Coseismic and postseismic gravity changes by the 2010 Chile Earthquake: Separating hydrological and tectonic signals in GRACE dataHeki, Kosuke; Matsuo, Koji After the 2004 great Sumatra-Andaman Earthquake, GRACE first detected coseismic (Han et al., Science, 2006) and postseismic (Ogawa and Heki, GRL, 2007) gravity and geoid height changes. The February 27, 2010, Chile Earthquake, which ruptured the Constitucion-Conception seismic gap, was the largest earthquake (Mw8.8) after that. Here we report its co- and postseismic gravity changes. Three months of GRACE data after the earthquake are available at the moment, and the gravity time series show significant negative jump reaching five microgals centered at the back arc side of the focal region, a signature similar to the 2004 Sumatra earthquake. The observed changes are consistent with those predicted for the realistic spherical layered earth (Sun et al., GJI, 2008) assuming fault parameters determined by coseismic displacements of GPS stations (e.g. Delouis et al., GRL, 2010). Although it is premature to discuss postseismic gravity changes, gravity appears to decrease around the focal plane after the earthquake, which is somewhat different from postseismic gravity increase observed after the 2004 Sumatra Earthquake. Gravity variations in southern South America, except those related to earthquakes, are governed by seasonal changes in soil moisture with amplitudes modulated by the ENSO index (Morishita and Heki, EPSL, 2008). Seasonal signals in central Chile are expected to show slight increase in the postseismic period (from March to summer), and it is of crucial importance to remove land hydrological signals in order to tell whether postseismic gravity in Chile is increasing or decreasing. |