Geographical variations of the 0S0 normal mode amplitude: predictions and observations after the Sumatra-Andaman earthquake
Résumé
The radial seismic normal mode 0S0 was strongly excited by the 2004 Mw = 9.3 Sumatra-Andaman earthquake at a period of 20.5 min. In a spherically symmetric Earth model, 0S0 amplitude is the same everywhere on the Earth's surface. However, when the ellipticity and rotation of the Earth are taken into consideration, theoretical computations predict an amplitude of 0S0 1% higher at the pole than at the equator. Based on a realistic three-dimensional heterogeneous rotating elliptic Earth model, our predictions indicate that the amplitude of 0S0 is 2% higher at the pole than at the equator. A longitude dependency of 0S0 amplitude is also shown. The analysis of 13 superconducting gravimeter (SG) records of the 2004 Sumatra-Andaman earthquake supports the predicted geographical variations of 0S0 amplitude. We have also obtained new estimates for the frequency and Q of 0S0: 0.8146566±1.6 10-6 mHz and 5506±19.