9304555 Langston This research is to conduct a study of the crustal and upper mantle structure in Tanzania by means of passive-source seismic recording with the PASSCAL array and by means of analysis of gravity data. The existence of thick, depleted mantle lithosphere beneath ancient continental regions forms the basis of the model for deep continental structure. A principal assertion of this model is that cratonic nuclei with their lithospheric keels are true islands of tectonic stability within a generally mobile and less stable lithosphere. This work will test this model of deep continental structure by examining the stability of cratonic lithosphere in an area of active tectonism, East Africa. The cratonic lithosphere in East Africa (the Tanzania Craton) has been subjected to Cenozoic extensional tectonism, providing a unique opportunity to determine if deep cratonic structure can "survive" an extensional event which has thermally and mechanically disrupted adjacent younger lithosphere. Similar structures in the U.S. are the sites of current seismic activity and these results will bear on the mechanism of the earthquake generating structure. This research is a component of the National Earthquake Hazard Reduction Program. ***
