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1.
本文是1986年古雷—石城剖面及嵩口—宜城剖面深地震测深资料的初步研究结果。 对古雷—石城的纵剖面资料,分析了震相特征,共识别出五个波组:P_2、P_3~0、P_4~0、P_5~0及P_n(P_n~0)。通过对波的走时反演,正演拟合和理论地震图方法等计算,得到了该区地壳与上地幔结构模型。 古雷—石城地区地壳具有多层结构,并可划分为上、中、下三层。古雷炮点给出的厚度分别为1.0km、15.7km、12.8km,地壳平均速度为6.29km/s,深度为29.5km,上地幔顶面P_n波速度为7.83km/s。石城炮点给出厚度分别为1.8km、18.3km、12.4km。地壳平均速度为6.29km/3,深度为32.4km,土地幔顶面P_n速度为8.00km/s。 在中地壳下部存在一低速层,其厚度为2.8km,速度为5.85km/s。根据其它研究结果,初步判断低速层介质是半熔融物质组成。 测区内横向变化比较强烈。从东向西有长乐—诏安、政和—海丰和邵武—河源三个大断裂穿过该区,并且都深切至莫霍面;在漳州盆地之下莫霍面隆起约3km,戴云山区下莫霍面凹陷近2km;永安—梅州莫霍面隆起接近3km。莫霍面分布显示出从东南向西北逐渐加深。 宜城—连城—嵩口非纵剖面显示了莫霍面在两处有明显断错,错距约2km邵。表明昭武—河源断裂是切割莫霍面的深大断裂。 相似文献
2.
The first P-arrival time data from local earthquakes are inverted for two-dimensional variation of the depths to the Conrad
and Moho discontinuities in the Kyushu district, southwest Japan. At the same time, earthquake hypocenters and station corrections
are determined from the data. The depths to the discontinuities are estimated by minimizing the travel time residuals of first
P-arrival phases for 608 earthquakes observed at 57 seismic stations. In the land area of Kyushu, the Conrad and Moho discontinuities
are located within the depth ranges of 16–18 and 34–40 km, respectively. The Conrad discontinuity is not as largely undulated
as the Moho discontinuity. The depth to the Moho is deep along the east coast of Kyushu, and the deepest Moho is closely related
to markedly low velocity of P wave. We regard the deepest Moho as reflecting the Kyushu–Palau ridge subducting beneath the
Kyushu district, together with the Philippine Sea slab. In western Kyushu, the shallow Moho is spreading in the north–northeast–south–southwest
direction in the Okinawa trough region. Based on the presence of low-velocity anomaly in three-dimensional velocity structure
and seismogenic stress field of shallow crustal earthquakes, the shallow Moho is interpreted as being due to lower crustal
erosion associated with a small-scale mantle upwelling in the Okinawa trough region. The velocity discontinuity undulation
basically has insignificant effect on hypocenter determination of the local earthquakes, but the Moho topography makes changes
in focal depths of some upper mantle earthquakes. The depth variation of the Moho discontinuity has a good correlation with
the Bouguer gravity anomaly map; i.e., the shallow Moho of western Kyushu and the deep Moho of eastern Kyushu closely correlate
with the positive and negative Bouguer gravity anomalies, respectively. 相似文献
3.
