共查询到20条相似文献，搜索用时 15 毫秒
1.
Xiaoqing Zhang Jiyan Lin Minghui Zhang Zhi Liu Baofeng Liu Youshan Liu Tao Xu Zhiming Bai 《地震科学（英文版）》2020,33(1):34-41
The North China Craton (NCC) is a key region to study the destruction of the ancient craton. Two groups of phases (denoted as “Pw1” and “Pw2”), which are parallel to the PmP phase reflected from the Moho discontinuity and the PLP phase reflected from the Lithosphere and Asthenosphere Boundary (LAB) respectively, are found on the record section of the Rongcheng-Xinzhou-Alxa long-range deep seismic sounding profile. The nature of the two phases is still unclear, although they are clearly observable and reverberant. In this paper, we use travel time inversion and amplitude forward modelling to fit the reflected and refracted phases in the lithosphere. The results show: (1) the Pw1 is a multiple reflected phase which is successively reflected by the crystalline basement, the surface, the Moho and then finally received on the surface; (2) the Pw2 phase is also a multiple reflected phase successively reflected by the crystalline basement, the surface, the LAB interface and then received on the surface. We conclude that the significant velocity difference between the thick sedimentary cover and the crystalline basement in the North China rifted basin may be the main reason for generating the multiple reflections. Furthermore, the two multiple reflections provide potent constraints on the lithospheric velocity model, and constitute seismological evidence for the lithospheric thinning in the eastern NCC. 相似文献
2.
IntroductionTrial-and-error forward modeling of wide-angle seismic reflection/refraction traveltimes for 2-D velocity structure is extremely time-consuming, even for experienced data interpreters. For wide-angle seismic reflection/refraction experiments that consist of numerous shots along a single line, it is quite difficult through repeated trial-and-error forward modeling to construct a 2-D model that fits the data within acceptable limits (Cerveny, et al, 1977; ZHANG, et al, 200 . In ad… 相似文献
3.
V. I. Starostenko T. Janik O. B. Gintov D. V. Lysynchuk P. Środa W. Czuba E. V. Kolomiyets P. Aleksandrowski V. D. Omelchenko K. Komminaho A. Guterch T. Tiira D. N. Gryn O. V. Legostaeva G. Thybo A. V. Tolkunov 《Izvestiya Physics of the Solid Earth》2017,53(2):193-204
For studying the structure of the lithosphere in southern Ukraine, wide-angle seismic studies that recorded the reflected and refracted waves were carried out under the DOBRE-4 project. The field works were conducted in October 2009. Thirteen chemical shot points spaced 35–50 km apart from each other were implemented with a charge weight varying from 600 to 1000 kg. Overall 230 recording stations with an interval of 2.5 km between them were used. The high quality of the obtained data allowed us to model the velocity section along the profile for P- and S-waves. Seismic modeling was carried out by two methods. Initially, trial-and-error ray tracing using the arrival times of the main reflected and refracted P- and S-phases was conducted. Next, the amplitudes of the recorded phases were analyzed by the finite-difference full waveform method. The resulting velocity model demonstrates a fairly homogeneous structure from the middle to lower crust both in the vertical and horizontal directions. A drastically different situation is observed in the upper crust, where the V p velocities decrease upwards along the section from 6.35 km/s at a depth of 15–20 km to 5.9–5.8 km/s on the surface of the crystalline basement; in the Neoproterozoic and Paleozoic deposits, it diminishes from 5.15 to 3.80 km/s, and in the Mesozoic layers, it decreases from 2.70 to 2.30 km/s. The subcrustal V p gradually increases downwards from 6.50 to 6.7–6.8 km/s at the crustal base, which complicates the problem of separating the middle and lower crust. The V p velocities above 6.80 km/s have not been revealed even in the lowermost part of the crust, in contrast to the similar profiles in the East European Platform. The Moho is clearly delineated by the velocity contrast of 1.3–1.7 km/s. The alternating pattern of the changes in the Moho depths corresponding to Moho undulations with a wavelength of about 150 km and the amplitude reaching 8 to 17 km is a peculiarity of the velocity model. 相似文献
4.
Wojciech Czuba 《Acta Geophysica》2013,61(5):1088-1100
Deep seismic sounding measurements were performed in the continent-ocean transition zone of the western Svalbard and Barents Sea margin, during the expeditions in 1985–2008. Seismic energy (airgun and TNT shots) was recorded along several profiles by onshore seismic stations and ocean bottom seismometers, and hydrophone systems. Good quality reflected and refracted P waves provided an excellent data base for a seismic modelling along the profiles. TNT sources were recorded even up to 300 km distances. A minimal depth of about 6 km of the Moho interface was found east of the Molloy Deep. The Moho discontinuity dips down to 28 km beneath the continental part of the northernmost profile and down to maximum 32 km beneath other profiles. The evolution of the region is considered to be within a shearrift tectonic setting. The continent-ocean transition zone along the northernmost profile is mostly dominated by extension; therefore, the last stage of the development of the margin can be classified as rifting. The uplifted Moho interface close to the Molloy Deep can be interpreted as a south-western end of the Molloy Ridge. The margin of the southern Spitsbergen is rather of sheared character while the western Barents Sea margin is of slow to ultraslow spreading type. 相似文献
5.
