Deep seismic sounding investigation into the deep structure of the magma system in Changbaishan-Tianchi volcanic region

IntroductionThe Changbaishan-Tianchi volcano, located in Jilin Province, northeast of China, is one of the well-known active volcanoes in China. In the year 1 215(15, the volcano underwent an eruption that is believed to be one of the greatest explosive eruptions on earth in the past 2000 years with regard to its scale and violence. The eruption amounted to over 100 km3, and the eruption cylinder reached a height of more than 30 km, the volcanic ashes floated and fell south of Hokkaido, Jap…     

四川盆地深部地壳结构——深地震反射剖面探测

四川盆地位于扬子地块的西北部,被褶皱构造带所围绕,受周缘构造带的侧向挤压作用,盆地卷入了多期次和多边界的构造变形,为开展盆山耦合作用及多边界、多期次构造叠加与复合关系的研究提供了不可多得的理想野外实验室.为揭示四川盆地地壳结构,本文通过对3条不同时间采集的深地震反射剖面数据进行拼接联线处理,获得跨越四川盆地的330 km深地震反射偏移成果剖面,揭示了四川盆地地壳上地幔细结构：沉积层从西北向东南逐渐变薄,在龙门山前沉积层厚度超过15 km,在华蓥山下沉积层减薄到~8 km,且褶皱变形形成华蓥山薄皮褶皱冲断带;莫霍面出现在13~15 s（双程走时）,埋深约40~45 km;并发现从下地壳延伸至地幔的东南向的倾斜反射,从13 s向下延伸至18 s,结合四川盆地及其周边地区其他地球物理和地球化学花岗岩同位素年龄等资料,我们认为这些倾斜反射层是扬子克拉通地台西北缘发生的新元古代俯冲的遗迹.

     

Investigation of the earth's crustal structure using earthquake and deep seismic sounding data obtained for the Carpathians

The joint analysis performed for the Carpathian region from seismological data (three-dimensional fields of velocities, areas of concentration of earthquake foci in the Vrancea focal zone) and interpretation of DSS data and those of other geophysical fields have permitted to obtain new evidence for the earth's crust and mantle structure in this region.     

华北克拉通东部地壳与地幔盖层结构——长观测距深地震测深剖面结果

利用文登—阿拉善左旗长观测距地震宽角反射/折射剖面东段资料,辩识出4组地壳震相和3组地幔盖层震相.采用二维射线追踪走时反演和正演拟合交替计算方法,得到了包括鲁东隆起和华北裂陷盆地在内的地壳和地幔盖层二维速度结构.研究结果表明:华北裂陷盆地基底深达6km以上,研究区壳内界面C1埋深约15km,C2界面深约25km,Moho面平均埋深约35km.上地壳速度6.0~6.1km·s-1,且横向变化较大;中地壳速度相对均匀约为6.2~6.4km·s-1;下地壳速度为6.5~7.0km·s-1,速度梯度较大.地壳平均速度与隆起和坳陷构造相关.研究区岩石圈底界面一般为75~80km,西端接近太行隆起构造时深至90km左右,向西呈明显加深趋势,地壳厚度呈现相同的增厚特征.地幔盖层上部速度8.0~8.2km·s-1,具明显正梯度特征.岩石圈平均速度在郯庐断裂带附近显著偏低.PmP和PLP震相存在不同程度的复杂性,意味着在本地区Moho界面和岩石圈界面有较为复杂的结构,可能具有一定厚度或过渡带性质.结合其他研究结果认为,地幔盖层和下地壳速度梯度、界面性质差异与华北克拉通破坏相关,意味着破坏是一个渐变、缓慢和不均匀的过程.郯庐断裂带附近的低速应是其为软弱带的证据.     

Deep structure of the Racha earthquake source zone from seismic tomography data

The Racha earthquake of 1991 was the strongest of the earthquakes recorded in the Caucasus. It was studied by an international epicentral expedition. Unique data gathered by this expedition included records of aftershocks whose swarm was very intense. A 3-D velocity model is obtained from analysis of these data by the method of local earthquake tomography. The ancient crystalline basement and the sedimentary-volcanic Mesozoic-Cenozoic cover could be identified from cross sections of the P wave field. The eastern and western boundaries of an uplift in the basement of the Dzirulskii Massif are delineated. Linear low velocity heterogeneities correlating with the active Kakheti-Lechkhumi fault zone and two Trans-Caucasian linear fault zones are discovered in the basement. The cloud of aftershock hypocenters is shown to correlate with a reflector coinciding with the cover-basement interface.     

