Strain Accommodation in the Walker Lane: Understanding the Evolution of a Diffuse Plate Boundary with Geochronology and Geodesy

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

This study brings together a team of scientists from Georgia Institute of Technology to investigate the discrepancies between short- and long-term strain rates in the Walker Lane region of eastern California and western Nevada; an evolving segment of the Pacific-North America plate boundary. To accomplish this objective, existing geodetic infrastructure, including regional campaign and continuous GPS data, is augmented with 10 new monuments in the region. All campaign sites will be measured in three annual campaigns between 2010 and 2012. Analysis of the GPS data will yield a detailed image of the present-day strain field. Geologic mapping incorporating evaluation of aerial photography, field surveying and cosmogenic nuclide geochronology of offset alluvial fans are used to determine the dates, and hence the long-term rates, of motion across normal faults. The integration of the long-term geologic and short-term geodetic datasets will yield a comprehensive view of the distributed strain field over late Pleistocene to Recent time scales along this important plate boundary fault system. Ultimately, this will lead to improved understanding of how the structurally complex lithosphere behaves along evolving plate boundaries. Along some plate boundary systems, including the San Andreas and North Anatolian faults, rates of tectonic deformation appear to be constant over a wide range of time scales. However, on parts of other plate boundary zones short-term rates determined from GPS measurements do not coincide with longer-term geologically inferred slip rates. For example, late Pleistocene rates of deformation across the eastern California shear zone in the Mojave Desert and in the central Walker Lane, determined from tectono-geomorphic fault studies, yield rates that are only one-half to one-third the short-term rate determined from GPS data. The mismatch between short- and long-term rates in the Walker Lane is contrary to current understanding, and has important implications for how tectonic deformation is accommodated in the lithosphere, and ultimately the relationship of this deformation to earthquake hazards. By determining rates of tectonic activity in the Walker Lave over annual to 100,000 year timescales will provide new insights into how fault systems behave and evolve over multiple earthquake cycles, and address several fundamental questions about crustal strain distribution: How constant are rates of strain accumulation and release in time and space? Are geologic slip rates averaged over multiple earthquake cycles comparable with short-term rates of deformation determined from GPS data? If discrepancies between short- and long-term rates of deformation exist, over what temporal and spatial scales does the discrepancy occur? Are these differences related to the structural complexity of a specific region or are they characteristic of entire plate boundaries?