6.
7.
2009年,中国地质科学院地质研究所与美国俄克拉荷马大学合作实施了一条长453 km的深地震反射、宽角反射与折射、三分量反射地震联合探测剖面. 剖面南起怀来盆地,向北依次穿过燕山造山带西缘、内蒙地轴、白乃庙弧带、温都尔庙杂岩带,到达索伦缝合带. 其中,宽角反射与折射剖面采用8个0.5~1.5 t炸药震源激发,使用300套Texan单分量数字检波器接收,获得了高质量的地震资料. 通过资料分析和处理,识别出沉积层及结晶基底的折射波（Pg）、来自上地壳底界面的反射波（Pcp）,中地壳底界面的反射波（Plp）,莫霍界面的反射波（Pmp）及上地幔顶部的折射波（Pn）等5个震相. 分别采用Hole有限差分层析成像和Rayinvr算法对华北克拉通北缘及中亚造山带南部进行了上地壳P波速度结构成像和全地壳二维射线追踪反演成像. 结果显示：（1）中亚造山带地壳厚度~40 km,变化平缓,低于全球平均造山带地壳平均厚度,可能为造山后区域伸展的结果. 阴山-燕山带附近莫霍明显加深,推测其为燕山期造山过程形成的山根,但该山根很可能在后期被改造. （2）测线中部地壳上部速度较高,对应地表大面积花岗岩出露,而下地壳速度较低,速度梯度低,呈通道状,推测其可能曾为古亚洲洋向南俯冲消亡的主动陆缘,并在碰撞后演变为伸展环境下岩浆侵入的通道. （3）华北克拉通北缘与中亚造山带显示出不同速度变化特征,前者变化相对缓而后者则变化剧烈,二者的分界出现在赤峰-白云鄂博断裂附近. 相似文献
8.
云南思茅—中甸宽角反射/折射地震剖面切割松潘—甘孜、扬子和华南三个构造单元的部分区域. 我们利用初至波和壳内反射波走时层析成像获得地壳纵波速度结构. 在获得新的地壳速度结构模型基础上，利用地震散射成像思想和低叠加次数的叠前深度偏移方法重建了研究区的地壳、上地幔反射结构. 综合分析研究区地壳P波速度模型和壳内地震反射剖面发现：沿测线从北至南地壳厚度从约50 km减薄至35 km左右，地壳厚度的减薄量主要体现在下地壳，剖面北段下地壳厚度约为30 km，剖面南段下地壳厚度仅为15 km左右；上地幔顶部局部位置P波速度值偏低，一般为76～78 km/s，反映出云南地区是典型的构造活动区的特点.剖面沿线地壳内地震反射发育，其中莫霍强反射出现在景云桥下方；在景云桥弧形断裂带8～10 km深处出现宽约50 km的强反射带. 相似文献
9.
井间地震资料具有极高的分辨率,但是,其波场十分复杂,特别是有效一次反射波场能量较弱,且往往被管波等强相干干扰淹没,波场的识别与分离难度较大.地震物理模拟技术是认识复杂地震波场的有效手段.我们通过单一地质体模型、复杂地质体模型和真实井间模拟模型等多种逼真地质模型的物理模拟,揭示了井间地震观测下直达波、透射波、反射波、折射波,多次波和导波等各类波型的特征.物理模拟试验表明,在炮检域平面上分析直达波的信噪比与能量分布,可以使处理人员对旅行时的误差有更直观的认识.所以识别初至与拾取旅行时间时,不仅要在共震源点道集(CSG)上分析拾取,而且还要在共炮检距道集(COG)上分析拾取,这样就提高了直达波识别的可靠性与拾取时间的精度. 相似文献
10.
多震相走时和波形三维地震成象方法及在祁连山地壳结构研究中的应用 总被引：1，自引：0，他引：1
本文的理论方法是以几何射线理论为基础发展起来的、天然地震走时反演技术及天然地震层析成像技术。它存在着震源函数与介质参数的解耦问题。本研究采取了五种方法来改善反演结果。包括,利用,Pg,Pn等震相增大约束条件;用已有精度较高的人工地震测深结果作速度约柬：用波形反演来修改模型,把诸多物理量开发出来互为约束,以修改后的模型再作反演,使解的稳定性大大提高：采用最优化过程,选择遗传算法。可以进行震源定位,走时反演,波形反演：得到任意深度的速度分布及从地表到Moho面的速度剖面。用于在祁连山地区的结果表明,这些层析剖面对认识大地构造、重大深部事件动力学是很有益的。 相似文献
11.
