【摘要】 2011年2月21日新西兰南岛发生Mw6.1地震,震中位置43.58°S,172.70°E,震源深度约5.0km,发震断层为新西兰第三大城市克赖斯特彻奇(Christchurch)南约9km一条近东西走向的未知隐伏断层,为逆冲断层机制.地震已经造成163人遇难,Christchurch城内多处建筑物严重损毁,距震中约1km的Heathcote Valley PrimarySchool(HVSC)台站强地面运动峰值加速度(PGA)高达2.0g.针对新西兰Mw6.1地震近场强地面运动偏高这一现象,利用HVSC台站的强震观测记录,计算地震震源谱参数,应用Brune圆盘模型估算其近场强地面运动的理论值,并建立动态复合震源模型进行模拟计算.研究结果表明,新西兰Mw6.1地震近断层强地面运动偏高的主要原因为复杂震源破裂过程中有效应力降(动态应力降,Δσd)过高造成的.未来工作中,需要加强对可能发生的、距离城市较近的中小型地震的重视,防止地震对城市的加强型破坏.更多还原

【Abstract】 The New Zealand earthquake of February 21,2011,Mw6.1 occurred in the South Island,New Zealand with the epicenter at longitude 172.70°E and latitude 43.58°S,and with depth of 5 km.The Mw6.1 earthquake occurred on an unknown blind fault involving oblique-thrust faulting,and this fault is 9 km south of Christchurch,which is the third largest city of New Zealand,with a striking direction from east toward west.At least 163 were killed and lots of structures were destroyed in Christchurch city.The Peak Value of Acceleration(PGA) observed at station Heathcote Valley Primary School(HVSC),which is 1 km away from the epicenter,is up to almost 2.0g.The ground-motion observation suggests that the New Zealand earthquake generated higher than normal near-fault ground motion.In this study,we analyzed the source spectral parameters based on the observations,and estimated the near-field ground motion based on the Brune′s circle model.The results indicate that the larger ground motion may be produced by higher effective stress drop(dynamic stress drop,Δσd) in this buried earthquake.A dynamical composite source model(DCSM) has been developed to simulate the near-fault strong ground motion with associated fault rupture properties from a kinematic point of view.For comparing purpose,we conduct broadband ground motion predictions for the station of HVSC;the synthetic seismogram produced for this station has good agreement with the observations in time histories,waveforms,peak values and frequency contents,which indicate that one of the key factors in ground-motion amplification was the higher effective stress drop.It should be pointed out that,in addition to the study of large earthquakes,the small and moderate earthquakes near the cities should be monitored in order to prevent the devastating destroy of the cities once earthquake occurs.更多还原