Ancient rifting zones in eastern North America revealed by the ambient noise surface wave tomography

We use the surface waves extracted from the cross-correlation of ambient noise data to invert for the group velocity structure in eastern North America. Stations of two regional seismic networks (networks deployed to monitor the New Madrid Seismic Zone and the eastern Tennessee seismic zone, respectively), together with the stations of national seismic network, greatly improve the ray coverage compared to earthquake waves. The short period (T=5 sec) group velocity map shows strong correlations with the depth to the Precambrian basement and appears to be positively correlated with the gravity. The long period (T=15 sec) group velocity map shows strong correlations with the regional geology. The most spectacular features are the prominent low velocity anomalies associated with the three arms of the triple junction located at the border of Oklahoma and Texas. The western arm of the triple junction (i.e. the Oklahoma Aulacogen) perpendicularly intersects a linear low velocity belt (LVB) possibly associated with the south portion of the Mid-continent rift. The eastern arm extends along the collision belt of the Ouachita orogeny to meet the south tip of the Appalachian Mountains. The nearly north-south striking LVB in the western Mississippi embayment is associated with the Reel Foot rift. However, the LVB extends further northward to the Great Lakes region and this feature is not present on the gravity anomaly map. One LVB extending from the Great lakes region southeastward to Michigan basin is possibly associated with the east portion of the Mid-continent rift. Those LVBs appear to be correlated with the high gravity anomalies that are associated with the rift belts.