侧向侵蚀相关的走滑断裂滑动速率计算新方法

doi:10.3969/j.issn.0253-4967.2014.04.007

摘要/Abstract

摘要：

断层滑动速率是活动构造研究中的重要内容, 是反映断裂活动性和地震危险性的重要参数之一.随着测年技术不断发展和测年精度大幅度提高, 全新世甚至千年尺度和百年尺度的年轻地质体的位错也越来越多地被用于断层滑动速率计算.用走滑断裂带上地质体实测年龄计算滑动速率, 会受到2种因素影响:1)累积位移时间是否与所测地质体年代相符合;2)地质体位移形成过程中会受到侵蚀.在利用全新世地质体计算断层滑动速率时, 应将侧向侵蚀的影响剔除.因此, 文中提出1种计算走滑断层滑动速率的新方法——差值法.走滑断层上河流阶地演化与断层位错分析表明, 在阶地拔河高度存在较大差异的情况下, 可以利用阶地拔河高度与年龄按比例进行计算.此方法在一定程度上提高了所计算滑动速率的精度, 但是需要至少有3级不同阶地的拔河高度、年龄以及位错信息.若阶地拔河高度近似呈等差排列, 即各级阶地上侧向侵蚀量近似相等的情况下, 利用高-低阶地累积位错量之差与对应阶地年龄差来计算滑动速率, 可以在一定程度上减少上述2种因素对滑动速率的影响.应用差值法计算得到阿尔金与昆仑断裂的滑动速率为4.7～8.8mm/a, 与前人获得的地质学滑动速率、测地学滑动速率、缩短速率以及强震复发周期结果一致.

关键词: 全新世, 断层滑动速率, 侧向侵蚀, 差值法

Abstract:

Fault slip rate is one of the most important subjects in active tectonics research, which reveals the activity and seismic potential of a fault. Due to the improvement of dating precision with the development of dating methods, Holocene geological markers, even the young markers of thousands or hundreds years old, are widely used in fault slip rate calculation. Usually, in strike-slip fault slip rate calculation, there are two types of uncertainties. The first is correspondence of the offset and accumulation time; the second is the lateral erosion of the accumulated offset. In this paper, we suggest that the effect of lateral erosion of the accumulated offset should be removed. We also propose a new method for determining slip rate of strike-slip fault—the differential method. According to analyses of river terrace evolution and displacements accumulation, terrace heights (relative height above river), corresponding ages and measured offsets on the terraces are correlated to each other. We could use the terrace height, corresponding ages and the measured offsets to calculate the offsets that could be used to obtain the fault slip rate. Usually, the heights, ages and offsets of at least three terrace levels are needed in this method. If the terrace height is graded in order, the lateral erosion to each terrace is almost the same. Consequently, direct difference of offset and corresponding ages of the terraces could be used to calculate the fault slip rate. This kind of differential method could avoid the uncertainties from the lateral erosion in fault slip rate determination. By applying the differential method, we got the revised slip rates of 4.7～8.8mm/a on the Altyn Tagh and Kunlun Faults. These low slip rates could fit previous geodetic and geological fault slip rates, shortening rates as well as the millennial recurrence intervals of strong earthquakes along the major segments of these faults.

Key words: Holocene, fault slip rate, lateral erosion of the accumulated offset, differential method

中图分类号:

P315.2

任治坤, 张竹琪, 陈涛, 王伟涛. 侧向侵蚀相关的走滑断裂滑动速率计算新方法[J]. 地震地质, 2014, 36(4): 1020-1028.

REN Zhi-kun, ZHANG Zhu-qi, CHEN Tao, WANG Wei-tao. A NEW METHOD FOR DETERMINING SLIP RATES OF STRIKE-SLIP FAULT ASSOCIATED WITH LATERAL EROSION OF ACCUMULATED OFFSET[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(4): 1020-1028.

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