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1.
The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from
zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999
in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a broadband
station located in Egypt (KEG station). The dispersion curves were obtained for periods between 3 and 40 s, by digital filtering
with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain
a dispersion curve for each source-station path. These dispersion curves were inverted according to generalized inversion
theory, to obtain shear wave velocity models for each source-station path, which is the main goal of this study. The shear
velocity structure obtained for the Sinai Peninsula is shown through the shear velocity distributions with depth. These results
agree well with the geology and other geophysical results, previously obtained from seismic and gravity data. The obtained
velocity models suggest the existence of lateral and vertical heterogeneity. The shear velocity increases generally with depth
for all paths analyzed in the study area. Nevertheless, in some paths a small low velocity channel in the upper or lower crust
occurs. Along these profiles, it is found that the crustal structure of the Sinai Peninsula consists of three principal layers:
upper crust with a sedimentary layer and lower crust. The upper crust has a sedimentary cover of 2 km thick with an average
S-velocity of 2.53 km/s. This upper crust has a variable thickness ranging from 12 to 18 km, with S-wave velocity ranging
from 3.24 to 3.69 km/s. The Moho discontinuity is located at a depth of 30 km, which is reflected by a sharp increase in the
S-velocity values that jump from 3.70–4.12 to 4.33–4.61 km/s. 相似文献
2.
A detailed dispersion analysis of Rayleigh waves generated by local earthquakes and occasionally by blasts that occurred in
southern Spain, was undertaken to obtain the shear-wave velocity structure of the region at shallow depth. Our database includes
seismograms generated by 35 seismic events that were recorded by 15 single-component short-period stations from 1990 to 1995.
All these events have focal depths less than 10 km and body-wave magnitudes between 3.0 and 4.0, and they were all recorded
at distances between 40 and 300 km from the epicentre. We analysed a total of 90 source-station Rayleigh-wave paths. The collected
data were processed by standard digital filtering techniques to obtain Rayleigh-wave group-velocity dispersion measurements.
The path-averaged group velocities vary from 1.12 to 2.25 km/s within the 1.0-6.0 s period interval. Then, using a stochastic
inversion approach we obtained 1-D shear-wave velocity–depth models across the study area, which were resolved to a depth
of circa 5 km. The inverted shear-wave velocities range approximately between 1.0 and 3.8 km/s with a standard deviation range
of 0.05–0.16 km/s, and show significant variations from region to region. These results were combined to produce 3-D images
via volumetric modelling and data visualization. We present images that show different shear velocity patterns for the Betic
Cordillera. Looking at the velocity distribution at various depths and at vertical sections, we discuss of the study area
in terms of subsurface structure and S-wave velocity distribution (low velocity channels, basement depth, etc.) at very shallow
depths (0–5 km). Our results characterize the region sufficiently and lead to a correlation of shear-wave velocity with the
different geological units features. 相似文献
3.
We report results from a detailed study of seismicity in central Kamchatka for the period from 1960 to 1997 using a modified
traditional approach. The basic elements of this approach include (a) segmentation of the seismic region concerned (the Kronotskii
and Shipunskii geoblocks, the continental slope and offshore blocks), (b) studying the variation in the rate of M = 4.5–7.0 earthquakes and in the amount of seismic energy release over time, (c) studying the seismicity variations, (d)
separate estimates of earthquake recurrence for depths of 0–50 and 50–100 km. As a result, besides corroborating the fact
that a quiescence occurred before the December 5, 1997, M = 7.9 Kronotskii earthquake, we also found a relationship between the start of the quiescence and the position of the seismic
zone with respect to the rupture initiation. The earliest date of the quiescence (decreasing seismicity rate and seismic energy
release) was due to the M = 4.5–7.0 earthquakes at depths of 0–100 km in the Kronotskii geoblock (8–9 years prior to the earthquake). The intermediate
start of the quiescence was due to distant seismic zones of the Shipunskii geoblock and the circular zone using the RTL method, combining the Shipunskii and Kronotskii geoblocks (6 years). Based on the low magnitude seismicity (M≥2.6) at depths of 0–70 km in the southwestern part of the epicentral zone (50–100 km from the mainshock epicenter), the quiescence
was inferred to have occurred a little over 3 years (40 months) before the mainshock time and a little over 2 years (25 months)
in the immediate vicinity of the epicenter (0–50 km). These results enable a more reliable identification of other types of
geophysical precursors during seismic quiescences before disastrous earthquakes. 相似文献
4.
