武定6.5级地震序列的地震应力降研究

摘要

以Brune提出的中小地震圆盘形破裂位错模式 为理论基础，研究了地面运动峰值参数(r.d)和(r.v)对地震应力降Δσ的依赖性，并考虑 地 球介质Q值对峰值参数的影响，利用武定M6.5级地震序列的近场数字记录地震资料，由此导 出了用峰值位移d和峰值速度v求地震应力降Δσ的关系式：lg(r.d/e-qr)= -10.56+2/3lgM0+1/3lgΔσ；lg(r.v/e-qr)=-2.566+1/3lgM0+2/3lgΔσ。用 上述公式测定了武定地震序列的地震应力降Δσ，结果给出地震序列的应力降Δσ绝大多数 在5.0～50MPa的范围内，是典型的高应力降序列。通过分析应力降的时空分布特 征，发现应力参数与余震活动的频度及强度相关，也与地震构造背景相关。研究结果还表 明用地面运动峰值参数估算地震应力降是一种新的实用性较强的方法。%Based on the source dislocation model for medium and small earthquakes suggested by Brune,the dependence of ground motion pead parameters(r,v)on the se ismic stress drop is studied,and considering influence of the Q value on the pea k parameters and usin nearfield digital seismic data of the Wuding Ms 6.5 earth quake sequence,the relations calculating the seismic stress drop Δσ from the peak displacement d and the peak velocity v,lg(r,d/e-qr)=-10.56+2/3lg Mo+ 1/3lg Mo+1/3lgΔσ and lg(r,v/e-qr)=-2.566+1/3lg Mo+2/3lgΔσ are derived .By using above,the seismic stress drops for the Wuding earthquake sequence are determined and most of them fell inside the limits of 5.0～50 Mpa and the W uding earthquake sequence is typical high stress sequence.It is found from analyzing time-space distribution characteristics that the stress parameters are correlated not only with the freq uency and intensity of aftershock activity,but also with seismotectonic backgrou nd.The results of this study also show that estimation of seismic stress drop fr om the peak parameters of ground motion will become a new practical method.