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1.
A. A. Baranov 《Izvestiya Physics of the Solid Earth》2010,46(1):34-46
We present a new regional three-layer crustal model for the Central and Southern Asia and surroundings (AsCRUST-08). The model
provides Moho boundary, thickness of different layers of consolidated crust and P-velocity distribution in these layers. A large volume of new data on seismic reflections and refractions as well as on surface
waves generated by earthquakes or blasts was analyzed. All these data were incorporated into a unified digital 3D integrated
model with 1° × 1° resolution. Results are represented as seven numerical maps imaging the distributions of the Moho depth,
the thickness of the upper, middle, and lower layers of the consolidated crust, and the P-wave velocities therein. 相似文献
2.
We present the 1-D crustal velocity structure of the major tectonic blocks of the North China Craton(NCC) along 36°N based on synthetic seismogram modeling of long-range wide-angle reflection/refraction data. This profile extends from southwest Yan'an of central Shaanxi Province of China(109.47°E), across the southern Trans-North China Orogen(TNCO), the southwestern part of the North China Plain(NCP), the Luxi Uplift(LU) and the Sulu Orogen(SLO), ending at Qingdao City of Shandong Province, the eastern margin of China(120.12°E) along 36°N. We utilized reflectivity synthetic seismogram modeling of the active source data to develop 1-D velocity structures of the sub-blocks of the NCC. Our final model shows that the NCC crust varies remarkably among the tectonic units with different velocity structure features. Higher lower crustal velocity and Moho depth ～42 km is a major feature of the crust beneath southern Ordos Blockt. The TNCO which is composed of Lyuliangshan Mountains(LM), Shanxi Graben(SXG) and Taihangshan Mountains(TM) shows dominant trans-orogenic features. The NCP shows a dominant thickening of sediments, sharp crust thinning with Moho depth ～32 km and significant lower average velocity. The SLO and the LU shows a stratified crust, higher average velocity and crust thinning with Moho depth of ～35 km. Our model shows the coincidence between the deep structure and the surface geology among all the tectonic sub-blocks of the NCC. 相似文献
3.
Fataneh Taghizadeh-Farahmand Forough Sodoudi Narges Afsari Mohammad R. Ghassemi 《Journal of Seismology》2010,14(4):839-836
We computed P and S receiver functions to investigate the lithospheric structure beneath the northwest Iran and compute the
Vp/Vs ratio within the crust of this seismologically active area. Our results enabled us to map the lateral variations of
the Moho as well as those of the lithosphere–asthenosphere boundary (LAB) beneath this region. We selected data from teleseismic
events (Mb > 5.5, epicentral distance between 30° and 95° for P receiver functions and Mb > 5.7, epicentral distance between 60° and 85° for S receiver functions) recorded from 1995 to 2008 at 8 three-component
short-period stations of Tabriz Telemetry Seismic Network. Our results obtained from P receiver functions indicate clear conversions
at the Moho boundary. The Moho depth was firstly estimated from the delay time of the Moho converted phase relative to the
direct P wave. Then we used the H-Vp/Vs stacking algorithm of Zhu and Kanamori to estimate the crustal thickness and Vp/Vs
ratio underneath the stations with clear Moho multiples. We found an average Moho depth of 48 km, which varies between 38.5
and 53 km. The Moho boundary showed a significant deepening towards east and north. This may reveal a crustal thickening towards
northeast possibly due to the collision between the Central Iran and South Caspian plates. The obtained average Vp/Vs ratio
was estimated to be 1.76, which varies between 1.73 and 1.82. The crustal structure was also determined by modeling of P receiver
functions. We obtained a three-layered model for the crust beneath this area. The thickness of the layers is estimated to
be 6–11, 18–35, and 38–53 km, respectively. The average of the shear wave velocity was calculated to be 3.4 km/s in the crust
and reaches 4.3 km/s below the Moho discontinuity. The crustal thickness values obtained from P receiver functions are in
good agreement with those derived by S receiver functions. In addition, clear conversions with negative polarity were observed
at ~8.7 s in S receiver functions, which could be related to the conversion at the LAB. This may show a relatively thin continental
lithosphere of about 85 km implying that the lithosphere was influenced by various geodynamical reworking processes in the
past. 相似文献
4.
Inversion of gravity and topography data for the crust thickness of China and its adjacent region 总被引：1，自引：0，他引：1
Introduction Since the middle of the century, gravitational isostasy has been a fundamental hypothesis for inverting the gravity data to find the crust thickness. Geophysicists have done a lot of researches on using gravity data to investigate the depth of Moho discontinuity. Since 1980, the International Lithosphere Program emphasized the importance of investigating the Moho depth variation. Thereafter a lot of results have been published in the world (Braitenberg et al, 2000; Kaban et al,… 相似文献
5.
