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1.
This study presents shear wave splitting analysis results observed at ISP (Isparta) broadband station in the Isparta Angle,
southwestern Turkey. We selected 21 good quality seismic events out of nearly 357 earthquakes and calculated splitting parameters
(polarization direction of fast wave, ϕ and delay time between fast and slow waves, δt) from mainly SKS and a few SKKS phases of the selected 21 seismic events. Then, we compared calculated splitting parameters
at ISP station (56° ≤ ϕ ≤ 205°; 0.37 s ≤ δt ≤ 4 s) with those previously calculated at ANTO (Ankara) and ISK (İstanbul) stations (27° ≤ ϕ ≤ 59°; 0.6 s ≤ δt ≤ 2.4 s and 26° ≤ ϕ ≤ 54°; 0.6 s ≤ δt ≤ 1.5 s) which are located at 230 and 379 km away from ISP station in central and northwestern Turkey, respectively. The
backazimuthal variations of the splitting parameters at ISP station indicate a different and complex mantle polarization anisotropy
for the Isparta Angle in southwestern Turkey compared to those obtained for Ankara and İstanbul stations. 相似文献
2.
《地学前缘(英文版)》2018,9(6):1911-1920
We estimate the shear wave splitting parameters vis-à-vis the thicknesses of the continental lithosphere beneath the two permanent seismic broadband stations located at Dhanbad (DHN) and Bokaro (BOKR) in the Eastern Indian Shield region. Broadband seismic data of 146 and 131 teleseismic earthquake events recorded at DHN and BOKR stations during 2007–2014 were analyzed for the present measurements. The study is carried out using rotation-correlation and transverse component minimization methods. We retain our “Good”, “Fair” and “Null” measurements, and estimate the splitting parameters using 13 “Good” results for DHN and 10 “Good” results for BOKR stations. The average splitting parameters (ϕ, δt) for DHN and BOKR stations are found to be 50.76°±5.46° and 0.82 ± 0.2 s and 56.30°±5.07° and 0.95 ± 0.17 s, and the estimated average thicknesses of the anisotropic layers beneath these two stations are ∼ 94 and ∼109 km, respectively. The measured deviation of azimuth of the fast axis direction (ϕ) from the absolute motion of the Indian plate ranges from ∼8° to 14°. The measured deviation of azimuth of the fast axis direction (ϕ) from the absolute motion of the Indian plate ranges from ∼8° to 14°. The eastward deviation of the fast axis azimuths from absolute plate motion direction is interpreted to be caused by induced outflow from the asthenosphere. Further, the delay time found in the present analysis is close to the global average for continental shield areas, and also coherent with other studies for Indian shield regions. The five “Null” results and the lower delay time of ∼0.5–0.6 s might be indicating multilayer anisotropy existing in the mantle lithosphere beneath the study area. 相似文献
3.
M. N. Luneva 《Russian Journal of Pacific Geology》2011,5(4):336-347
Shear wave splitting parameters from local deep-focus and crustal earthquakes beneath southern Sakhalin and northern Hokkaido
have been measured. The study of the split shear wave amplitude, polarization, and splitting parameter distribution revealed
their correlation with the geometry of the subsiding Pacific Plate and horizontal heterogeneity of the rheological properties
and viscosity of the medium. Comparison of the observed data with those modeled in anisotropic media allows the mantle flow
to be oriented NNW beneath southern Sakhalin and northern Hokkaido. Based on the split shear wave time delays, the degree
of mantle anisotropy is estimated to be around 1–2% beneath southern Sakhalin and 1.5–2.5% beneath northern Hokkaido. A relatively
high anisotropy (2–15%) from local crustal earthquakes is found beneath the Central Sakhalin Fault. 相似文献
4.
