地球介质衰减特性层析成像

发布时间：2017-12-28 20:02

  本文关键词：地球介质衰减特性层析成像　出处：《中国地震局地球物理研究所》2016年博士论文　论文类型：学位论文

  更多相关文章： 地方震层析成像 地震波衰减 衰减特性层析成像 背景噪声 水库库区 中国大陆 地球介质

【摘要】：与地震波衰减直接相关联的介质品质因子Q值描述了地球介质的非弹性和非均匀性,是了解地下裂隙的数量、孔隙密度与分布以及孔隙中存在的流体含量的重要参数。测定衰减的横向变化不仅能为了解地下热结构、粘性和流变特性提供额外约束,更重要的是对于解释三维速度结构有重要意义,是理解地震波速度和地球介质密度横向不均匀分布的重要参数。本论文基于不同类型的地震波形数据,采用层析成像的方法进行了不同尺度介质衰减结构的研究。首先基于地方震数据在3个典型水库库区进行了小区域三维精细衰减结构层析成像的研究,通过衰减结构的分布评估了地下流体的渗透和扩散状态。其中在紫坪埔水库库区,本论文通过汶川Ms8.0地震前后的三维衰减结构推断了紫坪埔水库库水渗透和扩散在Ms8.0地震发生发展过程中的可能作用。然后利用Lg波在新疆地区开展了区域尺度的衰减结构成像,得到了新疆地区高分辨率的Lg波衰减结构图像。最后分别基于中短周期地震面波和背景噪声面波,开展了中国大陆大尺度的衰减结构层析成像,通过改进振幅提取技术,极大的提高了计算效率。其中,利用背景噪声面波进行衰减结构成像的研究系首次基于完整的理论体系将背景噪声互相关技术应用于衰减结构成像中,并系统形成了背景噪声面波衰减结构成像的完整数据处理和计算程序,进而将该方法应用于中国大陆地区得到了研究区高分辨率的背景噪声面波衰减图像。地方震层析成像是研究小区域典型构造区介质结构的主要方法,广泛应用于断层带、俯冲带、火山区和水库库区。尤其在水库库区,地方震成像技术是研究地下流体分布和状态的重要方法,是推断地震活动与地壳结构的精细关系以及地震发生机理的重要依据。水库库区地壳介质中孔隙流体的渗透和扩散是水库诱发地震的一个重要原因,是研究水库诱发地震的成因机理和进一步判定水库诱发地震危险性的重要参数。将速度(VP)、波速比(VP/Vs)和衰减(Q值)结构成像相结合是分辨由于结构不连续或流体渗透导致的地下结构变化的最重要方法。本论文利用地方震成像技术在龙滩、三峡、紫坪铺三座大型水库库区开展了三维速度、波速比与衰减结构层析成像的研究。三个库区高分辨率的三维速度、波速比与衰减图像均揭示了水库库区周围介质的复杂性以及流体渗透对介质结构存在的影响,其中流体在库区下方断裂带中的渗透和扩散可能是地震发生的重要起点。龙滩和三峡库区的介质结构显示,库区下方浅层存在明显的低VP,高VP/VS,低QP和低Qs分布特征,表明浅层介质发生了明显的流体渗透现象。龙滩水库库首区和主要河流下方的低VP,高VP/Vs,低QP和低Qs的异常深度达到了4-7km左右,表明龙滩水库的库水渗透深度可能达到了4-7km。三峡水库库区的仙女山断裂周围流体的渗透可能达到6km左右,其他主要河流下方的库水渗透可能只有2km左右。紫坪铺水库库区的三维Vp,Vp/Vs,Qp和Qs图像表明紫坪铺水库的库水渗透深度可能达到了10km以上,可能与水库周围存在深大断裂有关。我们推断紫坪铺水库的库水渗透有可能是汶川Ms8.0地震发生的触发因素,进一步的证据需要结合水库蓄水前的三维介质结构进行更深入研究。汶川地震后,紫坪埔水库下方的高衰减区进一步扩大,表明该地震使得震源区周围的介质发生了明显破裂,流体沿断层和裂隙进一步渗透和扩散,导致高衰减区的范围比震前更大,深度更深。Lg波是区域范围内地震波中能量最强、振幅最大、在地震图上表现最为突出的震相,因此Lg波Q值成像是了解区域构造特征并寻找介质异常区的重要手段。本论文基于Lg波,对新疆及邻近地区开展了区域尺度的衰减结构成像。Lg波衰减图像显示,QLg的分布形态与研究区地质构造紧密相关。帕米尔高原东北缘、青藏高原西北缘、南天山西段、北天山及其北缘的准噶尔盆地内部区域属于低Q0区,塔里木盆地西部、塔里木盆地东部、包括吐鲁番-哈密盆地的东天山、南天山东段以及北天山都属于高Q0区。根据研究区QLg值分布图像与地形的明显相关性,我们认为Lg波具有明显的通道波特征。并由塔里木盆地和准噶尔盆QLg分布图像的分区性推断这两个大型刚性盆地内部可能存在隐伏断裂。由于面波的优势周期比体波大,因此面波主要对较大尺度的构造特征有较好的采样。在地震图中超过一定的震中距范围,面波的能量往往很大,且在地球表面衰减较慢,对台站覆盖较差的区域也可能得到较高分辨率的成像结果。因此,面波层析成像是了解大尺度构造特征的重要数据,在少震区和台站密度相对较低的地区也同样适用。本论文基于中国大陆国家地震台网和区域台网的188个宽频带台站的10s和20s周期的地震瑞利面波,在相匹配滤波的基础上,提取了瑞利面波振幅比,并基于双台谱比的方法反演了中国大陆10s和20s面波的衰减结构图像。我们开发了自动测定地震振幅谱的方法,并与手动测定的方法进行了对比,结果具有较好的一致性,大大提高了计算效率,实现了使用双台法基于大量地震数据反演得到了中国大陆高分辨率的二维衰减结构模型。在中国大陆中东部地区模型的分辨率达到了3°左右,在西部和中国大陆边缘地区,模型的分辨率在5°左右。本论文的成像结果与已有的中国大陆衰减结构的分布具有较好的相似性,与地质构造特征也具有较好的对应关系。近年来,噪声面波成像技术得到了飞速发展,摆脱了地震面波成像对地震定位和震源机制的影响,并不受地震发生无规律的限制。噪声面波成像已广泛应用于速度结构反演。由于背景噪声源的强度和分布随时间、位置和方向变化的复杂性,从背景噪声互相关中提取振幅进而进行衰减结构的研究要远远落后于速度结构的研究。本论文首先基于数值模拟数据开展了从背景噪声互相关中提取面波振幅并反演介质衰减系数的测试,表明可以从temporal flattening后的数据中正确提取瑞利波衰减。此后详细阐述了从背景噪声中提取瑞利波振幅的整个过程,并介绍了一种改进的temporal flattening方法。通过与实际地震面波中提取的衰减系数对比,我们认为从背景噪声中提取振幅计算一维衰减结构的方法是可行的。在此基础上,本论文进一步开展了二维衰减结构模型层析成像的研究。基于各向异性的噪声源分布和不均匀衰减结构模型,利用数值模拟的方法产生了100个台站长时间的背景噪声记录。采用180kmm和60km两种尺度的网格节点间距对研究区进行网格化,在两种尺度下进行了二维衰减结构层析成像。反演得到的衰减模型与设定的初始模型基本一致。检测板测试的结果也显示,本论文中提出的噪声面波振幅的提取方法和参数设置可以成功的反演二维衰减结构模型。最后,我们使用国家台网和区域台网146个宽频带地震台站记录的真实的背景噪声数据,开展了中国大陆噪声面波衰减结构成像的研究。首先利用窄带滤波和异步temporal flattening等方法对背景噪声数据进行处理。通过噪声互相关,得到了10s和20s周期的1万多条台站对间的瑞利波经验格林函数,利用相匹配滤波技术和双台成像方法反演了10s和20s周期的瑞利波衰减图像。其中新疆西南部、青藏高原西部、东部地区和研究区其他的边缘地区的图像分辨率在2.5°-5°之间,其他地区衰减图像的分辨率达到了2.5°左右。衰减图像与地质构造特征具有较好的对应性,与中国大陆已有的地震面波衰减结构图像也具有较好的一致性。表明利用真实的地震背景噪声记录,从背景噪声互相关中提取瑞利波振幅,并进行二维瑞利波衰减结构层析成像是可行的,为面波衰减结构层析成像的研究提供了另一条途径,摆脱了对地震发生的依赖且可以提高衰减图像的分辨率,具有重要的应用价值。
