共查询到20条相似文献，搜索用时 62 毫秒
1.
应用现代适配滤波频时分析技术对SRO/GDSN长周期面波记录进行处理,获得穿过太平洋盆地的117条波路径的勒夫波频散数据。我们用改进的分格频散反演方法,从混合路径频散数据中提取出对应于构成整个太平洋盆地的10°×10°分格的纯路径频散数据。所获得的18s到215s范围内的28个周期的太平洋勒夫波群速度的横向分布,揭示了速度随海底年龄的增大而逐渐增加的总趋势,以及其它变化细节。例如,对于同一等年龄线区而言,北太平洋及南太平洋的群速度要比中太平洋的低0.1-0.3km/s。在分格模型反演的基础上得出的深至300km的三维剪切波速度结构提供了太平洋盆地地壳及上地幔横向不均匀性的详尽的描述。 相似文献
2.
Long period Rayleigh wave and Love wave dispersion data, particularly for oceanic areas, have not been simultaneously satisfied by an isotropic structure. In this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. We assume that the surface wave data represents an azimuthal average of actual velocities. Thus, we can treat the mantle as transversely isotropic. The resulting models for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SH > SV in the vicinity of the low-velocity zone. Neat the East Pacific Rise, however, SV > SH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of ～50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures. A new model for average Earth is obtained which includes a thin LID. This model extends the fit of a PREM, type model to shorter period surface waves. 相似文献
3.
南海处于欧亚板块、 菲律宾海板块、 太平洋板块和印度-澳大利亚板块的交汇处, 其地质和构造作用十分复杂．通过面波群速度成像, 给出了南海及邻区的三维横波速度分布并分析了其地球动力学意义．南海西部和南部新布设的地震台站使得利用单台法时路径覆盖比过去更好. 特别是在华南地区, 新的台站分布能够弥补该地区地震少且台站少造成的射线密度不够的缺点． 首先运用多重滤波法得到南海周边48个台站周期为14——130 s范围内的基阶瑞雷波频散曲线图; 接着通过子空间反演得到整个区域在不同周期时的群速度分布; 最后通过阻尼最小二乘反演得到不同深度切片上的横波速度分布及不同纵剖面上的横波速度分布． 结果显示: ① 海盆速度较高, 且速度分布很好地勾勒出海盆的轮廓. 浅层较高的横波速度说明海盆都具有洋壳性质, 而深部较高的横波速度则可能对应扩张中心生成洋壳后残留的高速物质． 不同海盆速度上的差异与它们的热流值和年龄大小一致．海盆下的高速异常在60 km以下消失, 且在一定深度范围内由低速区替代． 在低速区下200 km深度, 在南海海盆观测到一条NE-SW走向的高速异常, 可能与古俯冲带有关. ② 环南海出现明显的高速区, 对应俯冲带特征, 且这些高速区速度差异明显且有间断, 说明俯冲带的非均质性和俯冲角度的差异. ③ 在环南海高速区内侧（向南海侧）观测到不连续的低速区． 在浅层, 这些低速区反映了沉积层和地壳的厚度特征. 在地幔, 这些低速区可能对应于古太平洋俯冲带的地幔楔或者也可能反映了南海海盆停止扩张后残留的地幔熔融物质. ④ 南海海盆岩石圈的厚度为60——85 km． 相似文献
4.
A linear relationship between the sea floor depth and the square root of age has been found for ocean lithosphere spreading from mid-ocean ridges. The asymptotic solution of depth as a function of age for the thermally contracting lithosphere predicts a linear dependence of depth ontwith a proportionality involving the initial lithosphere temperature, the thermal diffusivity, and the isostatic expansion coefficient averaged to include any temperature dependent phase changes. Empirical depth observations, when plotted as a function of the square root of age, bear out this prediction well, but there is a variation in the gradient,ht, along the ridge on a fine scale (up to 20% over 200 km). This implies a fundamental variation of the contraction parameter over the same scale, most probably of compositional origin. Details of a more complete cooling model near the ridge crest, including a crust of different thermal parameters than those of the mantle, predict a crestal height about 0.2 km below that of the simplified model. Individual profiles from the southeast Pacific show no such crestal deviation, and it is concluded that by quickly cooling the new crust, hydrothermal circulation may remove any effects of the crust which would be seen in the topography of a lithosphere cooled totally by conduction. The straightness of depth versust for older ocean data (to 80 m.y.) precludes any basal isothermal boundary shallower than 100 km. 相似文献
5.
