共查询到20条相似文献，搜索用时 31 毫秒
1.
N.N. Belyashova V.I. Shacilov N.N. Mikhailova I.I. Komarov Z.I. Sinyova A.V. Belyashov M.N. Malakhova 《Pure and Applied Geophysics》2001,158(1-2):193-209
—?Two chemical calibration explosions, conducted at the former Semipalatinsk nuclear test site in 1998 with charges of 25 tons and 100 tons TNT, have been used for developing travel-time curves and generalized one-dimensional velocity models of the crust and upper mantle of the platform region of Kazakhstan. The explosions were recorded by a number of digital seismic stations, located in Kazakhstan at distances ranging from 0 to 720?km. The travel-time tables developed in this paper cover the phases P, Pn, Pg, S, Sn, Lg in a range of 0–740?km and the velocity models apply to the crust down to 44?km depth and to the mantle down to 120?km. A comparison of the compiled travel-time tables with existing travel-time tables of CSE and IASPEI91 is presented. 相似文献
2.
v--vS/P amplitude ratios have proven to be a valuable discriminant in support of monitoring a Comprehensive Nuclear Test Ban Treaty. Regional S and P phases attenuate at different rates and the attenuation can vary geographically. Therefore, calibration is needed to apply the S/P discriminant in new regions. Calibration includes application of frequency-dependent source and distance corrections for regional Pn, Pg, Sn, and Lg phases.¶Jenkins et al. (1998) developed Pn, Pg, Sn, and Lg amplitude models for nine geographic regions and two global composite models, stable and tectonic. They determined frequency-dependent source and attenuation corrections from a large data set obtained from the Prototype International Data Center (PIDC). We use their corrections to evaluate calibrated S/P discriminants.¶Our discrimination data set includes >1000 amplitude ratios from earthquakes, industrial explosions, chemical explosions, and nuclear explosions from Lop Nor, India and Pakistan. We find that the calibrated S/P ratio is largest for earthquakes and smallest for the nuclear explosions, as expected. However, the discriminant is not universally valid. In particular, the S/P ratio for the Pakistan nuclear explosion fell within the normal range for the earthquakes. This event was recorded by only a few stations at far-regional distances and appears to have an anomalously high Sn amplitude. The industrial explosions overlap with the earthquake population, however the buried chemical explosions generally register lower S/P ratio than earthquakes. 相似文献
3.
A synthetic seismogram that closely resembles a seismic trace recorded at a well may not be at all reliable for, say, stratigraphic interpretation around the well. The most accurate synthetic seismogram is, in general, not the one that displays the smallest errors of fit to the trace but the one that best estimates the noise on the trace. If the match is confined to a short interval of interest or if the seismic reflection wavelet is allowed to be unduly long, there is considerable danger of forcing a spurious fit that treats the noise on the trace as part of the seismic reflection signal instead of making a genuine match with the signal itself. This paper outlines tests that allow an objective and quantitative evaluation of the accuracy of any match and illustrates their application with practical examples. The accuracy of estimation is summarized by the normalized mean square error (NMSE) in the estimated reflection signal, which is shown to be (/n)(PN/PS) where PS/PN is the signal-to-noise power ratio and n is the spectral smoothing factor. That is, the accuracy varies directly with the ratio of the power in the signal (taken to be the synthetic) to that in the noise on the seismic trace, and the smoothing acts to improve the accuracy of the predicted signal. The construction of confidence intervals for the NMSE is discussed. Guidelines for the choice of the spectral smoothing factor n are given. The variation of wavelet shape due to different realizations of the noise component is illustrated, and the use of confidence intervals on wavelet phase is recommended. Tests are described for examining the normality and stationarity of the errors of fit and their independence of the estimated reflection signal. 相似文献
4.
在地震勘探随机噪声压制领域,噪声通常被假设为平稳、高斯随机过程的信息.然而,在某些情况下,这样的假设并不准确.本文应用现代统计检验方法对地震勘探随机噪声的平稳性、高斯性和线性进行了研究.结果表明地震勘探随机噪声并不是传统意义上认为的平稳随机过程,其平稳性受到噪声时长和采集环境复杂程度的影响.发现噪声时间越长,采集环境越复杂,随机噪声的平稳性越差,但是对于短时长随机噪声而言,其可以近似认为是平稳的.同时,采集环境的复杂程度也影响着随机噪声的高斯性和线性特性,环境条件越复杂,随机噪声高斯性越好,线性特性越差,但总的来说随机噪声可以归为线性非高斯随机过程. 相似文献
5.
