唐山地震的破裂过程及其力学分析

张之立1, 李钦祖2, 谷继成1, 靳雅敏2, 杨懋源3, 刘万琴1

张之立1, 李钦祖2, 谷继成1, 靳雅敏2, 杨懋源3, 刘万琴1. 1980: 唐山地震的破裂过程及其力学分析. 地震学报, 2(2): 111-129.
引用本文: 张之立1, 李钦祖2, 谷继成1, 靳雅敏2, 杨懋源3, 刘万琴1. 1980: 唐山地震的破裂过程及其力学分析. 地震学报, 2(2): 111-129.
ZHANG ZHI-LIup, LI QIN-ZUup2, GU JI-CHENGup, JIN YA-MINup2, YANG MAO-YUANup3, LIU WAN-QINupers a. 1980: THE FRACTURE PROCESSES OF THE TANGSHAN EARTHQUAKE AND ITS MECHANICAL ANALYSIS. Acta Seismologica Sinica, 2(2): 111-129.
Citation: ZHANG ZHI-LIup, LI QIN-ZUup2, GU JI-CHENGup, JIN YA-MINup2, YANG MAO-YUANup3, LIU WAN-QINupers a. 1980: THE FRACTURE PROCESSES OF THE TANGSHAN EARTHQUAKE AND ITS MECHANICAL ANALYSIS. Acta Seismologica Sinica, 2(2): 111-129.

唐山地震的破裂过程及其力学分析

THE FRACTURE PROCESSES OF THE TANGSHAN EARTHQUAKE AND ITS MECHANICAL ANALYSIS

  • 摘要: 由 P 波初动符号资料在 DJS-6机上计算了主震及17个较大余震的断层面解,并按照有限移动源模式测定了主震及三个最大余震的震源参数.主震是发生在一个近似直立的右旋走滑断层上,走向 N30°E,破裂方式为不对称的双侧破裂,以2.7公里/秒的平均速度向北东传播70公里,向南西传播45公里.测定的主震震源参数例如平均位错136厘米,地震矩1.24×1027达因·厘米,应力降12巴等.大多数ML>5.0的余震是发生在主破裂面附近及主破裂面两端的扩展分支上,该扩展分支位于膨胀符号区并与主破裂偏离80°左右.较大余震的多数亦集中在这两个扩展分支上.本文试图从理论上分析这种断裂扩展的力学特征.对于脆性材料的复合变形情形,破裂不再沿原来平面扩展,而是与原来平面偏离一个角度的另一面内扩展.并提出一个力学模型,计算了断层扩展角,计算结果与观测事实比较吻合.根据以上结果,本文讨论了唐山地震特点及发生的力学条件,认为唐山地震不同于发生在大断层上能用粘滑机制解释的那类地震,它和海城地震类似的是,除水平应力场作用外,还可能有地下物质的变迁,由于这种变迁使局部地壳受到垂直力.它和海城地震不同的是,它发生在一个比较均匀的脆性介质内,因而能够积累能量发生大震而没有前震.
    Abstract: Fault-plane solutions of the mainshock and 17 large aftershocks are computed on the DJS-6 computer from the data of the first motions of P waves. Based on the model of finite moving source, the fracture processes and the source parameters of the mainshock and three largest aftershocks are estimated. The Mainshock occurred on a nearly vertical right-lateral strike-slip fault, striking N30°E, with an asymmetric bilateral fracture which propagated 70 km northeastward and 45 km southwestward with an average velocity of 2.7 km/sec. Source parameters of the mainshock such as the average dislocation, seismic moment and stress-drop are estimated to be 136 cm, 1.24×1027 dyne, cm and 12 bars respectively.Most of the aftershocks with ML>5.0 occurred near the main fault plane and along the fracture branches at both of its ends. These fracture branches are located in the dilatational quarters and make about 80 angles with the mam fault plane. On the two fracture branches, most of the major aftershocks are concentrated. A mechanical analysis of this phenomenon of fracture propagation is attempted in this paper.It is shown that for complex deformations, the fracture propagation no longer takes place along the original plane for brittle materials but deviates from it by a certain angle. The mechanical model used to calculate this deviation angle of fault yields results which agree essentially with the observation.Based on the above results, it can be inferred that the characteristics and mechanical conditions of the Tangshan earthquake as well as those of the Haicheng earthquake are quite different from those of the earthquakes occurring on some great faults which may be explained by stick-slip mechanisms. These two earthquakes are not only caused by the horizontal stress fields but also by local vertical forces induced from the movement of the underground materials. It is also worthy of note that Tangshan earthquake is different from Haicheng earthquake in that it occurs in a relatively homogeneous and brittle medium and therefore no foreshocks took place before the mainshock.
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