华北克拉通地壳三维密度结构与地质含义

利用重力异常揭示地壳三维密度结构是重力资料地质解释的目标和任务,密度反演的好坏至关重要.本文对华北克拉通进行了重力异常多尺度密度反演研究,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各层场源的平均深度,然后利用广义密度反演方法进行各层密度反演,对华北地区进行了多层密度反演,得到其密度结构,并进行地质解释和油气藏分析.结果显示了重力场多尺度密度反演方法的有效性,对华北地区密度结构的地质含义进行了初步分析,位于造山带中的低密度异常主要反映沿造山带展布的花岗岩体.对比华北东部区浅层密度扰动与油气坳陷位置,发现油气坳陷都表现为低幅度的低密度异常区.说明利用小波多尺度反演提取的密度信息对油气勘探的部署有一定指导意义.     

青藏高原地壳密度变形带及构造分区

将区域重力场多尺度刻痕分析用于提取青藏高原地壳变形带的信息,可了解高原内地壳变形带从浅到深的变化和平面分布特征,并对青藏高原主要地体的空间分布定位,为岩石圈研究提供地表地质难以取得的新信息.多尺度脊形化系数的图像刻划不同深度平面上的地壳变形带.青藏高原地壳变形带从上到下由细密逐渐变为粗稀型,而且细密型变形区分布的范围逐渐缩小,到下地壳完全消失.从这种情况可以推测,以垂直地面方向上看,地壳变形带应该是树形的,下地壳粗稀型的变形带为树的主干,而中地壳粗稀型的变形带为树的分枝,上地壳的变形带为树枝的小枝杈.上地壳细密型变形分布区反映了与中新生代地壳缩短变形区的范围,下地壳清晰连续的变形带反映了青藏高原的构造骨架.多尺度边界刻痕系数的图像刻画不同深度平面上的地体边界,下地壳的刻痕边界系数与密度剧烈变化带位置吻合;因此,由多尺度刻痕分析划分地体时同时取得地体密度信息.青藏高原内密度较高的地体包括喜马拉雅地体、克什米亚地体、察隅河地体、柴达木地体、巴颜喀拉地体和羌塘地体.柴达木地体、巴颜喀拉地体和羌塘地体是青藏高原中有壳根的核,而密度最高的克什米亚和察隅河地体在大陆碰撞时不易碎裂,对东西两个构造结的形成起了关键作用.     

基于欧拉反褶积方法估算华北地区重力变化的等效源参数

利用华北地区2009—2014年绝对重力与相对重力多期重复观测资料, 得到不同时空尺度的华北区域重力场动态变化图像。 采用欧拉反褶积方法, 通过对理论模型试算, 获得最优反演参数, 对引起华北地区重力场变化的场源深度和空间分布规律进行了反演计算和分析。 结果表明: 当构造指数为1时, 适合对流动重力场变化数据进行反演。 实际资料的反演结果在2009—2014年间的场源位置集中于河套断裂带。 本文研究方法可以用于重力场反演和以场求源的定量研究。 本工作为流动重力变化信号的反演和解释提供一条新思路, 也为构建地震重力预报指标体系提供了定量依据。     

重力密度界面反演方法研究进展

重力位场的界面反演是位场处理解释中的重要问题.本文针对重力密度界面的反演问题,较全面的介绍了一些有代表性的方法,包括空间域反演方法和频率域反演方法.重点阐述了当前占主流的频率域中的Parker-Oldenburg迭代方法,在此基础上讨论了重力密度界面反演目前存在的问题和以后的发展方向.     

