【作者】 苏有锦；

【导师】 傅容珊；

【作者基本信息】 中国科学技术大学 ， 固体地球物理， 2009， 博士

【摘要】 地震波衰减性质的研究是地震学研究的重要课题。地震波传播的路径效应（地震波衰减）,除了随距离存在几何衰减外,还有一个重要的影响因素——即介质的非弹性衰减,用介质品质因子Q值来度量。Q值是地球介质的基本物理参数之一,是对地震进行定量和研究震源性质（如震源参数的测定等）所必需的重要参数,在震源物理和工程地震研究中有重要应用。现有研究认为,地震波衰减Q值与地壳结构特征,如火山区的岩浆分布,地震活动,构造活动区的断层分布,壳内低速层等有密切关系。因而通过对地壳、上地幔衰减结构横向变化的研究,将有助于我们更准确地认识其构造活动性、动力学特征、地幔中的热结构及粘滞结构等。地震波的衰减Q值比波速对地球结构和介质组成的变化更敏感,精细的三维衰减结构研究,能深化地壳结构和组成横向非均匀性的本质认识。云南地区位于青藏高原隆起的东南边坡地带,其地势西北高,东南低:处于印度板块向中国大陆北东向挤压作用的前沿地带,使得这个地区构造复杂,强震活动频繁。云南历史强震活动图象的研究表明,破坏性强震活动的分布是不均匀的,主要集中在几个区（带）上。深化对这些破坏性大地震发生的深部介质和构造环境认识,以及大震多发区与无大震发生地区在深部介质和构造环境上的异同,对地震孕育发生的成因机制研究及其预测理论、技术方法等研究有重要意义。地震层析成像已经是比较成熟的一种技术,目前大量应用于地震波速度结构反演,将其应用到Q值研究中来,势必会大大促进地震波衰减特性的研究。近十年来,随着区域数字地震台网建设的快速发展,获取了大量的数字地震波形资料,为开展Q值的层析成像研究提供了条件。本研究应用云南区域数字地震台网记录（23个子台）的地震波形资料（1999年6月-2007年12月）,分别采用一维（1D）、二维（2D）、三维（3D）的反演方法,开展了云南地区地震波（S波）衰减结构（Q值结构）的反演研究:（1）采用Atkinson方法和遗传算法反演计算得到了云南地区及分区S波非弹性衰减Q值与频率（1～15Hz）的关系（既Q（f）=Q₀f^η关系）。（2）用测定地震波（S波）高频衰减因子t^*,再用t^*数据进行地震波衰减结构成像的技术方法,进行了云南地区地震波衰减（Q值）结构二维成像反演。研究并给出了实现衰减（Q值）结构二维成像反演的算法,在此基础上实现了用S波谱测定高频衰减因子t^*的反演程序和衰减（Q值）结构二维成像反演程序的设计和编制（Matlab编程）,反演得到了云南地区0.5°×0.5°网格的Q值结构二维成像结果。（3）采用地震层析成像技术,用与2D反演同样的数据,进行了云南地区地震波衰减（Q值）结构三维成像反演。研究并给出了实现衰减（Q值）结构三维成像反演的算法,并设计和编制了衰减（Q值）结构三维成像反演程序（Matlab编程）。反演得到了云南地区1°×1°网格（平面网格）、深度分层为0km、5km、15km、25km、45km共5个分层模型的Q值结构三维成像结果。通过本文的研究,获得了云南地区地壳介质衰减结构的基本认识。一维分区反演、二维成像反演和三维成像反演结果均表明,云南地区地壳S波衰减Q值横向变化显著,总体上金沙江-红河断裂带以东地区（云南东部地区）Q值相对较低,以西地区（云南西部地区）Q值相对较高;滇西北地区（丽江-永胜-大理-楚雄一带）,滇中地区（东川-昆明-玉溪-华宁-建水一带）存在两个明显的低Q值区。二维成像反演和三维成像反演结果进一步显示出,保山—腾冲和思茅-景洪一带还存在两个低Q值区域;而澜沧-耿马地区存在较明显的高Q值区。三维成像反演结果还表明,滇西北低Q值区、思茅-景洪低Q值区和保山—腾冲低Q值区大致到10km左右深度:而滇中低Q值区延伸到了20km左右深度。云南地区Q值的横向变化及其分布特征与该区构造活动、地震活动、地壳速度结构及热活动状态的区域差异性有较好的一致性,活动强烈、高热活动、低速区为相对低Q值区,地震波衰减较快。本文的研究结果还表明,澜沧-耿马强震活动区在Q值结构上与滇西北、滇中两个强震活动区存在明显差异,前者为高Q值区,后者为低Q值区。这种差异性在速度结构特征、热结构特征及活动构造特征等方面也存在。这可能进一步表明,云南地区强震活动确实存在两种不同的介质构造环境。总之,本文的研究,建立了开展S波非弹性衰减（Q值）一维（1D）、二维（2D）、三维（3D）反演研究的方法;并利用云南区域数字地震台网资料,实现了云南地区S波Q值1D、2D、3D反演,获得了云南地区地壳介质衰减结构的基本认识。1D反演结果（Q值与频率关系Q（f）=Q₀f^η）已被广泛应用于云南地区数字地震记录资料的分析、研究中,尤其是震源参数测定等方面的研究。2D、3D反演结果所揭示的云南地区地壳Q值结构特征,对深入认识云南地区强震发生的介质环境提供了新的资料和证据,进一步证实了云南地区强震活动存在两种不同的介质构造环境。更多还原

