面波波形反演中的模拟退火法

采用求解非线性全局优化问题的模拟退火法作为反演手段 ,对面波波形进行反演 ,研究青藏高原地壳上地幔速度结构。通过青藏高原的面波波形振幅谱显示出在周期为 2 0 s和4 0 s时存在两个极小值 ,这可能是由地壳中存在低速层引起的。面波波形反演得到的速度模型也证实了青藏高原在 2 0 km深度左右普遍存在低速层 ;喜马拉雅山造山带在 6 0 km深度附近也存在一低速层。壳内低速层是青藏高原变形及隆升过程最重要的动力学边界条件之一     

山东地区地壳及上地幔结构研究

利用布设在山东省境内的宽频带流动地震观测台阵和国家地震局固定地震观测台站记录的地震数据, 应用接收函数和SKS波分裂方法, 研究山东地区的地壳与上地幔结构, 得到该区域的地壳厚度、地壳平均P波与S波的波速比以及SKS波分裂延迟的分布情况。结果表明, 山东地区地壳厚度范围为28~39 km; 胶南隆起的北段和南段以及鲁西隆起北侧济阳凹陷的地壳厚度小于32 km, 鲁西隆起下方的地壳比较厚。研究区 P波与S波的波速比主要分布在1.67~1.94之间, 鲁西隆起西南部和胶南隆起北段该比值小于1.75, 可能是由中上地壳增厚以及下地壳减薄和拆沉造成。鲁西隆起南北P波与S波的波速比差异反映地壳活动的差异。地幔物质的各向异性显示, 山东地区西部的地壳减薄和拆沉可能仍在进行。     

从远震P波的尾波里分离高信噪比的S波

随着全球宽频地震台的迅速增加,P波接收函数技术已经成为探测地壳上地幔结构的标准工具之一,其基本原理就是从远震记录波形上分离出台站下方的间断面上产生的P_S转换相,从而确定间断面的深度和特性.文章介绍了三分量记录的远震资料经过坐标旋转、反褶积运算后从P波的尾波里分离出S波(P_S转换波)的P波接收函数技术.然而,近地表存在低速沉积层时,可能在接收函数波形里引起强烈的多次振荡相,为此引入了滤波技术消除这些振荡相对来自地壳上地幔速度间断面所产生的P_S转换波及其多次反射波P_pP_S,P_pS_S+P_SP_S的影响.另外,由于来自地壳上地幔速度间断面上产生的P_S转换波及其多次反射波P_pP_S,P_pS_S+P_SP_S是弱信号,文章还引入了相位权重叠加技术以增强P波接收函数的信噪比.     

山西断陷带的地震分布及地壳地震波速度结构

为了研究山西断陷带的地震活动性及其物理背景, 利用国家地震科学数据共享中心以及山西省地震局提供的地震震相数据, 通过 tomoDD方法对1990—2008年和2012—2016年期间的地震进行重定位, 并反演山西断陷带附近的地震波速度结构。地震集中于山西断陷带内, 基本上位于已知断层附近, 主要分布在太原盆地的东北?西南两侧。震源深度范围为0~30 km, 北部区域震源深度小, 震源深度超过20 km的地震主要分布在忻定盆地以南地区, 太原盆地两侧的地震集中区形成两个延伸深度最大的南北走向的垂直地震密集条带, 推测受太原盆地两侧两个近南北走向的活动的深大断裂控制。太原盆地两侧近南北走向的两个活动深大断裂如果贯通, 有可能发生7级以上强震。同时, 研究结果显示山西断陷带地壳的地震波速结构变化剧烈, 该断陷带下方的地壳普遍表现为低速, 但其中太原盆地下方地壳的波速略高, 其东北侧和西南侧断陷盆地下方的地壳则表现为更低的波速; 与此相反, 其西北侧和东南侧紧邻太原盆地的两个小区域下方的地壳则表现为明显的高速, 大同西部区域下方的地壳也表现为明显的高速。这些波速特征都与地表构造以及地表热流值有很好的对应关系, 太原盆地东北侧和西南侧都可能有热物质上涌, 并且可能侵入西部的鄂尔多斯地块内部; 相反地, 热物质可能没有侵入太原盆地西北侧、太原盆地以及太原盆地东南侧下方的地壳中, 说明太原盆地的拉张裂开可能并不是受热物质上涌控制, 而是受青藏高原的推挤力控制。     

