Regional mass fluxes due to transport and adjustment within the
Earth system that are implicitly contained in the monthly GRACE global
geopotential coefficients are revealed by localizing global spectra
using spatiospectrally concentrated window functions. We have
analyzed 45 monthly global GRACE harmonic coefficient series in order
to find the coseismic signature associated with the 2004 great
Sumatra-Andaman earthquake. A significant gravity change after the
earthquake is found in the time-series of the GRACE coefficients after
localization with a single band-limited window centered near the north
of the island of Sumatra. This change is undetectable from the
original global coefficients or from coefficients localized elsewhere
on the globe. A step function with its discontinuity at 26 December
2004 usefully models the coseismic gravity change. The localized
GRACE coefficients contain the jumps (associated with the earthquake)
up to degree and order 55, although not all of them within this band
produce changes that are statistically significant. The gravity
change calculated from the localized GRACE coefficients displays 30
µGal peak-to-peak variations which are very well correlated with an
independently derived seismic model based on elastic dislocation
theory.
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