Potential seismic hazards and tectonics of the upper Cook Inlet basin, Alaska, based on analysis of Pliocene and younger deformation

The Cook Inlet basin is a northeast-trending forearc basin above the Aleuti an subduction zone in southern Alaska. Folds in Cook Inlet are complex, dis continuous structures with variable shape and vergence that probably develo ped by right-transpressional deformation on oblique-slip faults extending d ownward into Mesozoic basement beneath the Tertiary basin. The most recent episode of deformation may have began as early as late Miocene time, but mo st of the deformation occurred after deposition of much of the Pliocene Ste rling Formation. Deformation continued into Quaternary time, and many struc tures are probably still active. One structure, the Castle Mountain fault, has Holocene fault scarps, an adjacent anticline with flower structure, and historical seismicity, If other structures in Cook Inlet are active, blind faults coring fault-propagation folds may generate M-w 6-7+ earthquakes. D extral transpression of Cook Inlet appears to have been driven by coupling between the North American and Pacific plates along the Alaska-Aleutian sub duction zone, and by lateral escape of the forearc to the southwest, due to collision and indentation of the Yakutat terrane 300 km to the east of the basin.