导　　师： 曾佐勋

学科专业： 070904

授予学位： 博士

作　　者： ;

机构地区： 中国地质大学

摘　　要： 在人类面临的所有自然灾害中,地震及其次生灾害造成的人员和经济损失最为严重。我国是全球内陆地区地震活动最为强烈的地区之一。据美国国家地震信息中心/(NEIC/)统计,1900年以来/(截止2014年1月1日/)全球共发生8级以上地震87次,其中有6次发生于我国。16世纪以来,仅我国南北地震带就发生7级以上地震30余次,其中1900年之后就发生了19次。2008年5月12日汶川Ms8.0级地震和2013年4月20日芦山Ms7.0级地震的发生更是既唐山地震之后,又一次给国人敲响防震减灾的警钟,也将国外内对地震成因及地震预测的研究推向高潮。 本文通过对青藏高原、龙门山、印尼爪哇岛、西太平洋岛弧及台湾地区的地震特征及震源分布规律的分析,阐述了板内地震与板缘地震的区别,认为对我国大陆地震的研究应该充分考虑板内地震的基本规律,采用与板缘地震不同的研究方法。 作者以大地电磁测深及地震层析资料圈定出的华北地区软流圈隆起位置为依据,指出了我国地震监测的重点区域。同时,以上资料显示软流圈上涌体中熔融组分相对集中,形成低密度/(2.9～3.0g//cm3/)的粥样物上涌,直到70-80km深度,其熔融组分可高达10-30/%,比同深度的岩石圈高出500～600℃。据此,认为地震的主要能量来自于软流圈隆起。通过研究华北地区唐山和汾渭裂谷两个地区的地壳结构、上地幔及软流圈隆起与地震震源的关系,发现两个地区震中下方的中下地壳中均存在韧性流变层,是地震能量主要的积聚和转化的场所,是地震的储能包。来自底部软流圈的流体和能量不断向上运移,使储能包内的能量缓慢而长期积聚,并使它与围岩物性差异的逐渐加大,形成三明治构造。三明治构造使韧性流变层内积聚的热能和化学能等地震能量转化为应变能,成为上覆脆性岩石的破裂的前提。而广泛发育在地球表层的脆性断层只是地震的触发构造和地震能量的释放机制,同时也是各种地震前兆现象能出现在地球表层的重要通道。 地震的本质是一个能量长期积聚和突发释放的地质过程。基于对华北地区地震地质背景的分析和研究,作者以能量的聚散为线索,建立了板内地震的三层次构造模式。基本思想是：在深层次上,软流圈隆起是地震能量的主要来源；在中层次上,中下地壳中的韧性流变层是地震能量积聚构造；在浅层次上,脆性断层是地震能量的触发和释放机制。 鉴于南北地震带近期活动的加剧,也为了检验板内地震三层构造模式的实际运用效果,作者将该地震成因模式推广到南北地震带中段的龙门山和天水两个地区,研究了两地的地震孕震发震机制和并开展了地震前兆的监测工作,为所在科研团队及时做出地震预测提供了可靠的依据。 在龙门山地区,根据前人所做的5条地球物理剖面研究了龙门山断裂带周边的壳幔结构。研究发现龙门山地震带下部存在一个宽度约200km左右的软流圈隆起,隆起幅度约为30kmm。软流圈隆起物质和能量的上涌使地壳熔融,形成厚度约为10km的韧性流变层,埋深约20-30km。韧性流变层的形成使能量在物质能干性差异最大的接触面或顶端,即龙门山断裂带的下部产生巨大的应力集中。在这种巨大应力的作用下,上部龙门山的脆性岩石开始发生“微破裂”,流体和能量伴随这一过程不断释放。一旦这一过程开始,释放出的流体和能量便会使上部原有断裂活动加剧,并产生新的破裂。随着“微破裂”逐渐扩展形成“破裂链”,流体进入岩石内部,降低了储能包周围脆性岩石的强度。当逐渐增强的应力积累超过了逐渐降低的岩石强度时,便引发地震。这一过程十分类似于流体包裹体的爆裂,它不仅可以造成上覆岩层的巨大坚硬岩石破碎、近水平抛出和高速远程滑移,还可以引起大范围山体或岩体发生粉碎性的破碎。另外,或者当上覆脆性岩层中的断裂活动不断发展,触及到储能包/(即韧性流变层/)时,储能包变也会发生突发性的爆裂,引发地震。 在天水地区,作者利用高分辨率地震折射剖面、大地电磁测深剖面、S波速度结构剖面及新生代火山岩等资料,探讨了天水地区壳幔结构特征,提出“天水地震核心区”这一新概念。认为天水地区存在一个巨型地幔热隆,顶面埋深约为1OOkm,直径约300km左右,该地幔热隆是南北构造带中段地震活动的根本动力,也是天水地震核心区形成的根本原因。同时发现,在地幔热隆的上部存在一个埋深约40km,厚度约20km的壳内韧性流变层。根据前人对该地区钾霞橄黄长岩地球化学和成因的研究,找到了该地区壳幔结构的直接证据。鉴于该地区地壳浅部构造走向为东西向,而深部构造为南北向,将该地区构造特征归纳为“立交桥式构造”。作者认为该“立交桥式”构造特征是导致天水地区强震频发,形成地震核心区,进而向四周辐射的原因。地幔热隆物质周期性的上涌导致了上覆岩石的周期性张开与闭合,是形成“开合构造”的动力来源。当上覆岩石圈张开时,幔源岩浆极易突破地壳薄弱点,形成超碱性岩或碳酸盐。幔源岩浆上涌的同时,也带上来大量的以热能和化学能为主的能量,其中一部分逐渐积聚在前文所讲的地壳高导低速层中。结合该地区的壳幔及地表构造特征,作者认为天水地区也符合板内地震的三层构造模式,其地震能量的供给、积聚和转化过程与龙门山地区相类似。 由于板内地震的三层次构造模式是以能量的供给-积聚-释放为线索,而流体在能量的聚散中起到了至关重要的作用。因此,本文讨论了深部流体的来源、作用及其监测方法。作者认为深部流体来源有地球演化过程中的残余流体和地球表层流体的下渗两种。在深部,这些流体处于超临界或亚临界状态,性质比较稳定；由于受到外界扰动,这些流体才变得活跃起来。流体上涌的作用主要有：导致物质的迁移、引起能量的运移、膨胀致震、润滑断层、产生宏观震兆等。根据流体运移的规律和特点,作者认为通过热红外温度异常监测、大气成分监测、地震云监测、地电监测、地下水环境监测能够及时抓住由流体活动引发的地震前兆,为地震预测提供可靠地依据。为验证这些理论的可靠性,作者针对南北地震中段开展了地震前兆信息的监测和分析工作,为后续地震预测提供了可靠地依据。 /(1/)利用风云二号卫星的热红外数据,研究了2009年6月30日绵竹Ms5.6级地震前卫星热红外增温异常的特征。研究表明,绵竹地震前中国北部新疆、内蒙古、河北及山东一带,卫星热红外图像出现明显异常增温区,距地震12小时左右,异常区亮温值达到220万km2左右。此后,异常区开始向南运移,到震前3小时异常增温区前锋抵达震中绵竹,并滞留不动至发震时刻。 /(2/)利用Aqua卫星红外探测器/(AIRS/)反演出的对流层顶部359hPa处的甲烷浓度和地面气温数据,研究了2013年4月20日芦山Ms7.0级地震前大气增温与甲烷排放的同步性及甲烷浓度特征与断层活动的关系。研究表明,芦山地震前甲烷的释放与气温异常升高有良好的对应关系；芦山地震前甲烷释放与龙门山构造特征及地震活动明显相关,随着地震的临近和地壳活动的加剧,沿龙门山断裂带的甲烷释放量显著增加,并逐渐向断裂带前沿扩展。震前地壳活动过程中产生的“微破裂”是甲烷释放的通道,而“破裂链”的产生可以使甲烷释放过程急剧加强,在温室效应的作用下形成震前气温的大幅度增温异常。 /(3/)根据气候要素的特征周期,利用小波分析方法,从Aqua卫星红外探测器/(AIRS/)反演出的对流层甲烷体积混合比产品中分解并识别出气候和人为因素对应甲烷浓度变化分量,进而提取出地质活动所引起的甲烷/(地源甲烷/)浓度变化信息。在此基础上,以汶川和玉树地区为例,研究了地源甲烷浓度变化和地震活动间的关系。研究表明,对流层中地源甲烷浓度与地震活动存在明显的对应关系；汶川地区3年间/(2004～2006年/)共出现地源甲烷峰值13次,玉树地区2年间/(2004～2005年/)共出现14次；其中21次/(78/%/)地源甲烷峰值与地震峰值间隔不超过2个月；汶川和玉树地区时间间隔随日期的演化非常同步,均呈现先降后升的规律；汶川地区地源甲烷浓度增幅与地震能量峰值存在明显的正相关关系。最后,初步探讨了地源甲烷的产生和变化原因,认为地源甲烷来源于壳幔流体的上涌；其波动与韧性流变层中地质流体的存储状态及中上地壳“微破裂”、“破裂链”的发育过程有密切关系。 /(4/)观测并分析了2013年7月8日都江堰Ms4.1级地震前的地震云及地球排气现象,为本次地震预测提供了可靠依据。研究认为,龙门山断裂带深部的软流圈为地壳韧性流变层提供了巨大的能量,经过长期的积聚和转化,使地震前龙门山断裂带的应变能突破了岩石的破裂强度,或原有裂隙的摩擦极限,从而引起了接触面的突发活动。热流体便通过这些新、老裂隙迅速上涌,使地温升高,加热空气,成为上升的气流,并以同心圆状扩散到同温层,进而使高空的雨云形成细长的索状的地震云。利用风云卫星云图对比了地球排气和地震云的关系,认为地震云和排气现象相结合可以较为准确的确定震中位置。都江堰地震是汶川/(Ms8.0/)地震的余震,二者具有相同的成因机制,北川-映秀断裂逆冲兼右行走滑活动,造成中地壳韧性流变层中所积累能量的突然释放是地震能量的主要来源。 /(5/)分析了2013年定西Ms6.6级地震前SW仪所接收的地电信号的指纹特征及其成因,为本次地震的成功预测提供了依据。本次地震的发震断层是临潭-礼县断裂,天水地幔热隆周期性的活动造成的远程效应导致了本次地电异常。同时,该地幔热隆不仅为地震的发生提供了物质和能量来源,还为上地壳构造带来了大量流体,既加剧了地壳流变层物性的差异,又润滑了断层,加速了地震的发生。 Earthquake and its secondary disaster cause the most seriously human and economic cost of all the natural disasters. China is one of the most active regions of global inland seismic activity. From the statistic data of National Earthquake Information Center /(NEIC/), it is87times earthquakes occurred that magnitude exceeding8in the world since1990/(as of Jan.1st2014/), six of them happened in China. It is over30times earthquakes occurred at South-North Earthquake Zone that magnitude exceeding7since the16th century, and19earthquakes happened after1900. The Wenchuan and Lushan earthquake, happened in May12th2008and April20th2013respectively, give Chinese a wake-up call for the earthquake prevention and disaster reduction. And also it promotes the study of seismic origin and earthquake prediction in China. We analysis of the focus distribution of Tibetan Plateau, Longmenshan, Java island of Indonesia, the western Pacific island arc and Taiwan region, and explain the difference between the intraplate earthquake and plates boundary earthquake. We indicate that we should begin with the intraplate earthquake features for the study of continental earthquake in China. We indicate key regions of earthquake monitoring according to the position of North China asthenosphere uplift based on the telluric electromagnetic sounding and seismic tomography data. At the same time, we figured that the melt fractions is relatively concentration in the asthenosphere upwelling and formed low density /(2.9～3.0g//cm3/) atherosclerosis upwelling. At the depth of70-80km, the melt fractions is up to10-30/%which is500-600℃hotter than that at the same depth. Based on the physical and chemical properties, we figured that the main earthquake energy came from atherosclerosis upwelling. By study of the relationship with earthquake focus among the crust structures, upper mantle and atherosclerosis upwelling in Tangshan and Fenwei rifting regions of North China area, we found that there are ductile layers beneath the epicenter in middle-lower crust, and the ductile layers is the main accumulation place of seismic energy and the energy storage bag od earthquake. The fluid and energy from the bottom of asthenosphere went up continually, so that the energy accumulating slow and long term in the storage bag and made the difference greater from the surrounding rock, and formed 'Sandwich structure'. The'Sandwich structure'changed the energy of ductile layer from thermal and chemical energy into strain energy, and it became the premise of cracking in the overlying brittle rock. The brittle faults prevalent distribute on the surface of earth is only the trigger structure and release mechanism of seismic energy. And also, it is the significant tunnel of earth surface expression of the earthquake precursory phenomena. The essential of earthquake is the geological process of the sudden releasing