Crustal Structure in the Southern Appalachians: A Comparison of Results Obtained from Broadband Data and Three-Component, Wide-Angle P and S Reflection Data

Abstract

Abstract Data for two broadband stations and three-component recordings of wide-angle reflections are used to constrain the velocity structure and depth to Moho beneath a portion of the southern Appalachians. Broadband data from the U.S. National Seismic Network (USNSN) station GOGA (Carolina terrane/Inner Piedmont boundary), constrained by average crustal V P derived from wide-angle data, suggest that crustal thickness for individual back azimuths ranges from 41 to 43 km. This is consistent with wide-angle estimates of 38–40 km for the Carolina terrane and 40–45 km for the Inner Piedmont. Average crustal V P / V S is 1.72–1.76, compared with 1.74–1.76 derived from SmS/PmP travel-time ratios for the Carolina terrane. The results for station MYNC (Blue Ridge Mountains), again constrained by wide-angle data, suggest a crustal thickness of 50–52 km for individual back azimuths. Average V P / V S is 1.75–1.77. The range in average V P / V S derived from wide-angle data is broader (1.74–1.80), indicating variations in average composition across the Blue Ridge Mountains, as suggested by gravity data. Large-amplitude direct P and Ps arrivals on transverse-component receiver functions also indicate significant lateral variations in structure beneath MYNC. Comparison of migrated images underscores the differences in resolution for single-station broadband data and wide-angle data recorded with short-aperture arrays. Ps waveforms for MYNC show a double peak. The earlier peak migrates to depths of 48.5–51 km, in agreement with wide-angle events interpreted as Moho. For the later peak, migrated depths range from 60 to 65 km, compared with 59–68 km for peaks in wide-angle reflectivity observed for the Blue Ridge Mountains. The two methods yield consistent estimates for crustal thickness that lend support to models that predict a significant crustal root beneath the high elevations of the Blue Ridge.