The spectrum of tomographic earth models     

S. Chevrot  J. P. Montagner  & R. Snieder 《Geophysical Journal International》1998,133(3):783-788

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Three-dimensional image of the anisotropic bodies beneath central Honshu, Japan     

Yoshihiro Hiramatsu  Masataka Ando  Tameshige Tsukuda  & Tooru Ooida 《Geophysical Journal International》1998,135(3):801-816

Shear-wave splitting from local deep earthquakes is investigated to clarify the volume and the location of two anisotropic bodies in the mantle wedge beneath central Honshu, Japan. We observe a spatial variation in splitting parameters depending on the combination of sources and receivers, nearly N–S fast in the northern region, nearly E–W fast in the southern region and small time delays in the eastern region. Using forward modelling, two models with 30 and 10 per cent anisotropy are tested by means of a global search for the locations of anisotropic bodies with various volumes. The optimum model is obtained for 30 per cent anisotropy, which means a 5 per cent velocity difference between fast and slow polarized waves. The northern anisotropic body has a volume of 1.00° (longitude) × 0.5° (latitude) × 75 km (depth), with the orientation of the symmetry axis being N20°E. The southern anisotropic body has a volume of 1.25° × 1.25° × 100 km with the symmetry axis along N95°E. Our results show that the anisotropic bodies are located in low-velocity and low- Q regions of the mantle. This, together with petrological data and the location of volcanoes in the arc, suggests that the possible cause of the anisotropy is the preferred alignment of cracks filled with melt.  相似文献   

Seismic wavefield calculation for laterally heterogeneous whole earth models using the pseudospectral method   总被引：4，自引：0，他引：4  

T. Furumura  B. L. N. Kennett  & M. Furumura 《Geophysical Journal International》1998,135(3):845-860

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Teleseismic delay-time tomography of the upper mantle beneath southeastern India: imprint of Indo–Antarctica rifting     

K.S.Prakasam  S.S.Rai 《Geophysical Journal International》1998,133(1):20-30

A 3-D P -velocity map of the crust and upper mantle beneath the southeastern part of India has been reconstructed through the inversion of teleseismic traveltimes. Salient geological features in the study region include the Archean Dharwar Craton and Eastern Ghat metamorphic belt (EGMB), and the Proterozoic Cuddapah and Godavari basins. The Krishna–Godavari basin, on the eastern coastal margin, evolved in response to the Indo–Antarctica breakup. A 24-station temporary network provided 1161 traveltimes, which were used to model 3-D P -velocity variation. The velocity model accounts of 80 per cent of the observed data variance. The velocity picture to a depth of 120 km shows two patterns: a high velocity beneath the interior domain (Dharwar craton and Cuddapah basin), and a lower velocity beneath the eastern margin region (EGMB and coastal basin). Across the array velocity variations of 7–10 per cent in the crust (0–40 km) and 3–5 per cent in the uppermost mantle (40–120 km) are observed. At deeper levels (120–210 km) the upper-mantle velocity differences are insignificant among different geological units. The presence of such a low velocity along the eastern margin suggests significantly thin lithosphere (<100 km) beneath it compared to a thick lithosphere (>200 km) beneath the eastern Dharwar craton. Such lithospheric thinning could be a consequence of Indo–Antarctica break-up.  相似文献   

Thickness estimates of the upper-mantle transition zone from bootstrapped velocity spectrum stacks of receiver functions   总被引：1，自引：0，他引：1  

HaroldGurrola  J.Bernard Minster 《Geophysical Journal International》1998,133(1):31-43

We modify the receiver-functions stacking technique known as velocity spectrum stacking (VSS) so as to estimate combinations of velocity model ( V_P and V_S ) and depth that stack the Ps conversion from upper-mantle discontinuities most coherently. We find that by estimating the differences in the depths to the 660 and 410 km discontinuities using velocities that maximize the stacked amplitudes of P410s and P660s phases we can estimate the thickness of the transition zone more accurately than the depths to either of these discontinuities. We present two examples indicating that the transition zone beneath Obninsk, Russia, is 252±6 km thick and that beneath Pasadena, California, is only 220±6 km thick.  相似文献   

