Velocity of elastic waves and structure of the crust in the vicinity of Ottawa, Canada*

1942 ◽  
Vol 32 (4) ◽  
pp. 249-255
Author(s):  
Ernest A. Hodgson
Keyword(s):  
Elastic Waves ◽  
Single Point ◽  
Focal Depth ◽  
The Other ◽  
Northern Europe ◽  
Earth Structure ◽  
Travel Times ◽  
Arrival Times ◽  
The Earth ◽  
Mohorovičić Discontinuity

Summary Ten seismograms, due to rockbursts at Lake Shore Mines, Kirkland Lake, Ontario, were recorded on a Benioff seismograph at Ottawa at a distance of 450 km. (279 mi.). The center of each burst was located within a few feet; but, for the purpose of preparing travel-time tables, they may all be considered to have occurred at a single point at the surface. Two of the bursts were accurately timed on the seismograph at the mine. Six phases were registered on each seismogram, being more sharply marked on some records than on others. Five of these are well defined on nearly all the records. It is thus possible to deduce a set of arrival times at a distance of 450 km. for a burst (or earthquake) occurring at the surface; and this set of times is known with fair precision, since all the readings may be combined. The distance is determined within one part in 7000, the depth within 2000 ft. and the travel times with an error of ±.5 sec. These travel times have been compared with those obtained by Joliat in computing his Tables for Near Earthquakes, based on the velocities deduced by Jeffreys for northern Europe and arbitrarily assuming an earth structure with two layers above the Mohorovičić discontinuity. The differences are minor and are to be explained as chiefly owing to the fact that Joliat assumed the focus to lie at the bottom instead of the top of the upper layer. On the strength of the comparisons afforded by the ten seismograms, the focal time of each burst may be considered as known within ±.5 sec. One of the bursts was so severe that it was registered also at Shawinigan Falls, Quebec (Δ = 576 km., 358 mi.) and at Weston, Massachusetts (Δ = 935 km., 581 mi.). These records will afford a means of deducing the earth structure and velocities in the vicinity of Ottawa, and will permit the construction of tables for rock-bursts and blasts in that area up to 10° (1110 km., 690 mi.). These will be prepared and issued, together with corrections permitting their being used for local earthquakes with finite focal depth. Should other bursts occur later at Kirkland Lake, timed by the mine seismograph and registered at Ottawa or the other stations, the data so made available may be directly used to check and add precision to the deductions made from the seismograms already in hand. Such further data would be most valuable.

Part 2. The deeper structure of the Atlantic - Geological hypotheses and the earth's crust under the oceans

1954 ◽  
Vol 222 (1150) ◽  
pp. 341-348 ◽  
Keyword(s):  
Heat Flow ◽  
Recent Work ◽  
Sea Water ◽  
Volcanic Rocks ◽  
The Other ◽  
Ocean Floor ◽  
Peridotite Xenoliths ◽  
The Earth ◽  
Southern Rhodesia ◽  
Mohorovičić Discontinuity

Recent work has determined the depth of the Mohorovičić discontinuity at sea and has made it likely that peridotite xenoliths in basaltic volcanic rocks are samples of material from below the discontinuity. It is now possible to produce a hypothetical section showing the transition from a continent to an ocean. This section is consistent with both the seismic and gravity results. The possible reactions of the crust to changes in the total volume of sea water are dis­cussed. It seems possible that the oceans were shallower and the crust thinner in the Archean than they are now. If this were so, some features of the oldest rocks of Canada and Southern Rhodesia could be explained. Three processes are described that might lead to the formation of oceanic ridges; one of these involves tension, one compression and the other quiet tectonic conditions. It is likely that not all ridges are formed in the same way. It is possible that serpentization of olivine by water rising from the interior of the earth plays an important part in producing changes of level in the ocean floor and anomalies in heat flow. Finally, a method of reducing gravity observations at sea is discussed.