济阳坳陷岩石圈热结构的二维模拟

基于济阳坳陷的深反射／折射地震测深资料以及华北地区地温场资料和地震波速度（υp）与放射性生热率（A）的实验关系,建立了二维稳态热传导模型,模拟了济阳坳陷岩石层温度分布．研究表明：壳幔边界温度与地壳厚度密切相关,地壳厚度大的地区壳幔边界温度相对较高,约为600～650℃,地壳厚度小的地区壳幔边界温度相对较低,在510～550℃之间;该地区居里面深度在30km左右,与Moho面的深度近似;计算得到该地区热岩石圈厚度在81-102km之间,其分布形态与莫霍面的分布形态相近．     

利用H-Kappa方法反演中国地区台站下地壳厚度

近年来,接收函数已经成为一种重要的计算地壳厚度的方法,它是利用直达P波和Moho面转换S波震相的到时和振幅差来反演计算地壳的厚度和速度结构的.本文在传统的接收函数基础上,采用了多次反射波能量扫描求极大值和波形叠加反演的方法(H-Kappa方法).该方法虽然需要较大的数据量,且要求数据的覆盖范围大,但具有能够同时快速准确地计算出地壳厚度H和Kappa值的突出优点.本文计算了中国国家台网记录到的大量震中距满足30°～90°、震级在5.5～7.0的远震P波的接收函数,从中挑选出了2 233个信噪比较高、震相清晰的接收函数进行H-Kappa方法反演.结果表明中国东部台站下方的地壳厚度为33～36 km, 中部地区的地壳厚度为38～45 km, 而青藏高原地区台站下方的地壳厚度则高达73 km左右.总体上看,青藏高原地区的地壳厚度最大,天山、准格尔盆地、内蒙古大部地区次之,中国华南沿海一带地壳厚度更小,呈现出地壳厚度自西到东逐渐减薄的规律.     

用人工地震初探川西地区的地壳结构

利用四川渡口及会东的两次矿山爆破的地震波走时进行反演,求得川西地区地壳及上地幔的P波速度结构模型。上地壳厚度约21公里,由中新生界沉积岩、古生界及前寒武系复理石建造和变质褶皱群组成。中地壳厚约14公里为低速层,推测为花岗岩层。下地壳厚约17公里,推测为玄武岩层。上地幔顶部P波速度仅7.8公里/秒。地壳平均厚度在龙门山及金河-箐河以东为52公里,一过断层急剧加深到60公里。证据在明地震活动性与甘孜-楚雄菱形块体上地壳向南南东方向运动有密切关系。     

青藏高原东缘岩石圈及软流圈结构

青藏高原东缘岩石圈及软流圈结构的研究是认识该区域地壳上地幔的构造形变及高原内部物质向东运移的重要手段。通过搜集四川区域数字地震台站和野外临时地震台站记录的观测资料,采用接收函数共转换点(CCP)偏移叠加成像方法对青藏高原东缘深部结构研究。研究结果揭示:青藏高原东缘的地壳厚度比四川盆地的地壳厚度大10~20km;在青藏高原东缘与四川盆地的过渡地带,莫霍面处存在大幅度的垂向错断和变形。从青藏高原东缘到四川盆地,岩石圈与软流圈分界面(LAB)显示出深度逐步增加、410km间断面深度则有变浅的趋势。在地壳的下界面和LAB界面间以及LAB界面与410km间断面间也存在多条不连续的分层。青藏高原东缘和四川盆地的LAB界面的下方都有明显的低速层分布,但它们之间存在差别,四川盆地的LAB界面的下方低速层分布较为完整,而青藏高原东缘LAB界面下方的低速层分布中可见离散的高速块体分布。青藏高原东缘与四川盆地深部结构的明显差异,体现了该地区的深部地球动力学背景的复杂性。     

