Crustal Underplating Beneath the Mid-Continental Rift System Imaged by USArray and SPREE

Date: 4/25/2019

Time: 11:15 AM

Room: Pike

More than 10-years of USArray deployments together with Flexible Array deployments have enabled us to compile a suite of seismic observables for constructing sharp images of the lithosphere beneath the contiguous US, particularly the central and eastern parts. In this presentation, we discuss the latest results with USArray and SPREE (Superior Province Rifting EarthScope Experiment) data using a combination of multiple seismic observables including 1) Rayleigh wave phase/group speeds from ambient noise and teleseismic earthquakes, 2) receiver functions, and 3) Rayleigh wave horizontal-to-vertical ratios (H/V). These observables are combined through a Bayesian Monte Carlo algorithm to invert for a shear-velocity model of the lithosphere with associated uncertainties. The new seismic images confirm a finite-gradient/complex Moho discontinuity beneath the rift from receiver-function data and reveal additional lithospheric characteristics beneath the Precambrian failed rift. A lower crust-uppermost mantle anomaly near the Moho is characterized by a shear-velocity speed of ~4.0-4.2 km/sec, representing the crustal underplating associated with the initiation of the rift. The spatial distribution of this anomaly extends beyond the west arm of the rift. By incorporating SPREE and USArray data near the central-eastern US, we find that the underplating extends north to Lake Superior and east toward the Michigan basin. Incorporating these observed features, an estimate of the total volume of the Proterozoic underplating can be obtained.

Presenting Author: Weisen Shen

Authors