Seismicity of the southeastern United States

Abstract

abstract Review and analysis of the existing data base for southeastern United States earthquakes indicate that the spatial pattern of energy release can be interpreted to occur in zones both parallel (southern Appalachian seismic zone) and transverse (central Virginia and South Carolina-Georgia seismic zones) to the regional Appalachian structural trend. The temporal pattern, for events V ≦ Io ≦ VIII, can be expressed by the recursion relationship, log N = 3.01 − 0.59 Io. Felt areas are, in general, one order of magnitude greater than for similar west coast events. Their configuration is elliptical and aligned with regional structure, except in central Virginia and Alabama and in coastal South Carolina. These latter areas have circular or lobate felt areas that may be caused by differences in focal depths and/or focal mechanisms. A tentative local magnitude formula is developed that employs the vertical component of the short-period Lg phase. It appears that the regional attenuation characteristics of this phase are similar to those found by Nuttli (1973a) in the central United States.