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1.
川滇地区地壳上地幔三维速度结构研究 总被引：95，自引：22，他引：95
根据云南和四川地震台网174个台站记录的4625个区域地震初至Ｐ波和Ｓ波走时资料，并结合其它深部地球物理资料，确定了川滇地区地壳上地幔三维速度结构．在上地壳速度异常分布中，四川盆地为正异常，川西高原为负异常，龙门山断裂带为正、负异常的边界．龙门山断裂、鲜水河断裂以及红河断裂等，在下地壳和上地幔的速度异常中仍显示出构造分界特征，说明它们可能穿透了莫霍界面．腾冲火山区和攀西构造带在50km深度上呈现负速度异常，与上地幔温度和物质组成的差异相联系．川滇地区地壳结构的总体特征是:地壳和上地幔的低平均速度，地壳厚度变化剧烈，地壳和（或）上地幔存在高导层、高热流值．这些同印度板块与欧亚板块碰撞的构造背景有关．川滇菱形块体在地壳内总体上为正常或正异常速度，而其边界的深大走滑断裂存在负速度异常，它有助于地壳块体沿断裂的侧向挤出．在主要的地震带上，中下地壳的负速度异常与地震活动性相关．多数强烈地震发生在具有正速度异常或正常速度分布的上中地壳深度上，而其下方则通常是负速度异常带． 相似文献
2.
A study on 3-D velocity structure of crust and upper mantle in Sichuan -Yunnan region, China 总被引：1，自引：0，他引：1
Many evidences indicate that the collision of two plates deformed strongly the crust of the SYR, and the deformation has been continued up to the present. In addition, the SYR is in the south segment of the South-North Seismic Zone of China, which is one of the regions in the Chinese mainland, where the seismic activity is very high, and the strong earthquakes frequently occurred. Since the 1970s, a series of large earthquakes with magnitude M>7.0 occurred in SYR, such as the 1970 Tongha… 相似文献
3.
本文使用川西密集地震台阵记录的面波资料，利用程函方程面波成像方法获得了周期为14—60 s的瑞雷波相速度及方位各向异性分布。结果显示:川滇菱形地块的川西北地块内部的低速异常明显，其下地壳各向异性快波方向以NS向为主，松潘—甘孜地块内部的低速异常稍弱，下地壳各向异性快波方向以NW?SESE向为主，表明川西北地块可能存在下地壳通道流，松潘—甘孜地块内部存在的通道流相对较弱；龙门山断裂带和丽江—小金河断裂两侧的速度结构和方位各向异性均有明显差异，可推测青藏高原内部的地壳流在东部和南部分别受高速、高强度的四川盆地和滇中地块阻挡，沿高原边界带发生了侧向流动；周期大于25 s的面波方位各向异性方向为NW?SE；与SKS分裂优势方向相近，说明四川盆地的剪切波各向异性可能主要源于上地幔；而龙门山断裂带附近壳幔各向异性较为复杂，面波方位各向异性与SKS分裂的NW?SE向弱各向异性存在差异，表明该处的剪切波各向异性可能来自地幔更深处，有待进一步研究。 相似文献
4.
In recent years, strong earthquakes of MS8.0 Wenchuan and MS7.0 Lushan occurred in the central-southern part of Longmenshan fault zone. The distance between the two earthquakes is less than 80 kilometers. So if we can obtain the inner structure of the crust and upper mantle, it will benefit us to understand the mechanism of the two earthquakes. Based on the high resolution dataset of Bouguer gravity anomaly data and the initial model constrained by three-dimensional tomography results of P-wave velocity in Sichuan-Yunnan region, with the help of the preconditioned conjugate gradient(PCG)inversion method, we established the three dimensional density structure model of the crust and upper mantle of the central-southern segment of Longmenshan, the spatial interval of which is 10 kilometers along the horizontal direction and 5 kilometers along the depth which is limited to 0~65km, respectively. This model also provides a new geophysical model for studying the crustal structure of western Sichuan plateau and Sichuan Basin. The results show obvious differences in the crustal density structure on both sides(Songpan-Ganzê block and Sichuan Basin)of Longmenshan fault zone which is a boundary fault and controls the inner crustal structure. In Sichuan Basin, the sedimentary layer is represented as low density structure which is about 10km thick. In contrast, the upper crust of Songpan-Ganzê block shows a thinner sedimentary layer and higher density structure where bedrock is exposed. Furthermore, there is a wide scale low density layer in the middle crust of the Songpan-Ganzê block. Based on this, we inferred that the medium intensity of the Songpan-Ganzê block is significantly lower than that of Sichuan Basin. As a result, the eastward movement