Polarization anomaly of Love waves caused by lateral heterogeneity   总被引：1，自引：0，他引：1  

Reiji Kobayashi 《Geophysical Journal International》1998,135(3):893-897

We calculate surface waves propagating in a laterally heterogeneous structure beneath the Kuril trench, where significant Love-wave polarization anomalies, called quasi-Love waves, are generated. Since 3-D wave propagation in the two-dimensionally heterogeneous structure can be assumed, we apply the 2.5-D finite difference method to the surface-wave calculations. The calculations show that a velocity contrast of 7 per cent at depths of less than 210 km beneath the Kuril trench cannot generate quasi-Love waves, and that an unlikely contrast of 20 per cent is required to generate clear quasi-Love waves. The possible cause of the quasi-Love waves inferred from previous studies on coupled free oscillations is a lateral variation in azimuthal anisotropy. The lateral variation in azimuthal anisotropy beneath the Kuril trench suggests a change in the mantle flow induced by the subducting slab.  相似文献   

大同阳高震区及其邻区壳幔速度结构与深部构造   总被引：2，自引：1，他引：1       下载免费PDF全文

张成科  张先康  盖玉杰  赵金仁  聂文英  任青芳 《地震地质》1998,20(4):104

利用通过本区６条宽角反射／折射剖面资料对大同阳高震区及邻区地壳上地幔速度结构与构造进行了详细的研究。结果表明,地壳上地幔速度结构与构造在纵向和横向上具有明显的不均一性。浅部基底断裂发育,而在其深部,根据波组特征、壳内界面及速度等值线起伏变化和低速异常体的边界等推测有３处地壳深断裂带。本区最明显的上地壳低速体位于大同—阳原附近,其南界存在地壳深断裂,大同阳高地震群与该低速异常体和深断裂有关。  相似文献   

天山上地幔结构及其对壳内构造运动的作用   总被引：17，自引：0，他引：17       下载免费PDF全文

胥颐  刘福田 《地震地质》1998,20(4):118-412

以深部地球物理资料为基础,介绍了天山地震带上地幔的基本结构,讨论了天山不同地区上地幔介质的动力学性质和可能的驱动机制。认为水平挤压形变是造成西天山和天山毗邻西昆仑附近区域上地幔岩石圈缩短和增厚的主要原因;而在中天山和东天山靠近准噶尔盆地南缘一带,除了板块运动造成的水平挤压力之外,上地幔热物质有可能上浮甚至侵入到地壳之中。它们与水平运动一样,对壳内脆性介质的构造活动起到非常重要的作用,特别是地壳底部莫霍面附近的低速滑脱层成为震源区深部构造的一个明显标志。此外,自从印度 亚洲大陆碰撞以来,天山部分地区固结冷却的山根有可能在多重挤压变形和小尺度热对流的共同作用下,脱离它们的原有的层位而沉入上地幔  相似文献   

高压超高压变质作用中流体—熔体—岩石相互作用   总被引：2，自引：0，他引：2  

张泽明  韩郁菁 《地质科技情报》1998,17(3):24-30

在高压超高压变质作用过程中所释放的流体对俯冲板块的演化起着重要作用,与岛弧岩浆活动有着直接联系,随着温度和压力的增加,俯冲板片将发生高压到超高榴辉岩相转变,大量的水将通过含水矿物的消失反应释放出来,这些流体可引起上覆岩圈大规模水化,并促进地幔楔状体的部分熔融,同时,通过流体的向上迁移可将某些组分带入上覆岩石圈板块,并改变其总体组成,许多含水矿物,同变质脉体,高压自形晶体组成的布丁,原生液态包裹体和  相似文献   

深基坑工程变形预报神经网络法的初步研究   总被引：33，自引：0，他引：33  

孙海涛  吴限 《岩土力学》1998,19(4):63-68

提出了深基坑变形预报的人工神经网络法,详细介绍了该方法的建模和应用实例。预报结果与实测值较为吻合,从而表现在深基坑工程中利用该方法进行变形预报是可行的。  相似文献