Three-dimensional crustal structure of eastern North America extracted from ambient noise

摘要

Group velocity dispersion curves of surface waves extracted from ambient seismic noise are inverted to find 3-D shear wave structure of the crust beneath eastern North America. The 3-D model consists of one sediment layer and another six layers with fixed depths at 5, 7.5, 10, 15, 25, and 43 km. Velocities of the seven layers together with the thickness of the sediment layer are determined by the simulated annealing method. We found that almost all failed ancient rifting events (e.g., the Reelfoot rift, Ouachita triple junction, and the Midcontinent rift) and rifting related events (e.g., the Ozark uplift and the Nashville dome) are associated with high-velocity bodies in the middle and lower crust. Our results also suggest the existence of a triple junction-like high-velocity body centered around the New Madrid and the Wabash Valley seismic zones with the Reelfoot rift, the Ozark uplift, and the Nashville dome being on its southwestern, northwestern, and southeastern arms, respectively. We also found that the western limb of the Midcontinent rift (MCR) extends southwestward to western Oklahoma and Texas, and the eastern limb of the MCR extends southeastward into western Ohio. The Appalachian Mountains are characterized by high-velocity upper crust underlain with relatively low velocity middle and lower crust. All major seismic zones are associated with either divergent or convergent events. The New Madrid seismic zone and Wabash Valley seismic zone are clearly associated with the failed Reelfoot rift. Both the eastern Tennessee seismic zone and Ouachita Orogen seismic zone are located along convergent boundaries.