红河断裂以西大理‒永平地区上地壳各向异性分层特征

对中国地震科学台阵探测项目一期于2011—2013年布设在红河断裂以西大理永平地区的5个流动台站进行横波分裂研究, 分别得到18, 14, 7, 9 和5个横波分裂参数测量结果, 并使用更精确的实际横波路径, 通过过量归一化方法进行改正, 研究该区域各向异性分层特征。结果显示, 研究区上地壳10 km深度之上存在各向异性强度大小相间的3层各向异性层, 其中第2层各向异性强度最小, 厚度为2~2.4 km; 第1层各向异性强度稍强, 厚度为4.1~5.0 km; 第3层各向异性强度最强。各向异性分层特征与前人在该区域的大地电磁测深结果吻合。结合滇西地区地壳中的低速异常、低电阻率和低Q值现象, 认为第3层的强各向异性是地幔物质上涌造成裂隙发育以及热流上传所致。     

中国大陆东部地区及朝鲜半岛上地幔深部间断面和各向异性

使用中国国家地震台网、区域内美国IRIS台站和日本OHP台站,收集到超过三年的震级大于6级的全球范围内的宽频带地震资料,采用接收函数和SKS分裂分析技术,研究了中国大陆东部地区及朝鲜半岛上地幔深部间断面和各向异性。在中国东北地区、华北地区及朝鲜半岛下方,存在大范围的更浅的"410km"间断面和更深的"660km"间断面,该特征与太平洋滞留板块的作用密切相关。区域内的上地幔各向异性主要由上地幔流引起,该地幔流与欧亚板块和太平洋板块相对运动有关,而SKS快轴方向的空间分布揭示了这种复杂的运动模式.     

Velocity structure of the crust and uppermost mantle in the boundary area of the Tianshan Mountains and the Tarim Basin

A portable 3-component broadband digital seismic array was deployed across the Tianshan orogenic belt (TOB) to investigate the lithospheric structure. Based on receiver function analysis of the teleseismic P-wave data, a 2-D S-wave velocity profile of the boundary area of the TOB and the Tarim Basin was obtained at the depths of 0--80 km.Our results reveal a vertical and lateral inhomogeneity in the crust and uppermost mantle. Four velocity interfaces divide the crystalline crust into the upper, middle and lower crust. A low velocity zone is widely observed in the upper-middle crust. The depth of Moho varies between 42 and 52 km. At the north end of the profile the Moho dips northward with a vertical offset of 4--6 km, which implies a subduction front of the Tarim Basin into the TOB. The Moho generally appears as a velocity transitional zone except beneath two stations in the northern Tarim Basin, where the Moho is characterized by a typical velocity discontinuity. The fine velocity structure and the deep contact deformation of the crust and upper most mantle delineate the north-south lithospheric shortening and thickening in the boundary area of the TOB and the Tarim Basin, which would be helpful to constructing the geodynamical model of the intracontinental mountain-basin-coupling system.     

Crustal structure of the southeastern margin of the Ordos Block

We use a profile made up of teleseismic receiver functions to study the crustal thickness and structure of the southeastern margin of the Ordos Block.The Mohorovii discontinuity(Moho) has been identified beneath all stations.Its depth gradually decreases towards the southeast,from about 43 km in the Ordos Block to ~30 km near the northern margin of the Qinling Orogen.Our results show clear lateral variations in the structure of the crust and the features of the Moho.Accordingly,the study region can be divided into four parts:(1) Beneath the Ordos Block,the Moho is visible and flat at a depth of ~40 km.The crustal structure is best characterized by stable cratonic crust.(2) In the Weihe-Shanxi Graben,the Moho is uplifted by about 3 km,which may be the result of upwelling of upper mantle materials.(3) Under the Xionger-Funiu Mountains,the Moho is flat at a depth between 36 and 33 km,but becomes shallower towards the southeast.(4) In the Hehuai Basin,adjacent to the northern margin of the Qinling Orogen,the Moho shows strong lateral variations with a mean depth of ~31 km.The crustal structure here is complex,which may indicate a complicated tectonic environment.Additionally,the Moho is clearly interrupted at two locations(beneath stations st11 and st18) near major tectonic boundaries.These results suggest that the structure of the deep crust along the southeastern margin of the Ordos Block has great lateral variability,which strongly affects the complex geological features on the surface.Furthermore,these results can help us understand the interrelationships of different parts of the southeastern margin of the Ordos Block.     

