At least some repeating FRBs are thought to occur in magnetars, and the similarity of magnetar activity to earthquakes and solar flares has been discussed in the literature. Here I present a brief review of studies on the occurrence times and energies of repeater FRBs and their correlations. I then report on our recent work based on the two-point correlation function. We found many notable similarities between FRBs and earthquakes, while they are different from solar flares. Based on the results of this analysis, the mechanism of the FRB phenomenon and its relation to magnetars and neutron stars in general will be discussed.