A new analytical method for finding the upper mantle velocity structure from P and S wave travel times of deep earthquakes

1969 ◽  
Vol 59 (2) ◽  
pp. 755-769
Author(s):  
K. L. Kaila
Keyword(s):  
Velocity Structure ◽  
Focal Depth ◽  
Least Square ◽  
Travel Times ◽  
S Wave ◽  
The Earth ◽  
Straight Line ◽  
Wave Travel ◽  
Deep Focus ◽  
Mantle Velocity

abstract A new analytical method for the determination of velocity at the hypocenter of a deep earthquake has been developed making use of P- and S-wave travel times. Unlike Gutenberg's method which is graphical in nature, the present method makes use of the least square technique and as such it yields more quantitative estimates of the velocities at depth. The essential features of this method are the determination from the travel times of a deep-focus earthquake the lower and upper limits Δ1 and Δ2 respectively of the epicentral distance between which p = (dT/dΔ) in the neighborhood of inflection point can be considered stationary so that the travel-time curve there can be approximated to a straight line T = pΔ + a. From p = (1/v*) determined from the straight line least-square fit made on the travel-time observation points between Δ1 and Δ2 for various focal depths, upper-mantle velocity structure can be obtained by making use of the well known relation v = v*(r0 − h)/r0, h being the focal depth of the earthquake, r0 the radius of the Earth, v* the apparent velocity at the point of inflection and v the true velocity at that depth. This method not only gives an accurate estimate of p, at the same time it also yields quite accurate value of a which is a function of focal depth. Calibration curves can be drawn between a and the focal depth h for various regions of the Earth where deep focus earthquakes occur, and these calibration curves can then be used with advantage to determine the focal depths of deep earthquakes in those areas.

Travel times from central Pacific nuclear explosions and inferred mantle structure

1964 ◽  
Vol 54 (6B) ◽  
pp. 2271-2294
Author(s):  
Dean S. Carder
Keyword(s):  
Single Point ◽  
P Wave ◽  
Graphical Form ◽  
Travel Times ◽  
Time Data ◽  
Central Pacific ◽  
Arrival Times ◽  
Nuclear Explosions ◽  
Straight Line ◽  
Travel Time Data

Abstract Travel time data, from widely recorded nuclear detonations in the Eniwetok and Bikini atolls of the central Pacific, have been compiled and are presented. Although a number of stations recorded ten or more events from each atoll, the resulting data may be considered as from a single point source, precisely known in time and place. Composite P-wave travel times are presented in a graphical form and, in the distance range from 3 to 102 degrees, are represented as eight near straight-line segments. P-wave speeds in the top of the mantle average about 8.2 km/sec to distances beyond 17 degrees, and a sharp discontinuity at 19.5 degrees is indicated. There is no evidence for or against a low-speed layer in the upper mantle nor for a regional shadow zone. A mantle model consisting of a number of discrete spherical shells has been constructed. A core depth of 2,870 km, 30 km short of the accepted value, is calculated from PcP arrival times at Matsushiro and College, which are 2.5 and 3.5 sec. earlier than are indicated in the Jeffreys-Bullen tables.

Velocity of P waves in the earth calculated from the Macelwane P curve, 1933*

1936 ◽  
Vol 26 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Cornelius G. Dahm
Keyword(s):  
Focal Depth ◽  
Outer Part ◽  
Long Beach ◽  
P Waves ◽  
Depth Function ◽  
The Earth ◽  
Distance Data ◽  
Mohorovičić Discontinuity

Summary The Macelwane P curve is based on the data of the Tango, Hawke Bay, and Long Beach earthquakes, all of 10–12 km. focal depth. This curve was modified and adjusted to fit a spheroid of 6355 km. radius, the outer part of which has the same properties as those immediately under the Mohorovičić discontinuity in Japan. The original and the adjusted P curve are given as well as the velocity-depth and depth-distance data obtained by applying the Herglotz-Wiechert method to the adjusted P curve. The inversion and slight decrease of the velocity-depth function at 2730 km. depth are discussed and the continued validity of the Herglotz-Wiechert method under those circumstances is shown.

