Constraints on the centroid moment tensors of the 2010 Maule and 2011 Tohoku earthquakes from radial modes

Abstract

Surface acceleration caused by the radial modes depends only on the Mrr component of the centroid moment tensor and on its depth assuming the isotropic component to be negligible. The 0S0‐mode amplitude enables one to obtain a relatively narrow interval ofMrr values, whereas 1S0‐mode amplitude is more sensitive to centroid depth. We have used these facts to analyze the 2010 Maule (Chile)Mw = 8.8 and 2011 Tohoku (Japan) Mw = 9.1 earthquakes using PREM. Superconducting gravimeter data available within the framework of the Global Geodynamic Project reveal that the Mrr components of these earthquakes should be in the interval 0.95–1.15 × 1022 Nm (Maule) and 1.50–1.75 × 1022Nm (Tohoku), respectively. Re‐evaluation of the modal quality factorsQ is needed to obtain constraints on Mrrself‐consistently. The joint analysis of gravity data from both events yieldsQ = 5500 ± 140 for the 0S0 mode and Q = 2000 ± 80 for the 1S0 mode. We were not able to determine the quality factor of the 2S0 mode with an accuracy sufficient to allow meaningful constraints (Q = 1120 ± 270).