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Elastic lenses in the Earth |
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Eos, Transactions American Geophysical Union,
Volume 65,
Issue 8,
1984,
Page 65-65
Peter M. Bell,
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PDF (146KB)
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摘要:
Seismic waves in the earth's crust and mantle are known to be sensitive to density contrasts over large volumes of rock, which contrasts tend to cause focusing effects. The end results of such effects observed at seismograph stations are hard to detect unless sufficient arrivals are sampled. It is a common fault to confuse such effects with those of local structures and properties. In a study of teleseismic, short‐period (1 s)P‐wave travel‐time residuals and variations of amplitudes in western North America. R. Butler of the Hawaii Institute of Geophysics has found a high level of correlation to which he attributes qualitatively the focusing and defocusing of seismic waves (Nature, December 15, 1983). The correlation indicating that slow travel times relate to higher, and fast travel times to lower, amplitudes of seismic waves measured in western North America. Conversely, faster travel times and higher amplitudes are generally observed in eastern North America (defined as stations located east of the Rocky Mountain front). Although there may be less attenuation of seismic waves in the upper mantle beneath eastern North America, indications are that the degree of attenuation is highly variable. According to Butler, “On the large scale, the variations between western and eastern North America are probably rooted in lateral differences in temperature. Higher temperatures beneath the tectonically active west produce higher attentuation ofP‐waves, lower velocities in the upper mantle, and high surface heat flow.” The focusing and defocusing effects of low and high velocity lenses, respectively, may be most effecitive if such lensese are located close to a seismic station. Butler noted that lenses, or anomalous regions, must have dimensions of one or more wavelengths of aP‐wave, which translates to a minimum dimension in the earth of 6–8 km (for 1‐s period waves). Positive correlations have been observed characteristically over large seismic arrays, suggeting the existence of lenses of several tens of square kilometers
ISSN:0002-8606
DOI:10.1029/EO065i008p00065-01
年代:1984
数据来源: WILEY
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2. |
Horton: Award, medal, and grant |
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Eos, Transactions American Geophysical Union,
Volume 65,
Issue 8,
1984,
Page 66-66
Peter S. Eagleson,
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PDF (1187KB)
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摘要:
In the January 17, 1984, issue ofEos(p. 22), you will find the citation and acceptance of the 1983 winner of the Robert E. Horton Award, David A. Woolhiser. This edition of WaterWatch contains a listing of past winners of both the Horton Award and the Horton Medal. In addition there is a call for proposals for the 1984 Horton Research Grant. That's a lot of Horton, and experience has shown it to generate considerable confusion. Here I hope to clarify matters by drawing upon the historical research of our past president, James R. Wallis.
ISSN:0002-8606
DOI:10.1029/EO065i008p00066-01
年代:1984
数据来源: WILEY
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3. |
Atmosphere, Weather, and Climate |
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Eos, Transactions American Geophysical Union,
Volume 65,
Issue 8,
1984,
Page 67-67
J. T. Houghton,
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摘要:
The fourth edition of this book, first published in 1968, is to be welcomed. It is widely used in geography courses in schools and universities and has had considerable success in introducing, with the minimum of mathematics, synoptic and dynamic meterology and climatology into such courses. Its chapters cover atmospheric composition and energy, atmospheric moisture, atmospheric motion, air masses, fronts and depressions, weather and climate in temperate latitudes, tropical weather and climate, small scale climates and climatic variability, trends and fluctuations.The main changes in the fourth edition have been in the last two chapters, which have been substantially rewritten. The chapter on small‐scale climates goes into considerable detail concerning the energy balance over different surfaces and also discusses the influence of pollution and urban conditions on the local climate. The first chapter on climate variability and change first presents evidence for climate change in the past and then briefly mentions, with virtually no discussion, a few possible causes of climate change. The possible influence of the ocean, for instance, is given only four sentence
ISSN:0002-8606
DOI:10.1029/EO065i008p00067-10
年代:1984
数据来源: WILEY
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4. |
1983 Bucher Medal: John W. Handin |
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Eos, Transactions American Geophysical Union,
Volume 65,
Issue 8,
1984,
Page 69-69
Barry Raleigh,
John Chandin,
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PDF (1538KB)
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摘要:
It is hard to think of any presentation of an award more pleasurable to give or more deserving of receipt. John Handin, this year's Walter H. Bucher Medalist, has been one of the most distinguished scientists in the Bucher tradition. John's research has been devoted to the application of mechanics to the understanding of the deformation of the earth's crust. He is the preeminent leader in experimental studies of rock deformation. Along with King Hubbert he put together the superb group of tectonophysicists at Shell's research labs in the 1950s and early 1960s. Since then, Texas A&M's outstanding Center for Tectonophysics, which originated with Handin, grew to its present excellence under his leadership.
ISSN:0002-8606
DOI:10.1029/EO065i008p00069
年代:1984
数据来源: WILEY
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