Seismicity of the New Madrid seismic zone derived from a deep-seated strike-slip fault


A conceptual three-dimensional flower structure model of strike-slip faulting is proposed to explain the occurrence of earthquakes in the New Madrid seismic zone (NMSZ) and to illustrate the potential rupture faults for the 1811-1812 earthquake sequences. The proposed NMSZ model is based on elastic dislocation theory and concepts of material failure under a stress field. Using a conceptual model of a strike-slip subsidiary fault array, we identify tectonic features (geological structures) that are oriented properly relative to regional stresses and classify the regions where stresses might be expected to be amplified. The brittle upper crust in the vicinity of the NMSZ is modeled as a uniform overburden with a horizontal-basal surface, which rests on a horizontal ductile lower crust that is cut by a vertical, northeast-striking right-lateral strike-slip shear zone. We acknowledge that many favorably oriented preexisting faults have been exploited as components of the flower structure. The brittle overburden material is subject to simple shearing stress parallel to the deep-seated lower crustal shear zone, and preexisting faults of the Reelfoot rift system give the upper crust a mechanical anisotropy (planes of weakness striking northeast) that is the correct orientation for development of P shear faults. The deep-seated fault movement deforms the overlying upper crust that controls the structural geometry, the modern seismicity, and the large earthquake sequences in the NMSZ. The three-dimensional NMSZ model of faulting developed in this study shows that the Bootheel and Big Creek lineaments, inferred to be two subparallel P shear faults rooted in a deep-seated fault in the lower crust, are significant in shaping the geometry of the NMSZ. These series of faults produce a large-scale flower structure in cross section. The proposed NMSZ model uses the intersections of the deep-seated fault and the two subparallel P shear faults for the locations of the 1811 and 1812 earthquakes. The model gives rise to a predictable pattern of surface deformation that is in good agreement with the observed seismicity patterns in the region.

Publication Title

Bulletin of the Seismological Society of America