Attenuation of the Lg phase and the determination of mb in the southeastern United States

1979 ◽  
Vol 69 (1) ◽  
pp. 45-63
Author(s):  
G. A. Bollinger
Keyword(s):  
United States ◽  
Phase Velocity ◽  
Group Velocity ◽  
Southeastern United States ◽  
Source Area ◽  
Wave Guide ◽  
Propagation Path ◽  
Lateral Heterogeneity ◽  
Related Effect

abstract A study of the Lg radiation from 17 southeastern U.S. earthquakes shows the attenuation of that phase to be at a 0.07°−1 rate for epicentral distances of 100 to 700 km. At longer distances, it is also at that rate for some of the earthquakes, but for five of the events it was at a somewhat greater (0.10°−1) rate. These different Lg attenuation rates are clearly a distance-related effect, but they are not caused by differences in source area, propagation path, radiation pattern, wave period, or group velocity. A possible explanation for the different attenuation rates is a shift from a normal-mode form of propagation to a leaking-mode form, brought about by slight phase-velocity variations in the crustal wave guide and/or in the underlying layer. Also, the influence of lateral heterogeneity and variations in the thickness of the crustal wave guide offer alternative explanations. Nuttli's (1973) mb (Lg) formulas, determined for central U.S. events, were found to be appropriate for use on southeastern U.S. shocks if their application is restricted to epicentral distances less than 2,000 km. This distance-restriction result agrees with that determined for the northeastern U.S. earthquakes by Street (1976).

Do centers of origin have a center?

Paleobiology ◽  
1981 ◽  
Vol 7 (3) ◽  
pp. 305-307 ◽  
Author(s):  
John C. Briggs
Keyword(s):  
United States ◽  
North America ◽  
Southeastern United States ◽  
Important Criterion ◽  
Centers Of Origin ◽  
Single Region ◽  
Evolutionary Radiation ◽  
A Current ◽  
Considerable Intensity

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

scholarly journals A SEISMIC WAVE GUIDE PHENOMENON

Geophysics ◽  
1951 ◽  
Vol 16 (4) ◽  
pp. 594-612 ◽  
Author(s):  
K. E. Burg ◽  
Maurice Ewing ◽  
Frank Press ◽  
E. J. Stulken
Keyword(s):  
Phase Velocity ◽  
Shallow Water ◽  
Group Velocity ◽  
Seismic Wave ◽  
Normal Modes ◽  
Seismic Energy ◽  
Wave Guide ◽  
Energy Propagation ◽  
Effective Wave ◽  
Favorable Conditions

On one particular prospect in shallow water repetitive patterns appeared on short spread seismograms in such prevalence as to jeopardize identification of desired reflections. It is demonstrated that under favorable conditions, less restrictive than thought necessary heretofore, a layer of water comprises an effective wave guide for seismic energy propagation. Reinforcement fronts formed by multiple reflection of sound in water can develop into a set of waves completely overshadowing other seismic arrivals. With but minor modifications conventional wave guide theory applies. Examples from the prospect are presented to illustrate various reinforcement patterns. Observed frequency characteristics, group velocity, and phase velocity magnitudes are investigated for normal modes of propagation.

scholarly journals Phylogenetic Diversity and Host Specialization of Corynespora cassiicola Responsible for Emerging Target Spot Disease of Cotton and Other Crops in the Southeastern United States

2018 ◽  
Vol 108 (7) ◽  
pp. 892-901 ◽  
Author(s):  
Leilani G. Sumabat ◽  
Robert C. Kemerait ◽  
Marin Talbot Brewer
Keyword(s):  
United States ◽  
Southeastern United States ◽  
Geographic Location ◽  
The United States ◽  
Plant Diseases ◽  
Host Specialization ◽  
Corynespora Cassiicola ◽  
Target Spot ◽  
Nuclear Loci

Corynespora cassiicola is a ubiquitous fungus causing emerging plant diseases worldwide, including target spot of cotton, soybean, and tomato, which have rapidly increased in incidence and severity throughout the southeastern United States. The objectives of this study were to understand the causes for the emerging target spot epidemics in the United States by comparing phylogenetic relationships of isolates from cotton, tomato, soybean, and other crop plants and ornamental hosts, and through the determination of the host range of isolates from emerging populations. Fifty-three isolates were sampled from plants in the southeastern United States and 1,380 nucleotides from four nuclear loci were sequenced. Additionally, sequences of the same loci from 23 isolates representing each of the distinct lineages of C. cassiicola described from previous studies were included. Isolates clustered based on host of origin, regardless of the geographic location of sampling. There was no genetic diversity detected among isolates from cotton, which were genetically distinct from isolates from other host species. Furthermore, pathogenicity and virulence assays of 40 isolates from various hosts onto cotton, soybean, tomato, and cucumber showed that isolates from cotton were more aggressive to cotton than those from other hosts. Soybean and tomato were most susceptible to isolates that originated from the same host, providing evidence of host specialization. These results suggest that emerging target spot epidemics in the United States are caused by either the introduction of host-specific isolates or the evolution of more aggressive strains on each host.

Determination of Critical Speed in Ice Breaking by Air Cushion Vehicle

2011 ◽  
Vol 138-139 ◽  
pp. 529-533
Author(s):  
Chong Wang ◽  
Zhi Hong Zhang ◽  
Tao Miao ◽  
Jun Yao ◽  
Liao Yuan Zhang ◽  
...  
Keyword(s):  
Differential Equation ◽  
Wave Propagation ◽  
Phase Velocity ◽  
Group Velocity ◽  
Critical Speed ◽  
Ice Sheet ◽  
Air Cushion ◽  
Air Cushion Vehicle ◽  
Vibrating Plate

On the basis of the differential equation governing small flexure of thin elastic vibrating plate, the formula for calculating the phase velocity and group velocity of ice sheet wave propagation under the air cushion load is induced. The minimum of the phase velocity is the critical speed about ice breaking by air cushion vehicle (ACV). If ACV moves at the critical speed, the energy causing the deformation of ice sheet is concentrated constantly, thus the amplitude of the wave is enlarged enough to break the ice by resonance.

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