滇南及临近地区基底结构--镇康-泸西深地震测深剖面结果

位于南北地震带南段的云南地区是中国大陆内部地震活动最强的地区之一,近年来该区地震活动频繁,展开对该区的探测与研究对人们认识地震孕震背景及板块相互运动具有重要意义.在中国地震局"中国地震科学台阵探测--南北地震带南段"行业专项的支持下,2011年底中国地震局地球物理勘探中心在滇南沿镇康-泸西一线布设一条近东西向的深地震宽角反射/折射探测剖面.该探测剖面跨越三江褶皱系、扬子地台、华南地块等多个地质构造单元,同时穿越南汀河断裂、澜沧江断裂、红河断裂带、小江断裂带等多个重要断裂带.探测剖面长600 km,沿线共布设11个炮点和400余台三分量地震数字仪进行爆破和接收.本文利用有限差分和时间项方法对沿线11炮初至波资料进行了计算处理,获取了探测剖面的基底速度结构.研究结果表明:沿线不同地质构造单元基底界面形态起伏变化剧烈,其深度在1.0~7.0 km范围内变化,速度横向不均匀性明显.在测线西端地表速度约4.6 km·s-1,基底深度较浅,起伏变化不大;地表速度在三江褶皱系下降至4.3 km·s-1,而基底埋深达7.0 km左右.在扬子地台基底埋深有一个缓慢的变浅,基底深度约5.0 km,地表速度约4.5 km·s-1.测线在东端进入华南块体,基底深度迅速变浅,甚至出露于地表,地表速度增至约5.2 km·s-1.在速度等值线变化剧烈的地方与该区分布的断裂带有很好的对应关系,尤其是在红河断裂带两侧速度等值线及界面形态变化剧烈,该特征在首波的记录截面图上也能清晰的体现.本结果为进一步研究该区强震发生背景及深部动力学意义提供了重要的科学依据.     

深地震探测的分辨率分析——以南海北部OBS数据为例

多次深地震探测结果表明南海北部陆缘地壳结构在走向和倾向上都有明显的变化.在一些相隔很近的测线上,探测的深部地壳结构却相差较大,为了分析这些探测结果中差异的原因和地壳结构变化的可靠性,本文以东沙东侧海域测线和东沙西侧海域测线为例,对采集的海底地震仪记录进行了时间、位置校正和初至波走时拾取,利用有限差分地震走时层析成像进行了走时反演,获得所在剖面的地壳速度结构,并分析了模型的横向分辨率,剔除模型中短波长的横向速度变化.分辨率检测结果表明,模型的横向分辨率随着深度快速下降,0～8 km深度范围可以分辨10 km的横向变化,8～17 km的范围能够分辨10～40 km,而17～33 km的范围只能分辨40～80 km.因此,折射波的横向分辨能力不高,在地壳深部难以分辨较小的横向速度变化,前人探测的南海北部6 km宽、延伸至莫霍面的滨外断裂带并不能清晰的识别.     

1927年古浪8级大震区及其周边地块的深部电性结构

沿穿过古浪大震震中区乐都—武威—白马岗北北东方向约340 km长的剖面,进行了16个测点的大地电磁探测.使用Robust技术处理观测数据,分析了视电阻率、阻抗相位、Swift二维偏离、最佳电性主轴方位角等参数,并采用NLCG二维反演技术对TE和TM两种模式的数据进行了二维反演模拟.结果表明：大通山—大坂山、西海原、皇城—双塔、龙首山和北大山5条断裂为明显的电性边界,其中西海原、皇城—双塔、龙首山和北大山断裂由西南向东北依次变浅变缓并在深部收敛于壳内低阻层上.沿剖面上地壳的电性构造较中下地壳的复杂,上地壳自西南向东北可分为中祁连隆起、北祁连褶皱带、冷龙岭隆起、武威盆地、潮水盆地和北大山隆起6个构造单元样式,显示与地表地质调查一致的构造格局;而在中、下地壳,武威盆地、潮水盆地和北大山隆起为一体,都属于阿拉善地块.中祁连和阿拉善地块电性成层性好,存在西南深、东北浅的壳内低阻层,北祁连褶皱带和冷龙岭隆起带电性结构复杂,高、低电阻体相间.1927年古浪地震震中区西南侧和上方区域的电阻率为高电阻率区,下方和东北侧区域为低电阻率区,处于电性结构明显呈台阶状陡变的地带,表明古浪地震是一次与断坡作用有关的地震.     

