Jacobi and his students developed rapid and rigorous methodologies to characterize fractures. They analyze digital images of the fracture patterns with the usual structural methods, but also with fractal and more advanced analyses, such as geostatistics. They have analysed fracture interactions in order to undertsand the differential stress involved at the time of fracture generation. The geostatistical and fractal fracture analyses, coupled with lineament identification on remotely sensed data, allow extension of fracture patterns into covered regions. This ability to extend fracture patterns into covered regions is extremely important in all aspects of Jacobi’s research.
Fracture scangrids (Figure 1a) (Figure 1b) and scanlines have contributed to our digital library of 100,000+ fractures in the Appalachian Plateau. These data have allowed us to define and recognize Fracture Intensification Domains (FIDs) (Figure2a) (Figure2c) Seismic reflection lines, stratigraphy, and lineament study demonstrate that FIDs are indicators of faults at depth (or in nearby covered areas). (Figure 3a) These data are also the basis for studies of interactive fracture geometries LINK to FIG 4 (“under construction”) and development of fracturing/faulting histories on the Appalachian Plateau. We have found that Precambrian (intra-Grenvillian) suture faults were reactivated over and over through the Paleozoic--first during Iapetan opening as listric rift faults, then as thrusts during Taconic collsion; they continued motion during Silurian, during the Acadian and Alleghanian orogenies, and some are seismically active now.
Other faults, such as the Alleghanian thrust faults, have a much shorter history. These latter faults have resulted in zones of pencil cleavage, scaly cleavage, and bedding-restricted tectonic melange. LINK TO FIG 5 (“under construction”) In one creek, we found 7 bedding-restricted thrust “flats” stacked in about 200’ of section! Our highly detailed mapping has shown the Appalachian Plateau has all the complexity and excitement of the “big boys” out in the fold and thrust belt--its just that the fold and thrusts here have an added challenge of being subtle.
Photograph by Gerry Smith Photograph by Travis Nelson
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