A Wide-Angle Reflection/Refraction Piggyback of the EDGE Chesapeake Bay Transect

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The EDGE program (supported by joint Earth and Ocean Sciences funding) is scheduled to collect its second transect of a continental margin in September, 1990 seaward of Chesapeake Bay. Drs. Holbrook and Purdy will simultaneously collect and process wide-angle ocean-bottom refraction data from a second vessel in a "piggy-back" experiment. Their plan is to complement and work in an iterative fashion with the vertical-incidence MCS data in order to: 1) derive accurate 2D velocities across the margin; 2) record lower crust and Moho arrivals; and 3) undershoot a carbonate buildup known to occur deep in the sedimentary section. These data will allow Holbrook and Purdy to: 1) determine Moho geometry; 2) determine the nature of rift-stage crust; 3) improve understanding of the nature of bounding continental and oceanic crust; 4) approach an understanding of the source of the East Coast Magnetic Anomaly; and 5) measure the depth to crystalline basement. Through ray-trace modeling based on existing knowledge of the region, these researchers have developed an optimal design of in which they plan to deploy 9 OBHs (5 digital - 1 day recording length with 120 db range; 4 analog, 10 days, 80 db) along 2 scheduled dip lines that cross known rift-stage basins.