鲜水河断裂带强震的破裂过程与地震活动

RUPTURE PROCESSES OF STRONG EARTHQUAKES ON X1ANSHUIHE FAULT BELT AND SEISMIC ACTIVITY

  • 摘要: 鲜水河断裂带是我国西南地区地震活动最强烈的断裂带。本文通过研究发生在断裂带上强震的震源机制、震源过程、余震分布、地震迁移并结合宏观等震线、地震裂缝分布等资料,研究强震破裂过程与地震活动的关系。研究结果表明:1.鲜水河断裂带的基本破裂方式是左旋走向滑动,强震的压应力主轴存在一致性较好的优势方向,即北东东-南西西方向,且均接近水平。2.用P波频谱及面波方向性函数等研究结果表明,除北西段及南东段几个地震外,七级以上地震及多数六——七级地震的破裂面均为北西向,与鲜水河断裂带的总体走向基本一致。3.1890年以来,鲜水河断裂带强震破裂面展布及1955年以来3.0级以上地震震中分布图表明,在道孚——乾宁间存在的破裂面空段(长约10多km)比1955年以来3.0级以上地震活动缺震段(长约40km)明显的短,这表明1890年乾宁地震破裂面在近期有所愈合。这个缺震段的长度约相当七级左右地震的破裂长度。4.自1890年以来,带上发生的四个七级以上地震有两头迁移的特点。考虑到最后一次七级地震是1973年的炉霍地震,估计下次七级地震的位置在南东段,且在道孚——乾宁间的可能性最大。

     

    Abstract: Xian Shuihe fault belt is the seismic ally strongest and most active of belts in Southwest China. In this paper the relationship between the fracture processes of strong earthquakes and the seismic activity was investigated toy studying the source mechanism, the distribution of afterslloks and the migration of strong earthquakes occurring on this belt and combining with the configuration of macroisoseismic lines and the distribution of ground fissures. The results show that:1) The foundimantal way of rupture of Xian Shuihe fuult belt is left-laterjal strike slip. There is a dominant direction with good coincidence with the principal compres-sive axes, that is in the ENE-WSWdirection, and nearly horizontal.2) The results of study by using Pwave spectra and directivity function of surface waves show that, except for some earthquakes in the NWand SEsegments, the rupture surfaces of the strong earthquakes of M7.0 and most of those of M=6—7 are in the NWdirection, which is foundmantally coincident with the general striek of Xian Shuihe belt.3) The distribution of rupture planes of the strong earthquakes in Xian Shuihe fault belt since 1890 and the distribution of the epicenters (M3.0) since 1955 show that the gap segment of the rupture surface (about 10 km in length) between Daofu and Qianning is distinctly shorter thau the segment of earthquake gap of M3.0 since 1955 (about 40 km in length) ; this indicated that, the rupture surface of the Qianning earthquake in1893 recently healed to some extent. The length of the segment without earthquakes is nearlyequal to a rupture length for an earthquake of about M=7.4) Those 4 earthquakes of M7.0 occurred in the belt since 1890 had a common feature of migration from one end of the belt to the other. And considering the fact that the last earthquake of M7.0 was the Luhuo earthquake of 1973, we can venture to estimate that maybe the Iqcation of the next earthquake will be in the SEsegment. It is most probable that it will occur in the segment of earthqiuake gap near Daofu—Qianning.

     

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