CRUSTAL STRUCTURE OF THE MID-ATLANTIC, EASTERN UNITED STATES

Our limited knowledge of the composition, crustal structure and deformation of plate interiors hinders our ability to appropriately assess the mechanisms responsible for and the hazard associated with intraplate seismicity. To characterize the crustal structure of the Mid-Atlantic US and understand its relationship with seismicity we generated receiver functions for 103 USArray TA and permanent stations. Strong P-to-S conversions are observed along the Appalachian Plateau, Orogen and Piedmont. Sediments in the Coastal Plain result in receiver functions dominated by delayed phases and reverberations. Our analysis focuses on 78 stations not affected by sediments; future work will address alternate methods for Coastal Plain stations.

Crustal thickness generally increases from the Piedmont towards the Appalachian Orogen. A steep gradient occurs where the Piedmont transitions to the Valley & Ridge and crustal thickness increases from ~30 to 40 km over a short distance. Under the Valley and Ridge and the Plateau the crust is 44-50 km thick. The Moho morphology is variable throughout the orogenic belt across the transition from the Central to Northern Appalachian. The Central Appalachian undergo a gradual thickening of the crust towards the orogenic belt followed by thinner crust beneath the Plateau. This pattern changes near the Scranton gravity high where a region of 2-6 km thinner crust is observed at the northern terminus of the Valley & Ridge province. The northern part of our study area shows progressive crustal thickening from the coast towards the Plateau. Vp/Vs values generally range from 1.74-1.82, with larger values observed from southeastern PA to northern NJ. Our preliminary analysis of earthquake locations shows events are mostly concentrated in the region of strong lateral gradient in crustal thickness while the thicker orogenic crust appears to be relatively aseismic.