利用阿拉斯加台阵资料分析2008年汶川大地震的破裂过程

Rupture process of the 2008 great Wenchuan earthquake from the analysis of the Alaska-array data

2008年5月12日,四川省汶川县发生M_S8.0地震.我们利用美国阿拉斯加区域台网的邵分宽频带地震台构成广义台阵,应用非平面波台阵技术——迁移叠加方法,获得了这次地震的高频(>0.1 Hz)能量辐射源随时间和空间变化的图像.图像表明,这次地震破裂从震中开始向北东方向扩展约300 km,震源过程至少长达90 s,平均破裂速度为3.4 km/s;整个过程可分为两大阶段,前段持续时间50s,破裂长度约110 km,破裂传播的平均速度为2.2km/s,后段持续时间约40 s,长度约190 km,平均破裂速度为4.8 km/s.这意味着地震过程的后期似乎发生了超S波破裂,而且后段很可能为前段动态触发所致.

On 12th of May, 2008, an Ms8.0 earthquake occurred in Wenchuan county, Sichuan province of China. We configured a generalized array with the broadband seismic stations of the Alaska Regional Network,USA, and imaged the temporal and spatial variation of high-frequency （〉0.1 Hz） energy radiation sources by means of one of the non plane wave array techniques migration stacking technique. The image shows that the earthquake faulting initiated at the instrumental epicenter and extended north-eastwards about 300 kin, the whole rupture process lasted for at least 90s, and the average rupture speed was about 3.4 km/s. The whole process may be divided into two major periods. The first period is 50 s and in this period the rupture propagated about 110 km, with an average rupture speed of 2.2 kin/s; the other period is 40 s and in this period the rupture propagated about 190 km, with an average speed of 4.8 km/s. It seems that supershear rupture appeared in the later process of the earthquake, and the second segment might be dynamically trigged by the first one.