Ki Young Kim Jung Mo Lee Wooil Moon Chang-Eob Baag Heeok Jung Myung Ho Hong 《Pure and Applied Geophysics》2007,164(1):97-113
In order to investigate the velocity structure of the southern part of the Korean peninsula, seismic refraction profiles were
obtained along a 294-km WNW-ESE line and a 335-km NNW-SSE line in 2002 and 2004, respectively. Seismic waves were generated
by detonating 500–1000 kg explosives in drill holes at depths of 80–150 m. The seismic signals were recorded by portable seismometers
at nominal intervals of 1.5–1.7 km. Separate velocity tomograms were derived from first arrival times using a series expansion
method of travel-time inversion. The raypaths indicate several mid-crust interfaces including those at approximate depths
of 2–3, 15–17, and 22 km. The Moho discontinuity with refraction velocity of 7.8 to 8.4 km/s has a maximum depth of 37–39
km under the southern central portion of the peninsula. The Moho becomes shallower as the Yellow Sea and the East Sea are
approached on the west and east coasts of the peninsula, respectively. The depth of the 7.6 km/s velocity contour varies from
29.4 km to 36.5 km. The discrepancy in depth between the seismological Moho and the interpreted critically refracting interface
may result from the presence of a gradual transition between the crust and mantle. The velocity tomograms show particular
crustal structures including (1) the existence of an over 70-km wide low-velocity zone centered at 6–7 km depth under the
Okchon fold belt and Ryeongnam massif, (2) existence of high-velocity materials under the Gyeongsang basin, and (3) the downward
extension of the Yeongdong fault to depths greater than 10 km. 相似文献
5.
A set of two hundred shear-wave velocity models of the crust and uppermost mantle in southeast Europe is determined by application
of a sequence of methods for surface-waves analysis. Group velocities for about 350 paths have been obtained after analysis
of more than 600 broadband waveform records. Two-dimensional surface-wave tomography is applied to the group-velocity measurements
at selected periods and after regionalisation, two sets of local dispersion curves (for Rayleigh and Love waves) are constructed
in the period range 8–40 s. The shear-wave velocity models are derived by applying non-linear iterative inversion of local
dispersion curves for grid cells predetermined by the resolving power of data. The period range of observations limits the
velocity models to depths of 70 km in accordance to the penetration of the surface waves with a maximum period of 40 s. Maps
of the Moho boundary depth, velocity distribution above and below Moho boundary, as well as velocity distribution at different
depths are constructed. Well-known geomorphologic units (e.g. the Pannonian basin, southeastern Carpathians, Dinarides, Hellenides,
Rodophean massif, Aegean Sea, western Turkey) are delineated in the obtained models. Specific patterns in the velocity models
characterise the southeast Carpathians and adjacent areas, coast of Albania, Adriatic coast of southern Italy and the southern
coast of the Black Sea. The models obtained in this study for the western Black Sea basin shows the presence of layers with
shear-wave velocities of 3.5 km/s–3.7 km/s in the crust and thus do not support the hypothesis of existence of oceanic structure
in this region. 相似文献
6.
Results are reported from a detailed study of central Kamchatka seismicity for the period 1962–1997 based on a modification
of the traditional approach. The approach involves (a) a detailed structure of the seismic region that recognizes the Kronotskii
and Shipunskii geoblocks and two further blocks, the continental slope, and the offshore portion, (b) a study of variations
in the rate of M = 3.0–7.2 earthquakes and the amount of seismic energy released at depths of 0–50 and 51–100 km, (c) a study
of seismicity variability, and (d) separate estimates of the recurrence of crust-mantle earthquakes (depths 0–50 km) and mantle
events (51–100 km). As a result, apart from corroborating the fact of a quiescence preceding the December 5, 1997 Kronotskii
earthquake (M 7.9), we also found that a relationship exists between its beginning and the position of the earthquake-generating
region relative to the mainshock epicenter. The quiescence dominates the seismic process during the pre-mainshock period and
is characterized by a decreased rate of earthquakes (the first feature) and a decreased amount of seismic energy release (the
second feature). Based on the first feature, we found that the quiescence started in 1987 throughout the entire depth range
(0–100 km) in both parts of the Kronotskii geoblock close to the rupture zone of the eponymous earthquake. As to the Shipunskii
geoblock, which is farther from the rupture zone, the quiescence began in the mantle of the inner area first (1988) and somewhat
later at depths of 0–50 km within the continental slope (1989). By the second feature, the quiescence began at shallower depths
in the inner area of the Kronotskii geoblock at the same time and later on (a year later) in the mantle (1988). Under the
continental slope of the trench in the Shipunskii geoblock the shallower quiescence also began in 1987, while it was 3 years
late in the inner zone (1990) and involved the earthquake-generating earth volume at depths of 0–100 km. These data are identical
with or sufficiently close to the estimate for the beginning of this quiescence using a circular area of radius 150 km that
combines the Kronotskii and Shipunskii geoblocks by the RTL method (1990). 相似文献
7.
