Comparison between computed (in red) and observed (in blue) waveforms for (a) the 2003 July 29 earthquake, (b) the 2004 December 13 earthquake, and (c) the 2006 June 21 earthquake. The waveforms have been filtered between 0.1 and 0.5 Hz. The goodness-of-fit factor fa is computed using the amplitude of the filtered waveforms, and is defined in eq. (3).