滇西地壳三维密度结构及其大地构造含义

重力异常揭示地壳三维密度结构是地球物理的重要目标和任务,其关键技术是密度反演.本文对滇西地区重力异常进行了多尺度密度反演,首先利用小波变换对重力异常进行多尺度分解,接着利用功率谱分析方法估算各层场源的平均深度,然后利用广义密度反演方法进行各层密度反演,取得区域地壳多个深度上的密度扰动图像.滇西上地壳高密度扰动出现在扬子克拉通内部和西缘,以及澜沧江断裂带西缘,后者对应昌宁—勐连蛇绿混杂岩带及岛弧岩浆岩带.上地壳低密度异常主要反映西昌裂谷带和高黎贡—腾冲一带的岩浆房,和兰坪—思茅盆地中的坳陷带指示钾盐等沉积矿产目的层较厚的区段.滇西上地壳和中地壳出现三条低密度扰动带,与三期大陆碰撞带的吻合.大部分6级以上地震分布在低密度异常区或它们的边缘,只有在西昌—元古谋裂带才分布在高密度异常区.克拉通内部古裂谷带地震可分布在高密度异常区.在26°N线以南下地壳为高密度区,以北为低密度区.因此,26°N线的一个属性是下地壳密度差异分界线.滇西由北向南地壳加厚缩短的程度是逐渐变弱的,在26°N线以南,南北向的地壳加厚缩短就不明显了.高黎贡走滑剪切带、澜沧江走滑剪切带、红河走滑剪切带在滇西中地壳密度扰动平面图中表现为密度急变的梯度带.表明这三条主要的走滑剪切断裂带都穿过中地壳并可能延深到下地壳.     

频率域波形反演中与频率相关的影响因素分析

波动方程深度偏移是解决复杂地质体成像的关键技术,基于波动方程的速度建模为其提供更为精确的速度模型.频率域波形反演是目前研究最为广泛的波动方程速度建模方法之一,它推动了波形反演在勘探尺度下的应用.本文通过对频率域波形反演的实现,分析对比了其有效执行过程中与频率相关的影响因素.介绍了时间域的多尺度反演方法在频率域的一种实现方式,对比分析了输入数据的频点带宽和应用的子波频带范围不同时对反演结果的影响.本文通过设计的山地地质模型对频率域波形反演进行了测试和对比,得到的结论为频率域波形反演的有效计算提供了依据和参考.     

不同高度数据联合欧拉反褶积法研究

基于不同测量高度重力场及其梯度数据可同时对应同一场源并用于反演场源位置的分析原理,拓展不同高度场数据在欧拉反褶积法中的应用范围.首先,立足于对欧拉反褶积方法的理论研究基础,提出不同高度数据融合联合欧拉反演公式.其次,在理论模型上对多种高度数据联合反演做了测试分析计算,验证了不同高度场数据融合联合欧拉反褶积法能够改善位场解释中单一观测面数据计算带来的解的发散问题,收敛过程由此改善.最后,将本文方法应用于龙门山地区实际重力数据的解释,获得了研究区断裂分布特征.     

分析研究基于小波分析与谱分析提高重力异常的分辨能力

重力数据是所有地下场源产生的重力场的叠加,探测对象经常被淹没在区域背景场之中,因此剩余异常的分离对于重力资料研究至关重要,而近来被引入位场领域的小波算子作为了滤波器和场源分析工具,在这里我们分析研究基于小波分析与谱分析的二维离散小波变换用于提高重力异常的分辨能力,再现出由简单形状场源描述密度不均匀的几何特征.本文先介绍二维多分辨率分析小波的基本理论及其提升算法,利用对数功率谱估计平均深度方法理论,接着对理论模型数据进行多尺度异常分解,估计地质体的形状、大小和深度,最后又对实测重力数据进行分析,并与传统常规方法进行比较分析,结果表明对于实际数据分析其方法也是具有可行性的.     