Siberian traps are the result of huge basalt eruptions which took place about 250 Ma ago over a vast territory of Siberia. The genesis of Siberian traps is attributed to a mantle plume with a center in the region of Iceland or beneath the central Urals in terms of their present coordinates. The eruption mechanism is associated with delamination—replacement of the mantle lithosphere by the deep magma material. The receiver function analysis of the records from the Norilsk seismic station (NRIL) allows comparing these hypotheses with the factual data on the depth structure of the region of Siberian traps. The S-wave velocity section place the seismic lithosphere/asthenosphere boundary (LAB) at a depth of 155–190 km, commensurate with the data for the other cratons. The mantle lithosphere has a high S-wave velocity characteristic of cratons (4.6–4.8 km/s instead of the typical value 4.5 km/s). The seismic boundary, which is located at a depth around 410 km beneath the continents is depressed by ~10 km in the region of the NRIL station. The phase diagram of olivine/wadsleyite transformation accounts for this depression by a 50–100°С increase in temperature. At the depths of 350–400 km, the S-wave velocity drops due to partial melting. A new reduction in the S-wave velocities is observed at a depth of 460 km. The similar anomalies (deepening of the 410-km seismic boundary and low shear wave velocity at depths of 350–400 and 460–500 km, respectively) were previously revealed in the other regions of the Meso-Cenozoic volcanism. In the case of a differently directed drift of the Siberian lithosphere and underlying mantle at depths down to 500 km, these anomalies are barely accountable. In particular, if the mantle at a depth ranging from 200 to 500 km is fixed, the anomalies should be observed at the original locations where they emerged 250 Ma ago, i.e. thousands of km from the Siberian traps. Our seismic data suggest that despite the low viscosity of the asthenosphere, the mantle drift at depths ranging from 200 to 500 km is correlated with the drift of the Siberian lithospheric plate. Furthermore, the position of the mantle plume beneath the Urals is easier to reconcile with the seismic data than its position beneath Iceland because of the Siberian traps being less remote from the Urals. 相似文献
4.
本文基于中国数字地震台网记录的发生于日本北海道地区的一次中源地震的三重震相资料研究了日本海俯冲区地幔转换带的速度结构．结果表明,该区域P波速度结构与S波速度结构的一致性整体上较强．冷的西太平洋俯冲板块导致410 km间断面出现了10 km的抬升,660 km间断面出现了25 km的下沉;410 km和660 km间断面之上均存在与俯冲板块相关的高速层;660 km间断面下方存在厚度为65 km的低速异常．纵横波波速比vP/vS值在210—400 km深度范围内偏低,约为1.827,体现出海洋板块低泊松比的特征;在560—685 km深度范围内,该值偏高,约为1.831,可能预示地幔转换带底部含有一定量的水． 相似文献
5.
6.
Haruhisa Nakamichi Satoru Tanaka Hiroyuki Hamaguchi 《Journal of Volcanology and Geothermal Research》2002,116(3-4)
A genetic algorithm inversion of receiver functions derived from a dense seismic network around Iwate volcano, northeastern Japan, provides the fine S wave velocity structure of the crust and uppermost mantle. Since receiver functions are insensitive to an absolute velocity, travel times of P and S waves propagating vertically from earthquakes in the subducting slab beneath the volcano are involved in the inversion. The distribution of velocity perturbations in relation to the hypocenters of the low-frequency (LF) earthquakes helps our understanding of deep magmatism beneath Iwate volcano. A high-velocity region (dVS/VS=10%) exists around the volcano at depths of 2–15 km, with the bottom depth decreasing to 11 km beneath the volcano’s summit. Just beneath the thinning high-velocity region, a low-velocity region (dVS/VS=−10%) exists at depths of 11–20 km. Intermediate-depth LF (ILF) events are distributed vertically in the high-velocity region down to the top of the low-velocity region. This distribution suggests that a magma reservoir situated in the low-velocity region supplies magma to a narrow conduit that is detectable by the hypocenters of LF earthquakes. Another broad low-velocity region (dVS/VS=−5 to −10%) occurs at depths of 17–35 km. Additional clusters of deep LF (DLF) events exist at depths of 32–37 km in the broad low-velocity zone. The DLF and ILF events are the manifestations of magma movement near the Moho discontinuity and in the conduit just beneath the volcano, respectively. 相似文献
7.
