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1.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(3):253-260
3-D elastic structures images of the Mediterranean basin are obtained by solving a tomographic problem by means of a simulated annealing algorithm. The database consists of local Rayleigh wave group velocities determined for the fundamental mode in the 10–90s period range. These local velocities were obtained from surface wavetrains recorded at very broad band stations of MEDNET network. From a methodological point of view, the characteristics of the annealing algorithm and the amount of time required for computation suggest the implementation of parallel computational procedures to shorten the computational time. According to the thermodynamic analogies used in the annealing algorithm, we propose an alternative procedure to estimate uncertainties and correlations for variables defining the elastic model (shear velocities and layer thicknesses) without necessity of computing partial derivatives. From an applied point of view, the 3-D elastic model obtained shows, as main results, relevant differences for the eastern and western pans of the Mediterranean basin, specially down to 60 km. The changes in the position of the top and bottom asthenosphere surfaces can also be followed throughout the Mediterranean basin; remarkably, these changes are in agreement with some tectonic features. 相似文献
2.
We present a new three-dimensional SV-wave velocity model for the upper mantle beneath South America and the surrounding oceans, built from the waveform inversion of 5850 Rayleigh wave seismograms. The dense path coverage and the use of higher modes to supplement the fundamental mode of surface waves allow us to constrain seismic heterogeneities with horizontal wavelengths of a few hundred kilometres in the uppermost 400 km of the mantle.The large scale features of our tomographic model confirm previous results from global and regional tomographic studies (e.g. the depth extent of the high velocity cratonic roots down to about 200–250 km).Several new features are highlighted in our model. Down to 100 km depth, the high velocity lid beneath the Amazonian craton is separated in two parts associated with the Guyana and Guapore shields, suggesting that the rifting episode responsible for the formation of the Amazon basin has involved a significant part of the lithosphere. Along the Andean subduction belt, the structure of the high velocity anomaly associated with the sudbduction of the Nazca plate beneath the South American plate reflects the along-strike variation in dip of the subducting plate. Slow velocities are observed down to about 100 km and 150 km at the intersection of the Carnegie and Chile ridges with the continent and are likely to represent the thermal anomalies associated with the subducted ridges. These lowered velocities might correspond to zones of weakness in the subducted plate and may have led to the formation of “slab windows” developed through unzipping of the subducted ridges; these windows might accommodate a transfer of asthenospheric mantle from the Pacific to the Atlantic ocean. From 150 to 250 km depth, the subducting Nazca plate is associated with high seismic velocities between 5°S and 37°S. We find high seismic velocities beneath the Paraná basin down to about 200 km depth, underlain by a low velocity anomaly in the depth range 200–400 km located beneath the Ponta Grossa arc at the southern tip of the basin. This high velocity anomaly is located southward of a narrow S-wave low velocity structure observed between 200 and 500–600 km depth in body wave studies, but irresolvable with our long period datasets. Both anomalies point to a model in which several, possibly diachronous, plumes have risen to the surface to generate the Paraná large igneous province (LIP). 相似文献
3.
A passive seismic experiment across the Longmenshan (LMS) fault belt had been conducted between August 2006 and July 2007 for the understanding of geodynamic process between the Eastern Tibet and Sichuan basin. We herein collected 3677 first P arrival times with high precision from seismograms of 288 teleseismic events so as to reconstruct the upper mantle velocity structure. Our results show that the depth of the Lithosphere–asthenosphere boundary (LAB) changes from 70 km beneath Eastern Tibet to about 110 km beneath Longquanshan, Sichuan Basin, which is consistent with the receiver function imaging results. The very thin mantle part of the lithosphere beneath Eastern Tibet may suggest the lithosphere delamination due to strong interaction between the Tibetan eastward escaping flow and the rigid resisting Sichuan basin, which can be further supported by the existences of two high-velocity anomalies beneath LAB in our imaging result. We also find there are two related low-velocity anomalies beneath the LMS fault belt, which may indicate magmatic upwelling from lithosphere delamination and account for the origin of tremendous energy needed by the devastating Wenchuan earthquake. 相似文献
4.
