张家口—宣化盆地断裂特征与活动性研究①

张家口—宣化盆地断裂特征与活动性研究①

周江林， 尤惠川， 唐方头

(中国地震局地球物理研究所，北京 100081)

摘要：运用地质地貌调查、地球物理勘探和年代测定等方法，对张家口—宣化盆地的四条主要断裂(张家口断裂、万全断裂、洗马林—水泉断裂和洋河断裂)的空间展布特征和活动性进行分析和研究，获得其活动时代、活动速率等参数。研究表明：上述断裂第四纪期间持续活动，以脆性变形为特征；总体上NW向断裂以高角度的正(或逆)倾滑断层为主，NE或NEE向的断裂以高角度的正断层为主；盆地内活动断裂总体来说活动强烈，多处可见断裂正断运动及左旋走滑运动的地质剖面，早更新世以来单条断层的平均垂直活动速率大于0.07～0.30 mm/a，总垂直活动速率可能达到1.33 mm/a。

关键词：张家口—宣化盆地； 活动断裂； 构造变形； 活动性

收稿日期：①2014-12-05

基金项目：河北省城市活断层探测与地震危险性评价项目(冀发改投资[2007]1684号)；地震行业科研专项(200908001)

作者简介：周江林,男,硕士,主要从事地震地质和活断层调查研究。E-mail：zhou.jiang.lin@163.com。

中图分类号:TP642； P542.3文献标志码：A

DOI:10.3969/j.issn.1000-0844.2015.03.0702

Characteristics and Tectonic Activities of Faults

in Zhangjiakou-Xuanhua Basin

ZHOU Jiang-lin, YOU Hui-chuan, TANG Fang-tou

(InstituteofGeophysics,ChinaEarthquakeAdministration,Beijing100081,China)

Abstract：An active fault leads to disaster in the world, and within the general development of disasters, an active fault’s frequency and the damage it causes is based on the degree of the fault layer, and gradually intensifies. In recent years, earthquake prediction research and engineering construction developments have vigorously promoted the study of active faults. The Zhangjiakou-Xuanhua Basin, situated in the intersection of the Zhangjiakou-Bohai fault zone and the Shanxi seismic tectonic zone, is a typical Cenozoic extensional fault-depression basin. There are many active faults in this basin, which control the basin’s development and evolution. However, there is scant research on the active faults in the Zhangjiakou-Xuanhua Basin, and existingresearch is confined to a few areas. As such, a systematic analysis of this area's active faults, the identification of quantitative information regarding active faults, and a better understanding of the characteristics of this basin's long-term activity is important in theory and practice. Based on an analysis and reorganization of relevant information from detailed field investigations and shallow seismic exploration, this study describes the geometric characteristics and tectonic activities of the active faults in the Zhangjiakou-Xuanhua Basin. The faults for which there are research data include the Zhangjiakou, Wanquan, Ximalin-Shuiquan, and Yanghe faults. The results showed that: The Zhangjiakou fault strikes mainly to the northwest and east-west, dipping to the north, and extending over 70 km. As a major geological and geomorphologic boundary, the Zhangjiakou fault controls the geotectonic movement in this region, in which its southern side is characterized by Late Quaternary unconsolidated basin deposits, and its northern side by Mesozoic volcano debris and Pre-Mesozoic metamorphic rocks in the form of lower mountains and hills. The Zhangjiakou faults are mainly high-angle inverse strike-slip faults with some normal strike-slip faults. The activity of the central segment of the Zhangjiakou fault is stronger than that in other segments. Since the late Pleistocene, the average vertical slip rate along a single fault is over 0.07～0.30 mm/a, while the total vertical slip rate over the entire fault is as high as 1.33 mm/a. The Wanquan fault lies in the northwest of the Zhangjiakou-Xuanhua Basin, striking mainly northeast or north-northeast, dipping southeast, and extending over 15 km. It is a major geological and geomorphic margin, controlling the neotectonic movement in this region. On the southeast side of the Wanquan fault there are Late Quaternary unconsolidated deposits, forming a basin or deposition; but on the other side there is Mesozoic volcano debris, forming lower mountains and hills. The Wanquan fault is a normal fault with southeast-dipping at a medium-high-angle. This fault was active in the Quaternary. Since the middle-late time of the late Pleistocene, the average rate with vertical slip of a single fault has been about 0.03～0.3 mm/a, but the fault has multiple slipping surfaces, and a total large-rate with vertical slip is yet to be estimated. The Ximalin-Shuiquan fault is located in the southwest of the Zhangjiakou-Xuanhua Basin, and can be divided into four sections. The fault strikes mainly northwest, with high-angle inverse strike-slip fault or normal strike-slip fault characteristics. The latest active time of the Ximalin-Shuiquan fault is in the late Middle Pleistocene. The Yanghe fault is a subsurface fault, and its active time was in the Middle Pleistocene. The fault strikes mainly northwest, and controlled the Yanghe River's flow direction and terrace development. The fault strikes mainly northwest, with high-angle slip fault characteristics.