of material of the Qinghai-Tibet plateau, blocked by the Sichuan Basin, is inevitably impacted, resulting in compressional deformation and uplift, forming the Longmenshan thrust-nappe tectonic belt at the same time. The result also presents that the crustal structure has a distinct segmental feature along the Longmenshan fault zone, which is characterized by obviously discontinuous changes in crustal density. Moreover, a lot of high- and low-density structures appear around the epicenters of Wenchuan and Lushan earthquakes. Combining with the projection of the precise locating earthquake results, it is found that Longmenshan fault zone in the upper crust shows obvious segmentation, both Wenchuan and Lushan earthquake occurred in the high density side of the density gradient zone. Wenchuan earthquake and its aftershocks are mainly distributed in the west of central Longmenshan fault zone. In the south of Maoxian-Beichuan, its aftershocks occurred in high density area and the majority of them are thrust earthquake. In the north of Maoxian-Beichuan, its aftershocks occurred in the low density area and the majority of them are strike-slip earthquake. The Lushan earthquake and its aftershocks are concentrated near the gradient zone of crustal density and tend to the side of the high density zone. The aftershocks of Lushan earthquake ended at the edge of low-density zone which is in EW direction in the north Baoxing. The leading edge of Sichuan Basin, which has high density in the lower crust, expands toward the Qinghai-Tibet Plateau with the increase of depth, and is close to the west of the Longmenshan fault zone at the top of upper mantle. Our results show that there are a lot of low density bodies in the middle and lower crust of Songpan-Ganzê Block. With the increase of the depth, the low density bodies are moving to the south and its direction changed. This phenomenon shows that the depth and surface structure of Songpan-Ganzê Block are not consistent, suggesting that the crust and upper mantle are decoupled. Although a certain scale of low-density bodies are distributed in the middle and lower crust of Songpan-Ganzê, their connectivity is poor. There are some low-density anomalies in the floor plan. It is hard to give clear evidence to prove whether the lower crust flow exists. 相似文献
5.
利用川滇地区长期积累的地震走时观测资料和汶川地震余震观测资料对汶川地震震源区及周边区域地壳和上地幔P波三维速度结构进行了研究.结果表明,浅部P波速度分布与地表地质之间具有很好的对应关系.龙门山断裂带在20 km以上深度表现为高速异常带,彭灌杂岩体和宝兴杂岩体为局部高速异常区.龙门山断裂带中上地壳的局部高速异常体对汶川地震的余震分布具有明显的控制作用.在余震带南端,余震全部发生在与宝兴杂岩体对应的高速异常体的东北侧;在余震带的中段,与彭灌杂岩体对应的高速异常体在一定程度上控制了余震的分布;在余震带的东北端,宁强-勉县一带的高速异常体可能阻止了余震进一步向东北扩展.龙门山断裂带中上地壳的P波高速异常表明介质具有相对较高的强度,在青藏高原物质向东挤出过程中起到了较强的阻挡作用,有利于深部能量积累.在30 km深度之下,扬子地块具有明显的高速特征,其前缘随深度增加向青藏高原方向扩展,在下地壳和上地幔顶部已达到龙门山断裂带以西. 相似文献
6.
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
7.
为了揭示巴颜喀拉地块东缘及邻区的壳幔速度结构差异，获取2017年九寨沟MS7.0地震的深部构造背景，本文收集了2009年5月至2016年8月期间四川及邻区数字测震台网的203个地震台站所记录到的远震P波走时数据，应用有限频体波走时层析成像方法，反演得到了巴颜喀拉地块东缘及邻区50—600 km深度范围内的三维壳幔P波速度结构。反演结果表明:巴颜喀拉地块东缘及邻区的壳幔速度结构具有明显的横向不均匀性和分区特征，松潘—甘孜地槽褶皱系、西秦岭和祁连山褶皱系的整体速度异常较低，研究区东部具有克拉通性质的四川盆地西北缘和鄂尔多斯地块南缘则呈明显的高速异常。上地幔P波速度结构特征差异表明松潘—甘孜地块的抬升可能与地幔上涌有关，巴颜喀拉地块东缘九寨沟震区及周边50—250 km深度范围内的上地幔存在低速异常，在400—600 km地幔过渡带深度范围内表现为明显的高速异常特征。巴颜喀拉地块向东南方向运移受到东部高速、高强度的扬子克拉通地块对青藏高原物质东向挤出的强烈阻挡，而九寨沟震区处于松潘—甘孜地块重要的北东边界断裂交会处附近，应力容易在此集中，这些因素均可能是东昆仑断裂塔藏段与岷江断裂北段交会处附近发生九寨沟MS7.0地震的深部动力学背景。 相似文献
8.