【Abstract】 The study of seismic attenuation property is a major subject in seismology. The path effect of seismic wave propagation (seismic attenuation) involves an important influential factor, the anelastic attenuation of medium, which is measured with quality factor Q, apart from geometric attenuation with the distance. As a basic physical parameter of the Earth medium, Q value is essential for quantitative study of earthquakes and source property (e.g. determination of source parameters), which is widely used in earthquake source physics and engineering seismology.There existed the osculatory relations between the seismic attenuation Q value and the crust structure features, such as the magma distribution of volcano zone, the earthquake activities, the active faults and the low velocity layer of the crust et al.. The study of the attenuation structure in the crust and the upper mantle, it will help us to understand more truly the tectonic activity, dynamic features of the crust and the upper mantle, as well as the thermal structure and the viscosity structure of the mantle. The seismic wave attenuation Q value is more sensitivity to the variation of the earth medium than the seismic wave velocity. The finely study of the three-dimensional attenuation structure, it can deepen the knowledge to the heterogeneous of the crust structure.Yunnan region is located at the southeast edge of Qinghai-Tibet plateau, the topography is high in northwest and low in southeast. It is a front zone where the India-Burma plate moves and pushes northeastward to the China Mainland, therefore, the tectonics is complicated, the strong earthquakes are very frequent in this region. The study of the activity of the historically strong earthquakes suggested that the distribution of the destructively large earthquakes in Yunnan is inhomogeneous, which are mainly concentrated at the several seismic zones or belts. The study and knowledge of the deep medium and tectonic environments for these large earthquakes occurrence, and the difference between the large earthquake-prone zones and the non-seismic zones in the deep medium and tectonic environments, it have important significance for the study of the seismogenesis, the theories and the technical methods of the earthquake prediction etc..At present, the seismic tomography method had been applied widely to the inversion of the seismic wave velocity structure. By using of this technique, it would improve greatly the study of the seismic wave attenuation Q value. Recently 10 years, a great deal of seismic waveform data had been obtained following the establishment and improvement of regional digital seismograph networks, they provide the conditions for the tomography of seismic attenuation structure.In this paper, the inversion of the seismic wave attenuation Q value in Yunnan region had been conducted by using of 1D, 2D and 3D inversion methods respectively, waveform data( June, 1999 to December, 2007) from Yunnan regional digital seismograph network.(1) The 1D inversion of Q value of S-wave anelastic attenuation in Yunnan region and its subregions had been conducted with Atkinson method and genetic algorithm, and the relations between Q( f) and frequency f in Yunnan region and its subregions had been established.(2) The 2D tomography of S-wave anelastic attenuation in Yunnan region had been conducted by using of the high-frequency attention operation t* of S wave. The algorithm and program of 2D attenuation tomography had been established. The 2D attenuation tomography of 0.5°×0.5°gridding model in Yunnan region had been accomplished.(3) The 3D tomography of S-wave anelastic attenuation in Yunnan region had been conducted by using of the high-frequency attention operation t* of S wave. The algorithm and program of 3D attenuation tomography had been established. The 3D attenuation tomography in Yunnan region had been accomplished, for the model of 1°×1°plane gridding and 0, 5,15,25,45km vertical layering.The basic characteristics and knowledge of the crust attenuation structure in Yunnan region had been achieved by this study. The results of the 1D inversion, 2D tomography and 3D tomography all indicated that there is a significant lateral heterogeneity on Q value spatial distribution in Yunnan region. Q value is relatively high in western Yunnan and low in eastern Yunnan, divided by the Jinshajiang-Honghe fault; There existed two obviously low Q zone in the northwest Yunnan (Lijiang - Yongshen - Dali - Chuxiong) and in the central Yunnan (Dongchuan - Kunming - Yixi - Huaning - Jianshui). The results of the 2D tomography and 3D tomography also indicated that there are two low Q zone in Baoshan - Tengchong and Simao - Jinhong; Lanchang - Genma zone is high Q zone. The results of the 3D tomography indicated that the depth is about 10km for the low Q zone in the northwest Yunnan, Baoshan - Tengchong and Simao - Jinhong, and about 20km for the the low Q zone in the central Yunnan. The lateral heterogeneity on Q value spatial distribution in Yunnan region, is quite consistent with the regional difference between tectonic activities, seismic activities, crustal velocity structure and thermal activities of the region. Areas with intense tectonic activities, high heat activities and low velocities are usually one of low Q values, where the seismic wave attenuation is fast.The study results in this paper also presented that there existed obviously difference on the Q structure between the strong earthquake active zone of Lanchang - Genma and that of the northwest Yunnan, the central Yunnan; the former high Q zone, and the after low Q zone. This difference same existed on the velocity structure, thermal structure and tectonic activities etc.. That suggested that there are two kinds of different medium structure conditions for the strong earthquake activity in Yunnan region.In conclusion, the methods of the 1D inversion, 2D tomography and 3D tomography for S wave attenuation had been established in this paper. The 1D inversion, 2D tomography and 3D tomography for S wave attenuation in Yunnan region had been accomplished by using of the waveform data from Yunana regional digital seismograph network, and the basic characteristics and knowledge of the crust attenuation structure in Yunnan region had been achieved. The 1D inversion result ( the relations between Q( f) and frequency f ) had been applied widely on the analysis and study of the waveform data from Yunana regional digital seismograph network, especially on the determination of the seismic source parameters. The features of the crust attenuation structure in Yunnan region revealed by the 2D tomography and 3D tomography, it provided the new data and evidence to understand deeply the medium structure conditions for the strong earthquake activity, and it suggested that there are two kinds of different medium structure conditions for the strong earthquake activity in Yunnan region.更多还原