自20世纪90年代首次探测到410-km间断面上覆低速层以来,全球多个俯冲带和大陆克拉通地区都陆续发现了该低速层结构.对其特性及形成机理的探讨是深部地幔结构、物性和动力学研究的热点问题.本文聚焦于西北太平洋俯冲地区410-km间断面上覆低速层的探测及特性研究上.通过对发生于日本北海道地区两个中等深度地震区域波形资料的分析,利用三重震相波形拟合方法获得了我国东北及日本海西北部下方410-km间断面附近的P波速度结构.速度模型明确显示,410-km间断面上方存在厚~47±14 km,异常值~2%的低速层,横向展布近700 km.结合区域地震层析成像、矿物高温高压物理实验及动力学模拟结果,我们否定了"从下至上"的上涌热物质导致410-km间断面上覆低速层的模型;认为较老且快速俯冲的太平洋板块在地幔过渡带顶部脱水导致硅酸盐矿物的部分熔融,由于熔体密度较大能够稳定存在于410-km间断面之上,从而产生了观测到的横向展布较广的410-km间断面上覆低速层结构. 相似文献
8.
The propagation of seismic waves through Earth models with slightly random lateral and vertical inhomogeneities superimposed on one composed of layers with vertical velocity gradients was investigated. The maximum deviation of velocity from a mean value at a given depth and a correlation distance derived from a two-dimensional smoothing filter were two parameters used to vary the amplitude and size of the velocity anomalies. The resulting models show short discontinuous reflectors scattered about at various depths throughout the model, and are thus in agreement with many deep seismic reflection experiments. On the other hand numerical experiments using ray-tracing techniques showed that the effect of the lateral and vertical velocity anomalies is to scatter the energy, and break up the continuous travel-time lines from vertical gradient models into travel-time segments with different slopes similar to those observed in many long range seismic refraction experiments, and to those resulting from layering effects in the media. Many of the numerical experiments which modelled the random crust produced a Pg segment and a P* segment with an apparent Conrad discontinuity at a depth of 10–20 km, this apparent depth being related to the correlation distance.When a seismic wave propagates through a heterogeneous Earth the amount of its energy which is converted into scattered energy will be a function of the inhomogeneous characteristics of the medium through which it has passed. If a ray passes through a homogeneous Earth the energy arriving at an array station should be relatively coherent whereas if the ray encounters lateral and vertical inhomogeneities its energy will be incoherent and much more complex. A series of coherency measurements done on array recordings of earthquakes at various distances showed that large lateral and vertical variations in complexity exist for different ray paths through the Earth with the region below the 650 km discontinuity in the mantle tending to be much simpler than the region just below the lithosphere. 相似文献
9.
We explain the global variation of Benioff zone seismicity with depth and the orientation of stress axes of deep and intermediate earthquakes using numerical models of subducting slabs. Models that match the seismicity and stress require a barrier to flow at the 670 km seismic discontinuity. The barrier may be a viscosity increase of at least an order of magnitude or a chemical discontinuity. Instantaneous flow is subparallel to the slabs for models with a viscosity increase but contorted for models with a chemical barrier. Log N (number of earthquakes) decreases linearly to 250–300 km depth and increases thereafter. Stress magnitude in our models shows the same pattern, in accord with experiments showing N proportional to ekσ, with k a constant and σ stress magnitude. The models predict downdip compression in the slabs at depths below 300–400 km, as observed for earthquake stress axes. 相似文献
10.
A study on 3-D velocity structure of crust and upper mantle in Sichuan -Yunnan region, China 总被引：1，自引：0，他引：1
Many evidences indicate that the collision of two plates deformed strongly the crust of the SYR, and the deformation has been continued up to the present. In addition, the SYR is in the south segment of the South-North Seismic Zone of China, which is one of the regions in the Chinese mainland, where the seismic activity is very high, and the strong earthquakes frequently occurred. Since the 1970s, a series of large earthquakes with magnitude M>7.0 occurred in SYR, such as the 1970 Tongha… 相似文献
11.