The measurements of the parameters of split shear (S) waves from local deep-focus earthquakes recorded in 2005–2007 by a network of 12 seismic stations in Southern Sakhalin are
presented. The results revealed the heterogeneous distribution of the anisotropic properties beneath Southern Sakhalin. The
azimuths of the fast S-wave polarization beneath the stations in the central part of the peninsula are oriented along the NNW and NNE-NE directions
normal to and along the Kuril Trench. Beneath the stations located along the western and eastern coasts, the azimuths of the
fast S-wave polarization change their direction from NNW in the northern area to E-SE in the southern area. The highest anisotropy
degree (up to 0.9–1.5%) is recorded beneath the central part of Southern Sakhalin. The maximum values of the discrepancy in
the arrival time of the split S-waves are observed when the azimuth of the fast S-wave is oriented along the NNE beneath the active fault zones. The analysis of the variations of the S-wave lag time shows their weak depth dependence. The highest anisotropy is assumed in the upper layers of the medium (down
to a depth of about 250 km). The results obtained for the dominating wave frequency of 1–5 Hz represent mainly the medium-scale
anisotropy of the top of the studied region. 相似文献
5.
Shear wave velocity is one of the most important input parameter in the analysis of geotechnical earthquake engineering problems,
particularly to estimate site-specific amplification factor and ground response study. Dynamic in situ tests such as spectral
analysis of surface waves (SASW) or multichannel analysis of surface waves (MASW) are very expensive. Also due to lack of
specialized personnel, these tests are generally avoided in many soil investigation programs. Worldwide, several researchers
have developed correlations between the SPT ‘N’ value and shear wave velocity ‘V
s’, which are useful for determining the dynamic soil properties. In the present study, more than 400 numbers of soil borehole
data were collected from various geotechnical investigation agencies, government engineering institutes and geotechnical laboratories
from different parts of Mumbai city, which is financial capital of India with highest population density. In this paper, an
attempt has been made to develop the correlation between the SPT ‘N’ value and shear wave velocity ‘V
s’ for various soil profile of Mumbai city and compared with other existing correlations for different cities in India. Using
Geographical Information System (GIS), a geospatial contour map of shear wave velocity profile for Mumbai city is prepared
with contour intervals of 25 and 50 m/s. The scarcity of database or maps of shear wave velocity profile for Mumbai city will
make the present geospatial contour maps extremely useful and beneficial to the designer, practitioners for seismic hazard
study involved in geotechnical earthquake engineering. 相似文献
6.
The presence of two regional seismic networks in southeastern France provides us high-quality data to investigate upper mantle flow by measuring the splitting of teleseismic shear waves induced by seismic anisotropy. The 10 three-component and broadband stations installed in Corsica, Provence, and western Alps efficiently complete the geographic coverage of anisotropy measurements performed in southern France using temporary experiments deployed on geodynamic targets such as the Pyrenees and the Massif Central. Teleseismic shear waves (mainly SKS and SKKS) are used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 1.0 and 1.5 s have been observed at most sites, but some larger delay times, above 2.0 s, have been observed at some stations, such as in northern Alps or Corsica, suggesting the presence of high strain zones in the upper mantle. The azimuths of the fast split shear waves define a simple and smooth pattern, trending homogeneously WNW–ESE in the Nice area and progressively rotating to NW–SE and to NS for stations located further North in the Alps. This pattern is in continuity with the measurements performed in the southern Massif Central and could be related to a large asthenospheric flow induced by the rotation of the Corsica–Sardinia lithospheric block and the retreat of the Apenninic slab. We show that seismic anisotropy nicely maps the route of the slab from the initial rifting phase along the Gulf of Lion (30–22 Ma) to the drifting of the Corsica–Sardinia lithospheric block accompanied by the creation of new oceanic lithosphere in the Liguro–Provençal basin (22–17 Ma). In the external and internal Alps, the pattern of the azimuth of the fast split waves follows the bend of the alpine arc. We propose that the mantle flow beneath this area could be influenced or perhaps controlled by the Alpine deep penetrative structures and that the Alpine lithospheric roots may have deflected part of the horizontal asthenospheric flow around its southernmost tip. 相似文献
7.
