A New Global Mode of Earth Deformation: Seasonal Cycle Detected
Geoffrey Blewitt,12*
David Lavallée,1
Peter Clarke,2
Konstantin Nurutdinov2
We have detected a global mode of Earth deformation that is
predicted by theory. Precise positioning of Global Positioning System
sites distributed worldwide reveals that during February to March, the
Northern Hemisphere compresses (and the Southern Hemisphere expands),
such that sites near the North Pole move downward by 3.0 millimeters,
and sites near the equator are pulled northward by 1.5 millimeters. The
opposite pattern of deformation occurs during August to September. We
identify this pattern as the degree-one spherical harmonic response of
an elastic Earth to increased winter loading of soil moisture, snow
cover, and atmosphere. Data inversion shows the load moment's
trajectory as a great circle traversing the continents, peaking at
6.9 × 1022 kilogram meters near the North Pole in
winter, indicating interhemispheric mass exchange of 1.0 × 1016 ± 0.2 × 1016 kilograms.
1 Nevada Bureau of Mines and Geology, and
Seismological Laboratory, University of Nevada, Reno, NV 89557, USA.
2 Department of Geomatics, University of Newcastle,
Newcastle upon Tyne, NE1 7RU, UK.
*
To whom correspondence should be addressed. E-mail:
gblewitt{at}unr.edu
