I lived several years in the quake prone area of Alaska. We always seemed to have the most quakes occur, and of strongest magnitude, from Late February until the first part of May and during full moons. (Yes, exceptions exist, I know, I know, I know). The native peoples attributed this to the Spring equinox as a time of the greatest gravitational pull from the moon, thus pressuring the fault lines. Could this be impacting the caldera?