川滇地区地壳上地幔三维速度结构研究 总被引：95，自引：22，他引：95
根据云南和四川地震台网174个台站记录的4625个区域地震初至Ｐ波和Ｓ波走时资料，并结合其它深部地球物理资料，确定了川滇地区地壳上地幔三维速度结构．在上地壳速度异常分布中，四川盆地为正异常，川西高原为负异常，龙门山断裂带为正、负异常的边界．龙门山断裂、鲜水河断裂以及红河断裂等，在下地壳和上地幔的速度异常中仍显示出构造分界特征，说明它们可能穿透了莫霍界面．腾冲火山区和攀西构造带在50km深度上呈现负速度异常，与上地幔温度和物质组成的差异相联系．川滇地区地壳结构的总体特征是:地壳和上地幔的低平均速度，地壳厚度变化剧烈，地壳和（或）上地幔存在高导层、高热流值．这些同印度板块与欧亚板块碰撞的构造背景有关．川滇菱形块体在地壳内总体上为正常或正异常速度，而其边界的深大走滑断裂存在负速度异常，它有助于地壳块体沿断裂的侧向挤出．在主要的地震带上，中下地壳的负速度异常与地震活动性相关．多数强烈地震发生在具有正速度异常或正常速度分布的上中地壳深度上，而其下方则通常是负速度异常带． 相似文献
12.
L.P. Vinnik R.A. Avetisjan N.G. Mikhailova 《Physics of the Earth and Planetary Interiors》1983,33(3):149-163
The method of detection of P-to-SV converted waves from distant earthquakes (Vinnik, 1977) was applied to sets of long-period records from a few seismograph stations in Europe and the west of North America. The results obtained suggest that the converted phases related to the major boundaries in the mantle can be reliably detected and the depths of conversion evaluated with an accuracy of a few kilometres. The depth of the olivine-spinel transition is close to 400 km and no difference between the estimates for the north of Europe and the west of North America is found. The depth of the boundary separating the upper and lower mantle is close to 640 km, which is 30 km less than in the recent Earth-reference models. Fine S velocity stratification of this transition changes laterally from a high-gradient layer 50 km thick, terminated at the bottom by a sharp discontinuity, to a gradient layer 100 km or more thick without the discontinuity. A striking anomaly of the mantle transition zone is found in the Rio Grande rift area where a well pronounced boundary is found at 510 km depth. 相似文献
13.
A total of 11 earthquakes with 15 Rayleigh wave paths, recorded at 11 broadband digital PASSCAL seismometers installed in the Tibet Plateau by the Sino-U.S. joint research group, were used to determine the phase velocity and attenuation coefficient of surface waves in periods of 10–130 s. The average shear wave velocity and quality factor {ie271-1} structures in the crust and upper mantle were obtained in this region. The result shows the average {ie271-2} is low and there exists a high attenuation ({ie271-3}=93–141) layer in the crust. The depth range of the low {ie271-4} value layer (16–42 km) is consistent with the range of low velocity layer (21–51 km) in the crust. Below 63 km in the lower crust, {ie271-5} decreases with depth from 114 to 34 at depth of 180 km. The low shear wave velocity and low value of {ie271-6} at the same depth range in the crust indicate that the rocks in the range is probably melted or partially melted. According to the shear wave velocity structure, the average thickness of the crust is about 71 km and a clear velocity discontiniuty appears at the depth of 51 km. The low-velocity zone (4. 26 km/s) at depth of 96–180 km may be corresponding to the asthenosphere. 相似文献
14.
本文根据北京台网、大连、长春、牡丹江、海参威等26个台站的记录,选用了从北京地区到阿留申群岛西端的300多个地震,研究了北京-萨哈林剖面的地幔纵向速度分布。 用Herglotz-Wiechert公式计算得出的V-h作为初始模型,计算理论走时曲线,找出了与实际走时曲线符合较好的速度结构。其特点为:上地幔顶部的速度为7.8公里/秒;高速盖层中有正速度梯度;在约60-120公里深度范围内为低速层;130公里以下速度缓慢增大;在370-440公里、600-740公里有两个速度梯度较大的过渡层,其中以370-440公里的正速度梯度最大,与之相应的震中距为19°。在1060公里以下有微弱的正梯度。 用Kaila方法计算了深度为400公里左右的地震震源深度处的速度值,与上述结果一致。 相似文献
15.
