Seismotectonic maps in the vicinity of the lower Wabash Valley, Illinois, Indiana, and Kentucky - Digital Spatial Database: Structure contours on Cambrian-Precambrian unconformity

This cover contains structure contours of the elevations of the
unconformity at the Cambrian-Precambrian boundary.
These data were contributed by
Glenn Bear of Indiana University as part of the work on
his doctoral thesis. The southern part of the map was produced by
James Drahovzal of the Kentucky Geological Survey and merged with
Bear's map of the rest of the map area and beyond. Use of public and
proprietary seismic
reflection and well data were used to define the
structure. Units are in thousands of feet below sea level.
A prominent east-west structure in the southern half of the map
area is the western end of the Rough Creek Graben. At its deepest
point the unconformity is more than 30,000 ft
(9,100 m) below sea level. Faulted strata at this depth mean that
the Rough Creek Fault System penetrates to hypocentral depths.
At the western edge of the map area, the graben bends to the
southwest into the Reelfoot Rift and becomes more shallow. North of
the Rough Creek Graben, and extending northward along the Wabash
River, is the Wabash Valley Fault System. This fault system cuts an
elliptical low in the unconformity. Some of the structure contours
show horizontal offsets at depths that are opposite to the offsets
expected from the known normal slip on the faults. Some authors
interpret this as evidence of strike slip motion on these faults.
This cover contains all the contours including the extents outside
the map area. "bcontours" is clipped to the map area.