[Abstract]:The medium quality factor Q, which is directly related to seismic attenuation, describes the inelasticity and non-uniformity of the earth's medium. It is an important parameter to understand the number, density and distribution of underground fissure, and the fluid content existing in the pores. The lateral variation of attenuation can not only provide additional constraints for understanding the underground thermal structure, viscosity and rheological properties, but also is important for explaining three-dimensional velocity structure, and is an important parameter to understand the lateral heterogeneity of seismic wave velocity and earth medium density. Based on different types of seismic waveform data, this paper uses the method of tomography to study the dielectric attenuation structure of different scales. Firstly, based on local seismic data, three dimensional fine attenuation structure tomography is studied in 3 typical reservoir areas, and the permeability and diffusion state of underground fluid is evaluated through the distribution of attenuation structure. In the Zipingpu Reservoir area, this paper deduces the possible role of reservoir infiltration and diffusion of Zipingpu Reservoir in the occurrence and development of Ms8.0 earthquake through the three-dimensional attenuation structure before and after the Wenchuan Ms8.0 earthquake. Then Lg wave is used in Xinjiang area to carry out the region scale attenuation structure imaging, and the high resolution Lg wave attenuation structure image of Xinjiang region is obtained. Finally, based on the Mid short period seismic surface wave and the background noise surface wave, we carried out the large-scale attenuation structure tomography in mainland China, and improved the amplitude extraction technology, which greatly improved the computation efficiency. Among them, the background noise of surface wave attenuation imaging system structure for the first time a complete theoretical system based on the cross-correlation technique applied to background noise attenuation structure imaging, and formed a complete system of data structure of image background noise attenuation of surface wave processing and calculation program, then this method is applied to the China mainland has been studied the background noise of high resolution surface wave attenuation image. Local seismic tomography (local seismic tomography) is the main method to study the medium structure of typical regional tectonic zones. It is widely used in fault zone, subduction zone, volcanic area and reservoir area. Especially in reservoir area, local seismic imaging technology is an important way to study the distribution and state of underground fluid, and it is an important basis for inferring the fine relationship between seismic activity and crustal structure and the mechanism of earthquake occurrence. The infiltration and diffusion of pore fluid in the crustal medium of reservoir area is an important reason for reservoir induced earthquake. It is an important parameter for studying the mechanism of reservoir induced earthquake and further determining the risk of reservoir induced earthquake. The combination of velocity (VP), wave velocity ratio (VP/Vs) and attenuation (Q) structure imaging is the most important way to distinguish the change of underground structure due to structural discontinuity or fluid penetration. In this paper, the Three Gorges, Longtan Reservoir Zipingpu three large reservoirs on the three-dimensional velocity, wave velocity and attenuation structure tomography using local seismic imaging technology. The three area high resolution three-dimensional velocity, wave velocity ratio and attenuation images reveal the complexity of the surrounding medium