Introduction Rayleigh wave is a kind of seismic wave propagating along the surface of the Earth, its propagation speed depends chiefly on the S-wave velocity structure of the Earth. Rayleigh wave energy of different periods concentrated in different depth ranges. The layered structure of the Earth causes the phenomenon of dispersion of surface waves, that is, surface waves of different periods are propagated with different speeds. By measuring the dispersion curves of surface waves the S-wav… 相似文献
6.
洋中脊速度结构是揭示大洋岩石圈演化过程的重要约束.为探讨不同扩张速率下洋中脊的洋壳速度结构特征,挑选了全球152处快速(全扩张速率 90mm·a-1)、慢速(全扩张速率20～50mm·a-1)和超慢速(全扩张速率20mm·a-1)扩张洋中脊和非洋中脊的洋壳1-D地震波速度结构剖面,通过筛选统计、求取平均值等方法对分类的洋壳1-D速度结构进行对比研究,获得了不同扩张速率下洋中脊洋壳速度结构差异以及洋中脊与非洋中脊洋壳速度结构差异的新认识:(1)快速、慢速和超慢速扩张洋中脊的平均正常洋壳厚度分别为6.4km、7.2km和5.3km,其中洋壳层2的厚度基本相似,洋壳厚度差异主要源自洋壳层3;其洋壳厚度变化范围分别为4.9～8.1km、4.6～8.7km和4.2～10.2km,随着洋中脊扩张速率减小,洋壳厚度的变化范围逐渐增大;(2)快速扩张洋中脊的洋壳速度大于慢速和超慢速,可能与快速扩张脊洋壳生成过程中深部高密度岩浆上涌比较充足有关;(3)非洋中脊(10Ma)的洋壳比洋中脊(10Ma)的洋壳厚～0.3km,表明洋壳厚度与洋壳年龄有一定的正相关性. 相似文献
7.
利用在鄂尔多斯块体内部布设的45个宽频带流动台站和固定台站的资料,用双平面波方法反演了20~143 s共12个周期的基阶瑞利面波的平均相速度和方位各向异性,并反演了一维S波速度结构.反演结果显示50~100 s中长周期的瑞利面波相速度高于AK135速度模型的相速度,为高速异常,S波速度显示高速异常主要位于180 km深度范围内,表明鄂尔多斯块体保留有厚的高速岩石圈.20~111 s周期的方位各向异性强度小于1%,较小的各向异性表明鄂尔多斯块体岩石圈变形较弱.20~50 s周期的平均快波方向为近EW向,67~143 s周期的平均快波方向为NW-SE向,相对发生了整体改变,快波方向的转变约开始于80~100 km深度范围,这表明岩石圈上下部存在着由不同变形机制导致的各向异性.上部岩石圈中各向异性可能主要为残留的“化石”各向异性,而下部岩石圈各向异性可能是现今板块构造运动导致的变形而形成.鄂尔多斯块体岩石圈垂向上的变形差异可能主要与岩石圈温度随深度的变化以及青藏高原NE-NNE向挤压引起的上部岩石圈逆时针旋转有关. 相似文献
8.
We obtain the wave velocities and quality factors of gas‐hydrate‐bearing sediments as a function of pore pressure, temperature, frequency and partial saturation. The model is based on a Biot‐type three‐phase theory that considers the existence of two solids (grains and gas hydrate) and a fluid mixture. Attenuation is described with the constant‐Q model and viscodynamic functions to model the high‐frequency behaviour. We apply a uniform gas/water mixing law that satisfies Wood's and Voigt's averages at low and high frequencies, respectively. The acoustic model is calibrated to agree with the patchy‐saturation theory at high frequencies (White's model). Pressure effects are accounted by using an effective stress law for the dry‐rock moduli and permeabilities. The dry‐rock moduli of the sediment are calibrated with data from the Cascadia margin. Moreover, we calculate the depth of the bottom simulating reflector (BSR) below the sea floor as a function of sea‐floor depth, geothermal gradient below the sea floor, and temperature at the sea floor. 相似文献
9.
使用斯克里普斯海洋研究所（SIO）整编的海洋上层（海表至400m）热储量资料，研究了热带太平洋上层热力状况季节变化的正压特征，指出与SST的分布不同，热储量在北纬5°N～10°N之间有一东西贯穿整个太平洋的带状热储量低值区，其季节变化率的分布特征分为两种，一是11月至2月为代表的“北半球冬季型”和5～8月的“北半球夏季型”，3月、4月和9月、10月为过渡阶段. 北半球10°N和2°N的季节变率的时间变化反位相，南半球的10°S、2°S?其季节变率随时间变化的位相则比较一致且与沿10°N位相大致相反. 东太平洋季节变化明显早于中、西太平洋，具有明显自东向西传播的特征. 10°S与10°N之间东、西太平洋的季节变率随时间的演变也基本上呈现反位相特征. 相似文献
10.