This paper investigates the shear velocity structure under the northern East Pacific Rise at the latitude range of 9–18°N, using intermediate-period Rayleigh and Love waves. The selected ocean-bottom seismic records provide source–receiver paths that ideally constrain the lithospheric mantle structure beneath the southern Rivera plate and the Mathematician paleoplate. The Rayleigh wave data infer a relatively thin ( 30 km) lithosphere under the eastern side of the present-day East Pacific Rise. The associated shear velocities are consistent with existing models of oceanic mantle beneath this region, and the estimated plate age of 2–3 million years agrees with results from magnetic dating. The west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank, and such structural differences suggest the presence of a relatively old Mathematician paleoplate. The discontinuous change in mantle structure across the East Pacific Rise spreading center are observed in both isotropic and anisotropic velocities. The young oceanic lithosphere east of the rise axis shows strong polarization anisotropy, where the dominant orientation of crystallographic axes roughly parallels the spreading direction. However, the western flank of the rise axis is approximately isotropic, and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation, propagation and dual-spreading on and around the Mathematician paleoplate. 相似文献
5.
Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green’s functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ∼8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore. 相似文献
6.
Structure and seismicity of the Aegean subduction zone 总被引：1，自引：0，他引：1
Tomographic results show the presence of a high-velocity anomaly dipping north beneath the Aegean Sea (Hellenic arc), down to a depth of at least 600 km. This anomaly is interpreted as the image of the subducting lithosphere of the African plate. No deep seismicity, however, is associated with this downgoing slab, although this would be expected on the basis of the age of the downbending lithosphere (approximately 100 Myr) and the inferred duration of the present ongoing episode of subduction. Using a thermo-mechanical model for the subduction zone we find that the non-stationary input of the subduction zone-both in convergence rate and in thermal structure of the downgoing lithosphere - adequately accounts for both the presence of a velocity anomaly associated with a slab and the absence of deep seismicity. The non-stationarity follows from the large-scale tectonic setting of the Eastern Mediterranean basin. 相似文献
7.
新生代以来,共和盆地及其周缘造山带无火山、岩浆活动,印支期隐伏花岗岩体岩浆余热与放射性元素衰变生热等难以构成共和盆地干热岩资源的主要热源,而共和盆地又为一高温地热异常盆地.目前已基本探明了共和县恰卜恰与贵德县热水泉干热岩体2处,圈定出干热岩勘查目标靶区16处.区域重力和区域航磁调查、区域天然地震成像、盆地尺度天然地震背景噪声层析成像勘查,以及超高分辨率重力异常、电阻率与Rayleigh波群相速度线性反演结果均表明共和盆地下伏发育有壳内部分熔融层,进而构成地处板内环境、高热流区共和盆地干热岩资源的区域性热源.盆地尺度MT勘查结果表明,共和盆地西盆地壳内部分熔融层埋深15~35 km,东西向长约41 km,南北向宽约34 km,厚度2~12 km.综合分析认为,该部分熔融层熔融程度最高可达4%~7%,15 km深处温度约为574℃,主体位于贵南南山推覆体系与共和准推覆体系深部主拆离滑脱推覆界面之下,兴海大型复合推覆体系主拆离滑脱推覆界面之上.挽近地质时期深构相、多层次、近水平展布的韧性拆离滑脱推覆构造界面的连续动态剪切摩擦生热,可能是部分熔融层形成的主要因素. 相似文献
8.
K. Priestley 《Lithos》1999,48(1-4):45-56
The velocity model for southern Africa of Qiu et al. [Qiu, X., Priestley, K., McKenzie, D., 1996. Average lithospheric structure of southern Africa. Geophys. J. Int. 127, 563–587] is revised so as to satisfy both the regional seismic waveform data and the fundamental mode Rayleigh wave phase velocity data for the region. The revised S-wave model is similar to the original model of Qiu et al. except that the high velocity, upper mantle lid extends to 160 km depth in the revised model rather than to 120 km in the original model. Sensitivity tests of the regional seismic data show that the minimum velocity in the S-wave low velocity zone can be as high as 4.45 km s−1 compared to 4.32 km s−1 in the Qiu et al. model. The vertical S-wave travel time for the revised south African model is compared with the vertical S-wave travel times for the global tomographic models S12WM13 and S16B30, and they are found to be similar. 相似文献
9.