reservoir and fluid infiltration effect on dielectric structure exists, where the fluid permeability reservoir beneath the fault zone and the diffusion may be an important starting point of the earthquake. The medium structure in Longtan and Three Gorges Reservoir area shows that there are obvious low VP, high VP/VS, low QP and low Qs distribution characteristics in the shallow layer below the reservoir area, which indicates that obvious fluid penetration phenomenon occurs in shallow media. The depth of low VP, high VP/Vs, low QP and low Qs of the Longtan Reservoir head and main river reaches about 4-7km, indicating that the reservoir depth of Longtan Reservoir can reach 4-7km. The seepage of the fluid around the fault of the fairy mountain in the reservoir area of the Three Gorges reservoir may reach about 6km, and the permeability of the reservoir water below the other main rivers may be only about 2km. The 3D Vp, the Zipingpu Reservoir Region of Vp/Vs, Qp and Qs images show that the depth of penetration of Zipingpu Reservoir water could reach more than 10km, and there are deep faults around the reservoir on the. We conclude that the Zipingpu Reservoir water permeability may be associated with the Wenchuan Ms8.0 earthquake triggering factors, further evidence of the need to combine three-dimensional medium reservoir structure in front of a more in-depth study. After the Wenchuan earthquake, the high attenuation area below the Zipingpu Reservoir further expanded, indicating that the earthquake caused the obvious rupture of the surrounding media, and the fluid further penetrated and diffused along the fault and fissure, resulting in the range of high attenuation area larger and deeper than that before the earthquake. The Lg wave is the most powerful seismic phase in the region, with the largest amplitude and the most prominent phase on the seismic map. Therefore, the Lg wave Q value imaging is an important way to understand the regional structural characteristics and find out the abnormal area of the medium. Based on the Lg wave, the attenuated structural imaging of regional scale is carried out in Xinjiang and adjacent areas. The Lg wave attenuation image shows that the distribution of QLg is closely related to the geological structure of the study area. Junggar basin, northeastern Pamir Plateau of the northwest of Qinghai Tibet Plateau, southern Shanxi, the northern margin of the North Tianshan Mountain and its belongs to the low Q0 zone in the Western Tarim Basin, Eastern Tarim Basin, including Turpan - Hami basin, East Tianshan, South and north section of Shandong mountain area belongs to the high Q0 days. According to the obvious correlation between the QLg value distribution image and the terrain in the study area, we think that the Lg wave has obvious channel wave characteristics. It is also deduced from the QLg distribution of the Tarim Basin and the Junggar basin that there may be hidden faults in the two large rigid basins. As the dominant period of the surface wave is larger than that of the body wave, the surface wave is mainly sampled for the structural features of the larger scale. Over a certain range of epicentral distances in an seismograph, the energy of the surface waves is often very large, and the attenuation of the earth's surface is slow, and the areas with poor coverage of the station may also be obtained.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P315.6
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