钦杭—武夷山成矿带上地壳速度结构与基底特征:万载—惠安宽角反射/折射地震剖面约束

钦杭成矿带和武夷山成矿带是华南大陆两个重要的成矿带,成矿作用主要发生于中生代陆内造山时期.地质研究表明,基底和地表断裂的特征对成矿过程有重要的控制作用,研究上地壳结构特征对成矿差异性特征的认识有重要的参考价值.为此,本文基于跨越钦杭、武夷山成矿带江西万载至福建惠安的NW-SE向深地震测深剖面初至波数据,利用有限差分走时反演方法,获得了钦杭、武夷山成矿带8 km深度范围内的上地壳P波速度结构,其主要特征为：（1）钦杭、武夷山成矿带上地壳P波速度横向非均匀特征明显,以5.8 km·s^-1速度等值线作为基底参考面,发现剖面基底埋深较浅,约1.0~3.0 km;钦杭成矿带的基底埋深总体小于武夷山成矿带,分别为0.5~2.0 km和1.5~3.0 km;（2）P波高速区（速度正异常区）与地表出露的岩浆岩对应较一致,P波低速区（速度负异常区）与主要的断裂位置或沉积盆地对应较一致,绍兴—江山—萍乡断裂和政和—大浦断裂下方的低速特征显示两条断裂至少向深部延伸8 km以上,暗示两条断裂具备深大断裂的性质,推测绍兴—江山—萍乡断裂可能是扬子块体和华夏块体的边界;（3）综合已有的地质、地球物理资料,我们推测钦杭成矿带和武夷山成矿带上地壳P波速度的不同,反映了深部岩浆作用过程的差异,基底深度及断裂性质是造成两个成矿带成矿差异的重要因素.

     

钦杭—武夷山成矿带上地壳速度结构与基底特征:万载—惠安宽角反射/折射地震剖面约束

钦杭成矿带和武夷山成矿带是华南大陆两个重要的成矿带,成矿作用主要发生于中生代陆内造山时期.地质研究表明,基底和地表断裂的特征对成矿过程有重要的控制作用,研究上地壳结构特征对成矿差异性特征的认识有重要的参考价值.为此,本文基于跨越钦杭、武夷山成矿带江西万载至福建惠安的NW-SE向深地震测深剖面初至波数据,利用有限差分走时反演方法,获得了钦杭、武夷山成矿带8 km深度范围内的上地壳P波速度结构,其主要特征为：（1）钦杭、武夷山成矿带上地壳P波速度横向非均匀特征明显,以5.8 km·s^-1速度等值线作为基底参考面,发现剖面基底埋深较浅,约1.0~3.0 km;钦杭成矿带的基底埋深总体小于武夷山成矿带,分别为0.5~2.0 km和1.5~3.0 km;（2）P波高速区（速度正异常区）与地表出露的岩浆岩对应较一致,P波低速区（速度负异常区）与主要的断裂位置或沉积盆地对应较一致,绍兴—江山—萍乡断裂和政和—大浦断裂下方的低速特征显示两条断裂至少向深部延伸8 km以上,暗示两条断裂具备深大断裂的性质,推测绍兴—江山—萍乡断裂可能是扬子块体和华夏块体的边界;（3）综合已有的地质、地球物理资料,我们推测钦杭成矿带和武夷山成矿带上地壳P波速度的不同,反映了深部岩浆作用过程的差异,基底深度及断裂性质是造成两个成矿带成矿差异的重要因素.     

Deep structure of the East European platform according to seismic data

The paper presents a review and analysis of new seismic data related to the structure of the mantle beneath the East European platform. Analysis of observations of long-range profiles revealed pronounced differences in the structure of the lower lithosphere beneath the Russian plate and the North Caspian coastal depression. The highest P-velocities found at depths around 100 km are in the range 8.4–8.5 km s^?1. Deep structure of the Baltic shield is different from the structures of both these regions. No evidence of azimuthal anisotropy in the upper mantle was found. A distribution of P-velocity in the upper mantle and in the transition zone consistent with accurate travel-time data was determined. The model involves several zones of small and large positive velocity gradients in the upper mantle, rapid increases of velocity near 400 and 640 km depths and an almost constant positive velocity gradient between the 400 and 640 km discontinuities. The depth of the 640 km discontinuity was determined from observations of waves converted from P to SV in the mantle.     