Key words： Zhangjiakou-Xuanhua Basin; active fault; structural deformation; activity

0引言

张家口—宣化盆地处于京、冀、晋、蒙四省市区交界处，该区域历史上发生过多次破坏性地震[1]，如1625年怀安—天镇6级地震和1998年张北6.2级地震[2-3]。盆地三面环山，地势呈西北高、东南低。位于张家口—渤海地震构造带与山西地震构造带的交汇区，盆地构造复杂，受NWW向张家口—渤海构造带和NNE向山西断陷带的复合作用[4-5]。

张家口—宣化盆地所在区域大地构造属华北地台，古近纪时期，该区处于剥蚀环境，形成准平原化地形。新近纪期间，断裂活动使早期准平原分化、瓦解，形成一系列断陷盆地，与周围的隆起断块(山地)一起形成盆岭构造[6-7]。断裂带附近区域主要发育NWW向、NE向和NW向3组断裂构造，前2组断裂第四纪活动性较强。第四纪期间，形成张家口—宣化等山间盆地，第四系厚度可达240 m以上[8]。

张家口—宣化盆地为洋河流域较大的一个山间盆地，大体呈三角形，周围由群山环抱, 洋河自西北向东南流经盆地中央,并发育有二级堆积阶地, 阶地之上则为山前发育起来的洪积、冲积扇所连成的山麓倾斜平原[9]。三条不同方向延伸的山脉使盆地整体呈现“三角形”地貌景观(图1)。另外，古近纪和新近纪发育的两级夷平面还说明这种垂直升降运动具有间歇性抬升特点，使得地块遭受河流切割，形成现代河谷和多级冲积、洪积阶地[10-11]。

1盆地主要断裂的展布

张家口—宣化盆地位于张家口—渤海活动构造带和山西活动构造带的交汇部位，受到两条构造带的复合作用，表现出NWW向和NE向两组断裂的发育和改造，形成复杂的盆断结构。NWW向构造占据更为主导的地位，而NE向构造也依稀可辨[12]。

根据前人研究结果，经高分辨率卫星影像遥感解译，区内发育有四条主要断裂带(图1)：北部是NWW向的张家口断裂(F1)，西部为NE-NNE的万全断裂(F2)，南部发育NW向的洗马林—水泉断裂(F4)，盆地内部发育有洋河隐伏断裂(F3)。盆地边界主控断裂为丘陵和山间盆地的分界线。

F 1：张家口断裂；F 2：万全断裂；F 3：洋河断裂；F 4：洗马林—水泉断裂；DZ1：地震勘探测线 图1　张家口—宣化盆地卫星影像及断层分布图 Fig.1　Satellite image of Zhangjiakou-Xuanhua Basin and its faults distribution

2断裂特征与活动性

2.1张家口断裂(F1)

2.1.1断裂概述及展布

张家口断裂是华北地区著名的张家口—渤海地震构造带西部的一条主要断裂[4-5]，为山西断陷带与燕山断块的构造分界之一，是张家口—宣化盆地的北缘边界主控断裂，控制了张家口—宣化盆地的北部边界(图1)。断裂总体上呈NWW走向展布，长达70 km，由NW向和近EW向2组多条次级高角度正(或逆)倾滑断层组成。

2.1.2断裂变形特征

地质地貌调查在多个地方发现了清晰的张家口断裂断层剖面，规模较大，可见其晚更新世以来的活动迹象，新地层错断现象十分清楚，为高角度正(或逆)倾滑断层。大多数段落表现为中生代火山-碎屑岩或太古代变质岩与第四系的冲洪积物相接，并发育断层破碎带，宽1～10 m，地貌上构成巨大的断层崖。

在清水河以西的张家口市区西北山前，断裂表现为侏罗纪山体与第四纪平地的截然相接，山地前缘发育一系列大型的左阶斜列构造透镜体[图3(a)]。在山前人工开挖剖面上，揭露出一条产状为75°/N∠45°的逆断层，使北盘的侏罗纪砂岩逆冲于南盘的晚更新世黄土之上[图3(b)]。侏罗系发生劈理化，内部发育一条低角度逆掩断层，主断裂面附近两盘地层相互混合，下盘黄土强烈片理化。需要指出的是，断层的逆冲性质和构造透镜体的斜列形式指示该段断裂同时具有左旋走滑活动属性。此外，断层剖面显示两盘黄土落差大于15 m，根据黄土的性状及与邻区资料对比，以50 ka B.P.估计其年龄，则该处断裂的平均垂直滑动速率大于0.30 mm/a。