Deep earthquakes located in the Tonga-Kermadec region produce exceptionally clear and sharp short-period P, S, PcP, ScP, and ScS phases which are recorded at many stations at distances of less than 60°. The data used in this study are produced by short-period stations located in oceanic-type regions (Fiji and New Caledonia), a mobile continental region (eastern Australia) and a shield region (central Australia). Differential travel-time residuals of the above phases at these stations are investigated to determine the contribution to the differential residuals from: (1) the upper part of the mantle (S-P residuals); (2) the core-to-station portion of the mantle (ScS-ScP residuals); and (3) the hypocenter-to core portion of the mantle (ScP-PcP residuals). The use of differential travel-time residuals considerably reduces near-station effects and effects due to inaccurate determination of the source parameters, and hence the results can be interpreted as due to variations along the propagation paths. The results show that (S-P) residuals from phases traveling along event-to-station paths are about 7 s smaller at the shield station than at the oceanic stations. This correlation with surface tectonic environments is equally strong for the (ScS-ScP) residuals, with the shield/oceanic station difference being about 4 s. Moreover, the data suggest that this correlation between differential residuals and surface tectonic environments is caused by variations in shear velocity within the upper part of the mantle. However, the data cannot uniquely resolve the required depth of these variations within the mantle. For example, if the shear velocity variations extend to a depth of 400 km beneath the recording stations, then the average shear velocity difference between shield- and oceanic-type environments is about 4%. However, if the variations extend only to a depth of 200 km, this difference is more than 8%.(ScP-PcP) and (ScS-PcS) residuals vary from about +1 to about +4 s at the different stations, apparently because of compressional velocity variations in the mantle along the Pc path. If the variation in compressional velocity within the mantle below a depth of about 600 km is about 10% and occurs near the source region, these results suggest that, in the vicinity of deep earthquake zones, variations in compressional velocity extend to a depth of about 1000 km. However, these results can equally be explained by a 1% variation in compressional velocity, evenly distributed along the entire Pc path. An estimate of Q determined from the observed predominant frequency of ScS waves, as recorded at the shield station, suggests that the average 〈Qs〉 of the mantle beneath about 600 km is about 1050 at frequencies of about 1 Hz. 相似文献
16.
Günter Bock 《Physics of the Earth and Planetary Interiors》1981,25(4):360-371
P-wave travel-time residuals at the Warramunga Seismic Array (WRA) in the Northern Territory, Australia, have been studied from 49 earthquakes with epicenters south of 19°S in the Fiji-Tonga region. Focal depths are between 42 and 679 km as determined from pP-P. Using the Jeffreys-Bullen and the Herrin travel-time tables the epicentral parameters have been redetermined by considering only “normal” seismic stations in the location procedure. These are those stations where P-wave travel times are probably not affected by lateral heterogeneities caused by the lithosphere descending beneath the Tonga trench. Epicenters of deep earthquakes below 300 km have been relocated by using stations at Δ > 25° only. Epicenters from shallower-depth earthquakes have been recalculated without using stations between 35 < Δ < 75° epicentral distance. In both cases focal depths were determined from pP-P times. The resulting pattern of P-residuals at WRA does not show any significant change with depth below 350 km. The residuals become more negative for shallower earthquakes above about 250 km. P-waves to WRA are advanced by approximately 2 s compared with those from deep earthquakes. The results do not essentially differ for the two different travel-time tables used. The observations can be interpreted by P-wave velocities that are higher in the sinking slab down to 350–400 km by 5±2% than in both the Jeffreys-Bullen and Herrin models. Without considering possible elevations of phase boundaries this estimate yields a temperature contrast of 1000±450°C between slab and normal mantle material in this depth range. 相似文献
17.
