PALEOEARTHQUAKE CHARACTERISTICS IN DUNHUANG SEGMENT OF THE SANWEISHAN FAULT

doi:10.3969/j.issn.0253-4967.2021.06.004

Abstract

Abstract:

The Sanweishan Fault is located in the front of the northwest growth of the northern margin of Tibetan plateau, a branch fault of the Altyn Tagh Fault which extends to the northwest. The latest seismic activity of the Sanweishan Fault reflects the tectonic deformation characteristics of the northern plateau. Meanwhile, it is of great significance for the seismic risk assessment of Dunhuang and its adjacent areas to understand the characteristics of earthquake recurrence. The Sanweishan Fault runs along the western piedmont of the Sanwei Shan, with a total length of 175km. The fault is characterized by left-lateral strike-slip and reverse faulting, with local normal fault features. Based on the geometry, the fault can be divided into three segments, i.e. the Shuangta-Shigongkouzi, the Shigongkouzi-Shugouzi and the Shugouzi-Xishuigou segment from east to west. Previous studies about the paleoearthquakes on the Sanweishan Fault mainly focus on the middle and east segments of the fault, while the west segment of the fault has been less studied. Meanwhile, the available research does not involve the recurrence characteristics and possible magnitude of the paleoearthquakes. Based on high-resolution satellite images, we found that the main fault has grown toward the basin and formed fault scarps in the western segment of the Sanweishan Fault. We have carried out a detailed study on these fault scarps. Based on trench excavation and chronological study on the latest fault scarps, this paper determines the sequence of the paleoseismic events on the fault and discusses the recurrence characteristics and possible magnitude of earthquake for the Sanweishan Fault.
In the western segment of the fault, through satellite image interpretation and field investigation, we found new fault scarps distributed on the alluvial fan in front of the mountain near Gedajing. We called it Dunhuang segment of the Sanweishan Fault. The activity characteristics of the fault scarps may reflect the latest seismic events in the western part of the Sanweishan Fault. Different from the sinistral strike slip of the main Sanweishan Fault, this fault segment shows the characteristics of thrust with low angle. According to the differential GPS survey, the height of the fault scarp is approximately 2.2m. The paleoseismic trench was excavated across the fault scarp. Based on the analysis of paleoseismological trenching and optical stimulated luminescence dating, two paleoseismic events are determined. Event E1 occurred at approximately(35.1±3.7)~(36.7±4.1)ka; event E2 occurred at approximately(76.5±8.8)~(76.7±8.3)ka. According to the strata offset and corresponding age, the vertical slip rate of the Sanweishan Fault is determined to be(0.03±0.01)mm/a, with a corresponding shortening rate of(0.09±0.01)mm/a. Together with the previous results, we consider that the Sanweishan Fault is characterized by segmentation. The middle and east segments may have the ability of independent rupture, and also the characteristics of cascading rupture with the Dunhuang segment. According to the existing results, we conclude that the recurrence interval for cascading rupture behavior on the Sanweishan Fault is approximately 40ka, which shows a characteristic of low slip rate and long-term recurrence. The best estimated magnitude is inferred to be in the range between M_W7.1 and M_W7.5 based on the empirical relationships between moment magnitude and rupture length.

Key words: Sanwei Shan Fault, Late Pleistocene, paleoearthquake, Dunhuang

摘要：

三危山断裂位于青藏高原北缘NW向扩展的前缘位置, 其最新地震活动反映了高原北部地区的构造变形特征。文中通过遥感影像解译、野外实地调查、古地震探槽及光释光年代样品测试, 对三危山断裂敦煌段的古地震活动特征开展了研究。结果表明, 断裂晚更新世以来发生过2次古地震事件, 事件E1发生的年代约为距今(35.1±3.7)~(36.7±4.1)ka; 事件E2发生的年代约为距今(76.5±8.8)~(76.7±8.3)ka。三危山断裂晚更新世以来的垂直滑动速率为(0.03±0.01)mm/a, 相应的缩短速率为(0.09±0.01)mm/a。综合前人的研究结果, 认为三危山断裂的地震活动具有分段性特征, 中段、东段可能具有独立破裂的能力, 也存在与敦煌段发生级联破裂的特征, 复发间隔约为40ka, 根据经验公式估算三危山断裂可能发生的震级范围为 M_W7.1 ~7.5。

关键词: 三危山断裂, 晚更新世, 古地震, 敦煌

CLC Number:

P315.2

LIU Xing-wan, YUAN Dao-yang, YAO Yun-sheng, ZOU Xiao-bo. PALEOEARTHQUAKE CHARACTERISTICS IN DUNHUANG SEGMENT OF THE SANWEISHAN FAULT[J]. SEISMOLOGY AND EGOLOGY, 2021, 43(6): 1398-1411.

刘兴旺, 袁道阳, 姚赟胜, 邹小波. 三危山断裂敦煌段古地震活动特征[J]. 地震地质, 2021, 43(6): 1398-1411.