We considered the seismic regime in the upper 70–100 km of the lithosphere and identified the layers (at depths of about 10,
20–30, and 60–80 km) characterized by relatively reduced effective strength and increased seismicity. The existence of such
layers is related to changes in the regime of fluid-rock interaction, namely, to the characteristic depths of a jump-like
decrease in the effective permeability of rocks and an increase in the spatial homogeneity of a fluid-rock system. 相似文献
8.
S. A. Kovachev I. P. Kuzin L. I. Lobkovskii 《Izvestiya Physics of the Solid Earth》2009,45(9):777-793
The results of detailed seismological observations with bottom seismographs in the Central Kurile segment in August-September,
2006 are discussed. The system of six bottom seismographs was placed on the island slope of the Kurile deep-sea trench southeast
of Urup Island and southwest of the Bussol Strait. Over 230 earthquakes with M
LH = 0.5–5.5 were registered in the area with a radius of 150 km around the center of the observation system at depths up to
300 km during 16 days. Records of 80 earthquakes with hypocenters in the earth crust (h = 0–30 km) beneath the island slope of the Kurile deep-sea trench were first obtained by bottom seismographs. These data
are inconsistent with previous concepts of aseismicity of this zone. The discovery of the unique morphological structure of
the Benioff zone beneath the central Kurile Arc represents the most important result of detailed seismological observations.
The zone consists of an inner seismoactive subzone, which is located beneath the island slope of the arc at depths of 15–210
km, being characterized by an angle of incline of 50° under the latter and crosses the ocean bottom approximately 80 km away
from the trench axis, and outer low-activity subzone. The latter is traceable beyond the trench almost parallel to the inner
zone beginning from a depth of 50 km below the sea bottom up to a depth of approximately 300 km. Due to the slightly lower
incline (∼45°) of the outer subzone, both subzones gradually converge downward. The integral thickness of the Benioff zone
varies from 150 km in its upper part to 125 km at depths of 210–260 km. The medium sandwiched between these subzones is practically
aseismic. The reality of this defined structure is confirmed by the distribution of aftershocks of the earthquake that occurred
on November 15, 2006 (M = 8.3). These seismic events served as foreshocks for the subsequent strong earthquake of January 13, 2007 (M = 8.1) with the hypocenter located beyond the trench under the ocean bottom. Such a structure of this zone within the central
Kurile Arc segment is unique, having no analogues either in the flanks of the Kurile-Kamchatka Arc or other arcs. The results
of detailed seismological observations obtained two months before the first of the catastrophic Central Kurile earthquakes
appeared to be typical for the period of foreshocks (the lower seismic activity of the Simushir block, which hosted the hypocenter
of the earthquake that occurred on November 15, 2006, particularly at depths of 0–50 km, the gentler incline of the recurrence
plot, and other features). 相似文献
9.
B. Růžek P. Hrubcová M. Novotný A. Špičák O. Karousová 《Studia Geophysica et Geodaetica》2007,51(1):141-164
A series of kinematic inversions based on robust non-linear optimization approach were performed using travel time data from
a series of seismic refraction experiments: CELEBRATION 2000, ALP 2002 and SUDETES 2003. These experiments were performed
in Central Europe from 2000 to 2003. Data from 8 profiles (CEL09, CEL10, Alp01, S01, S02, S03, S04 and S05) were processed
in this study. The goal of this work was to find seismic velocity models yielding travel times consistent with observed data.
Optimum 2D inhomogeneous isotropic P-wave velocity models were computed. We have developed and used a specialized two-step
inverse procedure. In the first “parametric” step, the velocity model contains interfaces whose shapes are defined by a number
of parameters. The velocity along each interface is supposed to be constant but may be different along the upper and lower
side of the interface. Linear vertical interpolation is used for points in between interfaces. All parameters are searched
for using robust non-linear optimization (Differential Evolution algorithm). Rays are continuously traced by the bending technique.
In the second “tomographic” step, small-scale velocity perturbations are introduced in a dense grid covering the currently
obtained velocity model. Rays are fixed in this step. Final velocity models yield travel time residuals comparable to typical
picking errors (RMS ∼ 0.1 s).
As a result, depth-velocity cross-sections of P waves along all processed profiles are obtained. The depth range of the models
is 35–50 km, the velocity varies in the range 3.5–8.2 km/s. Lowest velocities are detected in near-surface depth sections
crossing sedimentary formations. The middle crust is generally more homogeneous and has typical P wave velocity around 6 km/s.
