青藏高原东北缘海原—六盘山构造带深部电性结构特征及地壳变形

发布时间：2018-04-03 08:08

本文选题：青藏高原东北缘　切入点：海原-六盘山构造带　出处：《中国地震局地质研究所》2016年硕士论文

【摘要】：海原-六盘山构造带地处青藏高原东北缘和鄂尔多斯地块西南缘的接触区,是地壳结构分异、地球物理场变化的梯度带,也是我国晚第四纪构造变形最剧烈的地区之一。研究海原-六盘山构造带及其两侧块体的深部结构与接触关系,有助于认识青藏高原东北缘的扩展变形机制以及深部动力学环境。在前期已有数据的基础上,在地震动力学国家重点实验室项目“南北地震构造带和西秦岭交汇区三维深部结构及强震孕震环境”(LED2013A01)、地震行业科研专项“中国地震科学台阵探测—南北地震带北段”(201308011)资助下,在2013年跨海原-六盘山构造带的3个地段开展了大地电磁探测,获得了3条剖面共计189个测点数据。三条电磁剖面分别跨过构造带的固原段(北段)、隆德段(中段)和华亭段(南段)。数据采集使用了MTU-5A型大地电磁观测系统,采用远参考和"Robust"、相位张量分析等技术对数据进行了精细处理,采用NLCG方法进行二维反演；通过二维正演和采用部分测点进行三维反演计算,对二维反演结果的可信度进行了验证。2013年7月22日发生了岷县漳县6.6级地震,在地震发生时距离震中约300km范围内在3个地点采集了电磁数据。本文展示了这3个点上记录的同震电磁信号和震电磁信号波形,并与测点附近地震台记录到的地震波信号进行了对比；结合数值模拟、深部电性结构等,对震电磁信号与深部结构关系进行了分析。得到主要研究成果如下：(1)断裂带深部延伸状况：研究区内的会宁-义岗断裂、月亮山南麓断裂、海原-六盘山断裂和青铜峡-固原断裂都表现为较大的电性边界。在固原段,月亮山南麓和海原-六盘山断裂存在一定宽度、向西南倾斜的低阻条带,而且还有2个低阻条带,这4个低阻条带在深度约25km汇聚到中下地壳低阻层内,共同组成“正花状”结构；青铜峡-固原断裂是高低阻分界断裂。在隆德段,月亮山南麓断裂为倾向北东方向的低阻条带,六盘山断裂是向西南方向倾斜的低阻条带,两条断裂同样在深度约25km处汇聚并连接中下地壳低阻层,该段青铜峡-固原断裂与韦州-安国断裂电性差异较小。在华亭段六盘山断裂带不再具有“正花状”结构,而表现为单一向西南倾斜的低阻边界带。(2)地块深部电性结构：三条剖面自西南到东北都跨过陇中盆地、弧形构造带、鄂尔多斯地块。结果揭示弧形构造带深部具有高阻背景下镶嵌低阻条带的结构特征,低阻条带向下延伸归并到中下地壳低阻层中；陇中盆地具有较好的电性成层性,三条剖面的电阻率结构相似,浅表几百米到一定深度范围内都是高电阻,在深度25km左右存在低电阻层；鄂尔多斯西缘带表现为完整的高阻体,鄂尔多斯盆地则显示低-高-低电阻层状结构。(3)深部电性结构特征与地壳变形：海原-六盘山构造带西南侧的陇中盆地地壳内高阻体和低阻体相间分布、相互叠置,而其东北侧的鄂尔多斯西缘带为较完整的高阻块体。活动构造研究发现海原断裂带的左旋走滑位移已转换为六盘山断裂带的地壳缩短,GPS观测表明现今构造变形分布在六盘山以西上百公里的范围内,深部电性结构可以很好地解释这种变形状态：海原-六盘山构造带西南盘的地壳非常破碎,在青藏高原向北东方向的推挤下容易发生变形,而北东盘的地壳结构完整,很难发生构造变形。(4)六盘山构造带的深部结构特征及地震危险性：由深部电性结构图像推测,构造带西南侧陇中盆地是中、下地壳存在可能具有低粘滞度的低阻层结构的变形单元,六盘山构造带是闭锁单元,具有累积应力的能力,而层状稳定的鄂尔多斯地块是起阻挡地壳运动作用的支撑单元。六盘山构造带的变形特征和深部结构环境与发生汶川地震前的龙门山相似,应考虑其未来地震危险性。(5)2013年岷县漳县MS6.6地震震电磁信号和同震信号观测分析：2.013年岷县漳县MS6.6地震发生时,位于距震中约300km附近的3个地点正在实施大地电磁测量。3个测点上的大地电磁仪器不仅记录到了地震波传播过程中的同震电磁信号波形,而且记录到了地震破裂过程中所激发的震电磁信号。3个地点记录到的这种信号都在地震后约12秒同时出现,且持续4秒左右,远远早于地震P波到时。
[Abstract]:The contact area of Haiyuan - six Panshan tectonic belt located in the northeastern margin of the Tibetan Plateau and the southwestern margin of the Erdos plots, crustal structural differentiation, geophysical field gradient zone, is also China's late Quaternary tectonic deformation is one of the most intense research area. The Haiyuan six mountain tectonic belt and its both sides of the block and deep structure contact relationship, help to expand the understanding of the northeastern margin of the Tibetan Plateau deformation mechanism and geodynamic environment. Based on the previous data, the State Key Laboratory of Earthquake Dynamics Project "North South seismic tectonic belt and the West Qinling Mountains area at the intersection of 3D deep structure and strong seismogenic environment" (LED2013A01), seismic industry research projects China seismic array exploration - northern section of North South seismic belt "(201308011), in 2013 3 a lot of six cross the Haiyuan mountain tectonic belt to carry out magnetotelluric exploration, obtained A total of 3 profiles of 189 measured data. Three electromagnetic profile across Guyuan segment tectonic zone (North), Longde (middle) and Huating (South). Data acquisition used MTU-5A magnetotelluric observation system, the remote reference and "Robust" phase tensor analysis techniques for data fine processing, using NLCG method for two-dimensional inversion; through 2D Forward and the measuring point for 3D inversion calculation of 2D inversion results for the credibility of the Minxian Zhang county 6.6 earthquake happened verification of.2013 in July 22nd, at the time of the earthquake epicenter about 300km within the scope of 3 sites were collected. The electromagnetic data show the 3 points recorded on the coseismic electromagnetic signal and earthquake electromagnetic signal waveform, compared the seismic signal and measuring points near the seismic record; through numerical simulation, deep electric structure etc., On the relationship between seismic electromagnetic signals and deep structure are analyzed. The main research results are as follows: (1) the deep extension of the fault zone: the study area - ning Yi Gang fracture, the moon south foot fracture, six Panshan Haiyuan