华北克拉通从稳定到破坏的演化过程对有关地球动力学的经典理论提出了挑战,研究其独特的演化历史是固体地球科学研究的一项重要内容。上地幔矿物晶体的各向异性记录了上地幔发生构造变形的信息,研究上地幔地震波各向异性能够揭示现今和构造历史时期所发生的构造运动。本文总结了近年来作者在华北克拉通地区所进行的高密度、覆盖广泛的地震波横波分裂观测研究结果。横波分裂的快轴方向与绝对板块运动方向的不一致,以及横波分裂参数快速的空间变化特征表明了华北克拉通的SKS横波分裂主要反映上地幔的变形。观测结果表明：鄂尔多斯块体保留了克拉通较弱的各向异性特征,其西端体现了元古代克拉通拼合的变形特征; 中新生代华北克拉通破坏事件以不同的机制主导了华北克拉通中部和东部的上地幔变形,在东部地区北西-南东向的拉张应力作用使得快轴方向平行于拉张方向,而在中部则因受到较厚岩石圈的阻挡使得地幔流动改变了方向,因此造成了北东和北北东向的岩石圈拉张。 相似文献
8.
S. Dey-Barsukov H. Dürrast W. Rabbel S. Siegesmund S. Wende 《International Journal of Earth Sciences》2000,88(4):829-839
By vertical seismic profiling and shear wave analysis we show that a packet of carbonate reservoir rocks, found at nearly
3000 m depth in the North German Basin, is seismically anisotropic. For vertical paths of wave propagation the estimated velocity
difference of the split shear waves is 10%. No shear wave birefrigence is observed within the hangingwall which, therefore,
has to be regarded as isotropic or transversely isotropic. Additional laboratory investigations of the petrography of drilled
carbonate samples and of their seismic velocities show that the anisotropy is most probably caused by subvertical fractures
with preferred azimuthal orientation. The strike direction of the aligned fractures determined by analysis of split shear
waves is approximately N55°E. This value agrees with recently published directions of maximum horizontal tectonic stress in
pre-Zechstein sediments in the eastern part of the North German Basin, but it is in contrast to the world stress map.
Received: 20 April 1999 / Accepted: 25 August 1999 相似文献
9.
Sarah J. Titus L. Gordon Medaris Jr. Herbert F. Wang Basil Tikoff 《Tectonophysics》2007,429(1-2):1-20
The Coyote Lake basalt, located near the intersection of the Hayward and Calaveras faults in central California, contains spinel peridotite xenoliths from the mantle beneath the San Andreas fault system. Six upper mantle xenoliths were studied in detail by a combination of petrologic techniques. Temperature estimates, obtained from three two-pyroxene geothermometers and the Al-in-orthopyroxene geothermometer, indicate that the xenoliths equilibrated at 970–1100 °C. A thermal model was used to estimate the corresponding depth of equilibration for these xenoliths, resulting in depths between 38 and 43 km. The lattice preferred orientation of olivine measured in five of the xenolith samples show strong point distributions of olivine crystallographic axes suggesting that fabrics formed under high-temperature conditions. Calculated seismic anisotropy values indicate an average shear wave anisotropy of 6%, higher than the anisotropy calculated from xenoliths from other tectonic environments. Using this value, the anisotropic layer responsible for fault-parallel shear wave splitting in central California is less than 100 km thick. The strong fabric preserved in the xenoliths suggests that a mantle shear zone exists below the Calaveras fault to a depth of at least 40 km, and combining xenolith petrofabrics with shear wave splitting studies helps distinguish between different models for deformation at depth beneath the San Andrea fault system. 相似文献
10.