D. R. Baumgardt 《Pure and Applied Geophysics》2001,158(7):1207-1250
v--vThe phenomenon of "Lg blockage," where Lg is strongly attenuated by crustal heterogeneities, poses a serious problem to CTBT monitoring because Lg is an important seismic phase for discrimination. This paper examines blockage in three continental regions where the Lg blockages may be caused by large, enclosed sedimentary basins along the propagation path. The Barents Sea Basin blocks Lg propagation across the Barents Sea from the Russian nuclear test sites at Novaya Zemlya to Scandinavian stations. Also, "early Lg" waves are observed in Sn codas on NORSAR, NORESS, and ARCESS recordings of Novaya Zemlya explosions where direct Lg is blocked. Early Lg waves may have resulted from Sn-to-Lg mode conversion at the contact between the Barents Basin and the Kola Peninsula. The Northern and Southern Caspian Sea Basins also block Lg waves from PNEs and earthquakes, perhaps due to thick, low-velocity, low-Q sediments replacing the granitic layer rocks in the crust. Lg blockage has also been observed in the Western Mediterranean/Levantine Basin due to low-Q sediments and crustal thinning. A "basin capture" model is proposed to explain Lg blockage in sedimentary basins. In this model, shear waves that reverberate in the crust and constitute the Lg wave train are captured, delayed, and attenuated by thick, low-velocity sediments that replace the "granitic" layer rocks of the upper crust along part of the propagation path. Sn waves, which propagate below the basin, would not be blocked and in fact, the blocked Lg waves may be diverted downward into Sn waves by the low velocity sediments in the basin. 相似文献
6.
H. J. Patton 《Pure and Applied Geophysics》2001,158(11):1951-2015
—?Data sets of m b (Pn) and m b (Lg) measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude M w and event discrimination at small magnitudes. Compilations of published measurements are provided for eastern North American and central Asian earthquakes, and new measurements are reported for earthquakes located in western United States. Statistical tests on M w :m b relationships show that the m b (Lg) scale of Nuttli (1973) is transportable between tectonic regions, and a single, unified M w :m b (Lg) relationship satisfies observations for M w ～4.2–6.5 in all regions. A unified relationship is also developed for nuclear explosions detonated at the Nevada Test Site and test sites of the former Soviet Union. Regional m b for explosions scale at higher rates than for earthquakes, and of significance is the finding that m b (Pn) for explosions scales at a higher rate than m b (Lg). A model is proposed where differences in scaling rates are related to effects of spectral overshoot and near-field Rg scattering on the generation of Pn and Lg waves by explosions. For earthquakes, m b (Pn) and m b (Lg) scale similarly, showing rates near 1.0 or 2/3?·?log10 M o (seismic moment).¶M w :m b (Lg) scaling results are converted to unified M s :m b (Lg) relationships using scaling laws between log M o and M s . For earthquakes with M s greater than 3.0, the scaling rate is 0.69?·?M s , which is the same as it is for nuclear explosions if M s is proportional to 1.12?·?log M o, as determined by NTS observations. Thus, earthquake and explosion populations are parallel and separated by 0.68 m b units for large events. For small events (M s ?M s :m b (Lg) plots for stable and tectonic regions, respectively. While the scaling rate for explosions is ～0.69, this value is uncertain due to paucity of M o observations at small yields. Measurements of [m b (P)???m b (Lg)] for earthquakes in the western United States have an average value of ?0.33?±?.03 m b units, in good agreement with Nuttli's estimate of m b bias for NTS. This result suggests that Nuttli's method for estimating test site bias can be extended to earthquakes to make estimates of bias on regional scales. In addition, a new approach for quick assessments of regional bias is proposed where M s :m b (P) observations are compared with M s :m b (Lg) relationships. Catalog M s :m b (P) data suggest that m b bias is significant for tectonic regions of southern Asia, averaging about ?0.4 m b units. 相似文献
7.