川滇地区地壳结构的虚拟地表震源 反射测深法研究

基于中国地震局地质研究所在中国四川西部布设的流动地震观测台阵数据,用近年发展起来的虚拟地表震源反射测深方法研究川滇地区的地壳结构。结果表明,川滇地块、松潘-甘孜地块和杨子地块3个地块虚拟地表震源反射测深的莫霍面深度存在明显差异:1)四川盆地为40 km左右;2)川滇地块为45~50 km;3)松潘-甘孜地块为30~40 km。四川盆地虚拟地表震源反射测深的莫霍面深度与艾里重力均衡模型所预测的结果基本上一致,而川滇地块和松潘-甘孜地块虚拟地表震源反射测深的莫霍面深度明显小于前人得到的接收函数莫霍面深度和艾里重力均衡模型预测的结果。可能与四川盆地地壳结构简单,而川滇地块及松潘-甘孜地块地壳结构复杂有关。同时,结果显示,在鲜水河断裂和安宁河断裂处虚拟地表震源反射测深的莫霍面深度明显变浅,可能与这些深大断裂处地幔物质的上涌有关。研究结果可为认识青藏高原东南缘的构造变形模式提供新的约束。     

Three-dimensional crustal velocity structure of P-wave in East China from wide-angle reflection and refraction surveys

The 3-D crustal structure of P-wave velocity in East China is studied based on the data obtained by wide-angle seismic reflection and refraction surveys.The results suggest that a deep Moho disconti-nuity exists in the western zone of the study region,being 35―48 thick.High-velocity structure zones exist in the upper crust shallower than 20 km beneath the Sulu and Dabie regions.The cause of high-velocity zones is attributable to high-pressure metamorphic(HPM) and ultra-high-pressure metamorphic(UHPM) terran...     

The 3-D structure of shear wave in South China and the southward extension of Tanlu fault

By processing the CSND Rayleigh wave data with the matched filter FTAN technique, Rayleigh wave disper- sion for southeast China is obtained. The 4°×4°S wave dispersion of the pure path is calculated using random inversion scheme, and 3-D S wave velocity structure is set up. Incorporating the above-mentioned results with wide angle seismic sounding data, we studied structure framework and the extending of faults in this area, which demonstrates that the depth of Moho in South China varies from 30 to 40 km, shallower from west to east. The depth of Moho varies from 25 to 28 km for the offshore. The depth of the asthenosphere in upper mantle varies from 60 to 100 km. The depth difference of layers at the two sides of Tanlu fault is more than 10 km at the south part of the Yangtze River, and the fault extends downward more than 170 km. The fault exceeds the main land at Hainan Island and slips into the southern China Sea. Both Tanlu fault and the huge bend of gravity gradient anomaly are influenced by deep latent tectonics.     

Relocation of the mainshock and aftershock sequences of M S7.0 Sichuan Lushan earthquake

The mainshock of April 20, 2013 Sichuan Lushan M _S7.0 earthquake was relocated using a 3-D velocity model. Double difference algorithm was applied to relocate aftershock sequences of Lushan earthquake. The locations of 2405 aftershocks were determined. The location errors in E-W, N-S and U-D direction were 0.30, 0.29 and 0.59 km on average, respectively. The location of the mainshock is 102.983°E, 30.291°N and the focal depth is 17.6 km. The relocation results show that the aftershocks spread approximately 35 km in length and 16 km in width. The dominant distribution of the focal depth ranges from 10 to 20 km. A few earthquakes occurred in the shallow crust. Focal depth profiles show fault planes dip to the northwest, manifested itself as a listric thrust fault. The dip angle is steep in the shallow crust and gentle in the deep crust. Although the epicenters of aftershocks distributed mainly along both sides of the Shuangshi-Dachuan fault, the seismogenic fault may be a blind thrust fault on the eastern side of the Shuangshi-Dachuan fault. Earthquake relocation results reveal that there is a southeastward tilt aftershock belt intersecting with the seismogenic fault with y-shape. We speculate it is a back thrust fault that often appears in a thrust fault system. Lushan earthquake triggered the seismic activity of the back thrust fault.     

