Conversion of Sn to Lg at a continental margin

1975 ◽  
Vol 65 (1) ◽  
pp. 235-244 ◽  
Author(s):  
Bryan L. Isacks ◽  
Christopher Stephens
Keyword(s):  
North America ◽  
Gulf Of Mexico ◽  
Continental Margin ◽  
West Indies ◽  
Wave Train ◽  
Eastern North America ◽  
Substantial Fraction ◽  
The West ◽  
Short Period ◽  
Period Wave

abstract Examination of the seismic phase Sn from earthquakes in the West Indies as recorded by numerous stations in eastern North America reveals that a substantial fraction of the short-period energy carried by Sn across the suboceanic lithosphere of the Atlantic is fed into the continental crust near the continental margin and travels into North America as the crustal phase Lg. As distance within the continent increases, the Lg part of the short-period wave train becomes predominant, and can be identified at stations in northern Canada as far as 58° from the sources. Several estimates of the average Q for the attenuation of Lg in eastern North America agree upon values in the range of 600 to 1,400. Hydrophone recordings at Bermuda indicate an average Q as high as 4,000 for the attenuation of Sn in the suboceanic lithosphere. Conversion of Sn to Lg also appears to occur near the margin between the continental U.S. and the Gulf of Mexico. In this case, Sn travels northward across the Gulf from earthquakes located near the border between Mexico and Guatemala.

Brissus bridgeboroensis, a new spatangoid echinoid from the lower Oligocene of southwestern Georgia

1987 ◽  
Vol 61 (5) ◽  
pp. 1043-1046 ◽  
Author(s):  
Burchard D. Carter
Keyword(s):  
New Species ◽  
North America ◽  
Gulf Of Mexico ◽  
West Indies ◽  
The West ◽  
Lower Oligocene ◽  
A New Species

A new species of Brissus is described from the lower Oligocene (Rupelian–Vicksburgian) Bridgeboro limestone of southwestern Georgia. Brissus bridgeboroensis n. sp. most closely resembles the Recent Brissus unicolor (Leske) of the West Indies and the Gulf of Mexico, but it differs primarily in features of the posterior paired petals. Brissus bridgeboroensis is the oldest known member of the genus from continental North America.

The Achievements of the Douglass Company in North America: 1758–1774

1982 ◽  
Vol 23 (2) ◽  
pp. 141-149 ◽  
Author(s):  
David D. Mays
Keyword(s):  
New York ◽  
North America ◽  
West Indies ◽  
Theatre History ◽  
The West ◽  
American Theatre ◽  
History Of ◽  
American Theatre History ◽  
A Company

On Monday, October 16, 1758., Hugh Gaine reported a novelty. “Friday last,” he told his readers in the New-York Mercury, “arrived here from the West Indies, a Company of Comedians; some Part of which were here in the Year 1753.” This brief notice, which went on to assure its readers that the company had “an ample Certificate of their Private as well as publick Qualifications,” marks the beginning of the most significant event in American theatre history: the establishment of the professional theatre on this continent. The achievements of the Company of Comedians during its sixteen-year residence in North America are virtually without parallel in the history of the theatre, and have not received sufficient recognition by historians and scholars.

NEW SPECIES OF DOLICHOPODIDAE FROM NORTH AMERICA AND THE WEST INDIES

1930 ◽  
Vol 62 (4) ◽  
pp. 84-87 ◽  
Author(s):  
M. C. van Duzee
Keyword(s):  
New Species ◽  
North America ◽  
West Indies ◽  
The West ◽  
Tarsal Joint ◽  
Pale Yellow ◽  
Posterior Pair ◽  
Snow White

Male: Length 2.6-3 mm. Head, thorax, abdomen, legs and feet thickly white pruinose, but the ground color showing through; face moderately wide, wholly pollinose, this pollen yellow in the middle, reaching the orbits at the suture, sides of upper part narrowly, below the suture widely white pollinose, sonsetimes the yellow pollen covers most of upper part and extends onto the inner part of the palpi; palpi with snow white pollen, each nearly as large as upper part of face; antennae wholly yellow, small, arista whitish; orbital cilia white, rather long on the sides; occiput, front, thorax and abdomen reddish coppery, posterior margins of abdominal segments sometimes green ; bristles of thorax small, black; hairs of ahdomen very short, white; pleura and coxae black with ground color nearly concealed with white pollen, tips of coxae yellow; hypopygium small, with a long, straight, black appendage extending forward under the abdomen and small yellowish appendages inside of this long one; femora, tibiae and tarsi pale yellow, last two joints of all tarsi blackish; the minute hairs on all femora and tibiae white, the small bristles on tibiae black; fore tibiae with a row of long white hairs on upper surface, which are as long as diameter of tibiae and extend to fourth tarsal joint, becoming shorter towards the end; apical joint of middle tarsi very slightly widened; pulvilli not enlarged ; joints of fore tarsi as 20-8-6-5-7 ; of middle ones as 32-14-9-6-6; joints of posterior pair as 25-19-11-6-7.

