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Crustal P-wave velocity structure in the northeastern margin of the Qinghai-Tibetan Plateau and insights into crustal deformation 总被引：1，自引：0，他引：1
Shuaijun Wang Baojin Liu Xiaofeng Tian Baofeng Liu Xianghui Song Xiaoguo Deng Yinan Sun Cejun Ma Yudong Yang 《中国科学:地球科学(英文版)》2018,61(9):1221-1237
The transitional area between the northeastern margin of the Qinghai-Tibetan Plateau, Ordos Block and Alxa Block,also being the northern segment of the North-South Seismic Belt, is characterized by considerably high seismicity level and high risk of strong earthquakes. In view of the special tectonic environment and deep tectonic setting in this area, this study used two seismic wide-angle reflection/refraction cross profiles for double constraining, so as to more reliably obtain the fine-scale velocity structure characteristics in both the shallow and deep crust of individual blocks and their boundaries in the study area,and further discuss the seismogenic environment in seismic zones with strong historical earthquakes. In this paper, the P-wave data from the two profiles are processed and interpreted, and two-dimensional crustal velocity structure models along the two profiles are constructed by travel time forward modeling. The results show that there are great differences in velocity structure,shape of intra-crustal interfaces and crustal thickness among different blocks sampled by the two seismic profiles. The crustal thickness along the Lanzhou-Huianbu-Yulin seismic sounding profile(L1) increases from ~43 km in the western margin of Ordos Block to ~56 km in the Qilian Block to the west. In the Ordos Block, the velocity contours vary gently, and the average velocity of the crust is about 6.30 km s-1; On the other hand, the velocity structures in the crust of the Qilian Block and the arclike tectonic zone vary dramatically, and the average crustal velocities in these areas are about 0.10 km s-1 lower than that of the Ordos Block. In addition, discontinuous low-velocity bodies(LVZ1 and LVZ2) are identified in the crust of the Qilian Block and the arc-like tectonic zone, the velocity of which is 0.10–0.20 km s-1 lower than that of the surroundings. The average crustal thickness of the Ordos Block is consistently estimated to be around 43 km along both Profile L2(Tongchuan-Huianbu-Alashan left banner seismic sounding profile) and Profile L1. In contrast to the gently varying intra-crustal interfaces and velocity contours in the Ordos Block along Profile L1, which is a typical structure characteristic of stable cratons, the crustal structure in the Ordos Block along Profile L2 exhibits rather complex variations. This indicates the presence of significant structural differences in the crust within the Ordos Block. The crustal structure of the Helan Mountain Qilian Block and the Yinchuan Basin is featured by "uplift and depression" undulations, showing the characteristics of localized compressional deformation.Moreover, there are low-velocity zones with alternative high and low velocities in the middle and lower crust beneath the Helan Mountain, where the velocity is about 0.15–0.25 km s-1 lower than that of the surrounding areas. The crustal thickness of the Alxa Block is about 49 km, and the velocity contours in the upper and middle-lower crust of the block vary significantly. The complex crustal velocity structure images along the two seismic sounding profiles L1 and L2 reveal considerable structural differences among different tectonic blocks, their coupling relationships and velocity structural features in the seismic zones where strong historical earthquakes occurred. The imaging result of this study provides fine-scale crustal structure information for further understanding the seismogenic environment and mechanism in the study area. 相似文献
