THE NATURE OF THE MOHO BENEATH THE SOUTH GEORGIA BASIN FROM NEAR-VERTICAL REFLECTIONS

During March 2014 a deep crustal seismic profile was shot across the South Georgia basin, a failed Mesozoic rift basin in the southeastern U.S. The SUGAR (SUwanee suture and GA Rift) profile runs 300 km from north of Columbus, GA to the very northern part of Florida, crossing from the Carolina Terrane in the north to the coastal plain in the south. Eleven shots along the line were fired into an array of 1200 Texan seismographs.

Because of good coupling and relatively low attenuation many arrivals are seen from relatively small shots. These arrivals include Pg, Pn, and PmP, as well as strong S-wave arrivals from many of the shots. Most shots were 227 kg in size, with some shots only 45 kg in size. All shots were shot in large diameter boreholes, so that more efficiency could be obtained from a limited charge size.

The line was designed as a seismic tomography experiment, however we have also processed it as a single-fold, near-vertical reflection profile. Deep reflections are observed along much of the line. These are interpreted as Moho reflections with two-way traveltimes of 11 to 12 seconds two-way traveltime. To some extent these reflections coincide with near-vertical reflections seen in COCORP data collected 30 years ago. We present the results of reflection processing of refraction data and the processing flow used.