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

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.

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

Geophysics ◽  
1959 ◽  
Vol 24 (2) ◽  
pp. 262-284 ◽  
Author(s):  
T. C. Richards ◽  
D. J. Walker
Keyword(s):  
Rocky Mountains ◽  
Intermediate Layer ◽  
Earth’S Crust ◽  
Western Canada ◽  
American Continent ◽  
Minimum Depth ◽  
Earth's Crust ◽  
Mohorovičić Discontinuity

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.

HEAD WAVE TIME SECTIONS OF THE UPPER EARTH’S CRUST ALONG THE SURVEY BASE LINE 3-DV (NORTHEASTERN BLOCK)

2016 ◽  
pp. 86-95
Author(s):  
P. O. Polyansky ◽  
◽  
A. S. Salnikov ◽  
A. F. Emanov ◽  
V. V. Zhabin ◽  
...  
Keyword(s):  
Earth’S Crust ◽  
Head Wave ◽  
Base Line ◽  
Earth's Crust

scholarly journals COMPARATIVE ANALYSIS OF GEODYNAMIC PARAMETERS OBTAINED FROM ASTRONOMIC AND GPS OBSERVATIONS IN POLTAVA

2021 ◽  
pp. 11-16
Author(s):  
L. Halyavina ◽  
N. Zalivadnyj
Keyword(s):  
Deep Structure ◽  
Theoretical Explanation ◽  
Earth’S Crust ◽  
Plumb Line ◽  
Gps Data ◽  
The South ◽  
The North ◽  
Earth's Crust ◽  
Gps Station ◽  
Gps Observations

The functioning of the GPS station and regular astrometric observations with a prismatic astrolabe in Poltava provides series of local displacements of the earth's crust and plumb line in time, characterizing the changes in the gravitational field. The analysis of the N-component of the earth's crust movement and the displacement of the meridional projection of the plumb line was carried out on the basis of GPS data and from observations on the astrolabe, respectively, for the period 2002-2020. Comparison of the trends of these series showed that their shifts occur in opposite directions. It is noted that the movement of the point occurs in the northern direction at a speed of +0.3mm/yr, and the displacement of the plumb line - to the south, at a speed of -2.6mas/year. Similarly, an abrupt displacement of the N-component to the north by + 2mm at the turn of 2014 was accompanied by a displacement of the plumb line to the south by approximately -50 mas. These facts can be explained within the framework of the hypothesis of the existence of a deep structure in the vicinity of Poltava, in which a significant change in mass occurs. The spectra of both series show the presence of cyclicities with close periods: about 3.2, 2.8, 1.0, 0.5, and 0.3 yr. It is known that harmonics with those periods are present in many astrometric series. The geodynamic interpretation of the presented facts requires additional confirmation in observations of neighboring GPS stations, as well as a theoretical explanation and justification.

scholarly journals THE SPEED CHARACTERISTICS OF THE EARTH'S CRUST OF THE KOROSTEN PLUTON (UKRAINIAN SHIELD) ACCORDING TO THE DATA OF DEEP SEISMIC SOUNDING METHOD

2018 ◽  
pp. 46-50
Author(s):  
Y. Rozyhan ◽  
O. Trypilskiy ◽  
O. Topoliuk
Keyword(s):  
Short Interval ◽  
Earth’S Crust ◽  
Ukrainian Shield ◽  
Depth Interval ◽  
Basic Composition ◽  
Rate Of Increase ◽  
Seismic Sounding ◽  
Abrupt Changes ◽  
Earth's Crust ◽  
Basic Rocks

A detailed comparative analysis of the velocity characteristics of the Earth's crust of the Korosten pluton, Volyn and Chopovitsky massifs of the basic rocks of the Volyn megablock of the Ukrainian Shield was carried out. In the interval of depths of 3–13 km in the Earth's crust of the Korosten pluton, five sections are fixed, where the speed on a short interval first decreases with depth, then, on the contrary, increases. This is due to the presence in the section of a series of layers composed of rocks with reduced or elevated speeds, which alternate with increasing depth. Such changes in velocity are considered to be the results of alternation of rocks of the basic and acidic composition. With depth, the rate of increase in velocity (vertical velocity gradient), which characterizes the features of rooting into the crust of an intrusion with increased basicity, significantly decreases. These features lie in the fact that the molten masses coming from the upper mantle were concentrated mainly in the upper and middle parts of the Earth's crust. The distinction between the features of the speed characteristics of the Earth's crust of the Volynsky and Chopovitsky massifs of the main rocks is revealed. The velocity characteristics of the compared structures reflect the characteristics of the rooting of igneous melts of the basic composition into the Earth's crust. Despite the territorial proximity of the massifs, the nature of the rooting of the melts between them is significantly different. For example, abrupt changes in velocity in the depth interval of 0–12 km of the Volynsky massif can be attributed to the presence of, at least, 10 layers of rocks, predominantly of acidic and basic composition, which alternate each other. It should be emphasized that at depths of 8–12 km maximum speeds (up to 0.17–0.18 km/s) between individual layers are observed. In the same depth interval in the Chopovitsky massif, only 5 layers stand out with a maximum differential velocity of 0.18 km/s.

scholarly journals CHANNEL WAVES IN THE EARTH’S CRUST

Geophysics ◽  
1955 ◽  
Vol 20 (2) ◽  
pp. 283-294 ◽  
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.

THE PROPAGATION OF THE COMPRESSIONAL WAVE IN THE CRUST: I. A SIMPLE TREATMENT OF THE DATA

1965 ◽  
Vol 2 (6) ◽  
pp. 543-559 ◽  
Author(s):  
M. J. Keen ◽  
C. F. Tsong ◽  
J. E. Blanchard
Keyword(s):  
Nova Scotia ◽  
Velocity Gradient ◽  
Atlantic Coast ◽  
Compressional Wave ◽  
Earth’S Crust ◽  
Head Wave ◽  
Propagation Mechanism ◽  
Half Cycle ◽  
Simple Treatment ◽  
Earth's Crust

Seismic experiments have been undertaken along the Atlantic coast of Nova Scotia, and an attempt has been made to determine by what mechanism the compressional wave which is recorded as the first event in the range of distance 10 km to 180 km propagates, and to describe its attenuation. In this part of the paper the change in amplitude of the first half-cycle of the first event is investigated, and compared with the change in amplitude which might be expected if propagation occurred as a "head wave", and if propagation occurred because of the presence of a velocity gradient in the upper few kilometers of the earth's crust. We find that we cannot distinguish between the two mechanisms of propagation with any certainty, and although the suggestion is made that the value of Q is in the range 90 to 300, depending upon the propagation mechanism, the assumptions which underlie the approach are criticized, and a more reasonable one put forward.

Tides in the Earth's Crust

1915 ◽  
Vol 79 (2058supp) ◽  
pp. 382-383
Author(s):  
Alphonse Berget
Keyword(s):  
Earth’S Crust ◽  
Earth's Crust
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