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根据江苏及邻区大地构造单元和人工地震研究程度的不同,划分为下扬子地区、郯庐断裂带、大别山东段、苏鲁地块等地区,介绍了利用人工地震、天然地震层析成像及其它地球物理探测等方法对这一地区的深部构造研究结果。其中下扬子地区莫霍面的深度为28~33 km,横向不均匀,由西向东逐渐减薄;大别—苏鲁地区地表超高压变质带地壳波速特征主要表现在上地壳顶部的高速层,其厚度一般小于10 km;苏鲁地块地壳厚度约在32~33 km之间,明显高于周边地区;大别山地区沿造山带方向莫霍面变化平缓,地壳厚度33 km左右;横穿造山带方向起伏变化较大,莫霍面最深达41 km左右。天然层析成像研究范围大,分辨率较低。大别苏鲁地区人工地震测深工作较深入,但调查范围较小,主要在浅层,认识相对局部,有待于面上的大范围深部结构图像研究。 相似文献
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通过在上海地区开展深、浅地震反射、地震宽角反射/折射、高分辨地震折射和大地电磁测深等联合剖面探测, 获得了该地区近地表至Moho面的精细速度结构、电性结构和深浅构造关系.结果表明, 该地区地壳可划分为上、中、下三个组成部分.其中,上地壳厚为12～14 km,波速为57～59 km/s;中地壳厚度约为10 km,波速为59～62 km/s;下地壳厚为10～11 km, 波速为62～63 km/s,Moho面深度约为32 km.剖面浅部地质构造复杂,共解释出12条特征明显的断裂.其中,除3条断裂错断结晶基底（G界面）并向下延伸至上地壳底界面外,其他断裂均在深度3～5 km以上终止或收敛于G界面之上.此外,仅在剖面西侧基底下部约13～15 km埋深处发现一厚度在2 km左右的壳内高导层.所以,在综合各方面资料后分析认为,在剖面经过地区不存在发生大地震的深部构造条件,近地表所存在的活动断层是未来产生对该区有影响地震的震源区. 相似文献
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（王椿镛，张先康，林中洋，李学清）ＣｈａｒａｃｔｅｒｉｓｔｉｃｏｆｃｒｕｓｔａｌｓｔｒｕｃｔｕｒｅｉｎｔｈｅＳｈｕｌｕｆａｕｌｔｂａｓｉｎａｎｄｉｔｓｖｉｃｉｎｉｔｙ￥Ｃｈｕｎ－ＹｏｎｇＷＡＮＧＩ；Ｘｉａｎ－ＫａｎｇＺＨＡＮＧ；Ｚｈｏｎｇ－ＹａｎｇＬ... 相似文献
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福建地处欧亚大陆东南缘,新构造活动强烈,区内北东向断裂带异常发育,是华南震区中、强地震活动的频发区.为深入认识我国东南沿海地壳上地幔速度结构特征及其深部构造背景,福建省地震局联合中国地震局地球物理勘探中心于2010年至2012年在福建陆域实施由18次人工爆破、四条北西向原生纵测线和四条北东向集成纵测线构成的三维人工地震测深实验.本文对该实验中以北西-南东走向近似垂直穿过政和—海丰断裂的宁化—大田—惠安深地震测深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地壳速度模型.结果显示,沿剖面地壳厚度由西向东逐渐减薄,其西北侧地壳厚约31.8km,东南侧地壳厚达28.4km.剖面上地壳P波速度从5.90km·s~(-1)逐渐增加至6.20km·s~(-1),上地壳厚度横向变化不大,厚度在16~17km左右,但是下地壳厚度由西向东减薄较为明显.地壳以政和—海丰断裂为界,东西两段具有明显不同的速度结构,呈西段速度偏低、东段速度较高的特性,且西段在上下地壳分界面下方存在一个低速层.研究表明,剖面不同区段呈现出的速度结构差异与该区大地构造单元的划分基本吻合,剖面解释结果和以往远震接收函数研究结果均印证了作为闽西南坳陷带和闽东火山断陷带分界线的政和—海丰断裂是一条切割至下地壳底部的深大断裂. 相似文献
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AbstractThe Benzilan-Tangke deep seismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE.Based on the travel times and the related amplitudes of phases in therecord sections,the 2-D P-wave crustal structure was ascertained in this paper. The velocity structure has quitestrong lateral variation along the profile.The crust is divided into 5 layers,where the first,second and third layerbelong to the upper crust,the forth and fifth layer belong to the lower crust.The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile,and it integrates into the overlying low velocitybasement in the area to the north of Ma’erkang.The crustal structure in the section can be divided into 4 parts:inthe south of Garze-Litang fault,between Garze-Litang fault and Xiashuihe fault,between Xianshuihe fault andLongriba fault and in the north of Longriba fault,which are basically coincided with the regional tectonics division 相似文献
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G. A. Pavlenkova 《Izvestiya Physics of the Solid Earth》2012,48(5):375-384
