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1.
A crustal tomographic image, from the surface down to 35 km depth beneath the Betic Cordillera (southern Spain), is obtained using data on local earthquakes recorded at stations from the National and Andalusian Seismic Networks. The velocity structure and the hypocentre locations are derived from the inversion of P first arrival times, using an iterative simultaneous inversion method. The reliability of the results is assessed using different control parameters. The inverted velocity field in the uppermost layers shows a significant lateral variability which reflects most of the large-scale geological features of the Betic Cordillera. Well determined local surface anomalies allow to constrain the location and geometry of the most prominent Neogene sedimentary basins. The upper crust is well resolved throughout the whole region, and is characterized by relatively high velocities in the Internal Betics and in the South Iberian Massif and lower velocities within the External Betics. A relatively well constrained event cluster displays a NNE–SSW trend, and outlines the contact zone between the Internal and the External domains. The middle and lower crustal levels show reliable results beneath the central part of the Betic Cordillera. High averaged velocities are obtained within the South Iberian and the Alboran domains, in contrast to a relatively low velocity anomaly which characterizes the boundary between them. These findings support the hypothesis of the lack of well differentiated crustal levels below the contact zone, while crustal layering is better defined beneath the Alboran and the Iberian domains. 相似文献
2.
E. Banda A. Udias St. Mueller J. Mezcua M. Boloix J. Gallart A. Aparicio 《Physics of the Earth and Planetary Interiors》1983,31(4):277-280
Major tectonic units of Spain have been investigated by deep seismic sounding experiments since 1974 to determine crustal structures and to delineate their differences. These areas are the central part of the Hercynian Meseta, and the Alpine chains: the Betic Cordillera in the south, including the Balearic promontory and the Alboran Sea, and the Pyrenees in the north.The main features of the crust and the upper mantle along a NNE-SSW cross-section from the Pyrenees to the Alboran Sea are described.The crust under the Meseta is typical of Hercynian areas found elsewhere in Europe, with an average thickness of 31 km, whereas the two Alpine regions are characterized by very large lateral inhomogeneities, such as rapid thickening of the crust to 50 and 40 km under the Pyrenees and the Betics, respectively. The deep-reaching E-W-trending North Pyrenean fault has a throw of 10–15 km at the base of the crust. A Pn velocity of 8.1 km s?1 is found under the entire Iberian Peninsula.In the Alboran Sea, strongly varying thicknesses of sediments, shallow variable depths to the Moho (～ 13 km under the Alboran ridge), and strong variations of Pn velocity between 7.5 and 8.2 km s?1 have been found. 相似文献
3.
Within the Spain and Moroccan networks, a large volume of seismic data has been collected and used for investigating the lithosphere in the Betic–Rif Cordillera. The present study has two main goals: (1) Use the most actual seismological data from recent earthquakes in the Betic–Rif arc for investigating the lithosphere through the application of seismic local tomography techniques. (2) Define the possible structural blocks and explain the GPS velocities perturbation in this region. The resolution tests results indicate that the calculated images gave a close true structure for the studied regions from 5- to 60-km depth. The resulting tomographic image shows that the presence of two upper crust body (velocity 6.5 km/s) at 3- to 13-km depth between Iberian Betic and Moroccan Rif in the western and in the middle of Alboran Sea also shows the low velocity favoring the presence of melt in the base of these two bodies. The crustal bodies forms tectonic blocks in the Central Rif and in the Central Betic Cordillera. 相似文献
4.
Anisotropy beneath the Iberian Peninsula: The Contribution of the ILIHA-NARS Broad-band Experiment 总被引：1，自引：0，他引：1
—The presence of anisotropy beneath the Iberian Peninsula and its main distinctive features can be established through the analysis of teleseismic shear-wave splitting observed in the ILIHA-NARS experiment. In this experiment, an homogeneous data set is provided by a network of 14 broad-band stations deployed over the entire peninsula for about one year. Even if technical problems led to an amount of data smaller than expected, significant variations in the inferred fast velocity direction are observed for stations located in different Iberian domains. The stations in Central and East Iberia show a fast velocity direction oriented roughly E–W, coincident with previous results in Toledo. A clearly different NE–SW direction is observed in the Ossa-Morena zone, supporting the image from a previous regional experiment. The observed delay times lie between 0.5 and 1 s. Although large-scale mechanisms, such as the absolute plate motion of Eurasia, can be invoked to explain the origin of anisotropic features in many sites, the regional variations observed in some domains imply that differentiated origins of the anisotropy have to be considered, probably related to the particular tectonics in the area. An interesting example of this fact is provided by the stations in the Betic chain; the fast velocity direction inferred for a station located in the limit of the External Betics (South Iberian domain), oriented N80°E, is clearly different from the N15–35°E direction observed in the Internal Betics (Alboran crustal domain), the origin of which has to be related to the Alpine building of the chain. 相似文献
5.