Compressional (Vp) and shear (Vs) wave velocities have been measured to 10 kb in 32 cores of basalt from 14 Pacific sites of the Deep Sea Drilling Project. Both VpandVs show wide ranges (3.70to6.38km/sec forVpand1.77to3.40km/sec forVsat0.5kb) which are linearly related to density and sea floor age, confirming earlier findings by Christensen and Salisbury of decreasing velocity with progressive submarine weathering based on studies of basalts from five sites in the Atlantic. Combined Pacific and Atlantic data give rates of decreasing velocity of ?1.89and?1.35km/sec per100my forVpandVs respectively. New analyses of oceanic seismic refraction data indicate a decrease in layer 2 velocities with age similar to that observed in the laboratory, suggesting that weathering penetrates to several hundred meters in many regions and is largely responsible for the extreme range and variability of layer 2 refraction velocities. 相似文献
11.
Detailed regional body wave tomographic inversion of the Western Pacific region has been performed using P and S travel times from common sources and receivers, with a joint inversion in terms of bulk-sound and shear wave-speed variations in the mantle. This technique allows the separation of the influence of bulk and shear moduli, and hence a more direct comparison with mineral physics information. The study region is parameterized with cells of side 0.5° to 2° and 19 layers to a depth of 1500 km, while the rest of the mantle was parameterized with 5×5° cells with 16 layers between the surface and the core–mantle boundary. A simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image. A nested iterative inversion scheme is employed with local linearization and three-dimensional ray tracing through the successive model updates. The results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the Kurile–Kamchatka trench, while flattening of slabs above this depth is observed in the Japan and Izu–Bonin subduction zones on both the bulk-sound and shear wave-speed images. The penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the Bonin trench, Mariana, Philippine, and Java subduction zones. Fast shear wave-speed perturbations associated with the subducted slabs, down to the 410 km transition zone, are larger than the comparable bulk-sound perturbations for all these subduction zones except the Philippines. The bulk-sound signature for the subducted slab is more pronounced than for shear in the Philippines, Talaud, New Guinea, Solomon, and Tonga subduction zones, where penetration of the slab into the middle mantle is observed. Variation in the amplitude ratio between bulk-sound and shear wave-speed anomalies correlates well with the subduction parameters of the descending slab. Slabs younger than 90 Ma at the trench show bulk-sound dominance in the upper mantle, while older slabs have a stronger shear wave-speed signature. Spreading of the fast shear wave-speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration, but has no comparable expression in the bulk-sound images. This high-velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs. 相似文献
12.
We present the first regional three-dimensional model of the Atlantic Ocean with anisotropy. The model, derived from Rayleigh and Love wave phase velocity measurements, is defined from the Moho down to 300 km depth with a lateral resolution of about 500 km and is presented in terms of average isotropic S-wave velocity, azimuthal anisotropy and transverse isotropy.The cratons beneath North America, Brazil and Africa are clearly associated with fast S-wave velocity anomalies. The mid-Atlantic ridge (MAR) is a shallow structure in the north Atlantic corresponding to a negative velocity anomaly down to about 150 km depth. In contrast, the ridge negative signature is visible in the south Atlantic down to the deepest depth inverted, that is 300 km depth. This difference is probably related to the presence of hot-spots along or close to the ridge axis in the south Atlantic and may indicate a different mechanism for the ridge between the north and south Atlantic. Negative velocity anomalies are clearly associated with hot-spots from the surface down to at least 300 km depth, they are much broader than the supposed size of the hot-spots and seem to be connected along a north-south direction.Down to 100 km depth, a fast S-wave velocity anomaly is extenting from Africa into the Atlantic Ocean within the zone defined as the Africa superswell area. This result indicates that the hot material rising from below does not reach the surface in this area but may be pushing the lithosphere upward.In most parts of the Atlantic, the azimuthal anisotropy directions remain stable with increasing depth. Close to the ridge, the fast S-wave velocity direction is roughly parallel to the sea floor spreading direction. The hot-spot anisotropy signature is striking beneath Bermuda, Cape Verde and Fernando Noronha islands where the fast S-wave velocity direction seems to diverge radially from the hot-spots.The Atlantic average radial anisotropy is similar to that of the PREM model, that is positive down to about 220 km, but with slightly smaller amplitude and null deeper. Cratons have a lower than average radial anisotropy. As for the velocities, there is a difference between north and south Atlantic. Most hot-spots and the south-Atlantic ridge are associated with positive radial anisotropy perturbation whereas the north-Atlantic ridge corresponds to negative radial anisotropy perturbation. 相似文献
13.
