Earthquake seismology, exploration seismology, and engineering seismology: How Sweet It is — Listening to the Earth

The concept of “noise” plays a crucial role in the statistical analysis of data. As an example of a noisy record consider Figure 1 that shows the ground motion of the seismological station NE51 in St. Petersburg after an earthquake in Egypt. (In earthquake seismology, periods may be orders of magnitude larger than in exploration seismology, but the principles are the same.) This time series shows no distinct arrivals or other apparent signatures of an organized nature. Given the proximity of the recording station to a major population center and to the coast, such a noisy record does not seem to be very surprising.

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Earthquake seismology in Greenland – improved data with multiple applications

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v10.4910 ◽

2006 ◽

Vol 10 ◽

pp. 57-60 ◽

Cited By ~ 1

Author(s):

Tine B. Larsen ◽

Trine Dahl-Jensen ◽

Peter Voss ◽

Thomas Møller Jørgensen ◽

Søren Gregersen ◽

...

Keyword(s):

Continental Shelf ◽

High Frequency ◽

Regional Scale ◽

Broad Band ◽

Low Frequency ◽

Low Frequency Oscillations ◽

The Earth ◽

New Information ◽

Seismological Observatory ◽

Earthquake Seismology

Earthquake seismology is a rapidly evolving field that has provided a wealth of new information about deep geological structures on a regional scale over the last decade as well as information about dynamic processes in the Earth. A major leap forward was the development of portable digital broad band (BB) seismographs around 1990. Without any changes in configuration, these are able to record the signals from large distant earthquakes, as well as the signals from weak local events. BB seismographs typically cover a frequency range from 0.0083 Hz to 50 Hz, making them useful for studies ranging from the high frequency signals from explosions to the very low frequency oscillations following major earthquakes. The first seismological observatory in Greenland was established in 1907 in Qeqertarsuaq (GDH) and was in service for about five years (Hjelme 1996). Later, seismographs were established in Ivittut (1927) and Illoqqortoormiut (1928; SCO), and the network has been regularly upgraded and expanded ever since (Fig. 1). Prior to the development of BB seismographs, each station was equipped with a set of seismographs with different frequency sensitivities in an attempt to cover both distant and local earthquakes. Now just one small instrument is needed at each location. The Geological Survey of Denmark and Greenland (GEUS) operates four permanent BB seismographs in Greenland (Fig. 1), two of them in collaboration with foreign institutions. In addition to the permanent network, there are currently 13 temporary BB seismographs active in Greenland, of which eight are operated by GEUS. Three of the temporary seismograph stations were established as part of the Danish Continental Shelf Project (Marcussen et al. 2004), and the remainder in connection with research projects. Three temporary seismographs were deployed during 2005 as part of a research project aiming to resolve very deep regional structures in North Greenland: the Citronen Fjord station (CFJ, Continental Shelf Project), and the stations in Kullorsuaq (KUL) and Daneborg (DBG).

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Reply by the authors to B. Gurevich

Geophysics ◽

10.1190/1.1487028 ◽

1996 ◽

Vol 61 (4) ◽

pp. 1232-1232

Author(s):

N. Dai ◽

A. Vafidis ◽

E. R. Kanasewich

Keyword(s):

Porous Media ◽

Elastic Wave ◽

Wave Equations ◽

Velocity Structure ◽

Combined Effect ◽

Solid Matrix ◽

The Past ◽

The Earth ◽

Elastic Wave Equations ◽

Exploration Seismology

We thank B. Gurevich for interest shown in our paper. In exploration seismology, as noted by Dr. Gurevich, one can model effects in porous media by using the elastic wave equations with trial densities and velocities. Indeed we have, in the past, followed the approach discussed by Gurevich and modelled the earth with a single density and velocity structure in particular layers to simulate the combined effect of a fluid and a solid matrix on a number of occasions (Vafidis et al, 1992; Dai et al 1990) just to point out two papers. Our experience, particularly with higher frequency 3‐D data, is that the synthetic results never match field results and that more parameters are necessary to model partition of energy between different kinds of waves at the interfaces.

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The motion of a lunar orbiter

Symposium - International Astronomical Union ◽

10.1017/s0074180900105686 ◽

1966 ◽

Vol 25 ◽

pp. 373

Author(s):

Y. Kozai

Keyword(s):

Degrees Of Freedom ◽

Dimensional Space ◽

Artificial Satellite ◽

Equations Of Motion ◽

Triaxial Ellipsoid ◽

The Moon ◽

Secular Motion ◽

The Earth ◽

Close Satellite ◽

The Mean

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.

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Formation of Lunar Craters and Bright Rays as a Result of Meteorite Impacts

Symposium - International Astronomical Union ◽

10.1017/s0074180900178404 ◽

1962 ◽

Vol 14 ◽

pp. 415-418

Author(s):

K. P. Stanyukovich ◽

V. A. Bronshten

Keyword(s):

Explosive Charge ◽

The Moon ◽

Meteorite Impacts ◽

The Earth ◽

Lunar Craters ◽

The Impact

The phenomena accompanying the impact of large meteorites on the surface of the Moon or of the Earth can be examined on the basis of the theory of explosive phenomena if we assume that, instead of an exploding meteorite moving inside the rock, we have an explosive charge (equivalent in energy), situated at a certain distance under the surface.

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The Origin of the Moon

Symposium - International Astronomical Union ◽

10.1017/s0074180900178209 ◽

1962 ◽

Vol 14 ◽

pp. 149-155 ◽

Cited By ~ 1

Author(s):

E. L. Ruskol

Keyword(s):

Chemical Composition ◽

Solar System ◽

The Moon ◽

The Earth ◽

The Difference ◽

Origin Of The Moon

The difference between average densities of the Moon and Earth was interpreted in the preceding report by Professor H. Urey as indicating a difference in their chemical composition. Therefore, Urey assumes the Moon's formation to have taken place far away from the Earth, under conditions differing substantially from the conditions of Earth's formation. In such a case, the Earth should have captured the Moon. As is admitted by Professor Urey himself, such a capture is a very improbable event. In addition, an assumption that the “lunar” dimensions were representative of protoplanetary bodies in the entire solar system encounters great difficulties.

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The Origin of the Moon and its Relationship to the Origin of the Solar System

Symposium - International Astronomical Union ◽

10.1017/s0074180900178192 ◽

1962 ◽

Vol 14 ◽

pp. 133-148 ◽

Cited By ~ 2

Author(s):

Harold C. Urey

Keyword(s):

Solar System ◽

The Moon ◽

The Past ◽

The Earth ◽

Short Period ◽

Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

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Probable Structure and Nature of the Formations on the Reverse Side of the Moon According to Photometric Measurements of Lunar Photographs

Symposium - International Astronomical Union ◽

10.1017/s0074180900178076 ◽

1962 ◽

Vol 14 ◽

pp. 39-44

Author(s):

A. V. Markov

Keyword(s):

The Moon ◽

Probable Structure ◽

The Earth ◽

Interplanetary Station ◽

Photometric Measurements ◽

Automatic Interplanetary Station

Notwithstanding the fact that a number of defects and distortions, introduced in transmission of the images of the latter to the Earth, mar the negatives of the reverse side of the Moon, indirectly obtained on 7 October 1959 by the automatic interplanetary station (AIS), it was possible to use the photometric measurements of the secondary (terrestrial) positives of the reverse side of the Moon in the experiment of the first comparison of the characteristics of the surfaces of the visible and invisible hemispheres of the Moon.

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