峰值速度和持续时间的区域分布特征,发现:在青藏高原东北部边缘,较大的地形起伏对地面运动的峰值速度分布起主要影响作用;在青藏高原外围地区,地形起伏较小,而沉积层主要影响地面运动的峰值速度和持续时间,从而导致了明显的盆地效应,如地面运动的振幅放大和持续时间加长.因此,研究区剧烈的地形起伏和表层沉积层是影响地面运动的重要因素.

The 2013 MS6.6 earthquake,which occurred in Minxian county,Dingxi city of Gansu province,caused huge casualties and economic losses.This earthquake,located at the junction of the northeastern margin of the Tibet Plateau and the southeastern Gansu,is the largest earthquake in this region for more than a century.According to seismic observation of this earthquake,the seismic ground motions differ greatly in different geological regions.In this study,we constructed a three-dimensional transmission medium model of the Minxian county and surrounding area based on the CRUST1.0 and SRTM30 models to investigate the observed spatial variation of seismic ground motions.The parallel three-dimensional finite difference method is adopted to simulate seismic wave propagation of the Minxian earthquake,and the synthetic seismograms are compared with the seismic observation data recorded by the digital seismic network in the study region.Analyses of the regional distribution of peak ground velocity(PGV)and durations of seismic ground motions show clear evidence of seismic site effects.In the northeastern Tibet Plateau,the relatively large topographic fluctuation influences the spatial distribution pattern of PGV.While in regions surrounding the Tibet Plateau where the topographic fluctuation is relatively small,the sedimentary layers mainly affect the spatial distribution of PGV and durations of seismic ground motions.Obvious basin effects such as the amplification and prolongation of the durations of seismic ground motions are observed.Therefore,both the drastic topographic fluctuation and the sedimentary layers in the study region are important factors that affect the seismic ground motions.