Tests of the 2011 Tohoku earthquake source models using free-oscillation data from GOPE

Data from a superconducting gravimeter were obtained from the Geodetic Observatory Pecny (GOPE), Czech Republic, and compared with acceleration data from a broadband seismometer at the same location. We calculated synthetic seismograms for several point- and finite-source fast solutions of the 2011 Tohoku earthquake obtained from surface waves and tested them only against the observed gravity data because of high-noise levels in the low-frequency seismic data. We have obtained a good fit of the synthetic amplitude spectrum with the data up to 1.7 mHz without an additional increase of the moment magnitude M_w. In this aspect, the 2011 Tohoku earthquake was similar to the 2010 Maule earthquake and different from the 2004 Sumatra-Andaman earthquake, where the free-oscillations studies resulted in an increase of the early M_w values. The degree-one mode ₃S{ia1} dominates the ₃S_1?C2S_2?C1S₃ triplet at the GOPE station.