Alan R. Leeds 《Physics of the Earth and Planetary Interiors》1975,11(1):61-64
Rayleigh wave phase velocities were determined by the single-station method for ten paths in the western Pacific. The data show that even 100 m.y. after formation, the phase velocity and upper-mantle structure are still dependent upon age. Inversion of the data gave a model with a lithospheric thickness of 76 km at 100 m.y., increasing to 104 km at 150 m.y., measured from the base of the crust. 相似文献
14.
Barbara E John David A Foster Michael J Cheadle C.Mark Fanning 《Earth and Planetary Science Letters》2004,222(1):145-160
The cooling history and therefore thermal structure of oceanic lithosphere in slow-spreading environments is, to date, poorly constrained. Application of thermochronometric techniques to rocks from the very slow spreading SW Indian Ridge provide for the first time a direct measure of the age and thermal history of in situ lower oceanic crust. Crystallization of felsic veins (∼850°C) drilled in Hole 735B is estimated at 11.93±0.14 Ma, based on U-Pb analyses of zircon by ion probe. This crystallization age is older than the ‘crustal age’ from remanence inferred from both sea surface and near-bottom magnetic anomaly data gathered over Hole 735B which indicate magnetization between major normal polarity chrons C5n.2n and C5An.1n (10.949-11.935 Ma). 40Ar/39Ar analyses of biotite give plateau ages between 11 and 12 Ma (mean 11.42±0.21 Ma), implying cooling rates of >800°C/m.y. over the first 500,00 years to temperatures below ∼330-400°C. Fission-track ages on zircon (mean 9.35±1.2 Ma) and apatite reveal less rapid cooling to <110°C by ∼7 Ma, some 4-5 m.y. off axis.Comprehensive thermochronometric data from the structurally intact block of gabbro between ∼700 and 1100 m below sea floor suggest that crust traversed by ODP Hole 735B mimics conductive cooling over the temperature range ∼900-330°C, characteristic of a 2-D plate-cooling model for oceanic lithosphere. In contrast, lower temperature chronometers (fission track on zircon, titanite, and apatite; T≤280°C) are not consistent with these predictions and record anomalously high temperatures for crust >700 m below sea floor at 8-10 Ma (i.e. 2-4 m.y. off axis). We offer two hypotheses for this thermal anomaly:
- (i)
- Off-axis (or asymmetric) magmatism that caused anomalous reheating of the crust preserved in Hole 735B. This postulated magmatic event might be a consequence of the transtension, which affected the Atlantis II transform from ∼19.5 to 7.5 Ma.
- (ii)
- Late detachment faulting, which led to significant crustal denudation (2.5-3 km removed), further from the ridge axis than conventionally thought.
15.
Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock 相似文献
16.
《Earth and Planetary Science Letters》2006,241(3-4):901-912
We have constrained the shear-wave structure of crust and upper mantle beneath Iceland by analyzing fundamental mode Rayleigh waves recorded at the ICEMELT and HOTSPOT seismic stations in Iceland. The crust varies in thickness from 20 to 28 km in western and northern Iceland and from 26 to 34 km in eastern Iceland. The thickest crust of 34–40 km lies in central Iceland, roughly 100 km west to the current location of the Iceland hotspot. The crust at the hotspot is ∼32 km thick and is underlain by low shear-wave velocities of 4.0–4.1 km/s in the uppermost mantle, indicating that the Moho at the hotspot is probably a weak discontinuity. This low velocity anomaly beneath the hotspot could be associated with partial melting and hot temperature. The lithosphere in Iceland is confined above 60 km and a low velocity zone (LVZ) is imaged at depths of 60 to 120 km. Shear wave velocity in the LVZ is up to 10% lower than a global reference model, indicating the influence of the Mid-Atlantic Ridge and the hotspot in Iceland. The lowest velocities in the LVZ are found beneath the rift zones, suggesting that plume material is channeled along the Mid-Atlantic Ridge. At depths of 100 to 200 km, low velocity anomalies appear at the Tjornes fracture zone to the north of Iceland and beneath the western volcanic zone in southwestern Iceland. Interestingly, a relatively fast anomaly is imaged beneath the hotspot with its center at ∼135 km depth, which could be due to radial anisotropy associated with the strong upwelling within the plume stem or an Mg-enriched mantle residual caused by the extensive extraction of melts. 相似文献
17.
Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures. 相似文献
18.
