PROGRESS TOWARDS A GULF OF MEXICO PASSIVE MARGIN EXPERIMENT

Interdisciplinary geoscientific study of passive continental margins is an important scientific priority because of many unanswered questions, for example: What is the composition of transitional crust and how does it form? What is the nature of lithospheric mantle beneath the transitional crust? What is the strength and direction of asthenospheric flow beneath and across the transition? How does transitional crust and lithosphere control subsidence and thermal structure of the passive margin, as observed from the history of sedimentation? How do active rift zones and new sites of seafloor spreading become passive margins? In addition, a better understanding of passive margins is important to US national interests because it is a hydrocarbon storehouse and is a region of significant geohazards. The offshore Gulf of Mexico is the one part of the United States where exploration is finding significant new hydrocarbon reserves. It is likely that most of the world's undiscovered supplies of oil and gas will be found beneath passive continental margins. Geohazards such as tsunamis, hurricaines, and subsidence are associated with passive margins, potentially affecting the 19 US states with 132 million people (44% of the US population) that border passive margins. We continue to push for a national geoscientific experiment to study US passive margins, both offshore and onshore. It is imperative to begin studying US passive margins in the next few years because the effort should take advantage of the major deployment of seismometers by NSF's Earthscope Transportable Array (aka “Bigfoot”), which will reach the westernmost US passive margin (Texas & Louisiana) in 2009-2010. We have begun a dialog with NSF-EarthScope and NSF-MARGINS to endorse the effort to study the US passive margins. The first experiments should be planned for the westernmost Gulf of Mexico in 2009 and 2010. What we learn about how best to study passive margins there can be applied further east in subsequent experiments as Bigfoot steps east. We have already made progress, completing a shear-wave splitting experiment for the TX-OK-AR-LA region (Gao et al., in press, Geospheres) and starting a new deployment of passive seismometers SE from the Llano uplift towards the Texas Gulf coast; what has been done and plans for the future will be emphasized in this presentation.