Chapter 27: Reflection seismic studies of crustal structure in the eastern United States

Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings

“…8) are consistent with traveltimes for events interpreted as Moho refl ections on reprocessed COCORP lines (Phinney and Roy-Chowdhury, 1989;Cook and Vasudevan, 2006). Conversion of two-way traveltimes (11.5-11.8 s) to depth using the velocity models summarized in Table 1 yields Moho depths of 37-39 km for the Carolina terrane and a slightly greater depth of 39-40.5 km (12.5-13 s) for the southeastern fl ank of the Inner Piedmont (Cook and Vasudevan, 2006).…”

“…According to the latter interpretation, a gently dipping zone of weaker refl ections marks the southeastward continuation of the detachment beneath the coastal plain (Cook et al, 1979;Harris and Bayer, 1979). Interpretations based on extensive reprocessing of COCORP lines 1 and 5 suggest that rocks of the Kiokee and Charlotte belts occur as a stack of thrust sheets above thinned, rift-stage Grenville crust (Phinney and Roy-Chowdhury, 1989). Further reprocessing has enhanced the continuity of refl ections within basement rocks and extended coverage of the Moho northwestward beneath the southeast fl ank of the Inner Piedmont (Cook and Vasudevan, 2006).…”

Global geoscience transect 8: Quebec-Maine-Gulf of Maine transect, southeastern Canada, northeastern United States of America

“…All of these observations support the interpretation of extensive plastic flow in the lower crust, in the direction of ultimate crustal rupture. Examples of the rise of Moho beneath the footwall of listric faults and the development of a well-laminated lower crust are numerous on seismic reflection profiles from the northern Appalachians (Phinney and Roy-Chowdhury, 1989;Marillier and others, 1989), although determinations of the refraction velocity changes are lacking. A conspicuous example occurs beneath the Franklin rift basin at about kilometer 675 on the interpretive cross section.…”

“…A conspicuous example occurs beneath the Franklin rift basin at about kilometer 675 on the interpretive cross section. Phinney and Roy-Chowdhury (1989, fig. 12d) give another good example from the eastern end of line USGS 36 on the Long Island platform beneath the early Mesozoic Nantucket rift basin.…”

“…12d) give another good example from the eastern end of line USGS 36 on the Long Island platform beneath the early Mesozoic Nantucket rift basin. If th~ large normal displacements on mapped faults are consider~d (Lyons and others, 1991), COCORP line 6 in southwestern New Hampshire beneath the Bronson Hill anticlinorium and Central Maine synclinorium (Phinney and Roy-Chowdhury, 1989, fig. 16) can be Interpreted.…”