Seasonal variation of vertical crustal deformation possibly related to water mass storage in southeast Alaska
Abstract
Many glaciers and ice fields in southeast Alaska have been rapidly retreating since the end of the Little Ice Age (from the mid-14th century to the mid-19th century). Recently, rapid uplifting (considered as a effect of deglaciation) is detected by GPS observations in this region with the maximum rate reaching ~30 mm/yr (Larsen et al., GJI04). Therefore, this region is the best place in the world to study ongoing glacial isostatic adjustment (GIA) and its mechanism, by means of monitoring crustal deformation. GPS time series, however, contains some other effects except uplifting by global warming, such as interplate interaction, snow and atmospheric loading, ground water level, and excess path delay in atmosphere, which prevent from accurate estimation of secular uplifting rate. Consequently, it is important to reveal the cause of seasonal variation in GPS time series, and we examine amplitudes and phases of the seasonal variation at each GPS site. We analyze GPS data obtained at 35 sites of Plate Boundary Observatory for the period from January 2006 to December 2008. The GPS data are processed with the Precise Point Positioning (PPP) strategy (Zumberge et al., JGR97) implemented in GIPSY-OASIS II ver. 5 software. Global Mapping Function (GMF) is applied for the GPS data processing. We adopted the JPL final orbits and clocks for the PPP processing. For more precise GPS data analysis, we utilize the Ambizap algorithm (Blewitt, JGR08) for the carrier phase ambiguities determination. We then fit functions consisting of linear, annual and semiannual terms to GPS time series and estimate coefficients of each term by least-square method. As a result, vertical components show conspicuous seasonal variations, while insignificant in horizontal ones at all stations. Sites showing large annual amplitudes of about 11 mm are located near the glaciers and ice fields in south and southeast Alaska. Phases of the annual components are almost identical among each station, and the maximum uplift occur around October. The spatial distribution of the amplitudes for the annual components is correlated with that of mass change estimation deduced from the GRACE data (Luthcke et al., JGlaciol08). The estimated correlation coefficient between the elevation and the loading, which converted from mass change by GRACE, is ~2.2 mm/kPa. It is consistent with the value of 1.5 mm/kPa estimated for Tohoku district, northeast Japan by Heki (Science01). Our result suggests that the seasonal variation in vertical crustal deformation in southeast Alaska could be mainly attributed to snow loading in winter.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.G43A0714A
- Keywords:
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- 1200 GEODESY AND GRAVITY