J.L. Stevens G.E. Baker R.W. Cook G.L. D'Spain L.P. Berger S.M. Day 《Pure and Applied Geophysics》2001,158(3):531-565
—?T-phase propagation from ocean onto land is investigated by comparing data from hydrophones in the water column with data from the same events recorded on island and coastal seismometers. Several events located on Hawaii and the emerging seamount Loihi generated very large amplitude T phases that were recorded at both the preliminary IMS hydrophone station at Point Sur and land-based stations along the northern California coast. We use data from seismic stations operated by U. C. Berkeley along the coast of California, and from the PG&;E coastal California seismic network, to estimate the T-phase transfer functions. The transfer function and predicted signal from the Loihi events are modeled with a composite technique, using normal mode-based numerical propagation codes to calculate the hydroacoustic pressure field and an elastic finite difference code to calculate the seismic propagation to la nd-based stations. The modal code is used to calculate the acoustic pressure and particle velocity fields in the ocean off the California coast, which is used as input to the finite difference code TRES to model propagation onto land. We find both empirically and in the calculations that T phases observed near the conversion point consist primarily of surface waves, although the T phases propagate as P waves after the surface waves attenuate. Surface wave conversion occurs farther offshore and over a longer region than body wave conversion, which has the effect that surface waves may arrive at coastal stations before body waves. We also look at the nature of T phases after conversion from ocean to land by examining far inland T phases. We find that T phases propagate primarily as P waves once they are well inland from the coast, and can be observed in some cases hundreds of kilometers inland. T-phase conversion at tenuates higher frequencies, however we find that high frequency energy from underwater explosion sources can still be observed at T-phase stations. 相似文献
8.
Ota Kulhánek 《Pure and Applied Geophysics》1973,102(1):51-66
Summary Short-period vertical-componentP-wave spectra of seven presumed Semipalatinsk underground nuclear explosions, recorded by the Swedish seismic station network, are investigated. The events considered have closely spaced foci and cover the magnitude range fromm
b=5.5 tom
b=6.6. Spectra of six of these explosions show pronounced minima, varying from about 1.5 to 1.8 cps, which could be explained as principle minima due toP-pP interference. Supposing a nearsurfaceP-wave velocity at the test area of 4 km/sec, the shot depths are estimated to vary roughly from 750 to 1350 m. In order to obtain an estimate of the yield, the observed spectra are compared withHaskell's theoretical source spectra. For four events, relative yield estimates fit well the predicted values for explosions fired in a granitic medium. The behaviour of the remaining three explosions is discussed in detail. 相似文献
9.
A multi-event and multi-station inverse method is presented in the paper to simultaneously estimate the seismic moments (M
0) and source corner frequencies (f
c) of several Jiashi (Xinjiang, China) earthquakes, as well as the apparent Lg Q models for the paths from Jiashi to eight seismic stations (WMQ, AAK, TLG, MAKZ, KUR, VOS, ZRN and CHK) in Central Asia.
The resultant seismic moments correlate well with the M
0 values obtained by Harvard University using the centroid moment tensor (CMT) inversion and the surface-wave magnitudes as
well. After the correction by a typical value of average radiation coefficient for regional SV waves, the M
0 values from Lg spectral inversion are still close to the corresponding values obtained from CMT inversion. The obtained apparent
Q
0Lg values (Lg Q at 1 Hz) are consistent with the tectonic features of corresponding propagation paths. The Q
0Lg values are 351±87, 349±86 and 300±27 for the paths from Jiashi to AAK, TLG and MAKZ, respectively. They are smaller than
Q
0Lg values for the paths to KUR, VOS, ZRN and CHK, which are 553±72, 569±58, 550±57 and 603±65, respectively. These results agree
with the condition that the paths to AAK, TLG and MAKZ mainly propagate through the mountainous Tianshan area where relatively
strong seismic activities and large variations of topography are exhibited, while the paths to KUR, VOS, ZRN and CHK mainly
propagate through the stable area of Kazak platform. The Q
0Lg value for the path to WMQ is 462±56. This is also in agreement with the condition that the path to WMQ is basically along
the border area between Tianshan Mountain and Tarim Basin, and along this path the variations of topography and crustal thickness
are moderate in comparison with that along the path to MAKZ.
Foundation item: Foundation of Verification Researches for Army Control Technology (413290102). 相似文献
10.