fault and Qingtongxia Guyuan fault are electrically large. At the boundary Guyuan, the moon hill and Haiyuan - six Panshan fracture width, southwest dipping low resistance bands, and 2 low resistance bands, 4 bands of low resistivity at a depth of about 25km convergence to the low resistivity layer in the lower crust, to form a positive flower structure; the Guyuan fault is a boundary fault resistance level. In Longde, for the tendency of the north east direction low resistance strip moon foothill fault zone, six is inclined to the southwest mountain fracture of the low resistance bands, two faults in the same depth at 25km together and connect the lower crust low resistivity layer, the Qingtongxia - Guyuan fault and Wei - Anguo electric difference is small. The fracture section of the Huating fault zone in six Panshan longer has the positive flower structure, while the performance of low resistivity single boundary southwest dipping zone. (2) plots the deep electrical structure: three profiles from southwest to northeast across all of Gansu in the basin, arc tectonic belt, Ordos massif. Results reveal the deep arc structural belt has high impedance under the background of embedded low resistance band structure, low resistance bands extending down to merge the lower crust low resistivity layer in Longzhong basin; has good electrical resistivity layers, structures of three profiles it is similar to the high resistance of superficial a few hundred meters to a certain depth range, low resistance layer at the depth of about 25km; Ordos west margin belt is characterized by high resistivity body complete, Erdos basin showed low - high - low resistance layer structure. (3) the deep electrical structure. Sign and crustal deformation: the crust basin Haiyuan six Panshan tectonic belt of the southwest side of the Gansu in high resistivity and low resistivity and distribution, overlapping, and the northeast side of the western margin of Ordos high resistance block is complete. Active tectonics research found of Haiyuan fault zone strike slip displacement has been converted to shorten six Panshan fault zone of the earth's crust, GPS observations show that the tectonic deformation distribution in hundreds of miles west of the six mountain ranges, deep electric structure can well explain the deformation state: the Haiyuan tectonic belt of southwest six Panshan disc crust are broken, easy to deform in pushing North Tibetan Plateau under the direction of the East, North and east of the crustal structure, tectonic deformation is difficult to occur. (4) the characteristics of deep structure and seismic hazard six mountain tectonic belt: inferred by deep electric structure image, tectonic belt of southwest side of Longzhong basin is In the lower crust deformation unit may have a low resistivity layer structure of low viscosity, six mountain tectonic belt is the blocking unit, has the ability of accumulated stress, and stable block is Ordos layered support unit blocking effect. The crustal movement of Longmen mountain and the deformation characteristics of deep structure environment six mountain tectonic belt and before the Wenchuan earthquake is similar, should consider the future seismic risk. (5) analysis of the 2013 Minxian MS6.6 earthquake Zhangxian electromagnetic signal and the coseismic signal observation: Minxian MS6.6 earthquake occurred 2.013 years Zhang county, located in the epicenter about 3 locations near 300km is implementing magnetotelluricinstrument magnetotelluric measurement.3 the measuring point not only recorded coseismic electromagnetic wave propagation of seismic waves in this kind of signal, and recorded the earthquake rupture process of earthquake excitation electromagnetic signals recorded by.3 sites It all appeared at about 12 seconds after the earthquake, and lasted about 4 seconds, far earlier than the arrival of the earthquake P wave.

【学位授予单位】：中国地震局地质研究所
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P315;P631.325

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