A. Pérez-Peña J. Martín-Davila J. Gárate M. Berrocoso E. Buforn 《Journal of Geodynamics》2010,49(3-4):232-240
The goal of this paper is to study the velocity field and deformation parameters in Southern Spain and surrounding areas (Ibero-Maghrebian region) using GPS episodic measurements. Results are compared to those previously published as well as deformation parameters derived from seismic data. For this purpose, a geodetic GPS network of 12 stations was observed during eight field campaigns from 1998 to 2005 by the San Fernando Naval Observatory (ROA), Spain. Relative GPS velocities in the Gulf of Cadiz with respect to the stable part of Eurasia are ～4.1 mm/yr in a NW–SE to NNW–SSE direction. In the Betics, Alboran Sea and North of Morocco, velocities are ～4.4 mm/yr in a NW–SE direction, and they are ～2.3 mm/yr in a N–S direction in the eastern part of the Iberian Peninsula. These results are in agreement with the anticlockwise rotation of the African plate. GPS strain tensors are determined from the velocity model, to obtain a more realistic crustal deformation model. The Gulf of Cadiz is subjected to uniform horizontal compression in a NNW–SSE direction, with a rotation to N–S in the Alboran Sea and Northern Morocco. An extensional regime in a NW–SE direction, which rotates to W–E, is present in the Internal Betics area. In the Betic, Alboran Sea and North of Morocco regions we compare seismic deformation rates from shallow earthquakes with the determined GPS deformation rates. The comparison indicates a seismic coupling of 27%, while the remaining 73% might be generated in aseismic processes. Deformations measured in the Ibero-Maghrebian region with GPS could be interpreted in terms of either elastic loading or ductile deformation. 相似文献
6.
利用中国东部地震台网和ISC 报告1980~2004年的地震走时数据,反演了黄海及其邻近地区的Pn波速度和各向异性,根据岩石层地幔的横向非均匀性分析了区域地质构造的深部特点.Pn波速度的变化与区域地质构造有一定的对应关系,黄海地区上地幔顶部的P波平均速度较高,没有发现明显的低速异常,表明上地幔顶部不存在大范围的地幔扰动.速度异常的分布表明,南黄海东部和西部有可能分属于不同的构造块体,其间的分界大致对应于南北走向的黄海东部断裂带,具有相对较低的Pn波速度.边界东、西两侧的Pn波各向异性存在明显的差异：南黄海西部Pn波的快波方向以北东—北北东方向为主,反映了海区内部扬子块体向北运动产生的构造变形;南黄海东部Pn波的快波方向为南北方向,与黄海东部断裂带的走向基本一致,说明黄海东部和西部之间存在一个深达岩石层地幔的南北向转换边界.结合相关资料估计黄海东部断裂带在中生代时期发生了右旋走滑运动,以响应中国东部郯庐断裂带的大规模左旋剪切以及南黄海扬子块体的向北嵌入. 相似文献
7.
环渤海地区位于华北克拉通的中东部,是岩石圈破坏和减薄的主要地区,同时也是我国大陆东部强震的多发区和油气田产区,一直是国内外学者研究的重点区域.本研究利用环渤海地区1980—2015年期间中国地震台网高质量Pn波到时数据,反演得到环渤海地区Pn波速度结构及各向异性.结果显示,环渤海地区上地幔顶部的Pn波速度结构存在明显的横向不均匀性,且与区域地质构造有一定相关性.在地形隆起区,如太行山隆起、燕山隆起、鲁西隆起、胶辽隆起及苏鲁褶皱带地区,呈现为低波速异常,说明这些隆起区下方的上地幔存在热物质上涌,而凹陷地区,如华北盆地、南黄海北部盆地和南黄海南部盆地,则表现为高波速异常,说明这些凹陷地区上地幔顶部岩石圈强度较大.地壳内强震主要发生于低波速异常区和高低波速异常过渡带上,说明华北地区地壳强震的发生有可能受到上地幔深部构造的影响.太行山造山带地区Pn波各向异性快波方向为近NNE向,苏鲁褶皱带区域的Pn波各向异性快波方向为近NE向,与断裂带的走向基本一致,表明在地壳形变剧烈的地区,可能受上地幔顶部的深部动力学影响较大.华北盆地的北部和南部各向异性方向存在差异,可能与岩石圈的厚度及热状态的不均匀性有关. 相似文献
8.
