Importance of a priori climate signal modeling for delineation of the coseismic gravity change after the 2010 great Maule (central Chile) earthquake from GRACE

Shin-Chan Han, Jeanne Sauber, Scott Luthcke
Planetary Geodynamics Laboratory, Code 698;NASA Goddard Space Flight Center; Greenbelt, MD 20771, USA.

The analysis of 4 months of GRACE inter-satellite tracking data, two months before and two months after the Maule (central Chile) earthquake (Mw 8.8) on 27 February 2010, shows the sudden changes in satellite orbits and gravity fields after the rupture.

In general, the coseismic gravity perturbation was smaller than or similar with the seasonal and inter-annual mass variation found in the surrounding areas including the Amazon and La Plata river basins and the Patagonia glacier ice field. At the GRACE's spatial scale, those 'nuisance' signals are important to eliminate from the GRACE data as accurately as possible in order to localize the smaller coseismic signal associated with the 2010 Maule earthquake.

We have used a priori global hydrology model (albeit only soil moisture) and a priori determination of the periodic mass changes from the GRACE data between 2004 and 2009 in order to predict the seasonal and inter-annual signals in 2010. Also a short-term (two months) difference in gravity solutions before and after the event was helpful in particular to remove the inter-annual signals appeared in the Patagonia and Antarctica peninsular.

Finally, we report that the gravity anomaly of -5 µGal with a spatial scale of 500 km was found east of the epicenter after the earthquake. Our estimate of long-wavelength gravity changes based on alternate coseismic models indicates that the interior deformation (mostly associated with intrinsic density change and characterized with negative anomaly) exceeds the surface deformation (causing positive anomaly) in the total gravity change at such spatial scale.