The emergence of large-scale arrays of seismometers across several continents presents the opportunity to image the Earth's structure at unprecedented resolution, but methods must be developed to exploit the capabilities of these deployments. The capabilities and limitations of a method called “eikonal tomography” applied to ambient noise data are discussed here. In this method, surface wave wavefronts are tracked across an array and the gradient of the travel time field produces estimates of phase slowness and propagation direction. Application data from more than 1000 stations from EarthScope USArray in the central and western US and new Rayleigh wave isotropic and anisotropic phase velocity maps are presented together with an isotropic and azimuthally anisotropic 3D Vs model of the crust and uppermost mantle. As a ray theoretic method, eikonal tomography models bent rays but not other wavefield complexities. We present evidence, based on the systematics of an observed 1ψ component of anisotropy that we interpret as anisotropic bias caused by backscattering near an observing station, that finite frequency phenomena can be ignored in ambient noise tomography at periods shorter than ～ 40 to 50 s. At longer periods a higher order term based on wavefront amplitudes or finite frequency sensitivity kernels must be introduced if the amplitude of isotropic anomalies and the amplitude and fast-axis direction of azimuthal anisotropy are to be determined accurately. 相似文献
11.
Mohamed K.Salah 《地学前缘(英文版)》2012,3(5):681-696
Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting.Waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study.Although the station coverage is not uniform in the Iberian Peninsula and northwest Africa,significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains.Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia;being consistent with the absolute plate motion in the region.In the northern part of the Iberian Peninsula,fast velocity directions are oriented nearly E—W;coincident with previous results.Few stations located slightly north of the plate boundary and to the southeast of Iberia show E—W to NE-SW fast velocity directions,which may be related to the Alpine Orogeny and the extension direction in Iberia.Delay times vary significantly between 0.2 and 1.9 s for individual measurements,reflecting a highly anisotropic structure beneath the recording stations.The relative motion between Africa and Iberia represents the main reason for the observed NW-SE orientations of the fast velocity directions.However,different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region.Many geophysical observations such as the low Pn velocity,lower lithospheric Q values,higher heat flow and the presence of high conductive features support the mantle How in the western Mediterranean,which may contribute and even modify the splitting pattern beneath the studied region. 相似文献
12.
13.
Shear wave splitting as a diagnostic of variable anisotropic structure of the upper mantle beneath central Fennoscandia 总被引：1，自引：0，他引：1
We analyze splitting of shear waves recorded during the SVEKALAPKO passive seismic experiment in south-central Finland to study fabrics of the mantle lithosphere of the Precambrian region and thus to bring information into a debate on existence of plate tectonics or its forms in the early stage of continent formation. Geographical variations of the splitting parameters and their distinct dependence on direction of wave propagation through the upper mantle allow us to identify six domains of the central Fennoscandian mantle lithosphere, including the Proterozoic–Archean transition, and to model their fabrics by joint inversion of body wave anisotropic parameters. Fabrics of the Archean mantle lithosphere can be approximated by a peridotite aggregate with lineation a dipping to the NE. On the other hand, anisotropy of the Proterozoic mantle lithosphere is weaker and we model its fabric by the (a, c) foliations dipping to the SE. We present a 3D self-consistent anisotropic model of the Proterozoic and Archean upper mantle along the SW-NE profile in the south-central Finland. Boundaries of inter-growing wedges of the Proterozoic and Archean mantle lithospheres explain the longitudinal and shear wave propagation and polarization, mantle xenolith ages, surface wave tomography and location of the upper mantle reflectors. We interpret the six anisotropic domains as fragments of mantle lithosphere retaining an old fossil olivine fabric which was created before these micro-continents assembled. 相似文献
14.
Koushik Sen Ruchika Sharma B. R. Arora Vikram Gupta 《Journal of the Geological Society of India》2010,76(5):322-330
Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show
good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic
lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively.
Both Vp and Vs show positive correlation with the SiO2 content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility
(Km) having ‘r’ value of 0.86. The correlation between Vs-Km, Vp-P′, Vp-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested
that, in paramagnetic granites, Vp is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other
hand, Vs is more dependent on the mineralogy alone. 相似文献
15.