This work presents the results of reinterpretation of the deep seismic sounding (DSS) data for the Stepnoe-Bakuriani profile and the southern part of the Volgograd-Nakhichevan profile, carried out using new processing methods. Both the profiles cut the trend of the Greater Caucasus. They were acquired in the 1960s by multichannel continuous profiling, which provided high-quality records; however, only the travel-time curves for the main wave types have survived till now. The waves recorded on these profiles have a rather complex origin and their processing by the methods existing at that time was a challenge. At present, the modern computer technologies allowed us to invert the preserved travel-time curves for the velocity models of the Earth??s crust and the very tops of the mantle down to 80 km. It is shown that the crustal thickness increases under the Greater Caucasus up to 50?C60 km and this increase is not gradual, as implied in the previous reconstructions, but occurs through a system of deep dislocations. Traced by the oblique reflections and sharply contrasting seismic velocities, these dislocations extend into the crust. An extended, north-dipping boundary is revealed at a depth of 50?C80 km. The velocity model of the Greater Caucasian crust exhibits slightly decreased velocities compared to the surrounding platform regions. At the same time, the velocities sharply increase in the middle and even upper parts of the crust in the Kura depression. 相似文献
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Zhao Guoze Zhan Yan Tang Ji Zhao Junmeng Jin Guangwen Deng Qianhui and Wang Jijun 《中国地震研究》2000,14(1):75-85
Magnetotelluric sounding data obtalned recently in Manas earthquake area were processed. Inthe result, curves of apparent resistivity, impedance Phase, skewness and optimum rotationangle versus period and the real magnetic induction vectors were obtained. Then the data ofall measuring points were interpreted by 2D automatic inversion. The result indicates thatalong the sounding profile the shallow crust can be divided into 5 segments and the deep crustcan be divided into 3 segments, with faults or deep-seated fault zones as the contactboundaries between them. The sedimentary cover along the profile extents down to depthabout 12 km in maximum and a low-resistivity body exists in the crust in southern section ofthe profile. The interpretation results are well consistent with geological and othergeophysical data. The Manas M7. 7 earthquake occurred near a contact zone where theelectrical structure of the crust sharply changes. 相似文献
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Crustal structure beneath the Songpan—Garze orogenic belt 总被引：2，自引：0，他引：2
The Benzilan-Tangke deepseismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE.Based on the travel times and the related amplitudes of phases in the record sections,the 2-D P-wave crustal structure was ascertained in this paper.The velocity structure has quite strong lateral variation along the profile.The crust is divided into 5layers,where the first,second and third layer belong to the upper crust,the forth and fifth layer belong to the lower crust.The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile,and it integrates into the overlying low velocity basement in the area to the north of Ma‘erkang.The crustal structure in the section can be divided into 4parts:in the south of Garze-litang fault,between Garze-Litang fault and Xianshuihe fault,between Xianshuihe fault and Longriba fault and in the north of Longriba fault,which are basically coincided with the regional tectonics division.The crustal thickness decreases from southwest to northeast along the profile,that is ,from62km in the region of the Jinshajiang River to 52km in the region of the Yellow River.The Moho discontinuity does not obviously change across the Xianshuihe fault basesd on the PmP phase analysis.The crustal average velocity along the profile is lower,about 6.30 km/s.The Benzilan-Tangke profile reveals that the crust in the study area is orogenic.The Xianshuihe fault belt is located in the central part of the profile,and the velocity is positive anomaly on the upper crust,and negative anomaly on the lower crust and upper mantle.It is considered as a deep tectonhic setting in favor of strong earthquake‘s accumulation and occurrence. 相似文献