and long term accumulating of energy. Based on the analysis and study of background of seismic geology in North China, we made the releasing and accumulating of energy as the thread and established the Three-Level Tectonic Mode of intraplates. The basic idea is:in the deeper layer, atherosclerosis upwelling provides the main earthquake energy; in the middle layer, the ductile layer of the middle-lower crust is seismic energy accumulation structure; in the upper layer, the brittle faults is the trigger structure and release mechanism of seismic energy. Because of the increase of activities in north-south earthquake zone recently, and also to verify the Three-Level Tectonic Mode of intraplates, we apply the earthquake formation model into Longmenshan and Tianshui regions in the middle of north-south earthquake zone to study the origins of earthquake formation and the prediction of the epicenter. According to the former data of five geophysical profiles in Longmenshan region, we did research of crust-mantle structure in this area. From the results, we found that there is an atherosclerosis upwelling beneath the Longmenshan earthquake zone with about200km in width and about30km in height. The material and energy of the atherosclerosis uplift and transport that lead to the crust melting and formed10km thick ductile layer which is20-30km thick in deep. The formation of ductile layer made the energy focus on the interface or the peak of the greatest material competent difference, which means that beneath the Longmenshan fault there is a stress concentration3times as its interior stress. Under this great stress, brittle rock of upper Longmenshan fault formed the'microcracks', and was accompanied by liquid and energy release slightly. Once it began the upper pre-existing fractures activities were increased by the releasing fluid and energy. Meanwhile, the'microcracks'developed into'crack chains', then the strength of the energy storage bag around the brittle rock was reduced. When the accumulated stress is bigger than the strength of rocks, the earthquake happened. This process is similar with fluid inclusions burst. It could make the hard megablock rock of overlying strata fractured, oriental projected, high-speed and long-distance slide and a wide range of mountain rock comminuted fracture. Another possible way to trigger the earthquake is that the energy storage bag suddenly burst when fractured active in the brittle rock of overlying strata effect it. By analysis the crust-mantle structure features of Tianshui area on the base of high resolution seismic refraction profile, magnetotelluric sounding profile, velocity structure profile of S wave and dates of Cenozoic volcanic rocks. It is showed that there is a macromolecule mantle hot doming with the100km depth of top and300km diameters and it is the fundamental dynamic of forming the middle of north-south tectonic belt. There is a40km in depth and20km thick inter-crust ductile layer in upper mantle hot upwelling. The former research results of the geochemical and formation mechanism of kamafugite in this region provide evidence for the upper crust-mantle structure. In this region, the tectonic orientation is east-west in upper crust and that is north-south in deeper, so we call it 'overpass type'. Meanwhile, we believe that the overpass type structure of tectonic intersection in Tianshui area is the reason this