青藏高原东北缘重力场深部结构及其动力学特征

本文采用欧拉反褶积、场源参数成像(SPI)、场源边界提取(SED)、莫霍面反演、地壳三维可视化等多源方法,对青藏高原东北缘地区的布格重力场进行反演与分析,深入研究该地区的深部结构与变形特征,探讨区域深部孕震环境及动力学机制.研究表明,青藏高原东北缘的布格重力场整体呈负异常值,具有明显的分区性,表现出鄂尔多斯盆地异常值相对偏高、阿拉善块体次之、青藏高原块体极低的特点,其中海源断裂系形成了一条宽缓的弧形重力梯度条带,梯度值达1.2 mGal·km^-1.欧拉结果显示,鄂尔多斯盆地相比于青藏高原块体而言,场源点具有较强的均一性,场源强度值高(密度值高)且深度稳定在25~32 km范围内,而高原块体的中下地壳尺度广泛分布着低密度异常体.SPI图可知,海源弧形断裂系位于“浅源异常”弧形区,反映其地壳较为活跃,易发生中强地震.SED图揭示青藏高原地壳向东北扩展,经过几大断裂系的调节后运动矢量向东或东南转化,SED与GPS、SKS运动特征大致相同,说明地表-地壳-地幔的运动特征有着较强的一致性.青藏高原东北缘地区壳幔变形是连贯的,加之莫霍面由北向南、由东向西是逐渐加深的,因此属于垂向连贯变形机制,不符合下地壳管道流动力学模式.区域形成了似三联点构造格局,其中海源弧形断裂系的深部地壳结构复杂,高低密度异常体复杂交汇,是青藏高原、阿拉善、鄂尔多斯三大块体相互作用的重要枢纽,其运动学特征总体为中段走滑尾端逆冲,而断裂系正处于大型的弧形莫霍面斜坡带之上,具备强震的深部孕震环境,因此大尺度的运动调节与深部孕震条件共同促使了该地区中强震的多发.     

基于多尺度迭代求解三维频率-空间域声波方程的全波形速度反演研究-理论模型

使用广义最小残量方法迭代求解三维频率-空间域声波方程,反演时使用多尺度、多重网格的策略,探讨了如何快速实现高分辨率的三维频率-空间域迭代法声波全波形速度反演.通过对理论模型进行三维频率-空间域迭代法声波全波形反演数值试验,证实该方法的计算速度快、计算效率高,反演所得速度的分辨率高.从而为基于多尺度迭代求解三维频率-空间域声波方程的全波形速度反演成像打下方法基础.     

Three Dimensional Crustal Density Structure of Central Asia and its Geological Implications

This paper introduces the scale-depth law of multi-scale wavelet analysis for regional gravity data processing, and presents the results of its application to Central Asia for computation of the 3D crustal density structures. The wavelet analysis method is applied for characterizing 3D crustal density structure, producing five maps of density disturbance corresponding to different depths of equivalent layers in the crust. The results provide important evidence for the study of crustal structures and mass movement in Central Asia: (i) the small-scale and intensive linear density disturbances in the upper crust indicate Phanerozoic orogenic belts; (ii) there exists a horseshoe-shaped low-density belt in the middle crust coinciding with the Kazakhstan orocline; (iii) there is a very low density zone in the lower crust, extending from western Kunlun to Tianshan, probably indicating a lower-crust flow; (iv) there are a few lowdensity spots in the middle crust, which might be caused by low-density mass squeezing upward from the lower crust flows.     

从重力场识别与提取地壳变形带信息的方法研究

表面形貌识别是指用具体的参数表征表面各区段几何形态及属性并最终对不同类型的表面形貌进行识别,表面刻痕识别是其中的一种.以随机过程理论为基础的表面刻痕识别技术可以确切地识别表面形貌的各项特征,其各阶谱矩及统计不变量可以对表面的刻痕以及各向异性进行详细地刻画.区域重力场上的各向异性刻痕主要反映地壳线状变形带,它们常常是区域大地构造单元的边界.本文用重力场研究地壳变形带信息识别方法,将二阶谱矩、统计不变量等参数赋予一定的地质构造含义,并定义了脊形化系数、边界脊形化系数等,从而更详细地表征地壳变形带及大陆构造单元边界信息.理论模型与实际数据试验结果均表明,地壳变形带信息识别方法不但对重力场上地壳变形产生的线形刻痕进行了有效的刻画,而且提取出的刻痕信息,可为大陆构造单元划分提供客观依据.     

