Crust and upper mantle Q from seismic refraction data: Peace River region

1990 ◽  
Vol 27 (8) ◽  
pp. 1040-1047 ◽  
Author(s):  
C. A. Zelt ◽  
R. M. Ellis
Keyword(s):  
Upper Mantle ◽  
Seismic Refraction ◽  
Spectral Ratio ◽  
Ratio Method ◽  
Spectral Ratios ◽  
P Waves ◽  
Crust And Upper Mantle ◽  
Peace River ◽  
River Region ◽  
Refraction Data

Crustal refraction data from the Peace River region of Alberta, Canada, have been analyzed using the spectral ratio method to obtain Q. A total of 1205 first and later arrivals corresponding to turning and reflected P-waves within the crust and upper mantle were studied. Source spectra were estimated from near-offset traces assuming typical sedimentary Q values. The large scatter of measured spectral ratios restricted the resolution to a three-layer model of the crust and upper mantle with Q constant in each layer. This model was obtained using a linear inverse method since the measured spectral ratios and known traveltimes in each layer are linearly related through the attentuation (Q−1) in each layer. A weighted L1 norm was minimized using linear programming, the weights being a measure of the certainty of each spectral ratio. The inversion was performed using the 25% most certain spectral ratios, regardless of magnitude or sign. Model bounds taking account of the scattered data were estimated. The results suggest that Q is between 200 and 500 in the upper crust and greater than 600 in the lower crust and upper mantle. This model is generally consistent with Q obtained from studies on nearby crust.

Crustal characteristics from short-period P waves

1968 ◽  
Vol 58 (5) ◽  
pp. 1681-1700
Author(s):  
R. M. Ellis ◽  
P. W. Basham
Keyword(s):  
Upper Mantle ◽  
Matrix Theory ◽  
Spectral Ratio ◽  
Matrix Formulation ◽  
P Waves ◽  
Crust And Upper Mantle ◽  
Travel Path ◽  
Short Period ◽  
Teleseismic Events

Abstract Thirty-four teleseismic events, recorded on the deep horizontal sediments of central Alberta, using one fixed and one movable station, have been analyzed as a test of the Haskell matrix formulation applied to short period P waves. Only limited agreement is obtained between averaged experimental vertical-horizontal spectral ratio curves and those calculated theoretically using known layer thicknesses and velocities. Scattering in the crust and upper mantle is indicated by large transverse amplitudes including distict phases and by lower coherency for smaller epicentral distances where the travel path is confined to the crust and upper mantle. Anomalous SV/P ratios are believed to contribute to the difficulties. A study of 20 events in the azimuth range 285° to 310° indicates an apparent azimuth approximately 18° more northerly than the true azimuth. Localized dips of approximately 15° on the crustal boundaries are required to explain this deviation. It is concluded that this region for which the sediments are horizontally layered does not fulfill the requirements of the Haskell matrix theory due to scattering and anomalous PS conversions in the crust and upper mantle.

Crustal velocity structure in the southern Coast Belt, British Columbia

1993 ◽  
Vol 30 (12) ◽  
pp. 2389-2403 ◽  
Author(s):  
D. M. O'Leary ◽  
R. M. Clowes ◽  
R. M. Ellis
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Seismic Refraction ◽  
Velocity Model ◽  
Structural Features ◽  
P Wave ◽  
Crust And Upper Mantle ◽  
Near Surface ◽  
Collision Zone ◽  
Refraction Data

We applied an iterative combination of two-dimensional traveltime inversion and amplitude forward modelling to seismic refraction data along a 350 km along-strike profile in the Coast Belt of the southern Canadian Cordillera to determine crust and upper mantle P-wave velocity structure. The crustal model features a thin (0.5–3.0 km) near-surface layer with an average velocity of 4.4 km/s, and upper-, middle-, and lower-crustal strata which are each approximately 10 km thick and have velocities ranging from 6.2 to 6.7 km/s. The Moho appears as a 2 km thick transitional layer with an average depth of 35 km and overlies an upper mantle with a poorly constrained velocity of over 8 km/s. Other interpretations indicate that this profile lies within a collision zone between the Insular superterrane and the ancient North American margin and propose two collision-zone models: (i) crustal delamination, whereby the Insular superterrane was displaced along east-vergent faults over the terranes below; and (ii) crustal wedging, in which interfingering of Insular rocks occurs throughout the crust. The latter model involves thick layers of Insular material beneath the Coast Belt profile, but crustal velocities indicate predominantly non-Insular material, thereby favoring the crustal delamination model. Comparisons of the velocity model with data from the proximate reflection lines show that the top of the Moho transition zone corresponds with the reflection Moho. Comparisons with other studies suggest that likely sources for intracrustal wide-angle reflections observed in the refraction data are structural features, lithological contrasts, and transition zones surrounding a region of layered porosity in the crust.

scholarly journals A Seismic Refraction Study of the Crust and Upper Mantle in the Vicinity of Bass Strait