A comparison of earthquake damage areas as a function of magnitude across the United States

1993 ◽  
Vol 83 (4) ◽  
pp. 1064-1080 ◽  
Author(s):  
G. A. Bollinger ◽  
M. C. Chapman ◽  
M. S. Sibol
Keyword(s):  
United States ◽  
North America ◽  
Ground Motion ◽  
Epicentral Distance ◽  
The United States ◽  
Western United States ◽  
Eastern North America ◽  
Similar Response ◽  
Eastern United States ◽  
The West

Abstract This study investigates the relationship between earthquake magnitude and the size of damage areas in the eastern and western United States. To quantify damage area as a function of moment magnitude (M), 149 MMI VI and VII areas for 109 earthquakes (88 in the western United States, 21 in the eastern United States and Canada) were measured. Regression of isoseismal areas versus M indicated that areas in the East were larger than those in the West, at both intensity levels, by an average 5 × in the M 4.5 to 7.5 range. In terms of radii for circles of equivalent area, these results indicate that damaging ground motion from shocks of the same magnitude extend 2 × the epicentral distance in eastern North America compared to the West. To determine source and site parameters consistent with the above results, response spectral levels for eastern North America were stochastically simulated and compared with response spectral ordinates derived from recorded strong ground motion data in the western United States. Stress-drop values of 200 bars, combined with a surficial 2-km-thick low velocity “sedimentary” layer over rock basement, produced results that are compatible with the intensity observations, i.e., similar response spectral levels in the east at approximately twice their epicentral distance in the western U.S. distance. These results suggest that ground motion modeling in eastern North America may need to incorporate source and site parameters different from those presently in general use. The results are also of importance to eastern U.S. hazard assessments as they require allowance for the larger damage areas in preparedness and mitigation programs.

Appalachian Orogen in Canada

1979 ◽  
Vol 16 (3) ◽  
pp. 792-807 ◽  
Author(s):  
Harold Williams
Keyword(s):  
Continental Margin ◽  
Eastern North America ◽  
Early Paleozoic ◽  
The West ◽  
Late Precambrian ◽  
Northwest Africa ◽  
Iapetus Ocean ◽  
History Of ◽  
Appalachian Orogen ◽  
Andean Type

The Appalachian Orogen is divided into five broad zones based on stratigraphic and structural contrasts between Cambrian–Ordovician and older rocks. From west to east, these are the Humber, Dunnage, Gander, Avalon, and Meguma Zones.The westerly three zones fit present models for the development of the orogen through the generation and destruction of a late Precambrian – Early Paleozoic Iapetus Ocean. Thus, the Humber Zone records the development and destruction on an Atlantic-type continental margin, i.e., the ancient continental margin of Eastern North America that lay to the west of Iapetus; the Dunnage Zone represents vestiges of Iapetus with island arc sequences and mélanges built upon oceanic crust; and the Gander Zone records the development and destruction of a continental margin, at least in places of Andean type, that lay to the east of Iapetus.The Precambrian development of the Avalon Zone relates either to rifting and the initiation of Iapetus or to subduction and a cycle that preceded the opening of Iapetus. During the Cambrian Period, the Avalon Zone was a stable platform or marine shelf.Cambrian–Ordovician rocks of the Meguma Zone represent either a remnant of the continental embankment of ancient Northwest Africa or the marine fill of a graben developed within the Avalon Zone.Silurian and younger rocks of the Appalachian Orogen are mixed marine and terrestrial deposits that are unrelated to the earlier Paleozoic zonation of the system. Silurian and later development of the orogen is viewed as the history of deposition and deformation in successor basins that formed across the already destroyed margins and oceanic tract of Iapetus.

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