High rate GPS solutions from 2007 Mw7.7 Tocopilla, Chile Earthquake

The Mw 7.7 Tocopilla, Chile earthquake occurred within the CANTO (Central ANdean Tectonic Observatory) geodetic network, with ten stations recording at 5Hz. Because of the magnitude and proximity of the event, many of the stations recorded the dynamic as well as the static displacement from the earthquake. In order to provide the best time series for source modeling studies (see Minson et al, Fall AGU 2008), we have tested several high-rate analysis strategies. The high-rate solutions were analyzed in a baseline mode, fixing the position and clocks of a remote reference site, and estimating satellite clocks, tropospheric parameters, as well as the station position and clock of the non-stationary site. The station position was estimated at longer time intervals leading up to the onset of earthquake displacement (e.g., 10 minutes) to allow for a more robust position and troposphere estimate. During the earthquake, station positions were estimated at 5Hz. The station position estimates were reduced to 1 second and then 1 minute with time following the earthquake. We mitigated the effects of multipath by applying a modified sidereal filter correction to the phase observables. The multipath correction was estimated from static solutions based on 15 second data from the days prior to the earthquake. Given the potential for afterslip and aftershocks, we avoided using data from after the earthquake for estimation of the multipath correction. The multipath correction significantly reduced noise in the time series at the several minute to several hour period. We also compare 1Hz, and 5Hz solutions from the CANTO stations. While for some stations these solutions are very similar, there are other stations where the 5Hz solutions captures higher rate motion that were aliased in the 1Hz solutions. This result is a strong argument for increasing GPS data collection rates when looking for dynamic seismic motion.