A model for Mexican neotectonics based on nationwide GPS measurements, 1993-2001

Abstract

We combine velocities for 14 continuously operating GPS stations spanning Mexico, GPS sites on Soco o and Clarion islands on the Pacific plate west of Mexico, and 178 GPS sites on the North American and Pacific plates to de ve plate-based reference frames suitable for GPS-based s1udies of North American plate neotectonics. The motions of sites in exico north of and including Oaxaca are consistent with North American plate motion, implying negligible slip across the Me ican Volcanic Belt. Sites in the Yucatan peninsula move 3± 1 mmlyr eastward relative to the North American plate. Velocities for new GPS sites on Clarion and Socorro islands are consistent within their uncertainties with Pacific plate motion, and provide u eful new constraints on Pacific plate motion. Pacific-North America motion in the southern Gulf of California is 50.8±0.5 mrrilyr toward S55°E±0.5° degrees. This is consistent with 50-52 mmlyr geologic estimates, but slower than recently publishe 52-53 mmlyr geodetic estimates. Southeastward motion of La Paz near the tip of Baja California relative to the Pacific pl te agrees with previous results suggesting that Baja California is detached from the Pacific plate. The new plate angular velocity ectors amount to a well-constrained, geologically stable reference frame.