MEASUREMENT OF THE THICKNESS OF THE EARTH’S CRUST IN THE ALBERTAN PLAINS OF WESTERN CANADA

Following seismic observations in the Albertan Plains from the Ripple Rock explosion, a refraction line some 81 miles long and parallel to the frontal thrust of the Rocky Mountains and about 60 miles to the east thereof was observed by two‐way shooting. Fifteen seismic parties, spaced at roughly uniform intervals along the line and using the method of close geophone correlation, were employed, the object being to map as many refractors or reflectors as possible as far as the Mohorovicic discontinuity. The results indicate that this discontinuity occurs at a minimum depth of 43 km where the velocity is about 8.2 km/sec, while an intermediate layer with a minimum depth of 29 km and velocity 7.2 km/sec has been registered. Other intermediate refractors were observed. These results are compared with those obtaining in other parts of the American continent and elsewhere. The operational, instrumental, and theoretical aspects of the work are discussed.

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Determination of the gradient of seismic wave velocity in the lower Earth's crust from travel-time curves of waves reflected from the mohorovičić discontinuity

Studia Geophysica et Geodaetica ◽

10.1007/bf01615812 ◽

1975 ◽

Vol 19 (4) ◽

pp. 379-382

Author(s):

Vlastislav Červený ◽

J. Vaněk

Keyword(s):

Travel Time ◽

Wave Velocity ◽

Seismic Wave ◽

Earth’S Crust ◽

Seismic Wave Velocity ◽

Earth's Crust ◽

Mohorovičić Discontinuity

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Theoretical amplitude curves of waves reflected from Mohorovičić discontinuity for some models of one-layered Earth's crust

Studia Geophysica et Geodaetica ◽

10.1007/bf02607047 ◽

1964 ◽

Vol 8 (1) ◽

pp. 34-44 ◽

Cited By ~ 1

Author(s):

Vlastislav Červený ◽

Břetislav Novák

Keyword(s):

Earth’S Crust ◽

Earth's Crust ◽

Mohorovičić Discontinuity

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CHANNEL WAVES IN THE EARTH’S CRUST

Geophysics ◽

10.1190/1.1438141 ◽

1955 ◽

Vol 20 (2) ◽

pp. 283-294 ◽

Cited By ~ 54

Author(s):

B. Gutenberg

Keyword(s):

Southern California ◽

Earth’S Crust ◽

Low Velocity ◽

Earthquake Records ◽

Earth's Crust ◽

Mohorovičić Discontinuity

Three major low‐velocity layers seem to exist in the earth’s crust, of which two, the lithosphere channels, are found respectively in the “granitic” and “basaltic” (“gabbro”) layers of the continents; a third channel extends from the Mohorovičič discontinuity downward into the asthenosphere. Several types of waves are guided by these channels, especially Pa and Sa by the asthenosphere channel, Lg1, Lg2 and Rg by the lithosphere channels; waves guided by low‐velocity layers in sediments must also be expected. Many records of the Southern California earthquake of July 21, 1952 show channel waves with periods and velocities as reported for other paths. The regular microseisms with periods of 4 to 10 sec have properties similar to those of the Lg—Rg group in earthquake records and are probably propagated by the same mechanism. Most of these interpretations and conclusions are tentative; pertinent observations are scanty; and complications have thus far prevented development of adequate equations to calculate the amplitudes of waves guided by a given channel.

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Use of amplitudes, Part I: Pn from 3° to 23°*

Bulletin of the Seismological Society of America ◽

10.1785/bssa0450030219 ◽

1955 ◽

Vol 45 (3) ◽

pp. 219-244

Author(s):

J. Cl. De Bremaecker

Keyword(s):

Density Ratio ◽

Limited Range ◽

Theoretical Explanation ◽

Earth’S Crust ◽

Head Wave ◽

Rate Of Increase ◽

Earth's Crust ◽

Mohorovičić Discontinuity

Abstract Ten seisms with epicentral distances between 3° and 23° are studied. Gutenberg's method to find the variation of Pn amplitudes with distance is applied. It results in observations too scattered to permit any conclusion. The second method uses a combination of seisms, each observed in a limited range. A minimum is found around 7° and a maximum around 13⋅∘5. The essence of the proposed theoretical explanation is the coexistence of “Muskat's rays”† (refracted rays) and of “direct rays” and the existence of “Muskat's rays” along the boundary of two media, in one of which the velocity increases with depth. The results are well explained by comparing the amplitudes due to these two rays. The following structure of the earth's crust best explains the results: speed above the Mohorovičić discontinuity, 6.3 km/sec.; speed immediately below it, 8.1 km/sec.; speed at 80 km. depth, between 8.10 km/sec. and 8.128 km/sec.; around 80 km., decrease in the rate of increase of speed with depth, or decrease of speed with depth < 0.001293 km/sec/km.; depth of the discontinuity, 35 km.; σ1 = σ2 = 0.25; density ratio = 1.103. † Note added in proof: Since the time of this writing, various papers have been published by Macelwane's students using the term “head-wave” for what is here called “Muskat's rays.” As the former term is not ambiguous and is now in current use, it should be preferred.

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