Yu. F. Kopnichev I. N. Sokolova K. N. Sokolov 《Izvestiya Physics of the Solid Earth》2013,49(6):786-795
The characteristics of the attenuation field of short-period shear waves in the region of Nevada nuclear test site (NNTS) are studied. The seismograms of underground nuclear explosions (UNEs) and earthquakes recorded by three seismic stations in 1975–2012 at the epicentral distances of up to 1000 km are processed by the methods based on the analysis of the amplitude ratios of Sn to Pn and Lg to Pg waves, as well as the S-coda envelopes for close events. It is shown that the structure of the attenuation field in the Earth’s crust and upper mantle in the NNTS region experienced significant temporal variations during the interval of nuclear operations. The strongest variations were associated with UNEs conducted in the Pahute Mesa area, which held about two-thirds of the most intense explosions. Our data indicate that temporal variations in the structure of the attenuation field are related to the migration of deep fluids. A comparison of the general characteristics of the attenuation field in the regions of the three large nuclear test sites is presented. 相似文献
11.
—?In this paper we describe a technique for mapping the lateral variation of Lg characteristics such as Lg blockage, efficient Lg propagation, and regions of very high attenuation in the Middle East, North Africa, Europe and the Mediterranean regions. Lg is used in a variety of seismological applications from magnitude estimation to identification of nuclear explosions for monitoring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These applications can give significantly biased results if the Lg phase is reduced or blocked by discontinuous structure or thin crust. Mapping these structures using quantitative techniques for determining Lg amplitude attenuation can break down when the phase is below background noise. In such cases Lg blockage and inefficient propagation zones are often mapped out by hand. With our approach, we attempt to visually simplify this information by imaging crustal structure anomalies that significantly diminish the amplitude of Lg. The visualization of such anomalies is achieved by defining a grid of cells that covers the entire region of interest. We trace Lg rays for each event/station pair, which is simply the great circle path, and attribute to each cell a value equal to the maximum value of the Lg/P-coda amplitude ratio for all paths traversing that particular cell. The resulting map, from this empirical approach, is easily interpreted in terms of crustal structure and can successfully image small blockage features often missed by analysis of raypaths alone. This map can then be used to screen out events with blocked Lg prior to performing Q tomography, and to avoid using Lg-based methods of event identification for the CTBT in regions where they cannot work.¶For this study we applied our technique to one of the most tectonically complex regions on the earth. Nearly 9000 earthquake/station raypaths, traversing the vast region comprised of the Middle East, Mediterranean, Southern Europe and Northern Africa, have been analyzed. We measured the amplitude of Lg relative to the P-coda and mapped the lateral variation of Lg propagation efficiency. With the relatively dense coverage provided by the numerous crossing paths we are able to map out the pattern of crustal heterogeneity that gives rise to the observed character of Lg propagation. We observe that the propagation characteristics of Lg within the region of interest are very complicated but are readily correlated with the different tectonic environments within the region. For example, clear strong Lg arrivals are observed for paths crossing the stable continental interiors of Northern Africa and the Arabian Shield. In contrast, weakened to absent Lg is observed for paths crossing much of the Middle East, and Lg is absent for paths traversing the Mediterranean. Regions that block Lg transmission within the Middle East are very localized and include the Caspian Sea, the Iranian Plateau and the Red Sea. Resolution is variable throughout the region and strongly depends on the distribution of seismicity and recording stations. Lg propagation is best resolved within the Middle East where regions of crustal heterogeneity on the order of 100?km are imaged (e.g., South Caspian Sea and Red Sea). Crustal heterogeneity is resolvable but is poorest in seismically quiescent Northern Africa. 相似文献
12.
Ota Kulhánek 《Pure and Applied Geophysics》1971,88(1):121-136
Summary Short-period vertical-componentP-wave spectra have been determined for twelve Nevada underground nuclear explosions recorded by the Swedish seismic station network. Selected events cover the magnitude range fromm
b
=5.9 tom
b
=7.0 and the shot-depth range from 460 m to 1400 m. All explosion spectra show pronounced minima near 1 sec period. Within individual test areas the period at which the minimum occurs increases systematically with increasing shot-depth. This dependence makes it possible to interpret the observed minima in terms of interference betweenP- andpP-waves. One atmospheric explosion from Novaya Zemlya is analyzed to verify the inferred minima intrpretation.The minimum-period shows also a systematic linear dependence upon the magnitude. However, the physical explanation for this dependence is not evident and it may just be a consequence of a magnitude-depth relation.On leave from the Geophysical Institute, Czechosl. Acad. Sci., Prague 4-Spoilov, Boni II. 相似文献
13.
