Abstract
Abstract The M w 8.0 2003 Tokachi-oki earthquake offshore Hokkaido is the largest earthquake observed to date by a dense GPS network (GEONET). These GPS data are important both for resolving the geodetic signature of the earthquake itself and studies of postseismic deformation. Because GPS positions are generally estimated by averaging 24 hours of observations, it can be difficult to separate the effects of the earthquake and early postseismic deformation. In order to address this difficulty, a Kalman filtering methodology is developed that allows the estimation of the static offsets for the mainshock, its largest aftershock, and postseismic deformation in the first 24 hours. The static offsets computed for this study can be used for earthquake rupture studies while the early postseismic data can be used to evaluate frictional properties of the fault.
Highlights
Operating GPS networks are routinely used to estimate the “static” offsets associated with large earthquakes
The “static offset” of the earthquake was calculated for each component for each of the 55 GEONET sites
The static offset is subsequently removed from each component timeseries by subtracting the offset estimated for the epoch time
Summary
Operating GPS networks are routinely used to estimate the “static” offsets associated with large earthquakes. Random walk estimation has been shown to work well to suppress noise in volcanic monitoring environments (Larson et al, 2001) where deformation is slowly varying This processing technique would not work well where there are large ground displacements such as those caused by an earthquake. The estimate of the static offsets—for the mainshock in this example—is heavily influenced by which averaging (e.g. 15 minutes, 5 minutes) interval one uses For this particular earthquake, at least for the sites near the epicenter, one is restricted to using no more than one hour be-. Sec dataset, that combines white noise position estimation at the times of the earthquakes with random walk parameterization (Larson et al, 2001) at other times would yield both precise static offsets and postseismic deformation
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