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IntroductionGeologistsfirstlyfoundcoesite-bearingecologitesattheendof1980'sandthenthemicrodiamond(Xu,elal,1992)inDabieshanarea.Theultra-highpressure(UHP)metamorphismandthegeodynamicprocessesofDabieorogenhaveattractedmanygeoscientists(Wang,etal,1989,O... 相似文献
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基于甘肃省夏河县—陕西省靖边县剖面的8次人工地震初至波数据, 利用有限差分走时方法反演得到了沿该剖面长约650 km的上部地壳速度结构和结晶基底的深度分布． 反演结果显示: 海原构造区西侧的西秦岭—祁连山褶皱区上部地壳的横向非均匀性明显, 基底深度从1 km到5 km不等, 反映了褶皱区改造变形强烈的构造特征; 其东侧的鄂尔多斯盆地基底深度约为5—6 km, 其速度均匀、 稳定, 上地壳呈弱速度梯度特征; 海原构造区及海原弧形断裂带附近上部地壳的破坏变形最严重, 区内横向高低速相间分布． 综上可知, 海原构造区东西两侧上地壳结构的显著差异揭示了其结构复杂性的成因及其与地震活动性的关系． 相似文献
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The Working Group for Deep Seismic Sounding in the Alboran Sea 《Pure and Applied Geophysics》1978,116(1):167-180
In September 1974, deep seismic sounding experiments were performed in the Alboran Sea. The crustal seismic profiles were carried out with shotpoints at sea along approximately the 36°N parallel and along 3°W and 5°W meridians with stations on land in Morocco and Spain following these three directions. The first interpretation of the data indicates a thinned continental crust with a Moho depth of 16 km on top of a slightly anomalous upper mantle (7.5<V
p<7.9 km/s) beneath the center of the Alboran Sea. Towards Spain the transition to the continental margin is characterized by a very rapid thickening of the crust. Towards Morocco a rather abrupt thickening is observed only for the Rif region, while in the eastern part (north-south profile along 3°W) the dip of the Moho is very slight. 相似文献
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An explosive seismic sounding profile across the transition zone between west Kunlun Mts. and Tarim Basin 总被引：1，自引：0，他引：1
LI Qiusheng GAO Rui LU Deyuan Li Jingwei Fan Jingyi Zhang Zhiying LIU Wen LI Yingkang YAN Quanren LI Dexing 《中国科学D辑(英文版)》2001,44(7):666-672
The explosive seismic sounding profile across the transition zone from the west Kunlun Mts. to the Tarim Basin revealed the
complex deep structure formed by continent-continent collision on the northern margin of the Tibetan Plateau. The profile
shows that the attitude of the Moho is in agreement with that of the crystalline basement in the Tarim Basin and the whole
crust dips as a thick slate southwards with an angle from 5° to 7°. Meanwhile, the Moho depth increases from 40 km to 57 km
within a distance of 150 km in the southern Tarim region, depicting the subduction of the crust of this region towards the
west Kunlun Mts. The crust of the northern slope of the west Kunlun Mts. shows an evident compressed and shortened feature,
that is, the basement is uplifted, the interface dips northwards and the Moho rises abruptly to become flat, so that the lower
crust is as thick as 20 km. 相似文献