Seismic anisotropy has an important influence on seismic data processing and interpretation. Although the frequency-domain seismic wavefield simulation has a problem of solving the large scale linear sparse matrix due to the computational limitations, it has some advantages over the time-domain seismic wavefield simulation including efficient inversion using only a limited number of frequency components and easy implementation of multiple sources. To accurately simulate seismic wave propagation in the frequency domain, we also need to choose the absorbing boundary conditions to absorb artificial reflections from edges of the model as we do in the time domain. Compared with the classical boundary conditions including the perfectly matched layer and complex frequency-shifted perfectly matched layer, the complex frequency-shifted multi-axial perfectly matched layer has been proven to effectively suppress the unwanted reflections at grazing incidence and solve the instability problem in the time-domain seismic numerical modelling in anisotropic elastic media. In this paper, we propose to extend the complex frequency-shifted multi-axial perfectly matched layer absorbing boundary condition to the frequency-domain seismic wavefield simulation in anisotropic elastic media. To test the validity of our proposed algorithm, we compare the results (snapshots and seismograms) of the frequency-domain seismic wavefield simulation with those of the time-domain modelling. The model studies indicate that the complex frequency-shifted multi-axial perfectly matched layer absorbing boundary condition is stable in the frequency-domain seismic wavefield simulation in anisotropic media, and provides better absorbing performance than the complex frequency-shifted perfectly matched layer boundary condition. 相似文献
12.
The structure of the crust and the crust-mantle boundary in the Vogtland/West Bohemian region have been a target of several
seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90,
9HR), the refraction and wide-angle experiments (GRANU’95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic
studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower
crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift.
The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth
of 26–28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the
lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies
detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and
37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different
background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling
was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower
crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling
resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the
Moho reflection at a depth of 32–33 km. 相似文献
13.
在波数域中用重力反演莫霍面深度时通常假定壳幔密度差为一常数,但这只是一种近似的密度模型,本文采用了密度随深度呈指数变化的变密度模型来反演莫霍面深度,给出了利用指数密度模型在波数域中计算重力异常的正演公式及界面深度的反演公式.利用指数密度模型及重力资料反演了青藏高原莫霍面的深度,分析了莫霍面的特征.结果表明,青藏高原莫霍面呈现出边缘浅、中部深的特点,边缘变化快、梯度大,中间变化梯度趋缓.中心地带的羌塘地体莫霍面深度达74 km,向四周慢慢变浅至67 km左右,边缘地区突然变浅至50km左右.通过常密度模型、变密度模型及地震反演得到的莫霍面的比较,证实变密度模型更适合于莫霍面结构的反演. 相似文献
14.
Crustal structure of seismic velocity in southern tibet and east-westward escape of the crustal material 总被引：11，自引：0，他引：11
The reflecting events from Moho and other interfaces within the crust are recognized from the wavefield characteristics of
P- and S-wave for the 480km long wide-angle seismic profile between Peigu Tso and Pumoyong Tso. Then, seismic crustal structures
of P- and S-wave velocities and Poisson ratio under the nearly east-west profile in southern Tibet are interpreted by fitting
the observed traveltimes with the calculated ones by forward modelling. Our interpreting results demonstrate that the crustal
thickness varies remarkably in the east-west direction, showing a pattern that the crust could be divided into three parts
bounded by the west of Dingri and the east of Dinggyê, respectively, where the depth of Moho is about 71km for the western
part, about 76km for the middle and about 74km for the eastern. There is one lower velocity layer (LVL) at the bottom of the
upper crust with depth of 20–30 km. One of the distinct features is that the thickness of LVL abruptly thins from 24km on
the west to 6km on the east. The other is that the velocity variation in the crust along east-west direction for both P- and
S-wave displays a feature as quasi-periodic variation. The lower velocity (compared to the average value for the continent
of the globe) in the lower crust and three sets of north-southward active normal faults are probably attributed to the coupling
process of material delamination in the lower crust, crustal thicking and east-westward escape of the crustal material accompanied
with the continental collision between India and Eurasia Plate. 相似文献
15.
