Abstract
Great earthquakes introduce measurable co-seismic displacements over regions of hundreds and thousands of kilometers in width, which, if not accounted for, may significantly bias the long-term surface velocity field constrained by GPS observations performed during a period encompassing that event. Here, we first present an estimation of the far-field co-seismic off-sets associated with the 2011 Japan Mw 9.0 earthquake using GPS measurements from the Crustal Movement Observation Network of China (CMONOC) in North China. The uncertainties of co-seismic off-set, either at cGPS stations or at campaign sites, are better than 5 - 6 mm on average. We compare three methods to constrain the co-seismic off-sets at the campaign sites in northeastern China 1) interpolating cGPS coseismic offsets, 2) estimating in terms of sparsely sampled time-series, and 3) predicting by using a well-constrained slip model. We show that the interpolation of cGPS co-seismic off-sets onto the campaign sites yield the best co-seismic off-set solution for these sites. The source model gives a consistent prediction based on finite dislocation in a layered spherical Earth, which agrees with the best prediction with discrepancies of 2 - 10 mm for 32 campaign sites. Thus, the co-seismic off-set model prediction is still a reasonable choice if a good coverage cGPS network is not available for a very active region like the Tibetan Plateau in which numerous campaign GPS sites were displaced by the recent large earthquakes.
Highlights
Refining present-day surface velocity fields using space-borne geodetic techniques like GPS, SLR and VLBI is among the important goals in lithospheric deformation studies because this is a prerequisite for quantitatively understanding its nature, distribution, amount and the mechanical processes that drive it (Holt et al 2000), but is critical for seismic risk assessment in earthquake prone regions
> 2000 survey-mode GPS sites and 260 continuous GPS stations have been in operation by the end of 2011 as a result of large scientific infrastructure implementation “Crustal Movement Observation Network of China (CMONOC)” (Niu et al 2005; Li et al 2012)
It is anticipated that the uncertainty in the current velocity field will steadily decrease as more GPS data, in particular cGPS data that proved useful in maintaining reference frame and reducing various sorts of systemic errors in the coordinate time series, are obtained in years to come
Summary
Refining present-day surface velocity fields using space-borne geodetic techniques like GPS, SLR and VLBI is among the important goals in lithospheric deformation studies because this is a prerequisite for quantitatively understanding its nature, distribution, amount and the mechanical processes that drive it (Holt et al 2000), but is critical for seismic risk assessment in earthquake prone regions. The far-field co-seismic deformation has definitely disturbed the long-term deformation pattern of North China (Wang et al 2011a; Shestakov et al 2012; Zhao et al 2012; Zhou et al 2012), posing serious problems to explore all GPS data to analyze the regional strain field associated with local tectonic activities (Li et al 2012). Two-epoch observations acquired respectively pre- and post-earthquakes must be analyzed together with a long-term site velocity determination It is interpolated from a cluster of isolated off-sets for nearby cGPS stations with the homogeneous co-seismic deformation field assumption. In this paper we use a case study to investigate how to estimate co-seismic off-sets for campaign sites and access their precision, aiming at minimizing the effects caused by the 2011 Japan Mw 9.0 mega-thrust earthquake on the local strain field estimation
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