Sean C. Solomon 《Physics of the Earth and Planetary Interiors》1975,11(2):97-108
The top of the olivine-spinel phase change in subducted oceanic lithosphere can be located by the travel times of seismic waves which have propagated through the slab. P-wave travel-time residuals from deep earthquakes in the Tonga island are observed at Australian seismic stations are grouped according to the depth of the earthquake. The change in mean residual with a change in earthquake depth is related to the velocity contrast between slab and normal mantle at that depth. The curve mean residual versus earthquake depth displays a region of markedly increased slope between earthquake depths of about 250 and 350 km. The most probable explanation of this observation is an elevation by 100 km of the olivine-spinel phase change within the relatively cooler slab. No evidence was found for vertical displacements within the slab of any deeper phase changes.A temperature contrast between slab and normal mantle of about 1,000°C at 250 km depth is implied. This finding confirms current thermal models for subducted lithosphere but is inconsistent with the global intraplate stress field unless only a few percent of the negative buoyancy force at subduction zones is transmitted to the surface plates. 相似文献
18.
用接收函数方法研究上海地震台阵下地壳结构 总被引：1，自引：1，他引：0
利用上海地震台阵16个台站记录的远震资料,采用接收函数线性反演方法,对台阵下的地壳速度结构进行研究,获得了研究区域内地壳厚度和地壳速度的分布特征。研究结果表明,研究区域Moho面深度约为33±2 km,Moho面深度基本不变,地幔顶部S波速度约4.4 km/s,地壳内没有发现明显的低速层。 相似文献
19.
Compressional velocity in source regions of deep earthquakes: An application of the master earthquake technique 总被引：1，自引：0，他引：1
Thomas J. Fitch 《Earth and Planetary Science Letters》1975,26(2):156-166
The technique of earthquake location relative to a master event is used to estimate near-source velocity and take-off angles for rays travelling to selected stations. Computations of a reconnaissance nature were carried out with arrival times of P and pP from deep earthquakes beneath the northwest corner of the Fiji plateau, the Peru-Brazil border region and the basin separating Fiji from the Tonga arc. These data yield estimates of compressional velocity of 11.2 ± 0.4, 11.4 ± 0.7 and 10.7 ± 0.3 km/sec respectively. Each of these velocities and the other parameters of each model space are essentially independent of their starting values. The corresponding depth ranges are 600–660, 580–650 and 540–600 km. These in-situ velocities are 5–10% higher than those of the Helmberger and Wiggins model. To account for such high velocities by a thermal effect alone would require an improbably high thermal contrast of 1000°C between “normal” mantle and the cooler earthquake zones. Spinels of proposed mantle composition would have compressional velocities of about 10.4 km/sec at temperatures that are taken as normal for these depths. If the high values of near-source velocity are explained by the addition of a post-spinel assemblage, then by implication this transformation occurs at shallower depths in those seismic zones than in the “normal” mantle. 相似文献
20.
利用S波纯波形拟合法以及T函数法反演了苏鲁地区壳幔剪切波速度结构,并利用长周期P波T函数反演得到了连云港和莱阳台下方800km深度的速度结构。结果显示:(1)苏鲁地区大部分台站地壳表层及上地壳浅部速度偏高,分别对应高压、超高压物质和古老基底出露地区;(2)沿郯庐断裂带分布的台站均显示明显低速层,并具有北浅南深的特点;(3)连云港和莱阳台超深度反演结果显示两台均在150km深度下出现高速层,反映扬子板块的俯冲深度为100km以下,俯冲板片厚度在100km以上;板片拆离下沉深度甚至达到300km或者更深;(4)地震深度分布与低速层关系密切,沿郯庐断裂和烟台—五莲断裂的中小地震震源深度都比较深,有的甚至达到地壳的底部,反映这两条断裂目前切割深度都比较大,而且地幔物质相对比较活跃。 相似文献