Preliminary aeromagnetic, gravity, and generalized geologic maps of the USGS Basin and Range-Colorado Plateau transition zone study area in southwestern Utah, southeastern Nevada, and northwestern Arizona (the BARCO Project)

1989 ◽  
Author(s):  
H.R. Blank ◽  
R.P. Kucks
Keyword(s):  
Transition Zone ◽  
Colorado Plateau ◽  
Basin And Range ◽  
Geologic Maps

Signal penetration In the COCORP Basin and Range‐Colorado Plateau survey

Geophysics ◽  
1986 ◽  
Vol 51 (5) ◽  
pp. 1050-1055 ◽  
Author(s):  
James R. Mayer ◽  
Larry D. Brown
Keyword(s):  
Transition Zone ◽  
Colorado Plateau ◽  
Sedimentary Cover ◽  
Basin And Range ◽  
Eastern Basin ◽  
Arrival Times ◽  
Reflection Data ◽  
Temporal Decay ◽  
On Line ◽  
Seismic Sections

Seismic sections from COCORP’s 1982 survey from the eastern Basin and Range to the Colorado Plateau of central Utah exhibit distinct cutoff times after which reflections are rare to nonexistent. In the eastern Basin and Range, this cutoff time is approximately 11 s (33 km), but beneath the central Colorado Plateau it exceeds 15 s (45 km). These depths appear to correspond to the base of the crust (Moho), with the lack of reflections from greater depths indicating mantle homogeneity. In general, absence of deeper reflections may be due either to geologic homogeneity or to lack of signal penetration. COCORP line 3 in the Colorado Plateau‐Basin and Range transition zone shows that variations in penetration are significant. On line 3 few reflections are evident below the structurally complex sedimentary cover, which extends to only 4 s (8 km), and virtually none are identifiable later than 7 s (21 km). Lateral variations in the temporal decay of source‐generated energy, together with estimates of corresponding ambient noise levels, infer that limited signal penetration, rather than geologic homogeneity, causes the lack of subsedimentary reflections within the transition zone. Deep reflections, if any, from beneath the westernmost Colorado Plateau appear to be masked by unusually high local environmental noise. In contrast, continued decay of source‐generated energy at traveltimes significantly greater than Moho arrival times within the Basin and Range and Colorado Plateau suggests (though it cannot confirm) that the underlying mantle is seismically transparent. Variations in signal penetration, such as those documented here, severely constrain interpretations of nonreflective zones in deep reflection data and should be a standard estimation in any interpretational procedure.

Seismotectonics of the Grand Wash Arizona Area

2019 ◽  
Vol 109 (6) ◽  
pp. 2277-2287 ◽  
Author(s):  
David S. Brumbaugh
Keyword(s):  
Transition Zone ◽  
Colorado Plateau ◽  
Basin And Range ◽  
Gravitational Potential Energy ◽  
Clockwise Rotation ◽  
Wash Basin ◽  
Structural Style ◽  
Extensional Stress ◽  
Basin Area ◽  
East West

Abstract The Grand Wash basin is located in northwest Arizona adjacent to the physiographic boundary of the Colorado plateau. The area is well mapped geologically and is geophysically similar to the Basin and Range and Transition Zone in structural style and history. The occurrence of a rare swarm of earthquakes in 2016 in the basin area served as an opportunity to perform a seismotectonic analysis of the Grand Wash basin. Results of the analysis indicate the basin is presently undergoing mild east west extension. The east west extension and associated seismicity of the swarm are here suggested to be the result of stress created by negative gravitational potential energy of the Colorado plateau relative to the lower Basin and Range and Transition Zone. This is suggested by the clockwise rotation of the extensional stress at about 36° N on both the plateau and the Basin and Range and Transition zone.

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