STUDY ON THE LATEST ACTIVITY OF WUYUNSHAN-HEFEI FAULT IN HEFEI BASIN, THE WESTERN BRANCH OF THE TANLU FAULT ZONE

doi:10.3969/j.issn.0253-4967.2020.01.004

Abstract

Abstract:

Tanlu fault zone is the largest strike-slip fault system in eastern China. Since it was discovered by aeromagnetics in 1960s, it has been widely concerned by scholars at home and abroad, and a lot of research has been done on its formation and evolution. At the same time, the Tanlu fault zone is also the main seismic structural zone in China, with an obvious characteristic of segmentation of seismicity. Major earthquakes are mostly concentrated in the Bohai section and Weifang-Jiashan section. For example, the largest earthquake occurring in the Bohai section is M7.4 earthquake, and the largest earthquake occurring in the Weifang-Jiashan section is M8.5 earthquake. Therefore, the research on the active structure of the Tanlu fault zone is mainly concentrated in these two sections. With the deepening of research, some scholars carried out a lot of research on the middle section of Tanlu fault zone, which is distributed in Shandong and northern Jiangsu Province, including five nearly parallel fault systems, i.e. Changyi-Dadian Fault(F₁), Baifenzi-Fulaishan Fault(F₂), Yishui-Tangtou Fault(F₃), Tangwu-Gegou Fault(F₄)and Anqiu-Juxian Fault(F₅). They find that the faults F₃ and F₅ are still active since the late Quaternary. In recent years, we have got a further understanding of the geometric distribution, active age and active nature of Fault F₅, and found that it is still active in Holocene. At the same time, the latest research on the extension of F₅ into Anhui suggests that there is a late Pleistocene-Holocene fault existing near the Huaihe River in Anhui Province.
The Tanlu fault zone extends into Anhui Province and the extension section is completely buried, especially in the Hefei Basin south of Dingyuan. At present, there is little research on the activity of this fault segment, and it is very difficult to study its geometric structure and active nature, and even whether the fault exists has not been clear. Precisely determining the distribution, active properties and the latest active time of the hidden faults under urban areas is of great significance not only for studying the rupture behavior and segmentation characteristics of the southern section of the Tanlu fault zone, but also for providing important basis for urban seismic fortification. By using the method of shallow seismic prospecting and the combined drilling geological section, this paper carries out a detailed exploration and research on the Wuyunshan-Hefei Fault, the west branch fault of Tanlu fault zone buried in Hefei Basin. Four shallow seismic prospecting lines and two rows of joint borehole profiles are laid across the fault in Hefei urban area from north to south. Using ¹⁴C, OSL and ESR dating methods, ages of 34 samples of borehole stratigraphic profiles are obtained. The results show that the youngest stratum dislocated by the Wuyunshan-Hefei Fault is the Mesopleistocene blue-gray clay layer, and its activity is characterized by reverse faulting, with a maximum vertical offset of 2.4m. The latest active age is late Mesopleistocene, and the depth of the shallowest upper breaking point is 17m. This study confirms that the west branch of Tanlu fault zone cuts through Hefei Basin and is still active since Quaternary. Its latest activity age in Hefei Basin is late of Middle Pleistocene, and the latest activity is characterized by thrusting. The research results enrich the understanding of the overall activity of Tanlu fault zone in the buried section of Hefei Basin and provide reliable basic data for earthquake monitoring, prediction and earthquake damage prevention in Anhui Province.

Key words: Tanlu fault zone, buried fault, composite drilling geological section, latest activity, Hefei Basin

摘要：

前人对于郯庐断裂带安徽段出露部分的活动性开展了不同程度的研究, 并获得了丰富的成果, 而对于隐伏于合肥盆地中的段, 其活动性如何, 甚至断裂是否存在一直未能取得明确认识。文中利用浅层地震勘探及钻探联合地质剖面探测方法, 对隐伏于合肥盆地中的郯庐断裂带西分支断层——乌云山-合肥断裂开展了详细的探测研究工作, 在合肥城区由北向南跨断裂布设了4条浅层地震勘探测线和2排联合钻孔剖面, 采用¹⁴C、 OSL和ESR 3种测年手段共获得了34个钻孔地层剖面样品的年龄数据, 结果显示乌云山-合肥断裂错动的最新地层为中更新统青灰色黏土层, 断层活动表现为逆断性质, 最大垂直错距达2.4m, 最新活动时代为中更新世晚期, 上断点最浅埋深达17m。文中研究证实了郯庐断裂带穿切合肥盆地, 且第四纪以来仍有活动, 所得成果充实了对郯庐断裂带安徽段总体活动的认识。

关键词: 郯庐断裂带, 隐伏断层, 钻探联合地质剖面探测, 最新活动, 合肥盆地

CLC Number:

P315.2

ZHENG Ying-ping, YANG Xiao-ping, SHU Peng, LU Shuo, FANG Liang-hao, SHI Jin-hu, HUANG Xiong-nan, LIU Chun-ru. STUDY ON THE LATEST ACTIVITY OF WUYUNSHAN-HEFEI FAULT IN HEFEI BASIN, THE WESTERN BRANCH OF THE TANLU FAULT ZONE[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(1): 50-64.

