Automated Estimation and Tools to Extract Positions, Velocities, Breaks, and Seasonal Terms From Daily GNSS Measurements: Illuminating Nonlinear Salton Trough Deformation

Abstract

This paper describes the methods used to estimate positions, velocities, breaks, and seasonal terms from daily Global Navigation Satellite System (GNSS) measurements. Break detection and outlier removal have been automated so that decades of daily measurements from thousands of stations can be processed in a few hours. New measurements are added, and parameters are updated every week. Model parameters allow separation of interseismic, annual, coseismic, and postseismic signals. Tools available through GeoGateway (http://geo-gateway.org) allow rapid visualization and analysis of these terms for results that can be subsetted in time or space. Results show highly variable and nonlinear motion for GPS stations in southern California. The variable motion is related to seasonal motions, distributed tectonic motion, earthquakes, and postseismic motions that can continue for years. In some areas results suggest that additional processes are responsible for the observed motions. In general, following earthquakes, stations return to their long-term motions after 2-3 years, though some exceptions occur. The use of the tools shows nonlinear motion in the Salton Trough of southern California related to the 2010 M7.2 El Mayor-Cucapah earthquake, 2012 Brawley earthquake swarm, and a creep event on the Superstition Hills fault in 2017.

An Assessment of Global Positioning System Velocity Uncertainty in California

“…A complication with estimating vertical velocities is the interannual variability in station positions observed as time series increase in length. This nonlinear ground motion can result from changes in terrestrial water storage (e.g., Borsa et al., 2014), varying intensity of groundwater usage and recharge (e.g., Neely et al., 2020), and tectonic signals (e.g., Hammond et al., 2018; Heflin et al., 2020). Both the Central Valley (groundwater) and the Salton Trough (tectonics, groundwater), which we highlight as regions of high variability in vertical velocities, are impacted by strong nonlinear surface deformation.…”

“…Daily station positions and long‐term velocities for most western U.S. stations are estimated by multiple analysis centers using different processing algorithms, reference frames, troposphere and tidal corrections, and time‐series analysis techniques (Heflin et al., 2020; Herring et al., 2016). Each analysis center provides uncertainty estimates for their data products, but formal uncertainties calculated for geodetic datasets can underestimate time‐correlated error in position data and usually do not characterize variance introduced by different processing assumptions (Herring et al., 2016; Langbein, 2012).…”

Improving access to geodetic imaging crustal deformation data using GeoGateway

“…Standard daily position time series can be used to measure long-term deformation, temporal changes, and station displacements from events such as earthquakes (e.g. Heflin et al 2020). Accuracy of the products are 1-2 mm and <1 mm/yr velocity for horizontal displacement and velocity measurements respectively and about 3 mm and 0.5 mm/yr for vertical measurements (Heflin et al 2020).…”

“…Heflin et al 2020). Accuracy of the products are 1-2 mm and <1 mm/yr velocity for horizontal displacement and velocity measurements respectively and about 3 mm and 0.5 mm/yr for vertical measurements (Heflin et al 2020). Daily GNSS measurements are fully three dimensional and can provide continuous monitoring over decades but spatial sampling can be tens of km as is typically in California or hundreds of km in less tectonically active regions.…”

“…UAVSAR repeat pass interferometry (RPI) products (Hensley et al 2005) and UCERF3 (Field et al 2014) fault traces are provided by GIS services operated by the GeoGateway project and use the open source GeoServer software (http://geoserver.org/). GNSS data services (Heflin et al 2020) are operated by NASA JPL (https://sideshow.jpl.nasa. gov/post/series.html), and seismicity data are obtained from USGS earthquake catalog.…”