羌塘中央隆起带深部结构特征研究及其意义

羌塘含油气盆地是我国境内最大的中新生代海相沉积盆地.羌塘地体内的中央隆起将盆地分为南北两个盆地.中央隆起带构造属性认识存在两种截然不同的分歧,一是伸展环境下形成,整个羌塘盆地有着同一的基底.而另一认识其是一古特提斯缝合带,其两侧盆地具有不同的演化机制.调查羌塘中央隆起的深部结构特征及其与南北两侧的盆地间的构造关系是认识羌塘盆地基底性质及其油气远景之关键科学问题.尽管羌塘地体在青藏高原形成演化过程中遭到了强烈改造,但在收集并分析已有地球物理资料基础上认为其深部结构仍有可能被完整保存.因此,利用密集宽频带流动台网观测,获取其深部结构,进而研究其与两侧盆地关系,是当前羌塘含油气盆地研究之重要突破口,同时该项研究符合我国当前国家油气资源战略评估政策.     

Body-wave passive seismic interferometry revisited: mining exploration using the body waves of local microearthquakes

As the global need for mineral resources is constantly rising and the exploitable concentrations of these resources tend to become increasingly complex to explore and exploit, the mining industry is in a constant quest for innovative and cost-effective exploration solutions. In this context, and in the framework of the Smart Exploration action, an integrated passive seismic survey was launched in the Gerolekas bauxite mining site in Central Greece. A passive seismic network, consisting of 129 three-component short-period stations was installed and operated continuously for 4 months. The acquired data permitted detection of approximately 1000 microearthquakes of very small magnitude (duration magnitude ranging between –1.5 and 2.0), located within or at a very close distance from the study area. We use this microseismicity as input for the application of passive seismic interferometry for reflection retrieval, using the body waves (P- and S-wave coda) of the located microearthquakes. We retrieve by autocorrelation zero-offset virtual reflection responses, per component, below each of the recording stations. We process the acquired results using reflection processing techniques to obtain zero-offset time and depth sections, both for P- and for S-waves. In the context of the present work, we evaluate one of the acquired depth sections, using an existing seismic line passing through the Gerolekas passive seismic network, and we perform forward modelling to assess the quality and value of the acquired results. We confirm that passive seismic reflected-wave interferometry could constitute a cost-effective and environmentally friendly innovative exploration alternative, especially in cases of difficult exploration settings.     

班公—怒江构造带的电性结构特征——大地电磁探测结果

对青藏高原过班公—怒江构造带的三条大地电磁剖面进行探测,获得班公—怒江构造带及其邻区的电性结构模型,研究了班公—怒江构造带的深部结构与构造特征.研究结果表明：构造带及其两侧上地壳内广泛分布不连续高阻体,反映了岩浆岩的空间分布特征,表明构造带南北两侧岩浆的活动规律可能存在较大差别.研究区内的冈底斯及羌塘地体的中、下地壳普遍发育高导层,反映了印度大陆碰撞、俯冲过程的效应与痕迹,而高导层之下的高阻块体则可能是向北俯冲、冷的、刚性的印度大陆地壳.羌塘地体的电性结构模型可以分为南北两个区段,南羌塘块体的壳内高导层与班公—怒江构造带对印度板块俯冲的阻挡作用有关;而北羌塘块体壳内高导层与亚洲大陆对印度板块向北俯冲的“阻挡”与向南“对冲”有关.印度板块向北的俯冲与挤入,受到班公—怒江构造带及亚洲板块的阻挡,可能没有越过班公—怒江构造带,并在班公—怒江构造带附近向下插入软流圈,导致幔源物质上涌,形成壳、幔热交换与物质交换的通道和规模巨大、延伸至上地幔的高导体.班公—怒江构造带的电性结构证明了该构造带是一组产状陡立、巨型的超壳深断裂带.     

川滇活动地块东南边界基底结构——盐源-西昌-昭觉-马湖深地震测深剖面结果

在川滇活动地块东南边界区域完成了盐源-西昌-昭觉-马湖深地震宽角反射/折射探测剖面.利用该剖面获得的Pg初至折射波走时,采用走时特征分析、有限差分反演、时间项反演等方法,获得了沿剖面的基底P波速度结构和基底界面构造图像.结果表明,研究区基底结构呈现强烈的非均匀性,不同构造区显示出不同的地壳变形特征.盐源盆地盖层表现为推...     

陆地地震勘探随机噪声统计特性

在地震勘探随机噪声压制领域,噪声通常被假设为平稳、高斯随机过程的信息.然而,在某些情况下,这样的假设并不准确.本文应用现代统计检验方法对地震勘探随机噪声的平稳性、高斯性和线性进行了研究.结果表明地震勘探随机噪声并不是传统意义上认为的平稳随机过程,其平稳性受到噪声时长和采集环境复杂程度的影响.发现噪声时间越长,采集环境越复杂,随机噪声的平稳性越差,但是对于短时长随机噪声而言,其可以近似认为是平稳的.同时,采集环境的复杂程度也影响着随机噪声的高斯性和线性特性,环境条件越复杂,随机噪声高斯性越好,线性特性越差,但总的来说随机噪声可以归为线性非高斯随机过程.

