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

Surface acceleration caused by the radial modes depends only on the M rr component of the centroid moment tensor and on its depth assuming the isotropic component to be negligible. The 0 S 0 ‐mode amplitude enables one to obtain a relatively narrow interval of M rr values, whereas 1 S 0 ‐mode amplitude is more sensitive to centroid depth. We have used these facts to analyze the 2010 Maule (Chile) M w  = 8.8 and 2011 Tohoku (Japan) M w  = 9.1 earthquakes using PREM. Superconducting gravimeter data available within the framework of the Global Geodynamic Project reveal that the M rr components of these earthquakes should be in the interval 0.95–1.15 × 10 22 Nm (Maule) and 1.50–1.75 × 10 22 Nm (Tohoku), respectively. Re‐evaluation of the modal quality factors Q is needed to obtain constraints on M rr self‐consistently. The joint analysis of gravity data from both events yields Q  = 5500 ± 140 for the 0 S 0 mode and Q  = 2000 ± 80 for the 1 S 0 mode. We were not able to determine the quality factor of the 2 S 0 mode with an accuracy sufficient to allow meaningful constraints ( Q  = 1120 ± 270).