A deep seismic sounding profile across the Tianshan Mountains

The deep seismic sounding profile across the Tianshan Mountains revealed a two-layer crustal structure in the Tianshregion, namely the lower and upper crusts. Lateral variations of layer velocity and thickness are evidently shown. Low-velocity layers spread discontinuously at the bottom of the upper crust. The Moho depth is 47 km in the Kuytun area and 50 km in the Xayar area. In the Tianshan Mountains, the Moho becomes deeper with the maximum depth of 62 km around the boundary between the southern and northern Tianshan Mountains. The average velocity ranges from 6.1 to 6.3 km/s in the crust and 8.15 km/s at the top of the upper mantle. Two groups of reliable reflective seismic phases of the Moho (Pm1 and Pm2) are recognized on the shot record section of the Kuytun area. A staked and offset region, 20-30 km long, is displayed within a shot-geophone distance of 190-210 km in Pm1 and Pm2. Calculation shows that the Moho is offset by 10 km in the northern Tianshan region, 62 km deep in the south while 52 km deep in the north, and plunges northwards. In comparison with typical collisional orogenic belts, the structure of the Moho beneath the Tianshan Mountains presents a similar pattern. This can be used to explain the subduction of the Tarim plate towards the Tianshan Mountains. This intracontinental subduction is considered the dynamic mechanism of the Cenozoic uplifting of the Tianshan Mountains. The discovery of seismic phases Pm1 and Pm2 serves as the seismological evidence for the northward subduction of the Tarim plate.     

Crustal P-wave velocity structure in Lower Yangtze region： Reinterpretation of Fuliji-Fengxian deep seismic sounding profile

A deep seismic sounding profile in this paper, from Fuliji in Anhui Province to Fengxian of Shanghai City, is located at eastern China (Fig. 1). The field work was jointly accomplished by the Chinese Geological and Mineral Bureau, the China Seismological …     

The low-velocity layer at the depth of 620 km beneath Northeast China

Based on the 3-D Earth model, the common convert points-phase weighted stacks （CCP-PWS） migration method is used to image the upper mantle discontinuities beneath Northeast China （longitude 120°―132°; latitude 38°―40°） with 802 observed receiver functions. Teleseismic records are obtained from 4 stations belonging to CCDSN and 19 stations belonging to PASSCAL. A low-velocity layer has been detected at the depth of 620 km. This low-velocity layer rises to 600 km in the east of the study region close to the subducted slab. We consider that this low-velocity layer might be the accumulated oceanic crustal material delaminated from the western Pacific subducted slab. Additionally, we detect the obvious depression of 660 km discontinuity which was attributed to the interaction between the upper mantle and subducted slab. The maximum depth of 660 km discontinuity approaches 700 km, and 660 km discontinuity splits into multiple discontinuities in the northeast of the study region.     

小波分析在泰安—忻州折射/宽角反射剖面解释中的应用

泰安—忻州折射/宽角反射剖面穿过鲁西隆起、华北坳陷、太行山隆起几个构造单元,剖面中段穿过河北省的邢台地震区.利用小波多尺度分析处理了该剖面的几炮波形记录,得到邢台地震区和相邻地段的震相特征.结果表明,邢台地震区的下方莫霍面为复杂结构,可能为双层莫霍面,而在相邻地段莫霍面为较清晰的一级间断面.研究区的深反射剖面结果同样表明,邢台地震区的下方莫霍面为壳幔过渡带,并且在中、上地壳有滑脱构造和延伸到莫霍面的深断裂.复杂的莫霍面结构和形态是邢台地震区的深部构造背景.