1976年云南龙陵6.2级余震强震记录的理论模拟

1976年6月9日云南省龙陵地区发生了一次6.2级余震。本文对这次地震的强震记录进行了数值模拟,并通过合成地震图与观测资料的对比,研究了这次地震的断层长度、破裂方式以及位错分布的特点。分析结果得到这次地震是由北向南的右旋走滑型破裂,断层长度约为20km,破裂速度接近0.9倍剪切波速,断层上的平均错距为60cm,平均应力降约为23bar。近场记录中的丰富高频成分表明断层上的位错分布和上升时间分布是极不均匀的,相应的局部错距和局部应力降分别为189cm和200-300bar,远高于其平均值。通过模拟过程可以看出近场记录对于震源断层的长度和破裂方式等都有较强的约束作用,因此分析强震记录是研究震源过程的一种有效手段。

NEAR FIELD STRONG MOTION MODELING OF THE JUNE 9,1976 LONGLING YUNNAN, MAGNITUDE 6.2 AFTERSHOCK

The near field strong ground motion data recorded from June 9, 1976 Longling Yunnan aftershock （Ms = 6.2） provided a good opportunity to investigate the faulting process of this earthquake. By comparing the synthetic seismograms with the observed data we investigated the characteristics of the faulting process, especially the rupture velocity, rupture length and dislocation distribution. The results suggest a right-lateral faulting initialed from the north ead with a rupture velocity near 0.9 shear velocity and a rupture length of about 20 km. Over the entire ruptured surface the average dislocation is 60 cm, average stress drop is about 23 bars, and the total moment is 3.0 ×1016 N-m. The abundant high frequency contents in near field data suggest that the distribution of dislocation and rise time on the rupture surface are highly heterogeneous. From our model it is estimated that the maximum dislocation is 189 cm and maximum stress drop is 200-300 bars, much higher than their average values.