     

珠三角鼎湖—高明—金湾深地震测深剖面地壳构造与速度结构特征分析

为研究珠江三角洲及近海区域深部地壳结构,广东省地震局联合多家单位于2015年在珠江口区域实施了大规模三维人工地震测深实验.本文利用珠江口西侧NW向鼎湖—高明—金湾L1测线数据进行处理、解释,采用地震射线走时正演构建了该剖面二维速度模型.结果表明：沿剖面莫霍面深度从NW向SE,从30.0 km逐渐抬升到28.0 km,鼎湖至高明间存在莫霍面隆起;中地壳低速层非均匀连续,NW一侧速度低于SE一侧,且莫霍面隆起区之上为最显著的低速异常区域,中心最低速度为6.05 km·s^-1;吴川—四会断裂、广州—恩平断裂可能为深部物质上涌的主要通道之一,两条断裂所围限的从珠江口西侧的鼎湖、高明往北东延伸到珠江口东侧的清远、从化区域为可能的连续莫霍面隆起区.

     

Deep seismic reflection profiling revealing the complex crustal structure of the Tongling ore district

Deep seismic reflection profiling has been the dominant method for probing the deep structure of continental crust since the initiation of the COCORP in 1974[1,2]. Over the past few decades, this tool has been applied to diverse geologic features from the Appalachian area of the United States, to the Rhine-graben area in Western Europe and to the Tibetan Pla-teau[36]. In recent years, the Australian Geodynamic Cooperative Research Center ( AGCRC ) has applied this technique to the stu…     

龙门山断裂带北段深部结构与反射地震特征

2008年5月12日汶川M_W7.9特大地震发生在龙门山断裂带,龙门山断裂带深部结构的复杂性制约了地震的破裂过程.通过对研究区区域地质、汶川地震前后采集的地震反射剖面等研究,在对龙门山北段汶川地震断裂带的深部结构和反射地震特征进行了分析的基础上,探讨了它对地表破裂过程的制约.研究结果表明,在地震剖面上,断裂带表现为能量破碎、联系性差;频率剖面上显示整体剖面频率在5~45 Hz,断裂带呈现频率低（15~26 Hz）等特征.龙门山北段映秀—北川断裂在10 km以上是一条倾向北西的高角度走滑兼逆冲性质的断裂,倾角50°~70°.它分割了西侧的轿子顶杂岩和东侧的唐王寨推覆体,错断了早期形成的逆冲岩片,从南到北总位移量由大变小.它高角度的几何形态约束了断裂以走滑为主兼逆冲分量的运动性质,降低了地表滑移量,影响了地震破裂过程以及余震沿断裂带两侧分布的特性.

     

Upper crust structure of eastern A’nyemaqên suture zone: Results of Barkam-Luqu-Gulang deep seismic sounding profile

Barkam-Luqu-Gulang deep seismic sounding profile runs from north of Sichuan Province to south of Gansu Province. It is located at the northeastern edge of Tibetan Plateau and crosses eastern A’nyemaqên suture zone. The upper crust structures around eastern A’nyemaqên suture zone and its adjacent area are reconstructed based on the arrival times of refracted Pg and Sg waves by using finite difference method, ray tracing inversion, time-term method and travel-time curve analysis. The results show that the depth variation of basement along profile is very strong as indicated by Pg and Sg waves. The basement rose in Zoigê basin and depressed in eastern A’nyemaqên suture zone, and it gradually rose again northward and then depressed. The results also indicate that eastern A’nyemaqên suture zone behaves as inhomogeneous low velocity structures in the upper crust and is inclined toward the south. Hoh Sai Hu-Maqên fault, Wudu-Diebu fault and Zhouqu-Liangdang fault are characterized by low velocity distributions with various scales. The distinct variation in basement depth occurred near Hoh Sai Hu-Maqên fault and Zhouqu-Liangdang fault, which are main tectonic boundaries of A’nyemaqên suture zone. Wudu-Diebu fault, located at the depth variation zone of the basement, possibly has the same deep tectonic background with Zhouqu-Liangdang fault. The strongly depressed basement characterized by low velocity distribution and lateral inhomogeneity in A’nyemaqên suture zone implies crushed zone features under pinching action. Foundation item: National Natural Science Foundation of China (40334040).