ABSTRACT:GRACE satellites (the Gravity Recovery And climate Experiment) are very useful sensors to extract gravity anomalies after earthquakes. In this study, we reveal co-seismic signals of the two combined earthquakes, the 2006 Mw8.3 thrust and 2007 Mw8.1 normal fault earthquakes of the central Kuril Islands from GRACE observations. We compute monthly full gravitational gradient tensor in the local north-east-down frame for Kuril Islands earthquakes without spatial averaging and de-striping filters. Some of gravitational gradient components (e.g. ΔVxx, ΔVxz) enhance high frequency components of the earth gravity field and reveal more details in spatial and temporal domain. Therefore, co-seismic activity can be better illustrated. For the first time, we show that the positive-negative-positive co-seismic ΔVxx due to the Kuril Islands earthquakes ranges from − 0.13 to + 0.11 milli Eötvös, and ΔVxz shows a positive-negative-positive pattern ranges from − 0.16 to + 0.13 milli Eötvös, agree well with seismic model predictions.
In this study, the focal mechanism of Indian Ocean earthquake is determined by combination of GRACE gravity gradient change and analytical model of Okubo [1992). To do so, the co-seismic gravity gradient change resulting from Indian Ocean earthquake is derived using monthly solution of GRACE level 02 data after removing the contaminations from hydrological effects and post-seismic creep. Since, De-striping methods lead to reduction and distortion of a co-seismic gravity change signal, it is suggested to compute a set of gravity gradient tensor components e.g. ΔVxx and ΔVxz, because they are more sensitive to small-scale signals and they reduce the striping errors without need to any de-striping filtering. Then the computed gravity gradient components are compared with the gravity gradient components from Okubo model [1992], which accounts the focal mechanism of the earthquake. By the way, the nonlinear inversion algorithm is constructed and solved by Genetic algorithm to find the best values of fault parameters for Indian Ocean earthquake. For better constraining the fault parameters in the inversion process, a sensitivity analysis is also conducted which reveals that the selected model is highly sensitive to a strike angle, dip angle, length, width and average slip, although it is less sensitive to a depth of a fault. The ultimate optimal estimate of the fault parameters shows a good correspondence compared with some existing slip models obtained by various constraints or via inversion of seismic observations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.