Kinematics of the Sierra Nevada and Oregon Crustal Blocks

Northern California contains the intersection of the NW moving Sierra Nevada block and the clockwise rotating Oregon block. Adding to the tectonic complexity of the region are the interactions of the Pacific plate, Basin and Range, California Coast Ranges, Mendocino fracture zone, San Andreas fault and the Juan de Fuca plate. Our research focuses on how the interactions of these features influence the motions of the Oregon and Sierra Nevada blocks. We processed Global Positioning System (GPS) data collected during the 1998 and 1999 National Geodetic Survey High Accuracy Reference Network (HARN) surveys and by us in 2003. Our preliminary analysis of the velocity field indicates that the Oregon crustal block is rotating clockwise relative to the Sierra Nevada block around a pole approximately west of the Mendocino Triple Junction. Our future work involves finding a more exact location of the relative pole rotation between the blocks, the degree of rotation, and how this motion is being taken up.