1969 ◽  
Vol 22 (5) ◽  
pp. 573 ◽  
Author(s):  
R Underwood
Keyword(s):  
Crustal Structure ◽  
Upper Mantle ◽  
Seismic Refraction ◽  
Travel Times ◽  
Crust And Upper Mantle ◽  
Australian Institute ◽  
First Arrival Travel Times ◽  
First Arrival ◽  
Future Work

A reconnaissance seismic refraction study of the crust and upper mantle of Bass Strait and adjacent land was undertaken in 1966 under the sponsorship of the Geophysics Group of the Australian Institute of Physics. The shot locations and times, the station locations, distances, and first arrival travel times are presented. Analysis of these data is described; they indicate a P n velocity below 8 km sec-I. Time terms are less than expected and do not agree with previous work. Crustal thicknesses cannot be computed until studies of upper crustal structure are made. These, and several mantle refraction studies, are suggested for future work.

Crust and upper mantle structure along the flank of Kōko Seamount

1980 ◽  
Vol 70 (4) ◽  
pp. 1161-1169
Author(s):  
K. Furukawa ◽  
J. F. Gettrust ◽  
L. W. Kroenke ◽  
J. F. Campbell
Keyword(s):  
Upper Mantle ◽  
Seismic Refraction ◽  
Crustal Thickness ◽  
Mantle Structure ◽  
Crust And Upper Mantle ◽  
Velocity Gradients ◽  
Upper Mantle Structure ◽  
Hawaiian Ridge ◽  
Seamount Chain ◽  
Emperor Seamount Chain

abstract Inversion of an 80-km-long reversed seismic refraction profile near the northwestern flank of Kōko Seamount indicates that the crust adjacent to the southern end of the Emperor Seamount chain is approximately 9-km thick with no dip in the refracting horizons. These data require positive P-velocity gradients in the crust and upper mantle to fit the observed amplitudes. The crustal refractor P velocities and crustal thickness found are in general agreement with those found previously for the Emperor chain and near the Hawaiian Ridge. It is inferred from our data that the tectonic mechanism which created the Emperor and Hawaiian chains was highly localized.

SEISMIC STUDIES ON THE EASTERN SEABOARD OF CANADA: THE ATLANTIC COAST OF NOVA SCOTIA

1964 ◽  
Vol 1 (1) ◽  
pp. 10-22 ◽  
Author(s):  
D. L. Barrett ◽  
M. Berry ◽  
J. E. Blanchard ◽  
M. J. Keen ◽  
R. E. McAllister
Keyword(s):  
Nova Scotia ◽  
Upper Mantle ◽  
Atlantic Coast ◽  
Seismic Refraction ◽  
Compressional Wave ◽  
Crust And Upper Mantle ◽  
Compressional Waves ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Eastern Seaboard

The results of seismic refraction profiles on the Atlantic coast of Nova Scotia and on the continental shelf off Nova Scotia are presented. Compressional and shear waves have been observed in the crust and mantle and suggest that the thickness of the crust is about 34 km. The compressional wave velocities recorded in the main crust and upper mantle are 6.10 and 8.11 km s−1 respectively. No compressional waves with values of velocity between these values can be identified, and this suggests that any "intermediate" layer is thin or absent. The corresponding shear wave velocities are 3.68 and 4.53 km s−1. Values of Poisson's ratio in the crust and mantle are 0.22 and 0.28. Alternative models of the crust which, on the evidence of travel times, might fit the observed results are discussed.

Linear inversion of body wave data—Part II: Attenuation versus depth using spectral ratios

Geophysics ◽  
1981 ◽  
Vol 46 (2) ◽  
pp. 152-162 ◽  
Author(s):  
R. S. Jacobson ◽  
George G. Shor ◽  
LeRoy M. Dorman
Keyword(s):  
Body Wave ◽  
Seismic Refraction ◽  
Inverse Theory ◽  
Source Spectrum ◽  
Spectral Ratios ◽  
Linear Inversion ◽  
Source Signal ◽  
Seismic Refraction Data ◽  
Refraction Data ◽  
Preferred Solutions

We present a method for determining the specific quality factor [Formula: see text] by the use of spectral ratios of seismic refraction data. The only modifications to standard refraction profiles are that the source and receivers be sufficiently far away from reflective boundaries to eliminate the angular dependence of the source spectrum itself and of the observation of the source signal by the receiver. The last requirement may not be too significant. Application of this method for determining attenuation as a function of depth was applied to data obtained in a thick sedimentary section in the Bay of Bengal. Once an adequate velocity‐depth function is determined, attenuation as a function of depth is readily calculated by the use of linear inverse theory. Several preferred solutions are discussed, including a model of constant [Formula: see text] of 0.0115. A comparison of our data with a compilation of data from the published literature of attenuation with depth reveals a reasonable concordance, but with some slight differences. A peak of attenuation at 600-m depth probably represents the depth of lithification of the sediments into mudstone.

Sign in / Sign up

Export Citation Format

Share Document