青藏高原是全球造山带研究的热点地区,此前在青藏高原开展的三维层析成像研究大多基于线性反演方法.本文利用青藏高原东缘及邻区布设的127个宽频带固定地震台站记录的连续波形资料,首先通过噪声互相关提取了3～50sRayleigh波群速度频散曲线并反演得到群速度分布,再进一步采用模拟退火法反演了研究区的三维S波速度及泊松比结构.结果显示:(1)松潘—甘孜地块的中下地壳低速异常主要分布在龙日坝断裂带、鲜水河断裂带、龙门山断裂带和岷山隆起所围限的区域,而该区域的中下地壳仅具有中等泊松比值,推测松潘—甘孜地块中下地壳的低速物质可能是青藏高原与扬子块体长期相互作用产生的塑性低速滑脱层;上地壳脆性物质在板块作用下沿中地壳低速滑脱层顶界面发生逆冲增厚,造成龙门山的持续抬升和地形起伏,并在构造边界带形成了应变积累和应力集中;而龙门山断裂带的上地壳低速软弱物质为地壳发生破裂提供了有利条件,从而在某种程度上促进了汶川地震和芦山地震的发生.(2)岷山隆起一带中下地壳的高泊松比异常呈"凸起"形态,结合前人研究发现的较高热流和岩石快速抬升现象,推测岷山隆起一带可能存在岩石圈的拆沉,导致地幔热物质上涌而形成下地壳高泊松比物质.(3)川滇地块的北部和南部具有不同的S波速度和泊松比分布特征.30km深度下川滇地块北部具有明显的低速异常,而该深度下并不具有明显的高泊松比值特征;此外剖面成像结果也显示川滇地块内的低速异常与高泊松比的分布不一致,因此川滇地块的研究结果不支持下地壳流模型.综合其他地震学证据,本文认为川滇地块的变形模式为上地壳纯剪切增厚,块体变形主要受块体内部的走滑断裂及活动边界断裂控制. 相似文献
9.
利用云南和四川数字地震观测台网记录的数字化地震资料,开展了川滇地区不同频率的QLg层析成像研究,反演结果的空间分辨率小于100 km.反演结果表明,川滇地区介质的横向不均匀性强烈,QLg高低值差异显著.川滇地区显著的高衰减区有川滇菱形块体的东南边界（即沿鲜水河至安宁河以及思茅—澜沧—普洱区）,滇西北地区、龙门山断裂以西松潘—茂文地区、巴塘及理塘强震区等,Lg波高衰减区的分布与构造活动强烈、强震活动或大震破裂造成介质破碎区、低速区等相关,表明构造活动强烈或大震破裂造成的介质破碎、热物质沿活动断裂上涌等可能是川滇地区低QLg的主要成因.显著的低衰减区有川东盆地、滇东南地区以及金沙江、怒江断裂的中段区域,滇中块体内部也呈现出相对的低衰减特征.Lg波低衰减区与地震活动性弱、速度正异常等相关,表明川滇地区Lg波的低衰减区与地壳变形、地震活动性及水热活动弱、块体稳定等有关. 相似文献
10.
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
11.
龙门山断裂带位于青藏高原东缘,在中生代和晚新生代经历强烈的构造变形,急剧抬升,是研究青藏高原隆升和扩展动力学过程的重要窗口.本文利用起伏地形下的高精度成像方法,对"阿坝一龙门山一遂宁"宽角反射/折射地震数据重新处理,通过走时反演重建研究区地壳速度结构.剖面自西向东跨越松潘一甘孜块体、龙门山断裂带和四川盆地,不同块体速度结构表现了显著的差异.松潘甘孜块体地表复理石沉积层内有高速岩体侵入,低速层低界面起伏不平反映了该区的逆冲推覆构造.中下地壳速度横向上连续变化,平均速度较低(约6.26 km·s~(-1)).四川盆地沉积层西厚东薄,并在西侧出现与挤压和剥蚀作用相关的压扭形态.中下地壳西薄东厚,平均速度较高(约6.39 km.s~(-1)).龙门山断裂带是地壳速度和厚度的陡变带,Moho面自西向东抬升约13 km.在整个剖面上Moho面表现为韧性挠曲,中下地壳横向上连续变化,推测古扬子块体已到达松潘甘孜块体下方.松潘甘孜块体下方中下地壳韧性变形,并在底部拖曳着被断裂切割的脆性上地壳,应力在不同断裂上积累和释放,诱发大量地震. 相似文献
12.