Huajian Yao Pierre Gouédard John A. Collins Jeffrey J. McGuire Robert D. van der Hilst 《Comptes Rendus Geoscience》2011,343(8-9):571-583
Inter-station Green's functions estimated from ambient noise studies have been widely used to investigate crustal structure. However, most studies are restricted to continental areas and use fundamental-mode surface waves only. In this study, we recover inter-station surface (Scholte-Rayleigh) wave empirical Green's function (EGFs) of both the fundamental- and the first-higher mode using one year of continuous seismic noise records on the vertical component from 28 ocean bottom seismographs deployed in the Quebrada/Discovery/Gofar transform faults region on the East Pacific Rise. The average phase-velocity dispersion of the fundamental mode (period band 2–30 s) and the first-higher mode (period band 3–7 s) from all EGFs are used to invert for the 1-D average, shear-velocity structure in the crust and uppermost mantle using a model-space search algorithm. The preferred shear-velocity models reveal low velocities (4.29 km/s) between Moho and 25 km depth below sea-surface, suggesting the absence of a fast uppermost mantle lid in this young (0–2 Myr) oceanic region. An even more pronounced low-velocity zone, with shear velocities ～3.85 km/s, appears at a depth between 25–40 km below sea-surface. Along with previous results, our study indicates that the shear velocity in the uppermost oceanic mantle increases with increasing seafloor age, consistent with age-related lithospheric cooling. 相似文献
10.
We have used Rayleigh wave dispersion analysis and inversion to produce a high resolution S-wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the North China Craton (NCC). Using waveform data from 45 broadband NCISP stations, Rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the S-wave velocity structure from 15 km down to 120 km depth. The inverted lower crust and uppermost mantle velocities, about 3.75 km/s and 4.3 km/s on average, are low compared with the global average. The Moho was constrained in the depth range of 30–40 km, indicating a typical crustal thickness along the profile. However, a thin lithosphere of no more than 100 km was imaged under a large part of the profile, decreasing to only ~ 60 km under the Inner Mongolian Axis (IMA) where an abnormally slow anomaly was observed below 60 km depth. The overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern NCC during Mesozoic–Cenozoic time. Distinctly high velocities, up to ~ 4.6 km/s, were found immediately to the south of the IMA beneath the northern Yanshan Belt (YSB), extending down to > 100-km depth. The anomalous velocities are interpreted as the cratonic lithospheric lid of the region, which may have not been affected by the Mesozoic–Cenozoic deformation process as strongly as other regions in the eastern NCC. Based on our S-wave velocity structural image and other geophysical observations, we propose a possible lithosphere–asthenosphere interaction scenario at the northeastern boundary of the NCC. We speculate that significant undulations of the base of the lithosphere, which might have resulted from the uneven Mesozoic–Cenozoic lithospheric thinning, may induce mantle flows concentrating beneath the weak IMA zone. The relatively thick lithospheric lid in the northern YSB may serve as a tectonic barrier separating the on-craton and off-craton regions into different upper mantle convection systems at the present time. 相似文献
11.
中国岩石圈的基本特征 总被引：11，自引：2，他引：9
中国及邻区岩石圈结构构造十分复杂,并具有若干明显的特点:中国大陆地壳西厚东薄、南厚北薄,青藏高原地壳平均厚度为60~65 km,最厚达80 km;东部地区一般为30~35 km,南中国海中央海盆平均只有5 km;中国大陆地壳平均厚度为476 km,大大超过全球地壳392 km的平均厚度。中国大陆及邻区岩石圈亦呈西厚东薄、南厚北薄的变化趋势,青藏高原及西北地区岩石圈平均厚度为165 km,塔里木盆地中东部、帕米尔与昌都地区岩石圈厚度可达180~200 km。大兴安岭-太行山-武陵山以东,包括边缘海为岩石圈减薄区,厚度为50~85 km。西部岩石圈、软流圈“层状结构”明显,反映了板块碰撞汇聚的动力学环境;东部岩石圈、软流圈呈“块状镶嵌结构”,岩石圈薄,软流圈厚,反映了地壳拉张、软流圈物质上涌的特点,并在东亚及西太平洋地区85~250 km深处形成一巨型低速异常体。中国东部上、下地壳及地壳、岩石圈地幔之间普遍存在“上老下新”年龄结构。 相似文献
12.
We have studied seismic surface waves of 255 shallow regional earthquakes recently recorded at GEOFON station ISP (Isparta, Turkey) and have selected these 52 recordings with high signal-to-noise ratio for further analysis. An attempt was made by the simultaneous use of the Rayleigh and Love surface wave data to interpret the planar crust and uppermost mantle velocity structure beneath the Anatolian plate using a differential least-square inversion technique. The shear-wave velocities near the surface show a gradational change from approximately 2.2 to 3.6 km s− 1 in the depth range 0–10 km. The mid-crustal depth range indicating a weakly developed low velocity zone has shear-wave velocities around 3.55 km s− 1. The Moho discontinuity characterizing the crust–mantle velocity transition appears somewhat gradual between the depth range 25–45 km. The surface waves approaching from the northern Anatolia are estimated to travel a crustal thickness of 33 km whilst those from the southwestern Anatolia and part of east Mediterranean Sea indicate a thicker crust at 37 km. The eastern Anatolia events traveled even thicker crust at 41 km. A low sub-Moho velocity is estimated at 4.27 km s− 1, although consistent with other similar studies in the region. The current velocities are considerably slower than indicated by the Preliminary Reference Earth Model (PREM) in almost all depth ranges. 相似文献
13.