Narges Afsari Forogh Sodoudi Fataneh Taghizadeh Farahmand Mohammad Reza Ghassemi 《Journal of Seismology》2011,15(2):341-353
Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities
in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath
the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset
includes teleseismic data (M
b ≥ 5.5, epicentral distance from 30° to 95°) recorded at 12 three-component short-period stations of Kermanshah, Isfahan and
Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at the Moho
boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P
wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity
such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver
function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan
Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth
decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat
Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed
a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho
boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ
increases to 4.3 km/s beneath the Moho. 相似文献
6.
Crustal structure and the Moho depth are exceptionally well known beneath Europe. The first digital, high-resolution map of
the Moho depth for the whole European Plate was compiled in 2007 and recently published in Geophysical Journal International. In the past few years, considerable developments have taken place in the receiver function techniques. Different receiver
function techniques provide new, independent information, in particular on the S-wave velocity distribution in the crust and on the Moho depth. This gives an opportunity to compare the Moho depth from the
Moho depth map of the European Plate (H
MM) and the Moho depth from receiver function studies (H
RF). Herein, we also compile and analyze the uncertainty of the crustal thickness determinations data obtained with receiver
function analysis. The uncertainty is found to be ±2 km for 20-km-thick crust and about ±4 km for 60-km-thick crust. Comparison
of the Moho depths shows an approximately linear trend between H
RF and H
MM. For the Moho depth of 30–40 km, the values are approximately equal, while for thin crust, H
RF is about 5 km shallower than H
MM, and for thick crust, it is about 5 km deeper than H
MM. Possible reasons for this, the observed discrepancy between the Moho depths HMM and HRF, are discussed. 相似文献
7.
In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to
the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse
receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed
frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu
and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The
combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia
show high-shear-wave velocities (V
S) near the surface in the range of 3.4–3.6 km s − 1 attributed to crystalline rocks and 3.6–4.0 km s − 1 in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30–34 km where it
forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone
(BSI, GSI and PSI) complexity within the crust is high. Near the surface low V
S of 2.6–2.9 km s − 1 indicate sediment layers. High V
S of 4.2 km s − 1 are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth.
At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated
from the sediment layer by a 10 km wide gradient in V
S between 10 and 20 km depth. Within the subducting slab V
S ≈ 4.7 km s − 1. At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20° ± 8° in approximately N 60° E. A
velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found. 相似文献
8.
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
9.
10.
Introduction The gravity anomaly is an indicator of the density distribution of the underground material. Therefore the gravity anomalies have been important data used for studying the deep crustal struc-ture for a long time. Many people have made detailed researches on the regional crustal structure inverted by Bouguer anomalies. In particular some empirical formulae and practical algorithms about the crustal thickness were brought forward, and a series of results were obtained (MENG, 1996)… 相似文献
11.
12.
Fataneh Taghizadeh-Farahmand Forough Sodoudi Narges Afsari Mohammad R. Ghassemi 《Journal of Seismology》2010,14(4):823-836
We computed P and S receiver functions to investigate the lithospheric structure beneath the northwest Iran and compute the Vp/Vs ratio within the crust of this seismologically active area. Our results enabled us to map the lateral variations of the Moho as well as those of the lithosphere–asthenosphere boundary (LAB) beneath this region. We selected data from teleseismic events (Mb?>?5.5, epicentral distance between 30° and 95° for P receiver functions and Mb?>?5.7, epicentral distance between 60° and 85° for S receiver functions) recorded from 1995 to 2008 at 8 three-component short-period stations of Tabriz Telemetry Seismic Network. Our results obtained from P receiver functions indicate clear conversions at the Moho boundary. The Moho depth was firstly estimated from the delay time of the Moho converted phase relative to the direct P wave. Then we used the H-Vp/Vs stacking algorithm of Zhu and Kanamori to estimate the crustal thickness and Vp/Vs ratio underneath the stations with clear Moho multiples. We found an average Moho depth of 48 km, which varies between 38.5 and 53 km. The Moho boundary showed a significant deepening towards east and north. This may reveal a crustal thickening towards northeast possibly due to the collision between the Central Iran and South Caspian plates. The obtained average Vp/Vs ratio was estimated to be 1.76, which varies between 1.73 and 1.82. The crustal structure was also determined by modeling of P receiver functions. We obtained a three-layered model for the crust beneath this area. The thickness of the layers is estimated to be 6–11, 18–35, and 38–53 km, respectively. The average of the shear wave velocity was calculated to be 3.4 km/s in the crust and reaches 4.3 km/s below the Moho discontinuity. The crustal thickness values obtained from P receiver functions are in good agreement with those derived by S receiver functions. In addition, clear conversions with negative polarity were observed at ~8.7 s in S receiver functions, which could be related to the conversion at the LAB. This may show a relatively thin continental lithosphere of about 85 km implying that the lithosphere was influenced by various geodynamical reworking processes in the past. 相似文献
13.