Regional body-wave magnitude scalings are essential for quantification of small and moderate-size earthquakes that are observed
only up to regional distances. Crustally-guided shear waves, Lg, develop stably at regional distances in continental crusts and are minimally influenced by the source radiation patterns.
Lg body-wave magnitude scalings, mb(Lg),m_b(Lg), are widely used for assessment of sizes of regional crustal events. The mb(Lg)m_b(Lg) scaling has rarely been tested in continental margins where Lg waves are significantly attenuated due to abrupt lateral variation of crustal structures. We test the applicability of mb(Lg)m_b(Lg) scaling to the eastern margin of the Eurasian plate around the Korean Peninsula and Japanese islands. Both third-peak and
root-mean-square (rms) amplitudes of Lg vary significantly according to the crustal structures along raypaths, causing apparent underestimation of mb(Lg).m_b(Lg). Implementation of raypath-dependent quality factors (Q) allows accurate estimation of mb(Lg),m_b(Lg), retaining the transportability of mb(Lg)m_b(Lg) in the continental margin around Korea and Japan. The calibration constants for an rms-amplitude-based mb(Lg)m_b(Lg) scaling are not determined to vary by region in the continental margin due to complicated crustal structures. The calibration
constants are determined to be distance-dependent. Both the third-peak-amplitude-based and rms-amplitude-based mb(Lg)m_b(Lg) scalings yield accurate magnitude estimates when raypath-dependent quality factors are implemented. 相似文献
14.
利用布设在长白山地区临时地震台站接收到的朝鲜核爆的波形资料,对2009年5月25日和2013年2月12日两次朝鲜核试验的地震学特征进行比较.震中距范围从145km到420km.采用P/S型谱比值方法识别朝鲜核爆,通过与2009年3月20日长春地震和2013年1月23日沈阳地震事件的比较,表明在频率大于3 Hz时P/S型谱比值能够有效识别发生在中朝边境地区的地下核试验.选定参考台站,利用区域震相Pg波的振幅谱比值计算朝鲜核爆至各台站路径上的相对衰减.结合介质速度模型,在一定程度上反映了长白山地区衰减情况,为进一步研究长白山地区衰减层析成像提供初始模型. 相似文献
15.
Dr. Markus Bath 《Pure and Applied Geophysics》1957,38(1):19-31
Summary A study has been made of a new channel wave, denotedLi, using a total of 83 observations from the seismic records of Swedish stations, mainly from earthquakes at normal depth.Li resembles theLg waves in several respects: it propagates only through continental structures, it has a similar particle motion, i.e. mainly transverse horizontal, and only slightly larger period. ButLi has a higher velocity, 3.79±0.07 km/sec, and it is believed to propagate in the intermediate layer in the crust in a way similar to the propagation of theLg waves in the granitic layer.Li is identical withS
* in records of near-by earthquakes in the same way asLg2 is identical withSg. Li usually exhibits no clear dispersion.
Zusammenfassung Es wurden Untersuchungen angestellt über eine neue Kanalwelle, welcher die BezeichnungLi gegeben wurde, wobei insgesamt 83 Erdbebenregistrierungen von schwedischen Stationen Verwendung fanden. Hauptsächlich waren es Erdbeben mit normaler Herdtiefe. DieLi-Wellen haben in verschiedener Hinsicht Ähnlichkeit mit denLg-Wellen: Sie pflanzen sich nur im Bereich kontinentaler Struktur fort und sie haben eine ähnliche Partikelbewegung, d.h. hauptsächlich horizontaltransversal.Li hat eine nur unwesentlich höhere Periode als dieLg-Wellen. AberLi hat eine wesentlich höhere Geschwindigkeit, 3.79±0.07 km/sec, und es ist anzunehmen, dass sie sich in der Basaltschicht der Kruste in ähnlicher Weise fortpflanzt wieLg in der Granitschicht.Li ist identisch mitS * in Aufzeichnungen von Nahbeben, so wieLg2 identisch mitSg ist.Li weist gewöhnlich keine deutliche Dispersion auf.相似文献
16.
We re-examine the utility of teleseismic seismic complexity discriminants in a multivariate setting using United Kingdom array
data. We measure a complexity discriminant taken on array beams by simply taking the logarithm of the ratio of the P-wave coda signal to that of the first arriving direct P wave (βCF). The single station complexity discriminant shows marginal performance with shallow earthquakes having more complex signatures
than those from explosions or deep earthquakes. Inclusion of secondary phases in the coda window can also degrade performance.