斜切中亚的深部滑移构造带地球物理证据及对表层构造的制约 总被引：1，自引：0，他引：1
斜切中亚的帕米尔一阿尔泰滑移构造带向南延伸，可与恰曼转换断裂系统相接，影响其两侧表层断裂构造格局、中新生代盆山演化、现今地壳变形和地震活动．地球卫星重力异常带在滑移构造带两侧表现出显著的不连续性和系统位移特征，其深部滑移幅度达600km以上．从卫星资料反演计算出的地壳厚度图上可看出，新疆地区地壳厚度比中亚邻区厚4～8hn，岩石圈厚度比中亚邻区厚10-20km，新疆及邻区地震波速层析成像结果提供了不同深度速度结构，在平行于中国西部国界处的10km、30km、50km深处均有NE向速度结构不连续面的反映． 相似文献
14.
l.IntroductionAteleseismicprofilingwasconductedjointlybytheChineseAcademyofGeologicalSciencesandtheInstitUteofGeophysicsandInnerTectonics,JosephUniversity,France,alongthemainroadfromGonghetoYushuinQinghai,withanarrayof4Othree-componentMinititanstationsandl3one-componentCEISstations,fromJunetoNovember,1998.ThestUdycoversahugearearangingfromthenofthoftheBangong-NujiangFaulttothesouthoftheMid-QilianFault,andfromtheeastoftheQaidamBasintothewestoftheLongmenShanFault,goingthroughSouthQ… 相似文献
15.
Rayleigh wave group velocities provide a low-cost means for a quick assessment of averaged local properties of the Earth's crust in continental margin regions of the Atlantic type. Sufficiently accurate measurements (with a standard error of 0.3 km/s or less) of group velocities in continental shelf areas at periods between 5 and 30 seconds provide important information about structural parameters. They may resolve the Moho depth to within 4 or 5 km, depending on crustal thickness and give useful estimates of the average velocities in the upper part of the crust. The group velocities of Rayleigh waves in this period range are influenced most by the shear velocity at all depths and the compressional velocity and the density near the surface. For continental rise regions, the dominating influence of the water layer limits the effectiveness of the method. 相似文献
16.
青藏高原及邻区三角形发震构造域是全球大陆最显著的地震多发区.脆性活动断层及其弹性回跳模式无法合理解释该区深度集中分布在10~40 km的点状震源.针对发震构造和地震机理不明确这一重大科学问题, 以大陆动力学和地球系统动力学新思想为指导, 对青藏高原及邻区发震构造系统进行域、层、带、点相关研究, 阐明大陆地震构造系统的结构型式, 认为下地壳固态流变及其韧性剪切带是提供地震能量的孕震构造, 中地壳韧-脆性剪切带是累积地震能量的发震构造, 上地壳脆性断裂是释放地震能量的释震构造.在研究青藏高原及邻区地震构造系统及其形成背景的基础上, 进一步论证了大陆地震热流体撞击的形成机理: 地幔墙导致大洋中脊之下的软流圈热流物质层流到大陆特定部位汇聚加厚并底辟上升, 造成大陆下地壳部分熔融和固态流变, 并改变莫霍面的产状, 固态流变物质侧向非均匀流动, 形成大陆盆山体系, 流动的韧性下地壳与脆性上地壳之间具有韧-脆性剪切滑脱性质的中地壳不断积累由下地壳热能转换而来的应变能, 形成发震层, 震源定位于下地壳热流物质富集带("热河")中的固态-半固态流变物质撞击到强弱层块之间的构造边界, 不同热构造环境和撞击角度产生5种不同类型的地震.从而为大陆地震的科学预测奠定了全新的理论基础. 相似文献
17.
