A COMPREHENSIVE SEISMIC INVESTIGATION OF THE MID-CONTINENT RIFT FROM USARRAY AND SPREE

The mid-continent Rift (MCR) in North America is a failed Precambrian rift belt, filled by large volume of ~ 1.1 Ga old intrusive rocks that gives rise to the most prominent gravity and magnetic anomalies within the North America craton. Neither the mechanism that initiated the rifting process and produced the large volume of igneous rocks nor the cause of the later compressional episode that closed the rift are fully understood. Recent deployments of the Earthscope/USArray and the SPREE flexible array experiment enable us to perform a comprehensive seismic investigation of the crustal and uppermost mantle structure in the vicinity of the MCR including the part that lies in the southern Superior craton, and provides a better understanding of MCR geology. In this presentation, we introduce the latest maps of surface wave speeds generated from both ambient noise and teleseismic earthquakes, as well as Rayleigh wave vertical-to-horizontal (H/V) amplitude ratios. By combining these surface wave data sets with receiver functions, a refined seismic model for the MCR is constructed. The complementarity of various seismic observables assists in obtaining an unbiased shear velocity structure of the crustal and mantle beneath the MCR and surroundings. In particular, the joint Bayesian Monte-Carlo inversion finds a thickened crust and gradient Moho structure beneath the MCR, perhaps indicating crustal under-plating associated with the opening of the rift.