BSSA, Vol. 94:4

We decided to perform some supplementary tests on the window overlap. We apply our technique to different time shifts from the 1 hr used in the paper, to 72 hr for all the SG stations. The 72 hr shift gives no overlap, and hence completely independent estimates of A0 and Q for each shift. Fig A1 is the comparison for the recovery of the amplitude, for 9 different shifts. It can be seen that the amplitude remains quite constant up to about 16 hr, but then increases up to 24 hr. At the same time, the error bars on these estimates increases with the shift, no doubt because of the reduced number of data points used in the inversion when the shift gets longer. Thus statistically the amplitudes could all be the same, within the error bars. But smaller error bars are more consistent with the previous results of Davis et al. (2005), so we prefer our results with the shorter time shift (i.e. 1 hr).