DEEP STRUCTURE OF NORTHERN HENAN PROVINCE AND ADJACENT AREAS DERIVED FROM GRAVITY AND SEISMIC SOUNDING DATA IN RELATION TO DISTRIBUTION OF EARTHQUAKES

We conduct the wave field separation of the gravity field for northern Henan Province and adjacent areas by the wavelet multi-scale decomposition method, and obtain multi-order gravity wavelet details and regional gravity field information. Then the Parker density surface inversion is used to invert the Moho interface. Based on the analysis of wavelet details in different orders and results of three seismic sounding profiles available in this area, we attempt to reveal the deep crustal structure of the study area. Research results show that the crustal structure is dominated by uneven density distribution accompanied by uplifts and depressions in the region with obvious heterogeneities of the density in horizontal and vertical directions. The gravity field characteristics in the middle-upper crust correspond to the surface topography, the lower crust is dominated by the large-scale high-low gravity anomalies, and several major depression basins show the characteristics of low velocity and low density. At the same time, the depth of the Moho interface changes greatly, which forms the block structure pattern of the regional crustal thickness. Among these features, the area with relatively large variations of the Moho is located in the transition zone of the basin to the Taihang Mountains, or exactly the Moho mutation belt. The Moho interface of the basin area as a whole is dominated by the uplift intertwined with local variations, of which the least and largest depths are 31km and 37km, respectively. Due to the gravity isostasy, the crustal thickness is larger(about 41km)in the northwest of the Taihang Mountains, with less average crustal density. In the study area, earthquakes tend to occur around the transition zone with density changes where the Moho is locally convex. The seismogenic mechanism may be associated with upwelling of upper mantle materials, low-velocity and low-density structures in the middle-lower crust and connection of deep large faults. Moreover, the deep large faults play a controlling role in the distribution of regional earthquakes.     

利用小波分析研究河西地区地壳垂直形变特征

利用小波分析对河西地区1971—1979、1979—1983年的地壳垂直形变场进行计算,结果表明:三阶以内的小波分解结果与地质构造走向基本一致,说明河西地区地壳垂直运动的短波主要反应的是断层活动;四阶小波变换结果为地壳垂直形变的低频部分,反映的是大区域地质构造运动所引起的地壳垂直形变。1971—1979年,门源南部的地壳垂直运动相对剧烈,而到了1979—1983年,门源地区地壳垂直运动主要活动区域由门源南部地区转移到门源附近区域,这可能与门源6.4级地震孕育的区域构造活动有关。     

CHARACTERISTICS OF MULTI-SCALE GRAVITY FIELD VARIATION AND SEISMOGENIC MECHANISM ANALYSIS IN THE SOUTHEASTERN TIBETAN PLATEAU

As the most basic geophysical field, the earth gravity field has achieved wide attention, and its spatial anomaly characteristics and dynamic variation can provide important scientific basis for studying the internal structure and dynamics of the Earth. Based on the mobile gravity observation data of the southeastern Tibetan plateau from 2013 to 2016, the dynamic variation tendency and anomaly characteristics of the regional gravity field in different temporal resolutions are obtained before and after the Ludian and Jinggu earthquakes in the study area respectively. The method of wavelet multi-scale decomposition is used to analyze the relationships of gravity field variation with the earth movement, material density change, and strong earthquake preparation. The deep material variation, dynamic process and the mechanism of earthquake inoculation in the southeastern Tibetan plateau are further discussed. Results indicate that the gravity field variation in the source region before the Ludian and Jinggu earthquake respectively is characterized by obvious positive and negative anomalous transition zone and gradient zone that are consistent with the direction of fault tectonics, suggesting the strong crustal movement and mass migration during the earthquake incubation period. The result of wavelet multi-scale decomposition of the gravity field during the period from September 2013 to April 2014 shows that the gravity field variation at different depth and space scale in the crust and upper mantle of the southeastern Tibetan plateau is significantly correlated with seismic distribution and the location of active fault zone. This indicates that the earthquake inoculation in the study area is closely related to the fault movement and the distribution of material density in the crust and upper mantle, which may be affected by the complex deep dynamic process of the material migration in the crust and mantle. The characteristic that strong earthquakes always occur near positive and negative anomaly transition zones and gradient zones of gravity field change is preliminarily explained, based on the dynamic process of material migration in the crust and upper mantle of the southeastern Tibetan plateau. The research results of this paper have some reference value to the study on the earth movement and seismogenic mechanism.     