We have measured P- and S-wave velocities on two amphibolite and two gneiss samples from the Kola superdeep borehole as a function of pressure (up to 600 MPa) and temperature (up to 600 °C). The velocity measurements include compressional (Vp) and shear wave velocities (Vs1, Vs2) propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes. The measurements are accompanied by 3D-velocities calculations based on lattice preferred orientation (LPO) obtained by TOF (Time Of Flight) neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons. The LPO-based numerical velocity calculations give important information on the different contribution of the various rock-forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy, shear wave splitting, and shear wave polarization to the structural reference frame (foliation and lineation). Comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks (foliation and lineation) demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions. The study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation, respectively. 相似文献
16.
Seismic anisotropy structure beneath the southeastern Mediterranean from shear-wave splitting 总被引：1，自引：0，他引：1
Mohamed K. Salah 《Arabian Journal of Geosciences》2013,6(6):1717-1730
Analysis of seismic anisotropy in the crust and the uppermost mantle gives lots of information about the ambient mantle flow, stress state, and the dynamic processes inside the Earth. Thus, seismic anisotropy and its main distinctive features beneath the southeastern Mediterranean region are studied through the analysis of teleseismic shear-wave splitting observed at six broadband seismic stations belonging to the GEOFON and the MedNet. Although the number of the recording stations is small; a total of 495 splitting parameters are obtained, which revealed significant variations in the observed fast polarization directions beneath the study area. The stations in northern Egypt and Cyprus show fast velocity directions oriented roughly N–S to NNE–SSW, coincident with many previous results. A slightly different splitting pattern comprising NE–SW fast polarization directions is observed in the stations located along the Dead Sea fault in the southeastern Mediterranean; which are consistent with the current strike-slip motion between Africa and Arabia. In addition, NW–SE fast polarization directions are recognized in the latter group. The observed delay times vary greatly but their averages lie between 0.35 and 1 s. Although large-scale mechanisms, such as the absolute plate motion of Africa and Arabia towards Eurasia and the differential motion between Arabia and Africa can be invoked to predominantly explain the origin of anisotropic features, we suggest that density-driven flow in the asthenosphere is a possible additional cause of the wide range of the splitting pattern observed beneath some stations. 相似文献
17.
V. A. San’kov A. V. Parfeevets A. V. Lukhnev A. I. Miroshnichenko S. V. Ashurkov 《Geotectonics》2011,45(5):378-393
Comprehensive analysis of the parameters characterizing contemporary and neotectonic deformations of the Earth’s crust and
upper mantle developed in the Mongolia-Siberia area is presented. The orientation of the axes of horizontal deformation in
the geodetic network from the data of GPS geodesy is accepted as an indicator of current deformations at the Earth’s surface.
At the level of the middle crust, this is the orientation of the principal axes of the stress-tensors calculated from the
mechanisms of earthquake sources. The orientation of the axes of stress-tensors reconstructed on the basis of structural data
is accepted as an indicator of Late Cenozoic deformations in the upper crust. Data on seismic anisotropy of the upper mantle
derived from published sources on the results of splitting of shear waves from remote earthquakes serve as indicators of deformation
in the mantle. It is shown that the direction of extension (minimum compression) in the studied region coincides with the
direction of anisotropy of the upper mantle, the median value of which is 310–320° NW. Seismic anisotropy is interpreted as
the ordered orientation of olivine crystals induced by strong deformation owing to the flow of mantle matter. The observed
mechanical coupling of the crust and upper mantle of the Mongolia-Siberia mobile area shows that the lithospheric mantle participated
in the formation of neotectonic structural elements and makes it possible to ascertain the main processes determining the
Late Cenozoic tectogenesis in this territory. One of the main mechanisms driving neotectonic and contemporary deformations
in the eastern part of the Mongolia-Siberia area is the long-living and large-scale flow of the upper mantle matter from the
northwest to the southeast, which induces both the movement of the northern part of the continent as a whole and the divergence
of North Eurasia and the Amur Plate with the formation of the Baikal Rift System. In the western part of the region, deformation
of the lithosphere is related to collisional compression, while in the central part, it is due to the dynamic interaction
of these two large-scale processes. 相似文献
18.