四川盆地基底及深部地质结构研究的进展 总被引：6，自引：1，他引：6
根据对近年来区域地质、多种地球物理资料和深钻井资料的综合研究，认为四川盆地属扬子板块，岩石圈巨厚，最厚可达２００ｋｍ。川西高原属青藏板块的东缘，同时位于中国南北构造带中段，软流圈呈北东向上隆，岩石圈减薄，其最薄处厚度约７０ｋｍ左右。四川盆地的基底由结晶基底与沉积岩变质基底组成，上震旦统为该地区在扬子古板块形成后的第一套沉积盖层。基底的性质、厚度、埋深在不同地区各不相同，从而决定了盆地内部构造区的划分。基底深断裂对盆地的形成与盖层构造的发展也有重要的控制作用。 相似文献
18.
为了解准噶尔盆地深部构造特征,综合利用“深部探测技术与试验研究(SinoProbe)”项目在准噶尔盆地45°N 88°E处建立的大地电磁标准点实测资料,应用非线性共轭梯度法(NLCG)对该测站两条短剖面进行二维反演,结合新疆准噶尔盆地区域地质资料,对该地区地层电性结构进行了初步分析,发现准噶尔盆地中东部地区地下结构具有很好的电性分层.与现有地质资料相结合,分析发现其电性分层与地壳分层具有较好的对应.根据岩石层电导性推断:研究区域莫霍面埋深在46 km附近,岩石圈厚度在100 km左右.研究结果对准噶尔中东部地区深部地壳结构的认识具有一定的参考价值. 相似文献
19.
托云盆地新生代幔源岩浆源区起止深度的限定 总被引：2，自引：0，他引：2
在详细介绍了地幔熔融柱模型原理(Langmuir et al., 1992)的基础上,基于平衡熔融和分离熔融模型分别计算获得了上地幔橄榄岩源区在不同初始压力条件下发生绝热减压部分熔融时熔体相中FeO-MgO和FeO-Na2O成分的演化轨迹。依据深源岩石包体与托云玄武岩之间的寄主关系将本次研究的16件托云火山岩样品划分成Group-1(深源岩石包体寄主岩)和Group-2(非寄主岩)两群,将收集前人的40件样品依据是否测试获得FeO的质量百分含量划分成Group-3群(具有实测的FeO质量百分含量)和Group-4群(无实测FeO质量百分含量数据)。分别对以上四群样品运用地幔熔融柱模型进行反演获得上地幔部分熔融源区的起止深度范围：Group-1和Group-3样品具有相同的初始熔融深度113.2km (34.1kbar),但它们的部分熔融作用终止深度分别为110.1km (33.1kbar) 和88.4km (26.2kbar);Group-2样品数据所反演的岩浆起源的初始深度和终止深度分别为111.6km (33.6kbar)和84.3.1km(24.9kbar);Group-4样品反演所获得的岩浆源区的起止深度分别为121.7km(36.8kbar)和106.0km(31.8kbar)。依据实测FeO百分含量的样品群反演的结果,将托云火山岩部分熔融源区的深度限定在113.2 km至84.3km,即48.1Ma前托云盆地所处的岩石圈厚度为84.3km,对梁涛(2005)运用熔融柱模型反演的托云盆地岩石圈深度进行了修正。此外,由地幔熔融柱模型反演获得的托云火山岩部分熔融源区熔体的温度压力条件与基于玄武岩中高压巨晶所反演的岩浆演化温压轨迹具有十分吻合的继承演化关系。地球物理探测表明现今西南天山岩石圈的厚度为71km,区域岩石圈演化历程中深度上13.3km的差异足以证明岩石圈拆沉这一地球动力学过程的存在,为由宽SHRIMP年龄谱识别出的岩石圈拆沉作用提供了另一个有力的证据。 相似文献
20.
Claus Prodehl 《Tectonophysics》1985,111(3-4)
In February 1978 seismic-refraction profiles were recorded by the U.S. Geological Survey along a 1000 km line across the Arabian Shield in western Saudi Arabia. This report presents a traveltime and relative amplitude study in the form of velocity-depth functions for each individual profile assuming horizontally flat layering. The corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60–80 km.The crust thickens abruptly from 15 km beneath the Red Sea Rift to about 40 km beneath the Arabian Shield. The upper crust of the western Arabian Shield yields relatively high-velocity material at about 10 km depth underlain by velocity inversions, while the upper crust of the eastern Shield is relatively uniform. The lower crust with a velocity of about 7 km/s is underlain by a transitional crust-mantle boundary. For the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high-velocity zones are intermixed with zones of lower velocities. Beneath the crust-mantle boundary of the Red Sea rift most probably strong velocity inversions exist. Here, the data do not allow a detailed modelling, velocities as low as 6.0 km/s seem to be encountered between 25 and 44 km depth. 相似文献