Crustal displacements due to continental water loading

Abstract

The effects of long‐wavelength (>100 km), seasonal variability in continental water storage on vertical crustal motions are assessed. The modeled vertical displacements (Δ r M) have root‐mean‐square (RMS) values for 1994–1998 as large as 8 mm, with ranges up to 30 mm, and are predominantly annual in character. Regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for horizontal deformation. We compare Δ r M with observed Global Positioning System (GPS) heights (Δ r O) (which include adjustments to remove estimated effects of atmospheric pressure and annual tidal and non‐tidal ocean loading) for 147 globally distributed sites. When the Δ r O time series are adjusted by Δ r M, their variances are reduced, on average, by an amount equal to the variance of the Δ r M. Of the Δ r O 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 annual harmonic in the Δ r M. The Δ r M time series exhibit long‐period variations that could be mistaken for secular tectonic trends or postglacial rebound when observed over a time span of a few years.