Shear wave splitting measurements in South Kamchatka during the 3-year period (1996–1998) in which the Kronotsky Earthquake (M=7.7, December 5, 1997) occurred are used to determine anisotropic parameters of the subduction zone and shear wave splitting variations with time. The local small seismic events recorded at the Petropavlovskaya IRIS station (PET) were analyzed. The dominant azimuths of the fast shear wave polarizations for the 3-year period are defined within N95±15°E, which are consistent with the general Pacific Plate motion direction. Modeling of fast shear wave polarizations shows that HTI model with the symmetry axis oriented along N15°E±10° fit well the observed data for events the focal depths of which are less than 80 km. For the greater depths, the orthorhombic symmetry of medium is not excluded. The anisotropy coefficient increases generally with depth from 1–2% in the crust to 4–7.5% in the subducting plate. Variations in time delays show a general increase up to 10–15 ms/km during 1996–1997 before the large crustal earthquake series (M≈5.5–7) in the Avacha Bay and before the Kronotsky Earthquake. Analysis of fast S-wave azimuths of mantle events reveals a temporal cyclic variation. The most regular variations are observed for fast azimuths of deep events with a period of about 172 days over the 3-year period. The fast polarizations of crustal events behave comparatively stable. It is assumed that the major instabilities in stress state are localized in the descending slab and influenced the upper mantle and comparatively stable crust. 相似文献
19.
Sensitivity experiments are conducted for three cases of cyclones for investigating the impact of different vortex initialization
schemes on the structure and track prediction of the cyclone using India Meteorological Department’s Limited Area Model. The
surface wind and pressure profiles generated using Holland and Rankine initialization schemes differ from each other. These
different generated profiles are compared with the actual data and the root mean square error (RMSE) was calculated between
them. In case of the Holland vortex, ‘b’ is found to be equal to 1.5 and 2.0 respectively for two cases of very severe cyclonic storms in the Arabian Sea, namely
6–10 June 1998 and 16–20 May 1999 and 2.25 for the severe cyclonic storm in the Bay of Bengal. The ‘α’ parameter in Rankine’s
scheme was found to be 0.5 for two cases and 0.4 for the third system. This shows that cyclones differ even if they attain
the same intensity. The values of these parameters i.e. ‘b’ and ‘α’ are used for generating the synthetic wind data for individual cyclones and the same is used in the data assimilation
system. The analysis and forecast generated for the above cases using the Holland scheme show that the simulated structure
has characteristics closer to the actual storm; however, the Rankine scheme shows a weaker circulation. The mean track error
for three cases in the Holland scheme is 93, 149, 257 and 307 km in 12-, 24-, 36- and 48-h forecast. The mean track errors
for the Rankine scheme are 152, 274, 345 and 327 km, respectively, for the same period. 相似文献
20.
Kanchan Pande J. T. Padia R. Ramesh K. K. Sharma 《Journal of Earth System Science》2000,109(1):109-115
Stable hydrogen (δD) and oxygen (δ18O) isotope ratios of the headwaters of the Indus and its tributaries, surface ice in glaciers, saline and fresh water lakes
and thermal springs in the Himalayan and Trans-Himalayan (Kashmir) region are reported. The δ5D-δ18 relationship for the river samples shows a slope of 9.12 +-0.29 which agrees well with the estimate of 8.99 ±0.33 based on
a simple Rayleigh fractionation model. The unique signature of a higher deuterium excess (d) of the ‘Western Disturbance’ is preserved in these samples. An altitude effect of -0.9 per mil/km is observed in the δ18O of Indus waters. At a lower altitude (Beas) the altitude effect is almost double, indicating that the altitude effect decreases
with elevation in this region. 相似文献