Project Summary Understanding passive margins and the continental-oceanic transition has far-reaching economic and societal implications:

• They hide most of the undiscovered hydrocarbon reserves of the USA, and are excellent sites for sequestering carbon scrubbed from the atmosphere. This economic potential invites collaboration between industry and academia.

• Natural hazards of hurricanes, tsunamis, and rapid subsidence also make it imperative to better understand passive-margin evolution.

• Economic and societal concerns provide natural avenues for explaining the importance of this and other "hypothesis-driven" geoscientific research efforts to US taxpayers and political leaders, especially because much of the US population lives on or near our passive margins.

We are conducting a pilot study that consists of a six-month deployment of five three-component broadband stations in a portion of the Gulf Coast Plain for which there is already high-quality active-source reflection data, some vintage refraction data, and a proposed geophysical model to be tested (Mickus and Keller, to be submitted). This deployment will allow us to (1) apply, validate, and fine-tune receiver function techniques for imaging the crust and upper mantle beneath deep sediments and (2) test a geophysical model proposed for this region.

The need for such a pilot experiment arises from two sources:

• The importance of studying passive-as well as active-margins in order to understand continental evolution and to motivate students and the public who do not live near active margins and

• Difficulties in applying seismic analysis techniques to passive data recorded over thick sedimentary sequences, which typically exist in passive margins.

  The results of the pilot study proposed here will be critical to the design of an effective and cost-efficient proposal to learn how continental and oceanic lithosphere merge and, hopefully, to better reconstruct the extensive tectonic history of this passive margin.