area destructive earthquake-prone. The mantle upwelling material periodic uplift lead to the overlying rock periodic open and closed, it is the power source of opening-closing tectonics. When the overlying lithosphere is open, the mantle-derived magmas can easily break the thin crust and form ultra-alkaline rock and carbonate. It also took out energy dominated by heat and chemical, part of them accumulated into the high-conductivity and low-velocity layer. The accumulation of thermal energy and fluid melt the crust-mantle material, changed local mechanical properties of lithosphere and formed ductile layer. It also formed 'Sandwich structure' with the competent layers below and above it. The stress is focus on the most different physical properties direction and increasing the energy accumulation. The earthquake is not happen until the stress from the accumulated energy over the brittle layer break strength or limit of friction of upside and edge ductile layer which could make the interface breaking and decoupling. The main clue of the three-level tectonic model for intraplate earthquake is the energy supply-accumulate-release, but the fluid play an important role in the energy accumulate and release. So we discuss the source of deep fluid, its effect and monitoring approach. We indicate the deep fluid came from remain fluid of earth processes and the earth surface fluid infiltration. In deep portion, the fluid is in supercritical or subcritical state with stable properties. Due to the external disturbance, the fluid became active. Fluid upwelling mainly functions are as following: cause mass migration, cause the energy immigration, the fluid expansion can be directly induced earthquake, lubrication fault and produce the generation of seismic precursor. According to the features of fluid transport, we indicate we can notice the seismic precursor caused by fluid active from thermal infrared temperature anomaly monitoring, atmospheric composition monitoring, the earthquake cloud monitoring, geoelectric monitoring and the groundwater environmental monitoring and supplies reliable data for earthquake prediction. To test and verify these theories, we monitor and analysis the earthquake precursor information of the middle north-south earthquake zone. /(1/) We studied the satellite thermal infrared anomalies features of the Mianzhu Ms5.6pre-earthquake by the thermal infrared data of'Fengyun2'satellite. We found there are obviously increasing thermal anomalies along the north Xianjiang, Inner Mongolia, Hebei and Shandong areas in the satellite thermal images before the Mianzhu earthquake. The thermal anomalies grew up to about2.2million km212hours earlier before the earthquake. After that, the anomalies areas immigrated to south and the thermal anomalies front arrived at Mianzhu3hours earlier before the earthquake and stay till it happened. /(2/) By using the methane concentration data at top of troposphere359hPa and the ground temperature data extracted from Atmospheric Infrared Sounder /(AIRS/) on NASA's Aqua satellite, we studied the synchronism between atmosphere temperature increasing and methane emission, and the relationship between the variation of methane concentration and the fault activities of the atmosphere before the Lushan earthquake /(Ms7.0/) in the Longmenshan area. We found methane emission is correlation with atmosphere temperature increasing to some