Shear-wave splitting observations at the regions of northern Baja California and southern Basin and range in Mexico

Abstract

Recent installation of 3-component broadband digital stations around the Gulf of California allowed us to make shear wave splitting observation from records of 73 SKS and SKKS phases from 30 events recorded at 12 stations since January of 2001. Stations in the southern Basin and Range province yield upper mantle fast shear wave direction from NE-SW to E-W, consistent with both local direction of Miocene extension and North American absolute plate motion. The shear at the Pacific-North American plate limit seems to control tightly the anisotropy pattern of the closest station NE70. The anisotropic pattern along the Peninsular Range, east of the former trench between the North American plate and the now subducted Farallon plate, is almost uniform and is interpreted as asthenospheric flow induced by the sinking fragment of the Farallon plate although frozen anisotropy associated with in situ captured fragment of this plate cannot be ruled out. Copyright 2006 by the American Geophysical Union.