The Role of Seismic Refraction Data for Studies of the Origin and Evolution of Continental Rifts

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Olsen, K.H., 1983. The role of seismic refraction data for studies of the origin and evolution of continental rifts. In: P. Morgan and B.H. Baker (Editors), Processes of Continental Rifting. Tectonophysics , 94: 349–370. Universal attributes of continental rift systems are crustal extension with associated asthenospheric upwelling or modification of the mantle beneath the rift axis. Continental rifting is thus greatly controlled, if not driven, by geodynamic processes in the lower lithosphere. Seismic refraction profiling is a technique for obtaining high-resolution data on structures, seismic velocities, and petrologic conditions in the deep crust and upper mantle. Status of presently available seismic refraction data in four major Cenozoic continental rift systems (Rhinegraben of central Europe, Rio Grande rift of southwestern United States, Baikal rift of Eastern Siberia, and Kenya rift of East Africa) is reviewed in the light of extent of coverage in area and depth, reliability of velocity measurements, and outstanding structural and geodynamical problems that remain unanswered for each system. Evidence of crustal thinning, anomalous mantle at the Moho, as well as shallow and midcrustal velocity anomalies exist in all four examples. The Rhinegraben is the best constrained system from the point of view of seismic structure models. Seismic refraction structure data for the Kenya rift are sparse and raise more questions than answers. Since extensive geological, volcanological, and petrological data available for the East Africa system usually make it the standard for models of continental rifting, modern, high-resolution, deep seismic refraction profiles in Kenya are urgently needed in order to advance understanding of basic continental rifting processes.