简要总结了青藏高原地区Pn波速度结构、各向异性研究进展；介绍了Pn波速度结构、各向异性等在岩石圈结构、构造背景反映等方面的应用研究进展。分析了目前青藏高原Pn波研究中存在的一些问题。 相似文献
9.
—The Betic Cordillera has undergone recent Alpine deformations related to the Eurasian-African plate interaction boundary. Most of the present-day relief has been built up since Tortonian times, and is related to the development of folds and faults that are overprinted on older deformations, and some of the faults may be considered as out-of-sequence. The combination of geophysical and geological data makes it possible to determine the main features of the recent tectonic structures, or those recently active, in its central transect. The main fault is a crustal detachment that separates a footwall constituted by the Iberian Massif and a hanging wall formed by the rocks of the Betic Cordillera. While the footwall is practically undeformed, the hanging wall has been folded and faulted. The folds are mainly E-W to NE-SW and have larger sizes and higher related relieves towards the South. The reverse faults are mainly concentrated in the northern mountain front. However, normal faults affect the southern part of the Cordillera and are associated with the development of large asymmetrical basins such as the Granada Depression. In this setting, the slip along the crustal detachment is variable and should increase southwards. The model of the recent tectonics in the central transect of the Cordillera is compatible with the presence of an active subduction in the Alboran Sea, and contrasts notably with the setting of the eastern Betic Cordillera, mainly deformed by transcurrent faults. 相似文献
10.
Philippe Vernant Abdelali Fadil Taoufik Mourabit Driss Ouazar Achraf Koulali Jose Martin Davila Jorge Garate Simon McClusky Robert Reilinger 《Journal of Geodynamics》2010,49(3-4):123-129
We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ～1–2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains. 相似文献
11.
利用中国地震台网和ISC台站1980～2004年的地震数据，反演了南海东北部及其邻近地区的Pn波速度结构和各向异性.上地幔顶部的速度变化揭示出区域地质构造的深部特征：华南地区速度较高并且变化平缓，具有构造稳定地区的岩石层地幔特征；华南沿海尤其是滨海断裂带附近出现低速异常，表明该断裂可能穿过壳幔边界深达上地幔顶部.南海北部至台湾海峡较高的速度与华南地区类似，反映出大陆边缘和陆架地区的岩石层地幔性质；西沙海槽附近较高的速度不仅反映了华南大陆向南的延伸，而且与海槽裂谷拉张引起的地幔上拱有关，整个南海北部没有发现大规模地幔热流的活动痕迹.相比之下，南海东部次海盆的上地幔顶部存在明显的低速异常，对应于海底扩张中心的地幔上涌区，表明岩石层地幔强烈减薄甚至缺失；台湾东部－吕宋－菲律宾北部的低速异常与地震、火山活动以及岩浆作用紧密相关，揭示了西太平洋岛弧俯冲带的活动特征；南海东北部的洋－陆边界清晰，南海东部和菲律宾海西部较高的速度代表了海洋岩石层地幔的性质.Pn波各向异性反映出区域性构造应力状态及岩石层地幔的变形痕迹：华南地区的各向异性较小，说明这一构造稳定地区的岩石层地幔变形程度较弱；南海北部的快波方向与地壳浅表层构造的伸展方向一致，主要反映了中、新生代以来的大陆边缘张裂和剪切作用对岩石层地幔结构的影响；琉球－台湾－吕宋岛弧两侧各向异性十分强烈，平行于海沟的快波方向表明菲律宾海板块和欧亚大陆的相互作用导致俯冲板块前缘的岩石层地幔强烈变形；台湾东南海域快波方向的变化可能与欧亚大陆和菲律宾海板块俯冲机制的转换以及岩石层被撕裂有关. 相似文献
12.