芦山—康定地区是川滇块体、松潘—甘孜块体和华南块体三个块体过渡的"Y"型交汇区,构造变形十分强烈.本文对EGM2008计算的布格重力异常进行1~5阶离散小波变换,得到三方向分量平方和的平方根(HVDM)图像;利用实测剖面布格重力异常数据,得到剖面的布格重力异常归一化总梯度(NFG)图像.结果分析表明:(1)垂直于龙门山断裂带南段剖面的NFG图像显示推覆构造体前端切割较浅、后端逐步变深至中地壳,说明松潘—甘孜块体在深约10~30km之间存在滑脱构造,在青藏高原东向挤出和四川盆地的阻挡作用下,造成深、浅部构造差异性运动,形成逆冲推覆的龙门山构造带;(2)HVDM图像和剖面的NFG图像均显示龙门山断裂带西南段与中段和东北段不同,松潘—甘孜块体对四川盆地的逆冲推覆作用沿北东方向具有分段性;(3)雅江—洪雅剖面NFG图像显示鲜水河断裂带和龙门山断裂之间存在高梯度变化带,在鲜水河断裂带下方强变形带不仅在20km左右东倾至龙门山断裂带前缘,且逐渐近垂直向下伸入至少到下地壳,反映了两大断裂带交汇区域变形作用较强.川滇块体内部和四川盆地内部则显示低值,说明其变形作用较弱.强烈左旋剪切的鲜水河断裂带对芦山—康定地区构造活动具有主要的控制作用. 相似文献
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本文联合使用云南、四川和贵州地震台网的85个地震台站在2008年1月—2017年12月期间记录的49130个地震、317366个初至Pg震相绝对到时数据和2674110条高精度的相对到时数据,采用区域双差地震层析成像方法联合反演了川滇南部地壳三维P波速度结构和39621个地震的震源参数,探究了川滇南部中下地壳流和腾冲火山区岩浆囊的分布特征.研究结果表明：（1）川滇南部上地壳的速度异常特征与地表地形密切相关;（2）小江断裂带的中下地壳存在一条绵延近二百多公里的低速异常结构,最南端受到红河断裂带的阻挡而终止于断裂带南段北侧,这可能是川滇南部的一条中下地壳流,低速异常结构在红河断裂带南段转而向南东流动反映了红河断裂带可能为川滇菱形块体的西南边界;（3）红河断裂带各段速度异常存在明显的差异,重定位后的震源分布显示红河断裂带中段和南段虽然不如北段地震活动强烈,但地震震源深度分布较北段深;（4）腾冲火山区西侧和北侧下方10~20 km深度范围内存在的低速异常体推测为通过怒江断裂带形成的岩浆通道从中地壳涌入上地壳的岩浆囊,可能反映了自更新世延续至今的以橄榄玄武岩和安山岩为主要岩性的壳内岩浆活动,持续的岩浆活动为地表热活动提供了主要动力. 相似文献
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本文利用川西地震台阵记录到的远震P波走时数据和非线性层析成像算法,获得龙门山地区400 km深度范围内的三维P波速度结构.为了适应川西地区复杂的地质结构,本文的层析成像方法采用了快速行进三维走时计算算法和Tarantola非线性反演算法.我们的结果揭示了川滇地块、松潘-甘孜地块和四川盆地三个不同地块构造差异及该区深部动力学特征.本文的研究表明：1）研究区地壳上地幔P波速度结构具有较为明显的分区特征,松潘-甘孜地块和川滇地块岩石圈速度较低,四川盆地岩石圈速度较高,四川盆地的岩石圈厚度从南250 km向北逐渐减薄至100 km.松潘-甘孜地块上地幔存在地幔上涌的特征.2）川滇地块和四川盆地仅是垂直接触关系,而在龙门山地区四川盆地前缘存在减薄的现象,并伴随松潘-甘孜地块上地幔低速物质有侵入四川盆地岩石圈下方的特征,这显示了四川盆地与松潘-甘孜地块和川滇地块的动力学关系的差异.3）以映秀为界,龙门山断裂带被从松潘-甘孜侵入的低速异常分为南北两段：龙门山南段和龙门山北段,汶川大地震及其余震序列均分布在龙门山断裂带的北段.在青藏高原向东挤压和地幔上涌的双重作用下造成松潘-甘孜地块隆升,由于汶川处于龙门山北段的最南端,应力容易在此集中.这些因素可能是汶川MS8.0地震的基本动力学背景.本文的结果不支持四川盆地的俯冲及层间流动的动力学模型. 相似文献
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通过反演大量的纵、横波地震数据,获得了沿龙门山断裂带及周边区域的深部三维精细结构,结合前人二维大地电磁探测研究成果,提出龙门山断裂带地壳形变与深部速度结构和导电率不均匀性有关,探讨了2008年汶川和2013年芦山地震的诱发和产生与流体侵入及地壳形变的密切关系.本研究发现,2008年汶川地震发生在高速度、高泊松比和低电导率的区域,2013年芦山地震则位于高速度、低泊松比和低电导率的发震层.在上地壳中,四川前陆盆地的低速、低泊松比和低阻异常与松潘一甘孜地块的高速、高泊松比和高阻异常形成了鲜明的对比.在龙门山断裂带下方的两个低速和低阻块体,将龙门山断裂带分成南、中和北三段.我们的研究认为,这两个异常体与来自松潘甘孜地块的下地壳和(或)上地幔的局部熔融或流体侵入到龙门山断裂带的脆弱区有关.基于对汶川和芦山地震的余震分布特征及震源区的地震波速度、泊松比及电阻率参数分析,揭示了龙门山断裂带深部剧烈的地壳形变与流体应力积累对2008年汶川和2013年芦山地震的触发及其地震破裂过程具有重要的控制作用. 相似文献
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THE 3-D VELOCITY STRUCTURE OF CRUST AND UPPERMOST MANTLE AND ITS TECTONIC IMPLICATIONS IN FUJIAN PROVINCE 