scholarly journals Travel times of principal P and S phases over small distances in southern California*

1944 ◽  
Vol 34 (1) ◽  
pp. 13-32
Author(s):  
B. Gutenberg
Keyword(s):  
Sierra Nevada ◽  
Southern California ◽  
Epicentral Distance ◽  
Focal Depth ◽  
Coastal Areas ◽  
Travel Times ◽  
Mountain Areas ◽  
Arrival Times ◽  
Order Of Magnitude ◽  
Characteristic Values

Summary Study of arrival times of the principal phases in fifty of the larger and better recorded earthquakes in southern California resulted in the following travel times t (seconds) and apparent velocities V (km/sec.): Pt = 0.1793DV = 5.577St = −0.5 + 0.3066DV = 3.26Pyt = 1.2+0.1654ΔV = 6.047Syt = 2.1 + 0.274ΔV = 3.65Pnt = x + 0.124ΔV = 8.06Snt = y + 0.225ΔV = 4.45 Δ = epicentral distance, D2 = Δ2 + h2, h = focal depth. x and y depend on the region; the following are characteristic values Coastal areas,Mountain areas,NorthernSierralow valleyssoutheastern Calif.Owens ValleyNevadax67910±sec.y8½9½12½14±sec. The average true velocities of Py and Sy are about one-third of one per cent, those of Pn and Sn about one-half of one per cent, smaller than the corresponding apparent velocities. In the uppermost 50 km. the velocity increases with depth. The order of magnitude of this increase is roughly 1 per cent per 10 kilometers, but larger in the uppermost one or two kilometers. It can be found from a study of amplitudes (Gutenberg, 1943c); its effect on the travel times exceeds the limits of error by too small an amount to be ascertained beyond doubt from the data of the present paper. The curvature of the earth can be disregarded within the range of distances used (in general not exceeding 800 km.). The effect of “mountain roots” on the travel times of Pn and Sn is investigated. Reproduction of travel-time curves and recalculation of the thickness of the various layers must wait until a study of other (especially reflected) recorded phases now under way is finished. Preliminary values are 18 km. for the thickness of the granitic layer with small local variations, and about 35 km. for the total of the crustal layers in the coastal areas of southern California with an increase inland approaching twice that amount under the Sierra Nevada.

scholarly journals Travel times from blasts in southern California*

1951 ◽  
Vol 41 (1) ◽  
pp. 5-12 ◽  
Author(s):  
B. Gutenberg
Keyword(s):  
Southern California ◽  
Apparent Velocity ◽  
Travel Times ◽  
P Waves ◽  
Transverse Waves ◽  
Arrival Times ◽  
S Waves ◽  
Mohorovičić Discontinuity

abstract Seismograms recorded from a blast of about 70 tons of Du Pont “Nitramon” in tunnels at a quarry near Corona, southern California, are discussed. Arrival times of P waves indicate a velocity of between 5.7 and 6.0 km/sec. in the upper 6 km. of the region, and a velocity of about 6 1/2 km/sec. at a depth of 10 km. The Mohorovičić discontinuity is at a depth of the order of 40 km. The velocity below it is 8.1 to 8.2 km/sec. The amplitudes of S waves are only slightly more than one-tenth of those in an earthquake having P waves of equal amplitudes. The ratio of the velocity of P to that of the first recognizable S is found between 1.6 and 1.7. The first S waves at distances up to about 140 km. indicate a velocity of transverse waves of about 3¾ km/sec. at a depth of the order of 10 km. A phase with an apparent velocity of about 3 1/2 km/sec. can be traced to more than 400 km. It is followed by several slower phases. On the assumption that the amplitudes of Pn do not differ appreciably from those in an earthquake of the same magnitude, the blast would have had a magnitude of about 4.