郑颖平, 杨晓平, 疏鹏, 路硕, 方良好, 石金虎, 黄雄南, 刘春茹. 合肥盆地中郯庐断裂带西支乌云山-合肥断裂最新活动特征[J]. 地震地质, 2020, 42(1): 50-64.

Figures/Tables 9

References 20

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名称	样品编号	样品岩性	取样深度/m	测年方法	年龄/a	校正年龄/a
F_P2	F_P2-52.20	黏土	2.20	¹⁴C	14 315±40	17 441±90
联合	F_P2-54.65	黏土	4.65	¹⁴C	28 590±120	32 631±265
剖面	F_P2-56.40	黏土	6.40	¹⁴C	24 290±100	28 332±15

名称	样品编号	样品岩性	取样深度/m	测年方法	年龄/a	校正年龄/a
F_P2	F_P2-52.20	黏土	2.20	¹⁴C	14 315±40	17 441±90
联合	F_P2-54.65	黏土	4.65	¹⁴C	28 590±120	32 631±265
剖面	F_P2-56.40	黏土	6.40	¹⁴C	24 290±100	28 332±15

名称	样品编号	测年方法	取样深度 /m	U /ug·g	Th /ug·g	K₂O /%	含水量 /%	古剂量 /Gy	年剂量 /Gy·ka^-1	年龄 /ka
F_P2 联合剖面	F_P2-52.10	OSL	2.10	2.33	13.4	1.62	17.44	69.65±6.46	3.56	19.58±2.67
	F_P2-55.00	OSL	5.00	2.54	12.7	1.18	16.54	221.26±22.87	3.15	70.27±10.11
	F_P2-57.95	OSL	7.95	2.11	12.5	1.48	14.91	343.58±32.67	3.29	104.47±14.42
	F_P2-510.65	OSL	10.65	2.35	13.2	1.45	16.64	362.93±8.37	3.34	108.81±11.81
	F_P2-513.35	OSL	13.35	2.86	14.6	1.47	16.49	497.57±44.70	3.58	138.95±18.68
	F_P2-515.85	OSL	15.85	3.33	13.6	0.78	14.41	562.71±105.34	3.14	179.25±38.04
	F_P2-519.50	OSL	19.50	2.93	13.6	0.98	16.38	665.05±52.39	3.15	211.46±26.92
	F_P2-522.35	OSL	22.35	2.61	13.4	1.25	16.36	552.42±72.71	3.24	170.27±28.15
	F_P2-525.30	OSL	25.30	2.69	12.5	1.43	18.00	508.23±35.28	3.21	158.29±19.27
	F_P2-519.65	ESR	19.65	3.84	17.0	1.44	16.22	1 873±164	3.08	608±53
	F_P2-522.50	ESR	22.50	3.00	14.2	1.69	15.91	874±161	2.95	296±55
	F_P2-525.45	ESR	25.45	3.17	14.8	1.96	17.05	1 026±204	3.17	324±64
	F_P2-527.00	ESR	27.00	2.81	14.3	1.40	16.54	4 287±1 238	2.67	1 606±461
	F_P2-529.50	ESR	29.50	2.71	14.4	1.33	15.49	1 074±344	2.64	407±130
	F_P2-531.90	ESR	31.90	1.66	8.9	1.28	12.46	1 331±302	2.14	622±141
	F_P2-532.80	ESR	32.80	2.01	9.84	1.12	12.14	1 301±230	2.15	605±107
F_P13 联合剖面	F_P13-71.70	OSL	1.70	3.28	13.30	1.54	13.12		0.16	57.8±2.81
	F_P13-73.50	OSL	3.50	1.72	8.84	1.32	12.76		0.13	75.42±5.98
	F_P13-716.65	OSL	16.65	3.00	14.40	0.97	11.69		0.04	212.92±11.07
	F_P13-719.15	OSL	19.15	1.66	11.20	0.96	12.11		0.03	265.67±19.51
	F_P13-714.00	ESR	14.00	2.25	12.2	1.37	13.58	1 991±424	2.50	796±170
	F_P13-716.80	ESR	16.80	2.65	13.3	1.14	13.50	1 391±175	2.47	563±71
	F_P13-115.05	OSL	5.05	2.24	11.00	1.41	13.39		0.10	99.92±9.87
	F_P13-117.45	OSL	7.45	2.05	10.50	1.29	16.59		0.08	177.45±12.97
	F_P13-119.45	OSL	9.45	2.10	11.90	1.03	13.25		0.06	193.81±15.99
	F_P13-1112.55	OSL	12.55	1.77	9.03	1.37	12.75		0.05	237.62±21.39
	F_P13-1115.15	OSL	15.15	2.53	11.70	1.25	8.86		0.04	192.12±18.77
	F_P13-1116.15	OSL	16.15	1.81	12.20	1.10	11.44		0.04	212.49±21.58
	F_P13-1117.25	OSL	17.25	1.75	9.57	1.11	9.33		0.03	253.68±19.61
	F_P13-1119.50	OSL	19.50	1.56	9.42	0.91	11.02		0.03	270.35±25.69
	F_P13-1120.50	OSL	20.50	1.54	10.40	0.36	14.80		0.03	402.72±57.46