Figures/Tables 7

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样品编号	埋深 /m	²³⁸U/ Bq·kg^-1	²³²Th/ Bq·kg^-1	⁴⁰K/ Bq·kg^-1	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
SWSOSL-13	3	24±1.00	21±0.69	430±15.82	2.3±0.1	154.0±15.4	66.7±7.3
SWSOSL-14	2.6	16±0.75	19±0.65	433±15.83	2.2±0.1	74.2±7.1	34.1±3.6
SWSOSL-15	1.5	13±0.62	14±0.53	478±15.83	2.2±0.1	115.1±13.4	52.4±6.6
SWSOSL-16	1.1	13±0.75	14±0.53	497±15.83	2.3±0.1	104.0±9.2	45.5±4.6
SWSOSL-17	0.7	17±0.87	12±0.49	402±15.82	2.0±0.1	79.5±8.8	40.1±4.8
SWSOSL-18	1.9	20±0.87	21±0.69	399±15.82	2.3±0.1	70.7±7.5	32.4±3.7
SWSOSL-19	1.0	14±0.75	16±0.61	395±15.82	2.0±0.1	115.5±9.0	57.3±5.2
SWSOSL-20	0.6	25±1.00	25±0.85	361±12.66	2.3±0.1	63.6±5.8	28.1±2.9
SWSOSL-23	1.0	15±0.75	15±0.57	452±15.83	2.2±0.1	80.7±8.1	36.7±4.1

样品编号	埋深 /m	²³⁸U/ Bq·kg^-1	²³²Th/ Bq·kg^-1	⁴⁰K/ Bq·kg^-1	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
SWSOSL-13	3	24±1.00	21±0.69	430±15.82	2.3±0.1	154.0±15.4	66.7±7.3
SWSOSL-14	2.6	16±0.75	19±0.65	433±15.83	2.2±0.1	74.2±7.1	34.1±3.6
SWSOSL-15	1.5	13±0.62	14±0.53	478±15.83	2.2±0.1	115.1±13.4	52.4±6.6
SWSOSL-16	1.1	13±0.75	14±0.53	497±15.83	2.3±0.1	104.0±9.2	45.5±4.6
SWSOSL-17	0.7	17±0.87	12±0.49	402±15.82	2.0±0.1	79.5±8.8	40.1±4.8
SWSOSL-18	1.9	20±0.87	21±0.69	399±15.82	2.3±0.1	70.7±7.5	32.4±3.7
SWSOSL-19	1.0	14±0.75	16±0.61	395±15.82	2.0±0.1	115.5±9.0	57.3±5.2
SWSOSL-20	0.6	25±1.00	25±0.85	361±12.66	2.3±0.1	63.6±5.8	28.1±2.9
SWSOSL-23	1.0	15±0.75	15±0.57	452±15.83	2.2±0.1	80.7±8.1	36.7±4.1

样品编号	埋深/m	²³⁸U/ Bq·kg^-1	²³²Th/ Bq·kg^-1	⁴⁰K/ Bq·kg^-1	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
SWS-1	2.8	33.4±1.1	27.2±3.8	423.0±8.8	2.7±0.1	207.1±7.03	76.7±8.3
SWS-2	2.6	17.3±5.7	25.7±3.0	419.3±4.8	2.32±0.1	177.06±16.14	76.2±10.5
SWS-3	1.5	29.1±0.4	37.3±2.5	386.6±1.5	2.82±0.1	174.18±19.84	61.8±9.5
SWS-4	1.0	33.4±0.7	31.8±8.6	388.9±13.4	2.78±0.1	155.45±4.65	56.0±6.0
SWS-5	0.6	41.8±2.3	25.4±3.6	426.4±6.4	2.78±0.1	91.77±14.02	33.0±6.1
SWS-6	1.9	38.6±1.1	30.6±5.7	454.6±2.1	2.83±0.1	216.26±11.37	76.5±8.8
SWS-7	1.7	25.7±0.3	27.9±6.2	485.0±2.0	2.86±0.1	221.46±23.	77.3±11.4
SWS-8	0.4	45.9±1.1	34.5±2.6	352.1±8.5	2.98±0.1	104.64±3.03	35.1±3.7
SWS-9	0.3	23.8±0.3	32.7±4.5	452.4±10.3	2.87±0.1	41.21±1.22	14.4±1.5

样品编号	埋深/m	²³⁸U/ Bq·kg^-1	²³²Th/ Bq·kg^-1	⁴⁰K/ Bq·kg^-1	环境剂量率 /Gy·ka^-1	等效剂量 /Gy	年龄 /ka
SWS-1	2.8	33.4±1.1	27.2±3.8	423.0±8.8	2.7±0.1	207.1±7.03	76.7±8.3
SWS-2	2.6	17.3±5.7	25.7±3.0	419.3±4.8	2.32±0.1	177.06±16.14	76.2±10.5
SWS-3	1.5	29.1±0.4	37.3±2.5	386.6±1.5	2.82±0.1	174.18±19.84	61.8±9.5
SWS-4	1.0	33.4±0.7	31.8±8.6	388.9±13.4	2.78±0.1	155.45±4.65	56.0±6.0
SWS-5	0.6	41.8±2.3	25.4±3.6	426.4±6.4	2.78±0.1	91.77±14.02	33.0±6.1
SWS-6	1.9	38.6±1.1	30.6±5.7	454.6±2.1	2.83±0.1	216.26±11.37	76.5±8.8
SWS-7	1.7	25.7±0.3	27.9±6.2	485.0±2.0	2.86±0.1	221.46±23.	77.3±11.4
SWS-8	0.4	45.9±1.1	34.5±2.6	352.1±8.5	2.98±0.1	104.64±3.03	35.1±3.7
SWS-9	0.3	23.8±0.3	32.7±4.5	452.4±10.3	2.87±0.1	41.21±1.22	14.4±1.5