The Moho information under Tibet Plateau is important for a better understanding of the geodynamic processes associated with the continental collision of the Indian and Eurasian tectonic plates and subsequent formation of Himalayan and Tibetan orogens. However, under the central and western parts of Tibet, the existing Moho models are still relatively inaccurate due to a sparse and irregular distribution of seismic surveys. To overcome this problem, the gravimetric data could be used to interpolate the Moho information, where seismic data are missing. In this study, we apply the gravimetric method for a regional Moho recovery under Tibet. Compared to existing methods that use either the gravity or gravity-gradient data, the method presented here utilizes a more generic definition based on a functional relation between the Moho depth and the gravitational potential. Since the gravity and gravity-gradient data have more regional support than the potential field, a numerical test is conducted to find an optimal data area extension that is needed to solve a regional inversion problem in order to reduce errors caused by disregarding the far-zone contribution. Our analysis shows that for the potential field such extension should be at least 25°, while 5° for the gravity and only about 1° for the gravity gradient. The comparison of our gravimetric result with the CRUST1.0 seismic model shows differences at the level of expected accuracy of the gravimetric method of about 5 km and without the presence of significant bias. 相似文献
14.
用多震相地震走时成像法反演郯庐断裂带鲁苏皖段及邻区三维地壳速度结构。一些地区如郯庐断裂带临沭到定远及以东地区在中地壳的20~25km出现低速层,一些地区莫霍面埋深有变化。浅层速度结构的分段与断裂活动的分段相一致,表明新沂到泗洪是活动断裂的闭锁段。对比1668年山东郯城8级地震区和研究区的深部速度结构,结合与郯庐带相交的断裂、地震活动、活动断裂的闭锁段、中地壳低速层及莫霍面深度变化,综合判断郯庐断裂带江苏段未来可能发生大震的地区为33.4°~34.1°N,118.2°~118.8°E,重点是宿迁、沭阳、泗阳和泗洪。震级估计可达8级。 相似文献
15.
L. Matias N. A. Dias I. Morais D. Vales F. Carrilho J. Madeira J. L. Gaspar L. Senos A. B. Silveira 《Journal of Seismology》2007,11(3):275-298
The Faial earthquake (M
L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction
affecting more than 5,000 people. The main shock was located at sea, 10 km NE of the Faial Island, and triggered a seismic
sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity
model performed on the data collected by the permanent network complemented with a temporary network installed shortly after
the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences
in site effects at the stations, while the middle crust from ∼2.5 to 8 km in depth is quite homogeneous. The Moho is located
at a depth of about 12–13 km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in
the middle-lower crust (8–12 km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending.
This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution
for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis
on the aftershock distribution. The main event relocation points to a focal depth shallower than 5 km. The aftershocks pattern
shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main
tectonic directions, trending WNW–ESE and NNW–SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence
of a new tectonic direction trending WSW–ENE. 相似文献
16.
使用阻尼最小二乘法进行震源参数和地壳三维速度结构的走时联合反演．所用资料为Ｓ波和Ｐ波到时差,并用人工地震资料的二维解释结果作为三维速度模型的特定约束条件．为建立初始模型,又利用天然地震构成了准二维剖面．在走时反演基础上,利用遗传算法进行了几个地震事件的波形反演尝试,并对走时反演获得的地壳速度结构模型的局部进行了修正．以３４°～４２°Ｎ,９４°～１１２°Ｅ作为研究区域,在该区域中收集了１９８６年以来大量地震的Ｓ波和Ｐ波到时差资料,７条人工地震二维速度剖面资料和２个数字化地震台的几个地震的三分向记录资料．对这些资料进行了处理,最后得出了０～２５ｋｍ深度不同截面的速度分布,并对所得结果进行了分析． 相似文献
17.