However, performance improves markedly when two-station complexity discriminants are formed showing false alarm rates similar
to those observed for network mb − Ms. This suggests that multistation complexity discriminants may ameliorate some of the problems associated with mb – Ms discrimination at lower magnitudes. Additionally, when complexity discriminants are combined with mb – Ms there is a tendency for explosions, shallow earthquakes and deep earthquakes to form three distinct populations. Thus, complexity
discriminants may follow a logic that is similar to mb – Ms in terms of the separation of shallow earthquakes from nuclear explosions, although the underlying physics of the two discriminants
is significantly different. 相似文献
17.
Seismic data recorded at the broad-band teleseismic GRF array and theshort-period regional GERESS array, which is a designated IMS primarystation, are analyzed to determine the effectiveness of teleseismic P-wave complexity for the purpose of seismic event screening within theframework of Comprehensive Nuclear-Test-Ban Treaty verification. For theGRF array, seismic waveform data from nearly 200 nuclear explosions havebeen recorded since its installation in the late 1970's, which were studiedalong with several thousand earthquakes from the last few years.Additionally, we investigated teleseismic P wave complexity for a similarnumber of earthquakes recorded at GERESS. However, owing to itsoperation starting in 1991, only a limited number of nuclear explosionseismograms are available for study.For nuclear explosions, complexity does not exceed levels of 0.3 except fora number of events from the Nevada Test Site recorded only at the GRFarray and located at a large distance where PcP may interfere with the initialP wavelet. Since all events with complexity at GRF larger than 0.3 areexclusively located on Pahute Mesa within the Nevada Test Site,near-source geology or topography must play a dominant role for theseincreased complexity values, while PcP may not contribute significantly tothe high-frequency energy measured by the complexity parameter.Although many earthquakes show complexities below this level, for morethan 25% of the earthquakes investigated the complexities determined arelarger than 0.7, thus showing distinctly larger values than nuclearexplosions. Therefore, this percentage may be screened as earthquakes fromall seismic events detected. As currently only about half of the eventsdetected by the global IMS network are screened out based on focal depthand the m
b
:M
s criterion, teleseismic P-wavecomplexity may contribute significantly to the task of seismic eventscreening. 相似文献
18.
Coda site amplification factors are used to eliminate the site effect from records of three circum-PacificT phases recorded by the Hawaiian Volcano Observatory (HVO) network on the island of Hawaii. ObservedT-phase amplitudes across the island generally decrease with increasing distance from the conversion point where acoustic waves
in the SOFAR channel become seismic waves propagating through the crust. However, the decay of the observedT-phase signal across the island is not regular in regions of dense station coverage, in particular, the Kilauea caldera region.
We divide the maximum observedT-phase amplitudes at a given station by the coda site amplification factor obtained for the same station and frequency band
(3.0Hz); the distribution of these amplitudes reveals a smooth pattern over the entire island. The distance over which the
site effect-correctedT-phase amplitude decreases by one-half, combined with the apparent velocity of propagation ofT phases across the island, allows for an approximate determination of near-surfaceQ over much of the island of Hawaii. We found a region of lowQ in the Kilauea summit area (Q≈30) and east rift zone (Q≈60) with considerably higherQ in the Kaoiki and northern portions of the island (Q≈150 to 200). The lowQ values obtained in the Kilauea summit region and east rift zone are significantly lower than estimates of codaQ in the same region, suggestingT phases may be sampling the earth's near-surface properties. 相似文献
19.
Reidar Kanestrøm 《Pure and Applied Geophysics》1973,105(1):729-740
Summary Elastic waves from explosions were recorded at NORSAR and at a number of field stations, and the data were used for determining a crust-mantle model under the array. The number of explosions was eleven distributed on seven shot points. The total number of recording points was fifty-one, and the interpretation was based on 350 individual records.The velocities obtained for the crustal phases were 6.2, 6.6 and 8.2 km/sec for theP
g
,P
g
andP
n
waves respectively. A deep crustal phase with a velocity of about 7.4 km/sec was observed. The mean depths to the discontinuities within the crust were determined to be 17 and 26 km. The depth to Moho varied greatly across the array from 31.5 km in the central part to 38 km under the C-ring. The maximum dip observed for the Moho was 12o.Contribution No. 57 to Norwegian Geotraverse Project. 相似文献
20.