Detection of Instantaneous Gravity Anomalies of Large Earthquakes. The Case of Japan-Tohoku Earthquake of March 11, 2011.

Abstract:

Mega-earthquakes such as the Sumatra-Andaman (Mw=9.3, 26 dec. 2004), Maule-Chile (Mw=8.8, 27 feb. 2010) and Japan-Tohoku (Mw=9.1, 11 mar. 2011) earthquakes, are characterized by a large redistribution of mass. They induce instantaneous gravity anomalies at the local, regional and global scales. A first part of the gravimetric signal is concomitant with the rupture propagation and a second part is carried away by seismic waves originating in the rupture zone. We search for this kind of tiny instantaneous signal on gravimetric data presently available.

So far, only gravimetric data recorded by the superconductive gravimeter network (GGP) are sensitive enough to expect the detection of this signal. We investigate this kind of signal on the data recorded by the gravimeter at the Kamioka station during the Japan-Tohoku earthquake of 11th of March, 2011. We find that the first part of the signal, though extremely small, has been detected by this high precision gravimeter.

The amplitude of the observed signal is in agreement with the theoretical predictions calculated by different methods, (normal mode theory and Okubo's method (1991)). This gravimetric signal might be used for designing a future Early Warning System, but new innovative instruments must be designed to compete with present early warning systems.