Crustal displacements due to continental water loading

The effects of long-wavelength (> 100 km), seasonal variability in continen tal water storage on vertical crustal motions are assessed. The modeled ver tical displacements (Deltar(M)) have root-mean-square (RMS) values for 1994 -1998 as large as 8 mm, with ranges up to 30 mm, and are predominantly annu al in character. Regional strains are on the order of 20 nanostrain for til t and 5 nanostrain for horizontal deformation. We compare Deltar(M) with ob served Global Positioning System (GPS) heights (aro) (which include adjustm ents to remove estimated effects of atmospheric pressure and annual tidal a nd non-tidal ocean loading) for 147 globally distributed sites. When the ar o time series are adjusted by Deltar(M), their variances are reduced, on av erage, by an amount equal to the variance of the Deltar(M). Of the aro time series exhibiting a strong annual signal, more than half are found to have an annual harmonic that is in phase and of comparable amplitude with the a nnual harmonic in the Deltar(M). The Deltar(M) time series exhibit long-per iod variations that could be mistaken for secular tectonic trends or postgl acial rebound when observed over a time span of a few years.