Geologic structures related to New Madrid earthquakes near Memphis, Tennessee, based on gravity and magnetic interpretations

New inversions of gravity and magnetic data in the region north of Memphis, Tennessee, and south of latitude 36 degrees define boundaries of regional structures and igneous complexes in the upper crust. Microseismicity patter ns near interpreted boundaries suggest that igneous complexes influence the locations of microseismicity. A weak seismicity cluster occurs near one in trusion (Covington pluton), at the intersection of the southwest margin of the Missouri batholith and the southeast margin of the Reelfoot rift. A nar row seismicity trend along the Reelfoot rift axis becomes diffuse near a se cond intrusion (Osceola intrusive complex) and changes direction to an area along the northwest flank of the intrusion. The axial seismicity trend als o contains a tight cluster of earthquakes located just outside the Osceola intrusive complex. The mechanical explanation of the two seismicity pattern s is uncertain, but the first cluster may be caused by stress concentration due to the high elastic stiffness and strength of the Covington intrusion. The spatially changing seismicity pattern near the Osceola complex may be caused by the preceding factors plus interaction with faulting along the ri ft axis. The axial seismicity strand itself is one of several connected and interacting active strands that may produce stress concentrations at stran d ends and junctions. The microseismicity clusters at the peripheries of th e two intrusions lead us to conclude that these stress concentrations or st ressed volumes may be locations of future moderate to large earthquakes nea r Memphis. Published by Elsevier Science B.V.