Wave conversions from earthquakes and a new velocity model for the South Carolina coastal plain

Abstract

Abstract Phase conversions from P to SV and from SV to P occur at a high impedance boundary near the surface in Charleston, South Carolina. Four arrivals (P, converted P, converted S, and S) are observed on three-component records of earthquakes in this area. Using arrival-time differences between paired arrivals of direct and converted phases, a shallow surface layer Vp/Vs ratio of 2.9 was determined. Applying the Wadati method to travel times derived at the base of the surface layer yields a Vp/Vs ratio in deeper layers of 1.73. Relocating earthquakes using this more appropriate velocity structure for direct and converted shear waves alters hypocentral parameters such that epicenters diverge and depths converge. It is inferred that these relocated earthquakes are not exclusively associated with a single seismogenic fault.