①侏罗纪桔红色砂岩;②侏罗纪紫色砂泥岩; ③晚更新世偶含小碎石黄土,夹砂砾石石层 图3　清水河西张家口断裂及其地质剖面 Fig.3　Zhangjiakou fault in the west of Qingshuihe 　　　 River and its geological section

在梅家营以北的山前冲沟西壁，发现了清晰的张家口断裂构造剖面[图4(a)]：北侧为侏罗纪灰白色、灰黄色泥岩构成的山体；南侧是冲洪积台地，由白垩纪肉红色砾岩基座和其上的晚更新世含砾黄土状堆积组成；两者之间为逆断层，上部倾角变缓，顶部被很薄的现代坡积物覆盖。应该指出，该处断层具有最新活动性，形成3～4 m高的冲沟裂点。此外，此处还发生了明显的左旋位移。

①侏罗纪灰白色、灰黄色泥岩；②白垩纪肉红色砾岩； 　③晚更新世含砾次生黄生 图4　梅家营北张家口断裂及其地质剖面 Fig.4　Zhangjiakou fault in the north of Meijiaying 　　　 Village and its geological section

本文前述认为晚更新世中晚期以来单条断层的平均垂直活动速率大于0.30 mm/a。鉴于张家口断裂可能有多个滑动面，上述数据作为张家口断裂垂直活动速率估计是偏于保守的，更接近实际的估计有赖于今后进一步的调查和研究。从宏观的角度去估计张家口断裂的垂直活动速率。清水河沿岸跨越张家口断裂，利用河流阶地和钻孔资料是研究该断裂总垂直活动速率的有效方法。清水河共发育4级阶地，宽阔而连续的Ⅳ级阶地拔河高度约100 m。断裂附近的钻孔资料表明，下降盘晚更新世以来的堆积厚度多在60 m以上。至此，可以估计张家口断裂晚更新世以来的总垂直活动速率为：≥(100+60) m/120 ka=1.33 mm/a。

2.2万全断裂(F2)

2.2.1断裂概述及展布

万全断裂由北段和南段组成：北段北起万全镇西，经盆窑村、吴家庄至沙家庄村南，长约5 km；南段自沙家庄村南向东错列2 km，经张贵屯、赵家梁、瓦窑，止于邹家庄南，长约10 km(见图1、图2)。

万全断裂控制了盆地的西北边界，断裂地质地貌复杂，多处冲沟内可见其新活动特征[13]。断裂依次穿过下白垩系青石砬组、中上白垩系洗马林组、及上更新统山前冲洪积马兰黄土地层，走向NE 35°，倾向SE，倾角65°，多处断层露头表现为正断层，最新活动发生于晚更新世[14]。

万全断裂西北面为冀北山地，断裂东南为山前冲洪积扇及洋河河流堆积阶地。整条断裂地质上表现为西北侧中生代地层与东南侧第四系冲洪积扇的正(或逆)断层接触，地貌上构成低山丘陵与山间盆地的分界[15-16](图5)。

图5　万全断裂西南段断层陡坎地貌(镜向西南) Fig.5　Scarp landscape of the southwest segment 　　　 of Wanquan fault (view to southwest)

2.2.2断裂变形特征

在盆窑村北，褐色黄土状含圆砾土层和砾石层之中发育多条断层(图6)。其中，主断层产状为35°/SE∠80°，最大垂直错距约6 m，显示为正断层。取上盘黄土状土样品，经北京大学测定，其热释光年龄为(21.8±1.5)Ka B.P.。从地层颜色、岩性和构造地貌位置及样品年龄分析，该套地层应属中更新世晚期堆积。因此，该处断层的最新活动发生在中更新世晚期,其平均垂直活动速率达0.043～0.05 mm/a。

①灰色砾石层；②褐色含砾黄土状土；③钙结核层； ④褐色黄土；④-2粗砂砾石与含砂砾黄土互层； ④-3褐色含砾黄土状土；⑤:表部砂砾土；▲采样点 图6　盆窑村北万全断裂及其地质剖面 Fig.6　Wanquan fault in the north of Penyao 　　　 Village and its geological section

2.3洗马林-水泉断裂(F4)

2.3.1断裂概述

洗马林—水泉断裂位于张家口—宣化盆地西南，走向320°，长达50 km以上(图2)。断裂由一组NW走向的多段左行斜列断裂组成：一段，北起洗马林水库，经洗马林镇到兵民村南；二段，向东北错列约2 km，继而由黑石堰经高庙堡乡、大张窑继续向东南延伸至苏家咀村东；三段，又向东北错列约1 km，由胡山庄经蒋家梁至李受庄；四段又向东北错列由李受庄东北延伸到贾贤庄东南[17]。卫星影像显示(图1)，它是一条枢纽断层，控制着沿线地貌发育，或位错山盆地块，或构成山盆边界，多出露地表，也隐伏地下，各种微地貌特征非常清楚。

