95 The Geological Society of America Special Paper 509 2015 Regional seismic-wave propagation from the M5.8 23 August 2011, Mineral, Virginia, earthquake Fred F. Pollitz Walter D. Mooney U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, California 94025, USA ABSTRACT The M5.8 23 August 2011 Mineral, Virginia, earthquake was felt over nearly the entire eastern United States and was recorded by a wide array of seismic broadband instruments. The earthquake occurred ~200 km southeast of the boundary between two distinct geologic belts, the Piedmont and Blue Ridge terranes to the southeast and the Valley and Ridge Province to the northwest. At a dominant period of 3 s, coherent postcritical P-wave (i.e., direct longitudinal waves trapped in the crustal waveguide) arrivals persist to a much greater distance for propagation paths toward the north- west quadrant than toward other directions; this is probably related to the relatively high crustal thickness beneath and west of the Appalachian Mountains. The seismic surface-wave arrivals comprise two distinct classes: those with weakly dispersed Rayleigh waves and those with strongly dispersed Rayleigh waves. We attribute the character of Rayleigh wave arrivals in the first class to wave propagation through a predominantly crystalline crust (Blue Ridge Mountains and Piedmont terranes) with a relatively thin veneer of sedimentary rock, whereas the temporal extent of the Rayleigh wave arrivals in the second class are well explained as the effect of the thick sedimentary cover of the Valley and Ridge Province and adjacent Appalachian Plateau province to its northwest. Broadband surface-wave ground velocity is ampli- fied along both north-northwest and northeast azimuths from the Mineral, Virginia, source. The former may arise from lateral focusing effects arising from locally thick sedimentary cover in the Appalachian Basin, and the latter may result from directiv- ity effects due to a northeast rupture propagation along the finite fault plane. Pollitz, F.F., and Mooney, W.D., 2015, Regional seismic wave propagation from the M5.8 23 August 2011, Mineral, Virginia, earthquake, in Horton, J.W., Jr., Chapman, M.C., and Green, R.A., eds., The 2011 Mineral, Virginia, Earthquake, and Its Significance for Seismic Hazards in Eastern North America: Geological Society of America Special Paper 509, p. 95–116, doi:10.1130/2014.2509(06). For permission to copy, contact editing@geosociety.org. © 2014 The Geological Society of America. All rights reserved. INTRODUCTION The M5.8 23 August 2011 Mineral (Virginia, USA) earthquake is the largest event to have struck Virginia since 1897. The seismic waves generated by the event were felt as far away as New York and Montreal and were recorded by regional broadband instruments (Fig. 1). Observations of broadband seismic waveforms as much as 900 km from the epicenter complement observations of felt intensi- ties (Hough, 2012) and provide a unique opportunity to characterize the regional seismic-wave propagation, test current models of the seismic structure, and better understand the factors that lead to vari- able seismic-wave amplitude and duration. on September 23, 2015 specialpapers.gsapubs.org Downloaded from