extent before the Lushan earthquake; there are strong relevant between the methane emission before the Lushan earthquake and Longmenshan structure features and earthquake activities, and the amount of methane emission obvious grow and expound to overthrust belt while it is closed to the earthquake happened and crust activities increased. The'microcracks'is the tunnel of methane emission and the'crack chains' promote this process. It forms the thermal anomalies by the atmosphere temperature increasing under the greenhouse effect before earthquake. /(3/) According to the characteristic periods of climate elements, component signals caused by climate and human factors are decomposed and recognized from the volume mixing ratio of methane in the troposphere, using wavelet analysis method. And then, extract the variation of methane concentration signal caused by geological activity /(geological methane/). On this basis, analyze the relationship between the variation of geological methane concentration and seismic activity, take Wenchuan and Yushu areas for examples. The result shows that there is an obviously corresponding relationship between the variation of geological methane concentration and seismic activity. In addition,13peak values of geological methane concentration occurrence in Wenchuan area in2004～2006, and14peaks values occurrence in Yushu area in2004～2005. In total,21cases /(78/%/) of the time difference of geological methane and seismic activity peak are less than2months, and the time difference decrease firstly and then increase in February2005, in these two areas. And, there is a positive correlation between geological methane concentration and seismic activity peak values in Wenchuan area. Finally, preliminary study on the source and variation of geological methane, the results indicate that geological methane comes from upwelling of mantle and crust fluids, and its concentration correlated closely with the temperature and pressure of ductile rheological layer and "microcracks" and "Rupture chain" in mid-upper crust. /(4/)We studied the earthquake clouds and the earth exhaust of July8th2013Dujiangyan Ms4.1pre-earthquake. We figured that the arcuate rope clouds are formed due to the super-low vibration of the local ground surface acting on the water vapour and dust in the sky. We indicate that the Dujiangyan Ms4.1earthquake is an aftershock of the Wenchuan Ms8.0earthquake and both have the same formation mechanism. The Beichuan-Yingxiu thrusting with right-lateral slip resulted in a sudden release of the energy accumulated at the edge of the boundary between differential rheological layers, a density saltation position in the middle crust. /(5/)We analyzed the fingerprint characteristics and its causes of electrical signals from the SW monitor in the Minxian Ms6.6earthquake occurred in July22nd,2013. We believe that the cyclic activity of hot doming in Tianshui led to the abnormal of terrestrial electricity. This provides the basis for the success of the earthquake prediction. And the hot doming is not only the source of the material and energy during earthquake, but also brings plenty of fluids for the upper crustal structure. These fluids aggravate the physical differences of crustal rheological layers, lubricate the fault and accelerate the earthquake at the same time.

关 键 词： 南北地震带 三层次构造模式 天水地震核心区 甲烷

分 类 号： [P315]

领　　域： [天文地球] [天文地球] [天文地球]