2.3.2断裂变形特征

野外调查发现，该断裂的地质地貌现象极为丰富，断面清楚，滑动构造清晰，大幅度错断了晚更新世黄土[图7(a))]。在洗马林村东北，存在由白垩系组成的断层陡坎，陡坎断续延伸，高度大于10 m，坡度较缓。在陡坎下的剖面上见白垩系与中、上更新统和全新统呈断层接触。从断裂两侧的地貌差异和断层剖面反映的情况看，洗马林—水泉断裂晚更新世至全新世有活动，为晚更新世活动断裂，但活动水平较弱，其平均垂直滑动速率为0.1 mm/a左右。

图7　贾贤庄北洗马林—水泉断裂及其地质剖面 Fig.7　Ximalin-Shuiquan fault in the north of Jiaxianzhuang 　　　 Village and its geological section

在贾贤庄村北发现白垩纪砂砾岩逆冲到第四纪地层之上，断层走向NW，倾向NE，倾角40°～48°[图7(b)]。白垩纪砾岩中有多条次级断裂，最新断裂错断白垩纪砾岩与第四纪地层，沿断层破碎带处有白色条带物质填充，白垩纪砾岩定向排列，表层被第四纪坡积层覆盖，由地层颜色、岩性、构造位置等推断此处断裂最新活动时代为晚更新世。

2.4洋河断裂(F3)

洋河断裂隐伏于盆地之下，断层走向315°，长达40 km以上,控制着洋河的流向和阶地发育，断层最新活动时代推测为第四纪。断裂卫星影像显示清楚(图1)。

浅层地震勘探是洋河隐伏断层探测的主要手段[18]，以纵波反射勘探为主。根据洋河断裂区域以往地质、地球物理探测等进行综合分析，判断洋河断裂可能的空间展布，共布设6条浅层地震勘探测线(图1)。其探测剖面结果分析如下：

(1) DZ1测线在洋河南岸的中更新统以下发现有地层错断的现象，断层呈直立的产状，上断点的深度为150 m，推测其为洋河断裂，性质为走滑。DZ2测线在时间剖面和深度剖面上都有明显的地层错断现象；断层向上穿过了Q2的底界，其上断点在Q2地层之内，断层近乎直立，为走滑断层。表明洋河断裂在该段为中更新世活动断层，其上断点到达中更新世地层，上断点的深度为50 m。

图8　DZ5测线时间剖面、时深转换CDP 　　　深度剖面及断层 Fig.8　Stacked time section and depth section by CDP 　　　 of line DZ5 and fault

(2) DZ5测线在洋河北岸剖面上发现了清晰的洋河断裂的构造形态，为北倾的陡断层，倾角为83°。断层向上延伸至中更新世地层，未断错Q3底界，上断点的深度约为180 m。断层两侧中更新世及更早年代地层的深度有所差异，南高北低，断层为走滑加正断层性质(图8)。

3结论与认识

张家口—宣化盆地是一个第三纪末到第四纪早期的强烈断陷，盆地受NWW向和NE向两组断裂的发育和改造，共有四条主断裂带。

(1) 张家口断裂是盆地北缘边界的主控断裂，由NW-NWW向断层构成断裂主体，大多具有北倾逆断性质；近EW断层为前者的连接构造，长度较小，表现为正断性质。断裂在晚更新世期间仍在活动，主体段落的最新活动时代可能持续到全新世。晚更新世中期以来单条断层的平均垂直活动速率大于0.07～0.30 mm/a。

(2) 万全断裂是盆地西北缘一条重要的地质地貌构造分界线，控制着第四纪构造演化和地貌发育。总体呈NNE走向展布，倾向SE，断层露头表现为中高角度正断层，最新活动时代为晚更新世晚期，平均垂直活动速率达0.03～0.20 mm/a以上。

(3) 洗马林—水泉断裂位于盆地西南，由一组NW走向的多段左行斜列断裂组成。断裂有时表现出正断属性，有时具有逆冲性质，断层倾角都比较大。洗马林-水泉断裂为中更新世晚期活动断层，平均垂直滑动速率为0.1 mm/a左右。

(4) 洋河断裂隐伏于盆地之下，总体呈NW向展布，控制着洋河的流向和阶地发育，为中更新世活动的断裂。推测该断层主要为走滑性质，有部分断点为走滑加正断，断层呈近乎直立的产状。

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