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下载免费PDF全文 It is important to detect the fine velocity structures of the crust and uppermost mantle to understand the regional tectonic evolution, earthquake generation processes, and to conduct earthquake risk assessment. The inversion of uppermost mantle velocity and Moho depth are strongly influenced by crustal velocity heterogeneity. In this study, we collected first arrivals of Pg and Pn and secondary arrivals of Pg wave from the seismograms recorded at Fujian provincial seismic network stations. New 3-D P-wave velocities were inverted by multi-phase joint inversion method in Fujian Province. Our results show that the fault zones in Fujian Province have various velocity patterns. The shallow crust is characterized by high velocity that represents mountains, while the mid-lower crust shows low velocities. The anomalous velocities are correlated closely with tectonic faults in Fujian Province. Velocity anomalies mainly show NE-trending distribution, especially in the mid-lower crust and uppermost mantle, which is consistent with the NE-trending of the regional main fault zones. Meanwhile, a part of velocity patterns show NW trending, which is related to the secondary NW-oriented faults. Such velocity distribution also shows a geological structural pattern of "zoning in east-west direction and blocking in north-south direction" in Fujian area.
In the crust, a low velocity zone is found along Zhenghe-Dapu fault zone as mentioned by previous study, however our result shows the low velocity exists at depth of 20~30km in mid-lower crust. Compared with previous study, this low velocity zone is larger and deeper both in range and depth.
The crustal thickness of 28~35km from our joint inversion is similar to the results from the receiver functions of previous studies. The thinnest crust(28km)is observed at offshore in the north of Quanzhou; while the thickest crust(35km)is located west of Zhangzhou near the Zhenghe-Dapu fault zone. Generally, thinner crustal thickness is found in offshore of Fujian Province, and thicker crustal thickness is in the mainland. However, we also found that crustal thickness becomes thinner along the east side of Yongan-Jinjiang Fault.
The values of Pn velocities in the region vary from 7.71 to 8.26km/s. The velocity distribution of the uppermost mantle presents a large inhomogeneity, which is correlated with the distribution of the fault zone. High Pn velocity anomalies are found mainly along the west side of the Zhenghe-Dapu fault zone(F2), and the east side of the Shaowu-Heyuan fault zone(F1), which is strip-shaped throughout the central part of Fujian. Low Pn velocity anomalies are observed along the coast and Taiwan Straits, including the Changle-Zhaoan fault zone, the coastal fault zone, and the Fuzhou Basin. We also found a low Pn velocity anomaly zone, which extends to the coast, in the Shaowu-Heyuan fault zone at the junction of the Fujian, Guangdong and Jiangxi Provinces. In the west of Taiwan Straits, both high and low Pn velocity anomalies are observed.
