西藏阿里地区喀喇昆仑断裂断错地貌及最近强震活动时代的初步研究

doi:10.3969/j.issn.0253-4967.2022.04.007

摘要/Abstract

摘要：

喀喇昆仑断裂是青藏高原西部一条大型边界断裂, 调节了印度板块与欧亚板块的碰撞变形, 在青藏高原西部构造演化过程中扮演着重要角色。阿里地区断裂迹线清晰, 断错地貌显著, 显示出晚第四纪强烈活动的特征。目前, 断裂最近的强震活动时代、复发间隔等地震活动性参数尚不清楚, 极大地限制了地震危险性评估的准确性。文中对阿里地区的断裂几何结构、断错地貌进行了调查, 在扎西岗乡、门士乡、巴嘎乡等地对断错地貌面及断塞塘进行了光释光年代样品采集。研究结果表明, 断裂以扎西岗乡、索多村为界分可为3段, 各段断裂结构及性质差异显著; 断裂最近的强震活动在扎西岗乡西、门士乡东以及巴嘎乡一带, 时间分别约为2.34kaBP、 3.01kaBP及2.54kaBP。断裂最近的强震活动距今的时间可能已非常接近地震复发间隔, 其能量积累或已达到了非常高的程度, 再次发生强震事件的危险性很大, 需引起足够重视, 尽快对断裂的古地震事件、复发间隔等地震活动性参数开展细致的研究。

关键词: 喀喇昆仑断裂, 晚第四纪, 断错地貌, 最近强震活动时代

Abstract:

The Karakoram Fault is located in the west of the Qinghai-Tibet Plateau and crosses Kashmir, Xinjiang and Tibet in China. It is a large normal dextral strike-slip fault in the middle of the Asian continent. As a boundary fault dividing the Qinghai-Tibet Plateau and the Pamir Plateau-Karakoram Mountains, the Karakoram Fault plays a role in accommodating the collision deformation between the Indian plate and the Eurasian plate and in the tectonic evolution of the western Qinghai-Tibet Plateau. The fault trace in Ngari area is clear and the faulted landforms are obvious, which show strong activity characteristics in late Quaternary. As a large active fault, only one earthquake of magnitude 7 has been recorded on the Karakoram Fault since the recorded history, namely, the Tashkurgan earthquake of 1895 at its north end. There are no records of strong earthquakes of magnitude≥7 along the rest of the fault, and no paleo-seismic research has been carried out. Ages of recent strong earthquake activity and earthquake recurrence intervals are not clear, which greatly limit the accuracy of seismic risk assessment. In this study, we investigated the fault geometry and faulted landforms in Ngari area, collected OSL samples of the faulted landforms and sag ponds in Zhaxigang, Menshi and Baga towns and preliminarily discussed the ages of recent strong earthquake activity.

Study shows that the fault can be divided into three sections by Zhaxigang town and Suoduo village, and the structure and properties of each section are significantly different. In west Zhaxigang town section, the fault is dominated by dextral strike-slip with certain vertical movement, it is almost straight on the surface, with river terraces, alluvial-proluvial fans and water system faulted ranging from tens to hundreds of meters. In Zhaxigang town to Suoduo village section, the normal faulting is remarkable, the main fault constitutes the boundary fault between Ayilari Mountain and Gar Basin; fault facets and fault scarps are common along the fault line, there are also secondary faults with the same or opposite dip as the main fault developed near the piedmont basin. In east Suoduo village section, the main part of the fault is located at the south foot of Gangdise Mountain, and in addition to the piedmont fault, several approximately parallel faults are also developed on the southern alluvial-proluvial fans and moraine fans which are mainly dextrally faulted with certain vertical component.

According to the analysis of the faulted landforms and dating of the OSL samples collected from the sag ponds and faulted landforms in the west of Zhaxigang town, the east of Menshi town and the east of Baga town, the ages of recent strong earthquake activity on the fault are analyzed as follows. In the west of Zhaxigang town, the age of recent strong earthquake activity of the fault is constrained to be close to 2.34kaBP according to the average OSL dating results of KKF-3 and KKF-4. In the east of Menshi town, the recent earthquake activity age of fault f₂ is 4.67~3.01kaBP, but closer to 3.01kaBP according to the OSL dating results of KKF-11 of the youngest faulted geomorphic surface and average OSL dating results of KKF-6 and KKF-13 collected from sag ponds. In the area near Angwang village, Baga town, it is inferred that the recent strong earthquake activity age of the fault is close to 2.54kaBP according to the OSL dating results of KKF-2 collected from sag pond. If the faults of above three places are active at the same time, the age of recent strong earthquake activity of the fault is close to 2.63kaBP. The Karakorum Fault in Ngari area has obvious segment boundaries, and the activity of each segment and in its internal branch faults is most likely to be independent.

The earthquake recurrence interval on the fault is estimated to be 2.8ka according to the slip rate and the amount of displacement. From the above analysis, it can be seen the time since the last strong earthquake activity of Karakorum Fault may have been very close to the interval of earthquake recurrence. If the fault is characterized by a quasi-periodic in-situ recurrence, the energy accumulation in the fault may have reached a very high degree and the risk of recurrence of strong earthquake events of the fault may be very high, so more attention should be paid and more detailed research on the paleo-earthquake events and recurrence intervals should be carried out as quickly as possible.

Key words: Karakorum Fault, late Quaternary, faulted landform, ages of recent strong earthquake activity

中图分类号:

P315.2

徐伟, 刘志成, 王继, 高战武, 尹金辉. 西藏阿里地区喀喇昆仑断裂断错地貌及最近强震活动时代的初步研究[J]. 地震地质, 2022, 44(4): 925-943.