AVO investigations of shallow marine sediments 总被引：2，自引：0，他引：2
Amplitude‐variation‐with‐offset (AVO) analysis is based on the Zoeppritz equations, which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence. High‐frequency (up to 700 Hz) AVO studies, presented here, have been used to determine the physical properties of sediments in a shallow marine environment (20 m water depth). The properties that can be constrained are P‐ and S‐wave velocities, bulk density and acoustic attenuation. The use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections. In the past, marine sediments have been modelled as elastic materials. However, viscoelastic models which include absorption are more realistic. At angles of incidence greater than 40°, AVO functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence. The influence of S‐wave velocity on the reflection coefficient is small (especially for low S‐wave velocities encountered at the sea‐floor). Thus, it is difficult to extract the S‐wave parameter from AVO trends. On the other hand, P‐wave velocity and density show a considerably stronger effect. Attenuation (described by the quality factor Q) influences the reflection coefficient but could not be determined uniquely from the AVO functions. In order to measure the reflection coefficient in a seismogram, the amplitudes of the direct wave and the sea‐floor reflection in a common‐midpoint (CMP) gather are determined and corrected for spherical divergence as well as source and streamer directivity. At CMP locations showing the different AVO characteristics of a mud and a boulder clay, the sediment physical properties are determined by using a sequential‐quadratic‐programming (SQP) inversion technique. The inverted sediment physical properties for the mud are: P‐wave velocity α=1450±25 m/s, S‐wave velocity β=90±35 m/s, density ρ=1220±45 kg/m3, quality factor for P‐wave QP=15±200, quality factor for S‐wave QS=10±30. The inverted sediment physical properties for the boulder clay are: α=1620±45 m/s,β=360±200 m/s,ρ=1380±85 kg/m3,QP=790±660,QS=25±10. 相似文献
19.
Old, cold oceanic lithosphere is denser and therefore gravitationally more unstable than younger, hotter oceanic lithosphere. Hence, whereas old lithosphere will sink under its own weight, subduction of young lithosphere may require an additional force. Interarc spreading occurs or occurred recently in the western Pacific, in the southern Atlantic, and possibly in the Mediterranean, where the subducted sea floor appears to be more than 50 m.y. old, and in many cases, is more than 100 m.y. old. In most of these regions, the ease with which the old dense lithosphere sinks may have contributed to a seaward migration of the trenches, which led to interarc spreading. Cordilleran tectonics, including high mountains and broad zones of deformation, are present on the margins of the eastern Pacific where the subducted oceanic lithosphere is younger than about 50 m.y. An extra force, which we presume to be necessary to cause subduction of the young lithosphere, may be responsible for the deformation and mountains just as an extra force seems necessary to drive continental collision in Asia. The extensive early Tertiary deformation across a broad zone of western North America may be related to the long-term, continuous subduction of young lithosphere of the Farallon and Kula plates. 相似文献
20.
THREE-DIMENSIONAL S-WAVE VELOCITY DISTRIBUTION BASED ON AMBIENT NOISE ANALYSIS IN EASTERN NORTH 
下载免费PDF全文
下载免费PDF全文 We apply ambient noise tomography to continuous vertical component broadband seismic data between January 1, 2010 and December 31, 2011from the regional networks of 190 stations deployed by China Earthquake Administration in Hebei, Shanxi and Inner Mengolia. Ambient noise cross-correlations were performed to produce the Green's functions of each station-pair. Firstly, we used the multiple-filter analysis method to extract surface wave group and phase velocity dispersion curves from inter-station paths at periods from 7 to 40s. Then the study area was discretized into a 0.2°×0.2° grid to obtain the group and phase velocity distributions using O'ccam inversion method. After that, three dimensional (3-D) S-wave velocity structures from the surface down to 50km are inverted from group and phase velocities dispersion results. the results of S wave velocity distribution maps generally demonstrate good correlations with surface geological and tectonic features, and they also clearly revealed the lateral velocity variation in the crust. In the mid-upper crust, the basins are clearly resolved with low S wave velocity due to its thick sedimentary layer, and the Taihang and Yanshan uplifts show relative higher S wave velocity distribution. With the increase of depth (>30km), the S wave velocity distribution presents a contrary characteristic compared to that of the shallow layer, and the S wave velocity beneath the Taihang and Yanshan uplifts are much lower than basin areas, which is possibly correlated with the thickness of the crust. 3-D S wave velocity shows a low-velocity zone at~10~20km depth observed beneath the Tanshan-Hejian-Xintai-Cixian belt and Bohai Bay. the low-velocity zone at~20~30km depth beneath the Datong area may be associated with the thermal material in the crust-mantle. Our S wave velocity distribution maps clearly show that Taihang Mountains is not only the boundary of topography and tectonic zone, but also the transition zone of high and low S wave velocity. 相似文献