The reflecting events from Moho and other interfaces within the crust are recognized from the wavefield characteristics of P- and S-wave for the 480km long wide-angle seismic profile between Peigu Tso and Pumoyong Tso. Then, seismic crustal structures of P- and S-wave velocities and Poisson ratio under the nearly east-west profile in southern Tibet are interpreted by fitting the observed traveltimes with the calculated ones by forward modelling. Our interpreting results demonstrate that the crustal thickness varies remarkably in the east-west direction, showing a pattern that the crust could be divided into three parts bounded by the west of Dingri and the east of Dinggyê, respectively, where the depth of Moho is about 71km for the western part, about 76km for the middle and about 74km for the eastern. There is one lower velocity layer (LVL) at the bottom of the upper crust with depth of 20-30 km. One of the distinct features is that the thickness of LVL abruptly thins from 24km on the west to 6km on the east. The other is that the velocity variation in the crust along east-west direction for both P- and S-wave displays a feature as quasi-periodic variation. The lower velocity (compared to the average value for the continent of the globe) in the lower crust and three sets of north-southward active normal faults are probably attributed to the coupling process of material delamination in the lower crust, crustal thicking and east-westward escape of the crustal material accompanied with the continental collision between India and Eurasia Plate. 相似文献
16.
The interpretation of deep seismic sounding (DSS) data has been made on the basis of a two-dimensional inhomogeneous model. The refracted first arrivals as well as reflected and diffracted waves on the seismic records have been utilized. The seismic section was modeled in the iso-veolcity lines v(x, y) = const, taking into account the zones of diffraction associated with deep faults. Gravity observations have been used to construct a block model of the Earth's crust with vertical boundaries. It is suggested to define the base of the crust as the zone with velocities between 7.8 and 8.2 km/s. The reflecting boundaries of different length occurring in this zone can be conformal or unconformal with the iso-velocity lines near the base of the crust. As an example of our approach to the interpretation of DSS data the folded-blocky structure of the crust with horizontal inhomogeneities of velocity and density is shown in the Kzyl-Orda-Dzheskazgan profile in Central Kazakhstan. 相似文献
17.
18.
华北克拉通北缘—西伯利亚板块南缘（张家口—中蒙边界）的深地震测深剖面长600 km,跨越华北板块、内蒙造山带和西伯利亚板块.沿测线采用8个1.5t的爆炸震源激发地震波,使用300套数字地震仪接收,取得了高质量的地震资料.通过资料分析和处理,识别出沉积层及结晶基底的折射波（Pg）、上地壳底面的反射波（P2）、中地壳内的反射波（P3）、中地壳底面的反射波（P4）、下地壳内的反射波（P5,仅在镶黄旗—苏尼特右旗下方出现）和莫霍面的反射波（Pm）等6个震相.采用地震动力学射线方法（seis88）得到的地壳速度结构表明：（1）在华北板块与内蒙造山带之间,内蒙造山带与西伯利亚板块之间,上地壳中存在明显的高速度局部变化,在地表发育大量的古生代花岗岩体、超基性岩体.（2）在中下地壳华北板块南缘的地震波速度大,为6.3~6.7 km/s,西伯利亚板块北缘的速度小,为6.1~6.7 km/s,且界面比较平缓.原因是在内蒙造山带内地壳的缩短和隆升造山引起了中下地壳界面的剧烈起伏,不同海陆块的拼合和物质交换导致了不同区域速度的不均匀性.（3）莫霍面在赤峰断裂带（F2）以南和索伦敖包—阿鲁科尔沁旗断裂带（F4）以北较为平缓,平均深度为40~42 km.在F2—F4之间呈双莫霍面,莫霍面1明显上隆,深度为33.5 km,层速度为6.6~6.7 km/s.莫霍面2明显下凹,在西拉木伦河断裂带（F3）下方,最深达到47 km,速度达到最大为6.8~6.9 km/s,这可能是由壳幔物质混合引起的.依据莫霍面的特点,本文认为双莫霍面以南为华北板块北缘,以北为西伯利亚板块南缘,拼合位置在赤峰断裂带（F2）与索伦敖包—阿鲁科尔沁旗断裂带（F4）之间的区域. 相似文献
19.
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. 相似文献
20.
A. Vesnaver 《Geophysical Prospecting》2004,52(6):653-661
The shallowest few hundred metres of the earth cannot be adequately imaged by conventional seismic when tuned for deeper targets. Adding independent measurements (such as uphole or shallow refraction surveys) reduces this information gap, but in some arid areas (such as Saudi Arabia) the near‐surface complexities are not well resolved, even in this way. The joint tomographic inversion of different wave types can contribute to reducing these ambiguities further, by complementing the different penetration ranges and propagation directions of reflected, refracted and diving waves. Here, we demonstrate the weakness of diving waves when used alone, and the value of complementing them by available reflected and refracted arrivals. 相似文献