Our results show that the historical strong earthquakes(larger than magnitude 6.0) are mainly distributed between positive and negative anomaly zones at different depth profiles of the crust, and similar anomalies distribution also exists at the uppermost mantle, suggesting that the occurrence of strong earthquakes in the region is not only related to the anomalous crustal velocity structure, but also affected by the velocity anomaly structure from the uppermost mantle. 相似文献
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作为青藏高原的东南边界,小江断裂带在高原物质的侧向逃逸中发挥着重要的作用.本文利用流动地震台阵及固定台站的走时观测资料,对小江断裂带及周边区域的壳幔三维P波速度结构进行了研究.结果表明,在中上地壳,小江断裂带内部主要为低速异常,其东侧主要为高速异常.在中下地壳,小江断裂带中部为低速异常,北部和南部主要为高速异常,其中北部的高速异常可延伸到地表附近,南部的高速异常可一直延伸到上地幔.我们推测,小江断裂带中部的低速异常与深部热作用有关;北部的高速异常可能是晚古生代地幔柱活动导致大量基性和超基性幔源物质侵入地壳引起的,它的存在对青藏高原物质向南逃逸起到了一定的阻挡作用,可能是导致川滇活动块体北部次级块体快速抬升的重要因素;南部顶界面向北倾斜的高速异常体对川滇活动块体向南滑移起到了进一步的阻挡作用,导致其上覆的中上地壳低速异常区发生较强的变形和强烈的地震活动,同时在上地幔深度范围起到了稳定的作用,使其南部区域的介质受青藏高原物质向南挤出的影响明显减小. 相似文献
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Study on distribution characteristics of strong earthquakes in Sichuan-Yunnan area and their geological tectonic background 总被引：2，自引：0，他引：2
Introduction Both Sichuan and Yunnan are provinces with more earthquakes. Based on catalogue of strong earthquakes in China compiled by the Prediction Department of China Earthquake Administration, there are 639 M5.0 earthquakes during 26 B.C.~A.D. 2001. Among them, 475 are M=5.0~5.9 events, 124 are M=6.0~6.9 events, 39 are M=7.0~7.9 events, and one is M=8 event occurred in Sichuan and Yunnan area. Here is one of the areas where seismic activities are most active in China. Sichuan-Yun… 相似文献
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经过数十年的努力,中国学者针对青藏高原东缘地壳上地幔探测,累积完成超过20000 km的大地电磁测深剖面,取得了一系列重要科学数据和认识,为青藏高原东缘构造格局、地壳上地幔电性结构、地震机制和动力学研究奠定了基础.根据青藏高原东缘的主要构造和断裂分布特征,本文重点对龙门山构造带、川滇构造带和三江构造带三个构造带分区进行研究,主要依据大地电磁探测工作成果和壳幔电性结构特征,系统地对青藏高原东缘地壳上地幔电性结构、与扬子西缘接触关系、汶川地震和芦山地震的电性孕震环境及弱物质流通道等几个方面进行了梳理和分析.一是青藏高原东缘地壳表层岩块和物质沿壳内高导层向龙门山造山带仰冲推覆,表现为逆冲推覆特征的薄皮构造;二是高原东部地壳中下部及上地幔顶部向龙门山造山带和上扬子地块西缘岩石圈深部俯冲,呈现刚性的上扬子地块西缘高阻楔形体向西插入柔性青藏块体的楔形构造;三是将汶川地震和芦山地震的震源投影到大地电磁剖面上,发现震源位于剖面下方的高阻块体与低阻体之间靠近高阻体的一侧,龙门山构造带岩石圈表现出高阻、高密度和高速的"三高"特征,这种非均匀电性结构可能构成地震孕育发生条件;四是川滇和三江地区的多条大地电磁剖面探测结果表明,在青藏高原东缘中下地壳存在下地壳流和局部管道流,大地电磁结果对其空间分布形态、位置及大小进行了较好的刻画.根据研究区壳幔电性结构特征的构造解析和综合实例分析,总结了青藏高原东缘六类壳幔电性结构模型,提出了下一步重点研究领域和目标.总之,青藏高原东缘壳幔电性结构的研究对揭示研究区岩石圈结构和构造格局提供了重要依据,对油气及矿产资源远景评价提供了背景资料,对"Y"型多地震区的构造关系和发震机理研究具有重要指导意义. 相似文献