Present-Day Deformation in Northeastern California, Northwest Nevada and Southern Oregon

Abstract:

We use a newly expanded Global Positioning System (GPS) network in NE California, NW Nevada, and southern Oregon to estimate block rotation rates, slip rates on faults and internal block strain rates. The horizontal velocity field comprises 105 USGS campaign GPS sites surveyed during 1999-2014 and have velocity uncertainties less than 1 mm/yr, augmented by 21 continuous Plate Boundary Observatory sites operated since 2005. Sites near Mt. Shasta and Lassen volcanoes are excluded from the analysis to eliminate possible episodic magmatic deformation but stations near Medicine Lake Caldera are corrected for the known source of steady-state subsidence and local contraction. Most of the observed velocity field can be explained by counter-clockwise block rotation of ~0.3 deg/Ma about a pole located in northern Idaho and internal strain rates of < 20 ns/a. Slip rates on the known major extension faults (Surprise Valley, Klamath Graben, Goose Lake, and Hat Creek) are low, less than ~ 1 mm/yr. An earlier estimate of ~ 3 mm/yr of horizontal extension across the Hat Creek fault (Thatcher and Svarc, 2010 AGU) is not supported by the more accurate and spatially dense velocity field examined here.