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2014年8月3日,云南省昭通-鲁甸地区发生MS6.5级地震,造成了重大的人员伤亡和财产损失.鲁甸震区位于扬子块体的西缘,小江断裂带的东侧北东向的昭通-莲峰断裂带内.由于至今没有穿越该断裂带的人工源深地震测深剖面,而丽江-攀枝花-清镇650 km长深地震测深剖面距离鲁甸主震区不超过50 km,利用宽角地震资料的初至波震相,通过有限差分反演揭示该地区上地壳速度结构,可以为鲁甸震区的地震定位、地震孕育机制等提供深部速度模型.速度剖面显示：剖面结晶基底厚度平均为2 km左右;小江断裂带速度较低,东西两侧的速度较高;因此小江断裂带区域地壳强度比较低,加上断裂两侧的应变速率很高,所以小江断裂带和旁边的鲁甸-昭通断裂带,未来具有发生较大地震的可能,值得关注. 相似文献
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长度100 km、NW向穿过三河—平谷8.0级地震区和北京地区主要断裂构造的深地震反射剖面,揭示了该区地壳精细结构图像和断裂的深浅构造特征.结果表明,该区地壳以TWT6～7 s左右的强反射带为界分为上地壳和下地壳,上地壳厚约18～21 km,下地壳厚约13～15 km.剖面TWT3～4 s以上,反射层位丰富,构造形态清晰,且在剖面上具有明显不同的构造特征;在三河—平谷地震区以西,剖面揭示了2～3组反射能量较强的反射震相和一系列错断基底面的断裂,在三河—平谷地震区以东,为一套自东向西倾伏的密集强反射层,这套反射具有典型的沉积盆地特征,盆地最深处约为8～9 km.剖面揭示的地壳深断裂倾角陡直,该断裂切割、扰动了下地壳物质和壳幔过渡带,向上延伸至上地壳,将地壳深部构造与浅部断裂联系在一起,构成了该区最主要的深浅构造特征. 相似文献
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在云南西部,穿过红河、小江断裂带完成了一条长360 km、呈北东向的深地震宽角反射/折射剖面.通过对该测线的观测资料进行一维、二维模拟解释,得到了沿剖面的二维地壳速度模型.研究结果显示,沿测线Moho界面埋深横线变化大,其西南侧Moho埋深约35 km,东北侧Moho最大埋深可达43 km.沿剖面从西南到北东方向,地壳平均P波速度从5.9 km/s逐渐增加到6.13 km/s,但显著低于全球大陆平均值.结合以往的接收函数和面波联合反演结果,我们推算沿测线从西南到东北,其下方地壳泊松比介于0.23~0.25之间.剖面西南侧上地壳具有异常低的P波速度和泊松比,暗示其下方上地壳以α-相长英质组分为主;而剖面东北上地壳相对较高的P波速度和泊松比则暗示其物质组成以花岗岩-花岗闪长岩为主.研究区下地壳的P波速度和泊松比分别介于6.25~6.75 km/s和0.24~0.26 km/s之间,暗示其上部组成以花岗岩相的片麻岩为主,而下部组成则以角闪石类岩石为主.红河断裂两侧地壳速度显著不同,从浅到深其速度差异逐渐变弱,但红河断裂两侧地壳厚度变化较大.而小江断裂下方两侧地壳速度和地壳厚度变化并没有红河断裂那么明显. 相似文献
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1994年完成的大别造山带深地震测深剖面（全长420km）穿越了华北地块,大别造山带和扬子地块三个构造单元．获得了垂向成层、横向分块的地壳纵、横波速度结构．结合地质、地球化学研究成果,大别山地壳可分为三层：上地壳是多重叠覆的构造岩石层,中地壳为韧性变形层,下地壳整体成分偏酸性．大别山地表及浅部的超高压变质岩石具有典型的薄皮构造特征．本文提出大别山不同期双向俯冲造山模式和超高压变质岩石的反向加楔退拔折返机制;大别山腹地至今仍保留6-8km厚的山根． 相似文献
20.
《Physics of the Earth and Planetary Interiors》2005,148(2-4):215-232
The Narmada–Son Lineament (NSL) Zone is the second most important tectonic feature after Himalayas, in the Indian geology. Magnetotelluric (MT) studies were carried out in the NSL zone along a 130 km long NNE-SSW trending profile. The area of investigation extends from Edlabad (20°46′16″; 75°59′05″) in the South to Khandwa (21°53′51″; 76°18′05″) in the North. The data shows in general the validity of a two-dimensional (2D) approach. Besides providing details on the shallow crustal section, the 2D modeling results resolved four high conductive zones extending from the middle to deep crust, spatially coinciding with the major structural features in the area namely the Gavligarh, Tapti, Barwani-Sukta and Narmada South faults. The model for the shallow section has brought out a moderately resistive layer (30–150 Ω m) representing the exposed Deccan trap layer, overlying a conductive layer (10–30 Ω m) inferred to be the subtrappean Gondwana sediments, the latter resting on a high resistive basement/upper crust. The Deccan trap thickness varies from around a few hundred meters to as much as 1.5 km along the traverse. A subtrappean sedimentary basin like feature is delineated in the northern half of the traverse where a sudden thickening of subtrappean sediments amounting to as much as 2 km is noticed. The high resistive upper crust is relatively thick towards the southern end and tends to become thinner towards the middle and northern part of the traverse. The lower crustal segment is conductive over a major part of the profile. Considering the generally enhanced heat flow values in the NSL region, coupled with characteristic gravity highs and enhanced seismic velocities coinciding with the mid to lower crustal conductors delineated from MT, presence of zones of high density mafic bodies/intrusives with fluids, presumably associated with magmatic underplating of the crust in the zone of major tectonic faults in NSL region are inferred. 相似文献