名称	样品编号	测年方法	取样深度 /m	U /ug·g	Th /ug·g	K₂O /%	含水量 /%	古剂量 /Gy	年剂量 /Gy·ka^-1	年龄 /ka
F_P2 联合剖面	F_P2-52.10	OSL	2.10	2.33	13.4	1.62	17.44	69.65±6.46	3.56	19.58±2.67
	F_P2-55.00	OSL	5.00	2.54	12.7	1.18	16.54	221.26±22.87	3.15	70.27±10.11
	F_P2-57.95	OSL	7.95	2.11	12.5	1.48	14.91	343.58±32.67	3.29	104.47±14.42
	F_P2-510.65	OSL	10.65	2.35	13.2	1.45	16.64	362.93±8.37	3.34	108.81±11.81
	F_P2-513.35	OSL	13.35	2.86	14.6	1.47	16.49	497.57±44.70	3.58	138.95±18.68
	F_P2-515.85	OSL	15.85	3.33	13.6	0.78	14.41	562.71±105.34	3.14	179.25±38.04
	F_P2-519.50	OSL	19.50	2.93	13.6	0.98	16.38	665.05±52.39	3.15	211.46±26.92
	F_P2-522.35	OSL	22.35	2.61	13.4	1.25	16.36	552.42±72.71	3.24	170.27±28.15
	F_P2-525.30	OSL	25.30	2.69	12.5	1.43	18.00	508.23±35.28	3.21	158.29±19.27
	F_P2-519.65	ESR	19.65	3.84	17.0	1.44	16.22	1 873±164	3.08	608±53
	F_P2-522.50	ESR	22.50	3.00	14.2	1.69	15.91	874±161	2.95	296±55
	F_P2-525.45	ESR	25.45	3.17	14.8	1.96	17.05	1 026±204	3.17	324±64
	F_P2-527.00	ESR	27.00	2.81	14.3	1.40	16.54	4 287±1 238	2.67	1 606±461
	F_P2-529.50	ESR	29.50	2.71	14.4	1.33	15.49	1 074±344	2.64	407±130
	F_P2-531.90	ESR	31.90	1.66	8.9	1.28	12.46	1 331±302	2.14	622±141
	F_P2-532.80	ESR	32.80	2.01	9.84	1.12	12.14	1 301±230	2.15	605±107
F_P13 联合剖面	F_P13-71.70	OSL	1.70	3.28	13.30	1.54	13.12		0.16	57.8±2.81
	F_P13-73.50	OSL	3.50	1.72	8.84	1.32	12.76		0.13	75.42±5.98
	F_P13-716.65	OSL	16.65	3.00	14.40	0.97	11.69		0.04	212.92±11.07
	F_P13-719.15	OSL	19.15	1.66	11.20	0.96	12.11		0.03	265.67±19.51
	F_P13-714.00	ESR	14.00	2.25	12.2	1.37	13.58	1 991±424	2.50	796±170
	F_P13-716.80	ESR	16.80	2.65	13.3	1.14	13.50	1 391±175	2.47	563±71
	F_P13-115.05	OSL	5.05	2.24	11.00	1.41	13.39		0.10	99.92±9.87
	F_P13-117.45	OSL	7.45	2.05	10.50	1.29	16.59		0.08	177.45±12.97
	F_P13-119.45	OSL	9.45	2.10	11.90	1.03	13.25		0.06	193.81±15.99
	F_P13-1112.55	OSL	12.55	1.77	9.03	1.37	12.75		0.05	237.62±21.39
	F_P13-1115.15	OSL	15.15	2.53	11.70	1.25	8.86		0.04	192.12±18.77
	F_P13-1116.15	OSL	16.15	1.81	12.20	1.10	11.44		0.04	212.49±21.58
	F_P13-1117.25	OSL	17.25	1.75	9.57	1.11	9.33		0.03	253.68±19.61
	F_P13-1119.50	OSL	19.50	1.56	9.42	0.91	11.02		0.03	270.35±25.69
	F_P13-1120.50	OSL	20.50	1.54	10.40	0.36	14.80		0.03	402.72±57.46