郯庐断裂带是一条纵贯我国大陆东部NNE走向的巨型深断裂,其中南段及邻区(115°E—122°E,29°N—38°N)跨越了华北断块区、扬子断块区和华南褶皱系三大一级构造单元,由于其重要性和复杂性,长期以来一直是地学家们研究的热点.本文从国际地震中心(ISC)、中国地震台网及区域地震台网的地震观测报告中精心挑选出6381个Pn震相数据,用Pn波时间项层析成像法反演得到了郯庐断裂带中南段及邻区上地幔顶部Pn波速度结构和各向异性.结果显示,研究区上地幔顶部具有显著的横向非均匀性,相对于7.95km·s-1的平均速度而言,Pn波速度值在7.68~8.24km·s-1范围内变化.Pn波速度分布在郯庐断裂带中段和南段具有分段性:沿中段及周边存在一NE向低速异常带,低速可能是由于岩石圈的减薄和软流圈的高温物质沿郯庐带上涌导致;沿南段表现为一NNE向弱高波速异常带,作为高低速的边界带清晰地勾勒出了华北与扬子这两个不同块体,该边界在江苏域向华北地块NW方向凹进.Pn波速度各向异性的强弱与速度分布存在一定的相关性.总体上,如鲁西隆起及以南等低速区、茅山断裂附近的高低速过渡带,其速度各向异性较为强烈;而在具有高速异常的苏北盆地、合肥盆地等稳定区域下方其各向异性较弱.本文通过Pn波震相基本未能探测到郯庐断裂带中段的方位各向异性,推测是上地幔顶部被"冻结"下来的各向异性痕迹被软流圈热物质上涌这一强烈构造运动削弱所导致.南段具有与断裂伸展方向近乎平行的快波速方向.Pn波速度横向变化和强震活动存在一定关联.强震主要发生在Pn波低速异常区或高低速过渡带上.郯城8.5级地震震中位于中段和南段高低速过渡带,该区域也是速度横向变化最大的地方,最容易集中应力和产生应力差. 相似文献
13.
Upper mantle flow beneath the French Massif Central is investigated using teleseismic shear wave splitting induced by seismic anisotropy. About 25 three-component stations (short period, intermediate and broadband) were installed during the period 1998-1999 in the southern Massif Central, from the Clermont Ferrand volcanic area to the Mediterranean Sea. Teleseismic shear waves (SKS, SKKS and PKS) were used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 0.7 and 1.5 s have been observed at most of the sites. The azimuths of the fast split shear waves trend homogeneously NW-SE in the southern Massif Central suggesting a homogeneous mantle flow beneath this area. The observed NW-SE direction differs from the N100°E Pyrenean anisotropy further south. It does not appear to be correlated to Hercynian structures nor to the present-day motion of the plate but is well correlated to the Tertiary extension direction. We propose that the opening of the western Mediterranean induced by the rotation of the Corsica-Sardinia lithospheric block and the roll-back to the SE of the Tethys slab may have generated a large asthenospheric mantle flow beneath the southern Massif Central and a deflection of the up going plume centered beneath the northern Massif Central toward the SE. 相似文献
14.
The presence of continuous upper crustal blocks between the Iberian Betics and Moroccan Rif in the western and middle Alboran Sea, detected with tomography, can add new information about the lithosphere structure and geodynamic evolution in this region. A large volume of seismic data (P and S wave arrival times) has been collected for the period between 1 December 1988 and 31 December 2008 by 57 stations located in northern Morocco (National Institute of Geophysics, CNRST, Rabat), southern Portugal (Instituto de Meteorologia, Lisbon) and Spain (Instituto Geografico National, Madrid) and used to investigate the lithosphere in the western Alboran Sea region. We use a linearized inversion procedure comprising two steps: (1) finding the minimal 1-D model and simultaneous relocation of hypocenters and (2) determination of local velocity structure using linearized inversion. The model parameterization in this method assumes a continuous velocity field. The resolution tests indicate that the calculated images give near true structure imaged at 5 km depth for the Tanger peninsula, the Alhoceima region and southern Spain. At 15, 30 and 45 km depth we observe a near true structure imaged in northern Morocco, and southern Spain. At 60 and 100 km, southern Spain and the SW region of the Alboran Sea give a near true structure. The resulting tomographic image shows the presence of two upper crustal bodies (velocity 6.5 km/s) at 5–10 km depth between the Betics, Rif, western and central Alboran Sea. Low velocities at the base of these two bodies favor the presence of melt. This new evidence proves that the Tethysian ocean upper crust was not totally collapsed or broken down during the late Oligocene–early Miocene. These two blocks of upper crust were initially one block. The geodynamic process in the eastern of the Mediterranean is driven by slab rollback. The delamination process of the lithospheric mantle terminates with the proposed slab rollback in the western part of the Mediterranean. This can be explained by the removal of the major part of the lithosphere beneath the area, except in the SW part of the Alboran Sea where a small part of the lithospheric mantle is still attached and is extends and dips to SE beneath the Rif, slowly peeled back to the west. A second detached lithospheric mantle is located and extends to eastern part of the Rif and dips to the SE. The removal of lithosphere mantle from the base of the crust was replaced and heated by extrusion of asthenospheric material coming from depth to replace the part of crust detached. A combination of isostatic surface/topographic uplift and erosion induced a rapid exhumation and cooling of deep crustal rocks. 相似文献
15.
