北天山博罗可努-阿齐克库都克断裂精河段的古地震事件

doi:10.3969/j.issn.0253-4967.2020.04.001

摘要/Abstract

摘要： 博罗可努-阿齐克库都克断裂(简称博-阿断裂)是天山内部一条长约1 000km的右旋走滑活动断裂, 研究其晚第四纪的活动特征有助于理解大陆内挤压环境下活动走滑断裂在区域构造应变分配和造山过程中的作用并评价其地震危险性。文中选取博-阿断裂精河段作为研究对象, 利用遥感影像解译、野外调查、探槽开挖以及第四纪测年等方法进行了古地震研究。博-阿断裂精河段断错了多期洪积扇, 在Fan2和Fan3洪积扇上开挖了2个探槽。通过识别探槽内的地层与断层的切盖关系、裂缝、崩积楔等标志, 结合沉积层的光释光定年结果, 共识别出4次古地震事件。地震的发震时间分别为: E1(19.4±2.5)~(19.0±2.5)ka BP; E2(18.6±1.4)~(17.3±1.4)ka BP; E3(12.2±1.2)~(6.6±0.8)ka BP; E4 6.9~6.2ka BP。地震的复发间隔分别为(1.2±0.5)ka、 (8.7±3.0)ka和(2.8±3)ka。探槽内记录的最新一次古地震的离逝时间为6.2~6.9ka, 由断裂上单次事件的位移限定的最新一次地震的震级为M_W7.4。较长的古地震离逝时间揭示了博-阿断裂精河段可能存在较强的地震风险。

关键词: 走滑断裂, 古地震, 博-阿断裂, 天山山脉

Abstract: The Bolokenu-Aqikekuduk fault zone(B-A Fault)is a 1 000km long right-lateral strike-slip active fault in the Tianshan Mountains. Its late Quaternary activity characteristics are helpful to understand the role of active strike-slip faults in regional compressional strain distribution and orogenic processes in the continental compression environment, as well as seismic hazard assessment. In this paper, research on the paleoearthquakes is carried out by remote sensing image interpretation, field investigation, trench excavation and Quaternary dating in the Jinghe section of B-A Fault. In this paper, two trenches were excavated on in the pluvial fans of Fan2b in the bulge and Fan3a in the fault scarp. The markers such as different strata, cracks and colluvial wedges in the trenches are identified and the age of sedimentation is determined by means of OSL dating for different strata. Four most recent paleoearthquakes on the B-A Fault are revealed in trench TC1 and three most recent paleoearthquakes are revealed in trench TC2. Only the latest event was constrained by the OSL age among the three events revealed in the trench TC2. Therefore, when establishing the recurrence of the paleoearthquakes, we mainly rely on the paleoearthquake events in trench TC1, which are labeled E1-E4 from oldest to youngest, and their dates are constrained to the following time ranges: E1(19.4±2.5)~(19.0±2.5)ka BP, E2(18.6±1.4)~(17.3±1.4)ka BP, E3(12.2±1.2)~(6.6±0.8)ka BP, and E4 6.9~6.2ka BP, respectively. The earthquake recurrence intervals are(1.2±0.5)ka, (8.7±3.0)ka and(2.8±3)ka, respectively. According to the sedimentation rate of the stratum, it can be judged that there is a sedimentary discontinuity between the paleoearthquakes E2 and E3, and the paleoearthquake events between E2 and E3 may not be recorded by the stratum. Ignoring the sedimentary discontinuous strata and the earthquakes occurring during the sedimentary discontinuity, the earthquake recurrence interval of the Jinghe section of B-A Fault is ~1~3ka. This is consistent with the earthquake recurrence interval(~2ka)calculated from the slip rate and the minimum displacement. The elapsed time of the latest paleoearthquake recorded in the trench is ~6.9~6.2ka BP. The magnitude of the latest event defined by the single event displacement on the fault is ~M_W7.4, and a longer earthquake elapsed time indicates the higher seismic risk of the B-A Fault.

Key words: strike-slip structure, paleoearthquake, B-A Fault, Tian Shan

中图分类号:

P315.2

胡宗凯, 杨晓平, 杨海波, 吴国栋, 李军, 周本刚. 北天山博罗可努-阿齐克库都克断裂精河段的古地震事件[J]. 地震地质, 2020, 42(4): 773-790.

HU Zong-kai, YANG Xiao-ping, YANG Hai-bo, WU Guo-dong, LI Jun, ZHOU Ben-gang. STUDY ON PALEOEARTHQUAKES ALONG THE JINGHE SECTION OF BOLOKENU-AQIKEKUDUKE FAULT[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(4): 773-790.

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