F. Blume

Distributed Deformation across the Rio Grande Rift, Great Plains, and Colorado Plateau

We use continuous measurements of GPS sites from across the Rio Grande Rift, Great Plains, and Colorado Plateau to estimate present-day surface velocities and strain rates. Velocity gradients from five east-west profiles suggest an average of ∼1.2 nanostrains/yr east-west extensional strain rate across these three physiographic provinces. The extensional deformation is not concentrated in a narrow zone centered on the Rio Grande Rift but rather is distributed broadly from the western edge of the Colorado Plateau well into the western Great Plains. This unexpected pattern of broadly distributed deformation at the surface has important implications for our understanding of how low strain-rate deformation within continental interiors is accommodated.

Effects of earthquake ground motion on tracking characteristics of new Global Navigation Satellite System receivers

We use a shake table capable of large (7 G) three-dimensional accelerations with large payloads to simulate ground motion reconstructed from acceleration data collected during the February 2010 Mw = 8.8 Maule, Chile, earthquake. The tracking performance of five modern geodetic GNSS receiver and antenna combinations was investigated while undergoing simulated seismic shaking at three two levels of amplification. Individual system performance was characterized by the number of tracked GNSS observations. The L1 and L2 GPS signal tracking was significantly impacted for the majority of the receiver models during simulations with maximum accelerations of 4 G, and the tracking performance for all of the tested receiver types was significantly impaired during the 7 G simulations. Results show improved tracking when only the antenna was shaken suggesting that vibration-induced oscillator phase noise may contribute significantly to tracking degradation during shaking.