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利用全球台网中均匀分布的远场台站记录的39个长周期P波和SH波波形数据,研究了5月12日汶川8级地震的矩张量解、破裂过程及破裂特征.研究结果表明汶川地震由可分辨的5次7.3级以上地震组成,这5次子事件在时间上连续发生,空间上由在起始破裂点处的一次走滑破裂,距起始破裂点80km范围内的2次逆冲破裂,以及在北川附近的2次右旋走滑破裂组成.前3次破裂的震级分别为Mw7.3,7.6,7.4级,后2次的震级分别为Mw7.5和7.4级.破裂过程反演结果表明整个破裂在时间上持续了105s,在北川-映秀断裂上自起始破裂点所在的南西端向北东方向单侧扩展,造成沿断层地表破裂近230km,地表平均位错达4m.研究结果揭示此次地震破裂过程至少由2段组成,在起始破裂点所在的西南段即都江堰-汶川段,破裂以逆冲错动为主,最大错动位移达8.2m;在绵竹附近,破裂开始转变为向北东方向扩展的右旋走滑错动,断层错动区域较西南段浅,主要发生在北川-青川段10km深度以上,最大位移位于地表,为6.53m.相应地在地表出现了两个位移达6m以上的地段,其一是都江堰-汶川段,地表的最大位移为6.44m;其二是北川-青川段,最大位移6.53m.这种分段性存在一定的构造背景.
Based on the data of 39 long-period P-wave and SH-wave records recorded by far-field stations uniformly distributed in the global network, the moment tensor solution, rupture process and rupture characteristics of the Wenchuan Ms8.0 earthquake on May 12 were studied. It shows that the Wenchuan earthquake consists of five identifiable earthquakes of magnitude 7.3 and above. These five sub-events occur continuously in time and are spatially ruptured by a strike-slip at the initial rupture point within a range of 80km from the initial rupture point Two thrust faults and two dextral strike-slip faults near Beichuan.The magnitudes of the first three ruptures are Mw7.3, 7.6 and 7.4 respectively, and the magnitudes of the second two are Mw7.5 and 7.4 The inversion results of the rupture process show that the whole rupture lasted 105s in time and extended to the northeast direction on the Beichuan-Yingxiu fault from the southwest end where the rupture started, resulting in a surface rupture about 230km along the fault surface, The results show that the earthquake rupture process consists of at least two sections. In the southwestern section of the initial rupture point, namely Dujiangyan-Wenchuan section, the rupture is dominated by thrusting and the maximum displacement is up to 8.2m. In the vicinity of Mianzhu, the rupture began to turn to the right-hand path of expansion to the northeast Slip movement and fault dislocation area is shallower than the southwest section, mainly occurring above the depth of 10km in Beichuan-Qingchuan section with the maximum displacement at the surface of 6.53m. Correspondingly, there are two sections with displacements of more than 6m on the surface Is Dujiangyan - Wenchuan segment, the maximum displacement of the surface is 6.44m; the second is the Beichuan - Qingchuan segment, the maximum displacement of 6.53m.This segment has a certain tectonic setting.