RECEIVER FUNCTION ANALYSIS OF VARIATIONS IN CRUSTAL THICKNESS AND VP/VS ACROSS THE SOUTHERN APPALACHIANS FROM SESAME BROADBAND DATA

The Southeastern Suture of the Appalachian Margin Experiment (SESAME) is an investigation of the relationship between lithospheric structure and Paleozoic collisional tectonics and Mesozoic rifting. The broadband array will ultimately consist of approximately 85 seismometers along three profiles. We have deployed 34 instruments in western Georgia along a north-south trending profile that extends from Florida to the Blue Ridge Mountains. Eight additional seismometers were deployed along a northwest trending profile near the Georgia-South Carolina border. A second north-south trending profile will be deployed in eastern Georgia in May of 2012. Instruments are more densely spaced over the location of the proposed Alleghanian suture between Laurentian crust and the Suwanee terrane. This allows for greater accuracy interpreting the nature of the collision and origin of the Brunswick Magnetic Anomaly (BMA). We use teleseismic receiver functions from several stations along the existing north-south profile to estimate Moho depth and average crustal Vp/Vs. Initial results for one station in the western Blue Ridge indicate crustal thickness of 53-55 km and Vp/Vs of 1.72-1.74. Preliminary estimates from stations in the Piedmont indicate crustal thickness of 43-45 km and Vp/Vs of 1.76-1.80. The Zhu-Kanamori analysis is based on a limited number of teleseismic events, but the values are nonetheless consistent with earlier broadband and wide-angle data that show an increase in crustal thickness to the north and west of the coastal plain. Although the northwestward increase in crustal thickness shows that the mountains are supported by a crustal root, the configuration of the basal detachment is planar with a gentle southeastward dip. This suggests that the root either predates Alleghanian thrusting or formed by mechanisms unrelated to lithospheric flexure.