本文通过面波层析成像得到了中国东部海域及邻近地区的地壳上地幔S波速度图像,给出了主要构造单元的区划及其结构特征,并讨论了速度结构与现今构造活动及构造演化历史的关系.研究区内中下地壳的平均速度与地震活动存在比较显著的关系,强震基本都发生在低速区内或高低速过渡区.太行山以东地壳内存在几条北西向低速带,其中张家口—渤海地震带下方的低速带最为显著.东部海域划分成北黄海、南黄海、东海、和冲绳海槽等4个构造块体.北黄海具有较薄较高速的岩石圈,与南华北盆地类似,推测是中生代特提斯洋向北俯冲造成岩石圈减薄的遗迹.北华北地区具有低速的地壳和较厚的岩石圈,岩石圈地幔速度偏低且上下比较均匀,可能反映中生代沿北方缝合带持续碰撞作用的特点.南黄海具有相对较厚的岩石圈,较多地保存了下扬子克拉通的特征.在下扬子与华北地块的拼合过程中,洋壳俯冲可能是北黄海和苏皖地区上地幔低速特征的成因.在125°E以东的朝鲜半岛地区未发现这一拼合过程的遗迹.有可能整个朝鲜半岛都是华北地块的一部分;但也有可能是太平洋俯冲和日本海张开的作用完全改造了朝鲜半岛的岩石圈上地幔,抹去了以往构造运动的痕迹.东海地区的地壳厚度,特别是岩石圈厚度向冲绳海槽方向减小,反映出菲律宾海板块俯冲在弧后广大地区都有影响.冲绳海槽地区可见俯冲的菲律宾海板片以及板片上方显著低速的地壳和上地幔,为冲绳海槽的弧后扩张机制提供了证据. 相似文献
16.
从西藏南部的定日、嘎拉至青海铜铁山的天然地震探测剖面，实际路线长约２０００ｋｍ，布设了约１１０台便携地震仪，记录了数百次远震和近震事件，采用多种方法进行了资料处理与解释．依据ＳＫＳ，ＰＫＳ，ｐｓ等横波分裂特征计算的青藏高原中部上地幔的地震各向异性表明：研究区各构造单元内的地震各向异性有明显变化，发现上地幔各向异性快速波的偏振方向与造山带的走向不完全一致．在雅江缝合线、崩错－嘉黎、唐古拉山口、昆仑山口几条断裂带处南、北各向异性出现显著的差异，而金沙江缝合线和班公－怒江缝合线的南、北则没有明显的各向异性变化．由Ｐ波走时残差，利用层析技术反演了４００ｋｍ深度内的速度图像，可以看出近地表１００ｋｍ范围内速度的不均匀变化与地表划分的构造单元很吻合，进一步佐证了青藏高原是由不同时期的微板块拼合而成的认识．在青藏高原中部１５０ｋｍ深度以下发现了多处低速区．在金沙江缝合带下方约２００ｋｍ深度处有一长２５０ｋｍ以上、延伸１５０ｋｍ的低速体，推测可能是一地幔柱．利用ＰＳ转换波划分的界面，显示出青藏高原北部具有低速层和高速层交替出现的地壳结构． 相似文献
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对包含大别－苏鲁碰撞造山带在内的东经 １１２°－１２４°,北纬２８°－３９°区域进行地 震层析成像研究,重建其地壳及上部地幔的三维速度图像．结果表明：造山带岩石圈速度横 向不均匀性显著;大别造山带以商城－麻城断裂为界,东侧的大别地块与西侧红安地块在地 壳速度上是两个不同的速度块体;中地壳 １５-２５ｋｍ深度范围内存在低速带,与伸展滑脱构造 有关;南、北大别构造单元之下,莫霍面下凹,地壳内发育了速度为６．５－６．６ｋｍ／ｓ、向北倾斜的 相对高速体,与超高压变质岩体相对应;在大别－苏鲁造山带下方的上部地幔中存在向北倾 斜的板片状高速体,结合已有地质、地球化学证据推测,它是三叠纪俯冲的扬子地块的残留 体;俯冲板片在深部发生了断离．本文利用地震层析成像方法揭示的造山带岩石圈速度结构 细节,对研究与地表地质有关的地球动力学无疑是十分重要的． 相似文献
18.
