North American Lithospheric Discontinuity 1 Structure Imaged By Ps and Sp Receiver Functions 2 3 4 5 6 7

David L. Abt, Karen M. Fischer, Scott W. French, Heather A. Ford, Huaiyu Yuan, 8 and Barbara Romanowicz 9 10 Department of Geological Sciences, Brown University, Providence, Rhode Island, USA 11 Berkeley Seismological Laboratory, University of California-Berkeley, Berkeley, California, USA 12 Now at: ExxonMobil Exploration Company, Houston, Texas, USA 13 Now at: Department of Earth and Planetary Science, University of California-Berkeley, Berkeley, California, 14 USA 15 16