TRANSVERSE STRUCTURES FEATURES OF DIFFERENT DEPTHS DERIVED FROM BOUGUER GRAVITY ANOMALIES IN THE SOUTHERN SEGMENT OF TAN-LU FAULT ZONE

To research the faults distribution and deep structures in the southern segment of Tan-Lu fault zone(TLFZ) and its adjacent area, this paper collects the Bouguer gravity data and makes separation by the multi-scale wavelet analysis method to analyze the crustal transverse structure of different depths. Meanwhile Moho interface is inversed by Parker variable density model. Research indicates that the southern segment of TLFZ behaves as a NNE-directed large-scale regional field gravity gradient zone, which separates the west North China-Dabie orogen block and the east Yangtze block, cutting the whole crust and lithosphere mantle. There are quite differences of density structures and tectonic features between both sides of this gradient belt. The sedimentary and upper crustal density structure is complex. The two east branches of TLFZ behave as linear gravity anomalous belt throughout the region, whereas the two west branches of TLFZ continue to extend after truncating the EW-trending gravity anomaly body. The lower crustal density structure is relatively simple. TLFZ behaves as a broad and gentle low abnormal belt, which reflects the Cretaceous-Paleogene extension environment caused graben structure. The two west branches of TLFZ, running through Hefei city, extend southward along the west margin of Feidong depression and pinch out in Shucheng area due to the high density trap occlusions in the south of Shucheng. The Feizhong Fault, Liu'an-Hefei Fault, and Feixi-Hanbaidu Fault intersect the two west branch faults of TLFZ without extending to the east. Recent epicenters are mainly located in conversion zones between the high-density and the low-density anomaly, especially in TLFZ and the junction of the faults, where earthquakes frequently occurred in the upper and middle crust. As strong earthquakes rarely occur in the southern segment of TLFZ, considering its deep feature of abrupt change of the Moho and intersections with many EW-trending faults, the hazard of strong earthquake cannot be ignored.     

大别造山带东段重力异常多尺度分解及其构造意义

文中通过多源数据融合、模型构建、数据试验、二维离散小波变换和功率谱分析等方法获取了大别造山带东段深、浅部场源布格异常及其场源似深度,并结合地壳结构、地质构造、岩石圈有效弹性厚度和地震活动等资料,讨论了地壳深、浅部的结构特征及地震活动构造背景。结果表明,低频布格异常显示大别造山带东段与华北地块间深部构造缝合带在东部应位于青山-晓天断裂前缘,在落儿岭-土地岭断裂和商城-麻城断裂之间向N偏移至梅山-龙河口断裂之下,造山带南侧与扬子地块间深部构造缝合带位于襄樊-广济断裂以北约20km,造山带东侧与扬子地块间的深部构造转换带位于郯庐断裂带之下,造山带东段腹地显著的低频布格异常低值表明对应部位的莫霍面存在明显下凹,造山带内部的布格异常高梯度带表明其深部结构不完整;高频布格异常揭示肥中断裂、六安-合肥断裂、肥西-韩摆渡断裂和郯庐断裂带等主要断裂对地壳中上部密度结构的影响明显,落儿岭-土地岭断裂对地壳中上部密度结构的影响范围向N延伸至肥西-韩摆渡断裂前缘。结合地震活动资料进一步分析认为,大别造山带东段与华北地块在青山-晓天断裂前缘附近接触和相互作用,且大别造山带东段地壳深、浅部结构均不完整,不利于应力积累,趋向于在断裂交错的脆弱部位频繁释放应力,是霍山地区小地震活动频繁的主要原因。