Azimuthal anisotropy of Rayleigh waves beneath the Tibetan Plateau and adjacent areas 总被引：4，自引：0，他引：4
The crustal and upper mantle azimuthal anisotropy of the Tibetan Plateau and adjacent areas was studied by Rayleigh wave tomography. We collected sufficient broadband digital seismograms trav-ersing the Tibetan Plateau and adjacent areas from available stations, including especially some data from the temporary stations newly deployed in Yunnan, eastern Tibet, and western Sichuan. They made an adequate path coverage in most regions to achieve a reasonable resolution for the inversion. The model resolution tests show that the anisotropic features of scope greater than 400 km and strength greater than 2% are reliable. The azimuthal anisotropy pattern inside the Tibetan Plateau was similar to the characteristic of tectonic partition. The crustal anisotropy strength is greater than 2% in most re-gions of East Tibet, and the anisotropy shows clockwise rotation surrounding the eastern Himalayan syntaxis. Vertically, the anisotropy direction indicates a coherent pattern within the upper crust, lower crust, and lithosphere mantle of the Tibetan Plateau, which also is consistent with GPS velocity field and SKS fast polarization directions. The result supports that the crust-mantle deformation beneath the Tibetan Plateau is vertically coherent. The anisotropy strength of crust and lithospheric upper mantle in Yunnan outside the Tibetan Plateau is lower than 2%, so SKS splitting from core-mantle boundary to station should largely be attributed to the anisotropy of asthenosphere. 相似文献
19.
本研究拾取了中国数字测震台网固定台站记录的2008—2019年期间发生在山西断陷带及邻区2级以上天然地震事件及陕西神木、府谷等3级以上非天然地震事件共25304条高质量Pn到时数据,反演了山西断陷带及邻区上地幔顶部高分辨率Pn波速度结构与各向异性.研究结果显示,山西断陷带及邻区Pn波速度结构差异较大,大同火山及以南区域、忻定盆地、太行山造山带、华北盆地南部和吕梁山局部地区表现为显著的低波速异常,而运城盆地、临汾盆地北部、太原盆地、大同盆地北部、华北盆地北部和鄂尔多斯块体呈现明显的高波速异常.大同火山下方上地幔顶部的低波速异常与Pn快波方向呈现以火山为中心的近发散状结构特征,结合已有的远震上地幔成像结果,暗示大同火山岩浆可能来源于地幔深部,岩浆的底侵或热侵蚀作用造成了该地区岩石圈的破坏以及整个华北克拉通的"活化",这一推论符合克拉通的热-化学侵蚀破坏模型.山西断陷带上地幔顶部速度异常形态较好的对应了研究区的地质构造,Pn快波速方向与地质构造的展布方向和SKS波各向异性的特征基本一致,说明变形形式以简单剪切为主,表明其形成和演化过程与上地幔物质运移过程有密切关系. 相似文献
20.
本文分析了华北地区近50个台站下方800 km深度内的剪切波速度结构.结果发现华北地区不同构造单元之间速度结构差异很大，稳定地块速度随深度稳定增加，构造带内速度结构复杂，而且即使在同一构造单元内，不同区段之间速度结构也明显不同，如太行山构造带，反映了不同构造单元或各区段经历了各自不同的地质演化历史.环渤海地区及相关区域多个台站的速度结构显示，华北东部地区地幔软流层埋深浅、厚度大、速度低，反映了地幔上涌的特点；而在软流层或更深层次的地幔中没有发现埋深或厚度比较统一的高速或低速体，因此可能没有岩石圈或下地壳介质曾经拆沉进入地幔，这为东部岩石圈减薄的动力学机制提供了一定的深部地球物理约束. 相似文献