Seismotectonic maps in the vicinity of the lower Wabash Valley, Illinois, Indiana, and Kentucky - Digital Spatial Database: Geophysical lineaments

Lines in this cover show lineaments or boundaries of large lineaments interpreted from gravity and magnetic data. These lineaments are thought to reflect structures in the crust that may be related to earthquake generation or control of earthquake location.
The broad Paducah gravity lineament trends southeast across the SW corner of the map area. Hildenbrand and others (1996) have interpreted that the lineament represents numerous upper-crustal mafic intrustions. Within and west of the map area, small earthquakes are aligned with the NE edge of the lineament and their abundance decreases abruptly NE across the edge.
The Commerce geophysical lineament trends NE across the map area. Langenheim and Hildenbrand (1997) attribute the lineament to a mafic dike swarm of unknown age. Topographic lineaments, Quaternary offsets on mapped faults, igneous intrusions, and a few earthquakes align along the lineament.
The south-central magnetic lineament trends NW across the center of the map area and extends far beyond the map area in both directions. Hildenbrand and others (1996) interpret the lineament as a 40 km wide zone of high susceptibility intrusions of intermediate composition and probable Pc age. Heigold and Kolata (1993)suggest that the lineament may represent Precambrian Proterozoic terrane boundary. Seismicity south of the lineament (Reelfoot Rift) is greater than seismicity north of the boundary (Wabash Valley), but this boundary is located further to the south and trends more northerly than the south- central magnetic lineament. Present evidence implies that this lineament is the least likely to be causally related to modern seismicity.