【作者】 杜龙；

【导师】 周本刚；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2008， 硕士

【摘要】 大兴安岭断块隆起区属于弱地震活动区,对于该区中强地震的地震构造研究以前并没有引起足够的重视,地震构造研究基础较为薄弱,局部地段属于研究空白区。但是,本区存在一些中强地震及小地震活动,仅以区域南部为例,无论在大兴安岭还是在西部二连盆地区,中强地震的活动频次较高,历史上5级以上的地震就达11次。尤其是,本区2003年8月16日和2004年3月24日先后发生了两次5.9级地震,为该地区有记载以来的最高震级,这两次地震的发生突破了以往我们对这一地区地震构造背景的认识,反映在震中区位于现有潜在震源区以外,所以,研究该地区的地震构造及潜在震源区划分问题,具有必要性及迫切性。本研究对于深化大兴安岭断块隆起区发震构造的认识具有科学意义,对该地区潜在震源区合理划分,进而提高本区地震危险性评价结果的合理性,具有实际价值。本研究在对2003年8月16日内蒙古巴林左旗5.9级地震发震构造调查与分析的基础上,系统收集目前大兴安岭断块隆起区的地震构造特征和地震活动资料基础上,分析该区现有中强地震震例的地震构造特征,系统总结该地区地震发生的构造条件,提出该区的潜在震源区划分的依据,并对大兴安岭断块隆起区的潜在震源区作了重新划分。通过对研究区晚新生代构造活动特征的分析,认为新构造期以来该区的构造运动以隆升为主,但在隆升背景下存在差异性活动的特点,该区的构造地貌分界线和新构造的主体构造线方向均为北东方向。而这一地区的发震构造除受北东向构造控制外,还受北西向断裂的控制。该区有相当数量的第四纪火山分布;断裂活动的总体水平较低。2003年内蒙古巴林左旗Ms5.9级地震在大兴安岭地区显得颇为凸出,为有记载以来的最高震级,突破了以往我们对这一地区地震构造背景的认识,研究基于对内蒙古巴林左旗Ms5.9级地震相关的地球物理、地震学资料收集,结合震区及周边地区的航卫片解译,对整个震区进行野外地质地貌调查,发现了北西向水泉子沟-天山口断裂的存在,初步得出该断裂的长度为60km,该断裂分为北西西向的水泉子沟-西山湾段与北西向的杨树林-天山口段,其中,水泉子沟-西山湾段的活动相对较新,断错中更新统,而据断层泥ESR样品的年龄测试,其最新活动时代为325±32ka,即Qp~2中期;综合分析该次地震的震源机制解、震害分布特征以及余震序列的研究结果,从而推测,水泉子沟-天山口断裂之水泉子沟-西山湾段为2003年内蒙古巴林左旗Ms5.9级地震的发震断裂。NWW向的水泉子沟-西山湾段为一SW倾的活动较弱的中更新世中期的活动断裂,为左旋正断。大兴安岭断块隆起区以整体掀斜式抬升为特征,但抬升的幅度比较微弱,即不属于强烈活动的构造区。在这一总体背景下,出现局部的差异运动,西部出现呼伦湖—贝尔湖凹陷,东部出现斜坡带,中部发生隆起。其中,呼伦湖—贝尔湖凹陷的两侧是垂直差异运动较强烈的地段,继承性新构造运动形成现代的呼伦湖和贝尔湖,并在呼伦湖东、西两侧产生第四纪活动断裂。而对于中部扎兰屯—乌兰浩特隆起,在总体北东向带状隆起的基础上,产生了一组北西向的断裂,其中主要的有雅鲁河断裂、阿伦河断裂等,它们主要活动于早、中更新世,局部活动于晚更新世。伴随这些断裂活动,火山喷发作用也很烈,这种成群的地震活动与火山活动关系也较密切。东部的斜坡带是走向北东的活动较明显的构造带。基于大兴安岭隆起区主要以沿NW-SE一线具有差异性活动的特点,提出该区潜在震源区的划分原则,具体为:(1)在大兴安岭西部,跟北东-北东东向的盆地发育相关的断裂具有第四纪以来的活动特征,如呼伦湖断陷盆地、乌拉盖盆地。(2)大兴安岭主脊及其东部斜坡带,主要依据NE向主干断裂的展布及与之交汇的NW向的断裂的活动性的差异来划分。(3)隆起区边缘的嫩江断裂,一直以来具有明显的活动特征,因此,其主要延续了以前的划分原则。更多还原

【Abstract】 Less attention has been paid to the study of seismic tectonics of the Daxing’anling Uplift because of the location in the area of low seismicity in the past. However, the distribution as belts or clusters for moderate and small earthquakes clearly indicates modern crustal movement. There is a high frequency of moderate earthquake in this area, especially, two 5.9 earthquake took place in 2003 and 2004 respectively, which is beyond our understanding.According to analysis of the characteristic of tectonic deformation in late Cenozoic in the target area, we infer that the tectonic movement is represented by gradually uplifting. The main geotectonic curve is characterized by NE trend. The causative tectonics is controlled by the interaction of NE trend and NW trend.The determination of seismogenic structure is of importance in seismic hazard analysis (SHA). It is challenging as to the identification of seimogenic structure of moderate earthquake. It’s absolutely well-marked that the 2003 Balinzuoqi MS5.9 earthquake occurred because of the low seismicity of the whole Daxing’anling Uplift. The penetrating research of conditions that“2003 event”took place, which can make sense to the understanding of seimogenic structure of Daxing’anling Uplift. According to the evidences derived geologically in the target area, we find the distribution of fault caused the 2003 earthquake, that is, the Shuiquanzigou-Xishanwan-Tianshankou fault cut the stratum of 498±49Ka which dated by ESR, showing property of left-lateral normal. meanwhile, we acquire the latest active information of the seismogenic fault based on the materials collection of geophysics and seismology related to this event and the interpretation of remote sensing images.Seismicity and geotectonic movement are characterized by intergrowth. Earthquakes often occurred along active tectonic zones, such as boundaries between different geotectonic units, including the margins of great depressions with development of secondary depressions. Along the boundaries of great uplifts with exposures of Quaternary volcanic rocks, moderate strong earthquake also easily occurred. Moderate strong earthquake often occurred along the regional Quaternary active fault zones. The regional faults on the margin of great uplifts (such as the Daxing’anling Uplift) with the development of secondary basins, even though they did not show clear activity in the Quaternary, may be the occurrence sites for earthquake with M = 5-5~1/2. For example, in the Wulagai Basin, Hulunhu faulted Basin, some earthquakes with M=5.0 or so have occurred. Moderate strong earthquakes are related to the clustered zones of recent small earthqukes. For recent moderate strong earthquakes, the clustered zones can show the scale of seismic focus. Historical moderate strong earthquake were generally related to the intersection between seismic zones of small earthquakes though sometimes the cluster of small earthquake was not clear. In the Quaternary buried regions, the secondary Cenozoic faulted depressions where recent small earthquakes occurred frequently are also the seismogenetic sites for moderate strong earthquakes. The Quaternary fault zones with the exposures of Cenozoic basaltic rocks, and the clustered belts of modern small earthquakes are all the occurrence sites of moderate strong earthquakes.更多还原