XU Wei, LIU Zhi-cheng, WANG Ji, GAO Zhan-wu, YIN Jin-hui. PRELIMINARY STUDY ON FAULTED LANDFORMS AND AGES OF RECENT STRONG EARTHQUAKE ACTIVITY ON THE KARAKORUM FAULT IN NGARI, TIBET[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(4): 925-943.

图/表 12

图1 喀喇昆仑断裂区域的构造格局(改自Cowgill, 2010) MPT主帕米尔逆冲断裂; DF达瓦孜断裂; TF塔尼玛斯断裂; KES公格尔拉张正断裂系; PF帕萨特断裂; MKT主喀喇昆仑逆冲断裂; KKF喀喇昆仑断裂; KYTS喀什一叶城转换断裂; KXF康西瓦断裂; ATF阿尔金断裂; LGF龙木错-郭扎错断裂;AKMS阿尼玛卿-昆仑-慕士塔格缝合带; LSS龙木错-双湖缝合带; BG-NJS 班公湖-怒江缝合带; IYS印度-雅鲁藏布江缝合带; STDS藏南拆离系; MMT喜马拉雅主地幔逆冲断裂; MCT喜马拉雅主中央逆冲断裂; MBT喜马拉雅主边界逆冲断裂;MFT喜马拉雅主前缘逆冲断裂

Fig. 1 Regional tectonic framework of Karakorum Fault( modified from Cowgill, 2010)

图2 阿里地区喀喇昆仑断裂的展布特征

Fig. 2 Distribution characteristics of Karakorum Fault in Ngari Prefecture.

图3 扎西岗乡以西段的卫星影像及典型部位断错地貌 a 扎西岗乡西断裂的卫星影像; b 扎西岗乡西阶地及水系右旋位错的卫星影像; c 扎西岗乡一带的断层陡坎照片;d 扎西岗乡南近SN向断裂的卫星影像; e 近SN向断裂的断层陡坎照片

Fig. 3 Satellite image and typical faulted landforms of the west Zhaxigang town section.

图4 扎西岗乡-索多村段典型部位的断裂展布、断层三角面及断层陡坎照片 a 次隆村一带断裂展布的卫星影像; b 定列塘咔村一带断裂展布的卫星影像; c 次隆村附近断层三角面的照片;d 新嘎仲措村南阶地位错陡坎的照片

Fig. 4 Typical fault distribution, fault facets and fault scarps of Zhaxigang town to Suoduo village section.

图5 索多村以东段典型部位的断裂展布及断错地貌 a 门士乡东亚尔钦曲一带断裂展布的卫星影像; b 亚尔钦曲两侧f2断裂的迹线; c 亚尔钦曲东f3断裂的迹线; d 亚尔钦曲东侧f2断裂水系右旋位错的照片; e 亚尔钦曲东侧f2断裂断层陡坎的照片

Fig. 5 Typical fault distribution satellite image and faulted landforms of the east Suoduo village section.

图6 扎西岗乡西断塞塘采样位置(a、 b)及采样剖面图(c、 d)

Fig. 6 Sampling locations(a, b)and profiles(c, d)in sag pond west of Zhaxigang town.

图7 亚尔钦曲东侧断裂沿线的DEM影像(a)、典型部位的高程测线(b)及地貌面解译(c)

Fig. 7 DEM image(a), typical topographic elevation lines(b), river offset and geomorphic surface interpretation(c)along the fault east of Yaerqin River.

图8 断塞塘P1、 P2内S3、 S4的位置及采样剖面

Fig. 8 Sampling location S3 and S4 in sag pond P1 and P2, and corresponding sampling profiles.

图9 昂旺村南的断裂迹线及断塞塘分布(a)、 DEM影像(b)及典型部位的地形高程测线(c)

Fig. 9 Fault trace and sag pond distribution(a), DEM image(b), and typical topographic elevation line(c)south of Angwang village.

图10 巴嘎乡昂旺村南S6、 S7 2处采样照片及剖面图

Fig. 10 Photos showing the sampling at site S6 and S7, and corresponding sampling profiles.

表1 样品光释光测试参数及年龄

Table 1 OSL test parameters and age of samples

样品编号	埋深 /m	U /μg·g^-1	Th /μg·g^-1	K /%	含水量 /%	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
KKF-1	0.28	4.04±0.08	16.5±0.26	3.00±0.02	14.09	5.83±0.38	74.93±10.88	12.84±2.04
KKF-2	0.34	1.7±0.01	18.5±0.14	2.14±0.01	7.39	4.84±0.32	12.3±1.15	2.54±0.29
KKF-3	0.21	1.67±0.03	19.5±0.30	2.74±0.01	22.86	4.74±0.28	13.35±1.00	2.82±0.27
KKF-4	0.24	2.36±0.03	28.8±0.29	2.81±0.01	26.37	5.59±0.31	10.39±0.56	1.86±0.15
KKF-6	0.18	3.38±0.06	20.2±0.26	2.61±0.01	6.37	6.09±0.42	19.93±1.56	3.27±0.34
KKF-11	0.25	2.26±0.04	15.7±0.20	1.76±0.01	4.93	4.51±0.31	21.07±1.69	4.67±0.49
KKF-12	0.17	2.27±0.04	14±0.16	1.67±0.01	2.52	4.39±0.30	12.01±0.78	2.74±0.26

图11 不同部位断裂最近的强震活动时代对比

Fig. 11 Comparison of ages of recent strong earthquake activity in different parts of the fault.

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