Abstract: The Kunlunshan M_s 8.1 earthquake of 2001 is a large earthquake produced by a large-scale intraplate strike slip faulting. Field observation shows that the surface rupture of this earthquake is about 426km long,and the maximum sinistral displacement is about 6m. As compared with the other similar intraplate large earthquakes,its rupture length is extraordinarily longer but its horizontal displacement is relatively small. The distribution of horizontal displacement along the surface ruptures is markedly controlled by fault structure. At the section where the horizontal displacement is small,the vertical displacement is also smaller,and no transformation of horizontal and vertical displacements is observed. This feature is also different from that of the other earthquakes. The relationship among rupture length,displacement and seismic magnitude follows a certain empirical equation,in which the ratio between the average displacement amount and rupture length is called "Ultimate linear strain",and is constantly within the range of 10^-5 for the rupture in the earth's crust. This feature can be used as criterion for testing the independency and integrality of the rupture segments. In this paper,we calculated the "ultimate linear strain" of the entire rupture zones and sub-segments of several large earthquakes,including the 1920 Haiyuan earthquake,1951 Bong Co earthquake,1932 Changma earthquake and 2001 Kunlunshan earthquake. The results show that average values of ultimate linear strain of the Haiyuan,Bong Co and Changma earthquakes are approximately close to the statistic value,but the values of ultimate linear strain of their sub-segments are significantly higher. In contrast,the value of ultimate linear strain for the entire surface rupture of the Kunlunshan earthquake is much lower than the statistic value,but the values of ultimate linear strain of its four sub-segments,except the west Taiyanghu segments,are close to the statistic value. Therefore,the Kunlunshan earthquake (M_s 8.1) should be produced by four relatively independent faulting events,instead of a uniform faulting. These characters provide geological evidence supporting the deduction that the Kunlunshan earthquake is successively triggered multiple earthquake events,rather than a single earthquake.

Key words: fault segmentation, ultimate linear strain, rupture parameters, triggered earthquake, west of Kunlunshan Pass M_s 8.1 earthquake

摘要： 地震地表破裂带调查表明,昆仑山口西8.1级地震的破裂长度为426km,最大水平位移6m左右,地震破裂位移的分布明显地受断层活动段控制。该次地震的破裂长度远大于统计值,文中应用地壳极限线应变的概念,通过比较中国大陆内部几次走滑型强震的地震破裂最大位移与破裂长度的关系,论述了昆仑山口西8.1级地震中各次级段破裂的相对独立特征,认为该次强震不是一次整体性破裂事件,而是由连续触发的几次地震组成。

关键词: 活断层分段, 极限线应变, 破裂参数, 触发地震, 昆仑山口西8.1级地震