Note on Selection of Coordinate Systems for Geodynamics

1975 ◽  
Vol 26 ◽  
pp. 395-407
Author(s):  
S. Henriksen
Keyword(s):  
Sea Level ◽  
The Other ◽  
Coordinate Systems ◽  
Mean Sea Level ◽  
The Earth ◽  
The One ◽  
Static Systems ◽  
Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

scholarly journals Geocomputing, New Technologies and Historical Analysis: Tools for a Changing Planet

Proceedings ◽  
2019 ◽  
Vol 30 (1) ◽  
pp. 9
Author(s):  
Sebastiano Trevisani
Keyword(s):  
Quantitative Analysis ◽  
Philosophy Of Science ◽  
New Technologies ◽  
Historical Analysis ◽  
Holistic Approach ◽  
Research Topic ◽  
The Other ◽  
Historical Records ◽  
The Earth ◽  
The Relationship

Modern Earth Scientists need also to interact with other disciplines, apparently far from the Earth Sciences and Engineering. Disciplines related to history and philosophy of science are emblematic from this perspective. From one side, the quantitative analysis of information extracted from historical records (documents, maps, paintings, etc.) represents an exciting research topic, requiring a truly holistic approach. On the other side, epistemological and philosophy of science considerations on the relationship between geoscience and society in history are of fundamental importance for understanding past, present and future geosphere-anthroposphere interlinked dynamics.

scholarly journals The Critical Raw Materials Issue between Scarcity, Supply Risk, and Unique Properties

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1826
Author(s):  
Mihaela Girtan ◽  
Antje Wittenberg ◽  
Maria Luisa Grilli ◽  
Daniel P. S. de Oliveira ◽  
Chiara Giosuè ◽  
...  
Keyword(s):  
Scientific Community ◽  
Chemical Elements ◽  
Raw Materials ◽  
The Other ◽  
Innovation Networks ◽  
Supply Risk ◽  
European Cooperation ◽  
Research And Innovation ◽  
The Earth ◽  
Critical Raw Materials

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology).

scholarly journals Estimating the Earth’s Outgoing Longwave Radiation Measured from a Moon-Based Platform

2021 ◽  
Vol 13 (11) ◽  
pp. 2201
Author(s):  
Hanlin Ye ◽  
Huadong Guo ◽  
Guang Liu ◽  
Jinsong Ping ◽  
Lu Zhang ◽  
...  
Keyword(s):  
Outgoing Longwave Radiation ◽  
Large Scale ◽  
Single Point ◽  
Longwave Radiation ◽  
Earth Observation ◽  
Artificial Satellites ◽  
Earth Observations ◽  
The Earth ◽  
Observation Geometry ◽  
Global Mean

Moon-based Earth observations have attracted significant attention across many large-scale phenomena. As the only natural satellite of the Earth, and having a stable lunar surface as well as a particular orbit, Moon-based Earth observations allow the Earth to be viewed as a single point. Furthermore, in contrast with artificial satellites, the varied inclination of Moon-based observations can improve angular samplings of specific locations on Earth. However, the potential for estimating the global outgoing longwave radiation (OLR) from the Earth with such a platform has not yet been fully explored. To evaluate the possibility of calculating OLR using specific Earth observation geometry, we constructed a model to estimate Moon-based OLR measurements and investigated the potential of a Moon-based platform to acquire the necessary data to estimate global mean OLR. The primary method of our study is the discretization of the observational scope into various elements and the consequent integration of the OLR of all elements. Our results indicate that a Moon-based platform is suitable for global sampling related to the calculation of global mean OLR. By separating the geometric and anisotropic factors from the measurement calculations, we ensured that measured values include the effects of the Moon-based Earth observation geometry and the anisotropy of the scenes in the observational scope. Although our results indicate that higher measured values can be achieved if the platform is located near the center of the lunar disk, a maximum difference between locations of approximately 9 × 10−4 W m−2 indicates that the effect of location is too small to remarkably improve observation performance of the platform. In conclusion, our analysis demonstrates that a Moon-based platform has the potential to provide continuous, adequate, and long-term data for estimating global mean OLR.

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