The latest seismic data and improved information about the subglacial bedrock relief are used in this study to estimate the sediment and crustal thickness under the Antarctic continent. Since large parts of Antarctica are not yet covered by seismic surveys, the gravity and crustal structure models are used to interpolate the Moho information where seismic data are missing. The gravity information is also extended offshore to detect the Moho under continental margins and neighboring oceanic crust. The processing strategy involves the solution to the Vening Meinesz-Moritz’s inverse problem of isostasy constrained on seismic data. A comparison of our new results with existing studies indicates a substantial improvement in the sediment and crustal models. The seismic data analysis shows significant sediment accumulations in Antarctica, with broad sedimentary basins. According to our result, the maximum sediment thickness in Antarctica is about 15 km under Filchner-Ronne Ice Shelf. The Moho relief closely resembles major geological and tectonic features. A rather thick continental crust of East Antarctic Craton is separated from a complex geological/tectonic structure of West Antarctica by the Transantarctic Mountains. The average Moho depth of 34.1 km under the Antarctic continent slightly differs from previous estimates. A maximum Moho deepening of 58.2 km under the Gamburtsev Subglacial Mountains in East Antarctica confirmed the presence of deep and compact orogenic roots. Another large Moho depth in East Antarctica is detected under Dronning Maud Land with two orogenic roots under Wohlthat Massif (48–50 km) and the Kottas Mountains (48–50 km) that are separated by a relatively thin crust along Jutulstraumen Rift. The Moho depth under central parts of the Transantarctic Mountains reaches 46 km. The maximum Moho deepening (34–38 km) in West Antarctica is under the Antarctic Peninsula. The Moho depth minima in East Antarctica are found under the Lambert Trench (24–28 km), while in West Antarctica the Moho depth minima are along the West Antarctic Rift System under the Bentley depression (20–22 km) and Ross Sea Ice Shelf (16–24 km). The gravimetric result confirmed a maximum extension of the Antarctic continental margins under the Ross Sea Embayment and the Weddell Sea Embayment with an extremely thin continental crust (10–20 km). 相似文献
18.
本文利用地面实测重力资料和地形高程资料,采用普拉特-海福特(Pratt-ttayford)重力均衡理论模型,取1°×1°方格网,通过使用现成改正表格查取改正值与个别计算点用理论公式计算作校核的方法,计算了我国东北地区75个计算点的均衡重力异常值;并对局部第四系覆盖较厚地区作了第四系密度改正;在此基础上,构制了我国东北N39°—49°,E121°—131°大部分地区的均衡重力异常图;结合区域布格重力异常和区域空间重力异常特征以及莫霍界面的起伏特点作了对比分析和讨论 相似文献
19.
The structure of the crust and the crust-mantle boundary in the Vogtland/West Bohemian region have been a target of several
seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90,
9HR), the refraction and wide-angle experiments (GRANU’95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic
studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower
crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift.
The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth
of 26–28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the
lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies
detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and
37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different
background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling
was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower
crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling
resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the
Moho reflection at a depth of 32–33 km. 相似文献
20.
Crustal structure of northeastern margin of the Tibetan Plateau by receiver function inversion 总被引：11，自引：0，他引：11
Using seismic data of about one year recorded by 18 broadband stations of ASCENT project,we obtained 2547 receiver functions in the northeastern Tibetan Plateau.The Moho depths under 14 stations were calculated by applying the H-κ domain search algorithm.The Moho depths under the stations with lower signal-noise ratio(SNR) were estimated by the time delay of the PS conversion.Results show that the Moho depth varies in a range of ~40–60 km.The Moho near the Haiyuan fault is vague,and its depth is larger than those on its two sides.In the Qinling-Qilian Block,the Moho becomes shallower gradually from west to east.To the east of 105°E,the average depth of the Moho is 45 km,whereas the west is 50 km or even deeper.Combining our results with surface wave research,we suggest a boundary between the Qinling and the Qilian Mountains at around 105°E.S wave velocities beneath 15 stations have been obtained through a linear inversion by using Crust2.0 as an initial model,and the crustal thickness that was derived by H-κ domain search algorithm was also taken into account.The results are very similar to the results of previous active source studies.The resulting figure indicates that low velocity layers developed in the middle and lower crust beneath the transition zone of the Tibet Block and western Qinling,which may be related to regional faults and deep earth dynamics.The velocity of the middle and lower crust increases from the Songpan Block to the northeastern margin of Tibetan Plateau.Based on the velocity of the crust,the distribution of the low velocity zone and the composition of the curst(Poisson's ratio),we infer that the crust thickening results from the crust shortening along the direction of compression. 相似文献