Surprisingly the lower crust is less homogeneous and the computed velocity is in the range 6.5–7.5 km/s. The MOHO is detected
in the depth ≈30–45 km. 相似文献
10.
Prantik Mandal R. K. Chadha N. Kumar I. P. Raju C. Satyamurty 《Pure and Applied Geophysics》2007,164(10):1963-1983
During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological
network of 5–8 broadband seismographs and 10–20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective
to monitor the continued aftershock activity of the 2001 Mw 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October Mw 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate
the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India.
Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert
these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model
suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values
for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based
on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms of the Kashmir
earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed
(0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km. 相似文献
11.
Summary The records at Athens of 85 earthquakes with epicenters in several regions on the earth were used to determine group velocities along thirty five paths. The mean crustal thickness along each path has been estimated by comparing the observations withPress's standard curves. A linear relation has been found between the mean crustal thickness and mean elevation along each path. This relation is in agreement with Airy's isostatic hypothesis. Determination of Love wave dispersion along five paths and Rayleigh wave dispersion along two paths in southeastern Europe and northern Asia Minor gave values from 35 to 45 km for the crustal thickness in this region. 相似文献
12.
We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif,
Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles
(~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified
version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase
velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are
analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion
curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent
apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling.
An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true
propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of
the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the
profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the
upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We
obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area
of the Eger Rift (Teplá-Barrandian–Saxothuringian unit contact) is significantly different from all other three units. Low
upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake
swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming. 相似文献
13.
Group velocities of Rayleigh and Love waves along the paths across the Black Sea and partly Asia Minor and the Balkan Peninsula are used to estimate lateral variations of the crustal structure in the region. As a first step, lateral variations of group velocities for periods in the range 10–20 s are determined using a 2D tomography method. Since the paths are oriented predominantly in NE–SW or N–S direction, the resolution is estimated as a function of azimuth. The local dispersion curves are actually averaged over the extended areas stretched in the predominant direction of the paths. The size of the averaging area in the direction of the best resolution is approximately 200 km. As a second step, the local averaged dispersion curves are inverted to vertical sections of S-wave velocities. Since the dispersion curves in the 10–20 s period range are mostly affected by the upper crustal structure, the velocities are estimated to a depth of approximately 25 km. Velocity sections along 43° N latitude are determined separately from Rayleigh and Love wave data. It is shown that the crust under the sea contains a low-velocity sedimentary layer of 2–3 km thickness, localized in the eastern and western deeps, as found earlier from DSS data. Beneath the sedimentary layer, two layers are present with velocity values lying between those of granite and consolidated sediments. Velocities in these layers are slightly lower in the deeps, and the boundaries of the layers are lowered. S-wave velocities obtained from Love wave data are found to be larger than those from Rayleigh wave data, the difference being most pronounced in the basaltic layer. If this difference is attributed to anisotropy, the anisotropy coefficient = (SH - SV)/Smean is reasonable (2–3%) in the upper layers, and exceeds 9% in the basaltic layer. 相似文献
14.
T. B. Yanovskaya E. L. Lyskova T. Yu. Koroleva 《Izvestiya Physics of the Solid Earth》2014,50(5):632-640
The dispersion curves of the Rayleigh wave group velocities are constructed along 60 interstation seismic paths in Central Europe based on the cross-correlation function of seismic noise. Together with the previous data (Yanovskaya and Lyskova, 2013), this information was used for reconstructing the three-dimensional distribution of S-wave velocities in the upper mantle of the Carpathian region. In the present work, the previous results are refined by expanding the data set by the additional seismic paths that intersect the Carpathian region and by modifying the procedure for constructing the locally averaged dispersion curves so as to obtain a more compact resolution. The results of the study suggest the complex, multidirectional character of the plate motion in the region. 相似文献
15.
ZHANG Zhongjie BAI Zhiming WANG Chunyong TENG Jiwen Lü Qingtian LI Jiliang LIU Yifeng & LIU Zhenkuan . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Institute of Geophysics China Seismological Bureau Beijing China . Institute of Deposition Resource Chinese Academy of Geosciences Beijing China . School of Exploration Information China University of Geosciences Beijing China 《中国科学D辑(英文版)》2005,48(9):1329-1336
The Sanjiang area in southwest China is considered as a tectonic intersection belt between the Tethys-Alps and the western Pacific, and has endured three-phase evolution processes: Proto-Tethys,Paleo-Tethys and Meso-Tethys[1―4]. In this area, its tectonics and struc- ture are extremely complicated, and intensively extru-sive deformation and faults are widely developed[1―3]. For that, the area is considered as the ideal na- ture-laboratory to study the evolution of Paleo-Tethys and also … 相似文献
16.
We measured and interpreted 30 physical magnetotelluric sounding sites using an SGS-E station and 20 km of electrical profiling
observations using SDVR-4M instrumentation. We constructed a map of seismicity, an interpretation map, and four geoelectric
sections, which give an idea of the deep structure for the Kulu earthquake-generating zone. A general geoelectric upper crustal
model was developed for the zone down to depths of 20–22 km. Three nearly vertical conductive volumes were identified (thickness
3–5 km, depth 10–22 km), which provide the positions of seismically active deep-seated faults that pinpoint the Kulu earthquake-generating
zone. The preliminary boundary of the zone was determined. It was found that earth-quake epicenters are confined to lithosphere
volumes with increased concentrations of conductive layers and zones. 相似文献
17.
Eleven PASSCAL broadband digital seismic stations were employed in the Tibetan Plateau by the Sino-US team from September,
1991 to June, 1992. Seven of them were distributed along the Qinghai-Tibet highway, others in Maqin and Yushu of Qinghai Province,
Linzhi and Xigatze of Tibet. The data included 31 local earthquakes recorded by these stations from July, 1991 to January,
1992. Considering the characters of digital data, we identified the seismic phases carefully in several methods using SAC
softwares (Seismic Analysis Code) in SUN workstation. We compared the seismic phases after converting the seismograms of the
single stations to the seismic profiles; analyzed the first arrivals of P waves in the incident planes by rotating 3 component
seismic records; identified the seismic phases from the particle motion pictures. The Pn apparent velocities were calculated
in the distance range of 230–1200 km from Linzhi earthquakes, western Changtang earthquakes, Xitieshan and Gonghe earthquakes
and the earthquakes in India. The results show that the Pn velocities change slightly in the Tibetan Plateau (8.0–8.1 km/s).
These values near the velocities at the uppermost mantle of the normal continents. The Moho undulation in the Tibetan Plateau
was also studied by using Pn data by the time-term method. The primary results indicate that the Moho beneath the Tibetan
Plateau is flat, and its depths are 67–70 km.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 593–600, 1992. 相似文献
18.
Digital seismograms from 25 earthquakes located in the southeastern part of Europe, recorded by three-component very broadband seismometers at the stations Vitosha (Bulgaria) and Muntele Rosu (Romania), were processed to obtain the dispersion properties of Rayleigh and Love surface waves. Rayleigh and Love group-velocity dispersion curves were obtained by frequency–time analysis (FTAN). The path-averaged shear-wave velocity models were computed from the obtained dispersion curves. The inversion of the dispersion curves was performed using an approach based on the Backus–Gilbert inversion method. Finally, 70 path-averaged velocity models (35 R-models computed from Rayleigh dispersion curves and 35 L-models computed from Love dispersion curves) were obtained for southeastern Europe. For most of the paths, the comparison between each pair of models (R-model and L-models for the same path) shows that for almost all layers the shear-wave velocities in the L-models are higher than in the R-models. The upper sedimentary layers are the only exception. The analysis of both models shows that the depth of the Moho boundary in the L-models is shallower than its depth in the R-models. The existence of an anisotropic layer associated with the Moho boundary at depths of 30–45 km may explain this phenomenon. The anisotropy coefficient was calculated as the relative velocity difference between both R- and L-models at the same depths. The value of this coefficient varies between 0% and 20%. Generally, the anisotropy of the medium caused by the polarization anisotropy is up to 10–12%, so the maximum observed discrepancies between both types of models are also due to the lateral heterogeneity of the shear-wave velocity structure of the crust and the upper mantle in the region. 相似文献
19.
Brett S. Ketter Aaron A. Velasco Charles J. Ammon George E. Randall 《Pure and Applied Geophysics》2006,163(7):1235-1255
We develop one-dimensional (1-D) path-specific velocity models in western China using new Rayleigh and Love wave group and
phase velocity dispersion measurements for 20 events in the region. The earthquakes were grouped into three geographic clusters
from which we compute the average phase and group velocity dispersion. We invert the average dispersion curves simultaneously
for 1-D shear-velocity models appropriate for the three central Asian paths, using three previous shear-velocity models as
initial models. The models are validated by forward modeling waveforms of recent events. The crustal thickness beneath western
China in the vicinity of the Lop Nor test site is 50–60 km and our velocity models are consistent with major geologic features
(e.g., basins and mountain ranges) and previous structural models for this region. 相似文献
20.
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