Roger and Dennis...maybe you want to work together on this? The Kp graph is probably what you want to use...the one on the bottom....The top of the scale is severe or extreme or something...Kp9. The the last two 3 hour bars look like Kp6 then 7. This is probably logarithmic...you could just take duration of Kp of 7 or higher against quakes...or you could try just any reports of Kp9 and not deal with the duration, or 8 and higher, or whatever. You might take into consideration that if it has been a long time since the last severe storm, the stress may have had time to build up in a system prone to such triggering...if there is any such triggering. You would need to know to what low end a catalogue was complete: you might limit to some California area (long Valley) to M2.5+ and to past 1980 or whatever (you know much more about catalogues than I do). I guess you have to be careful about places with geothermal fluid pumping like geysers, Coso (last few years), and south of Salton Sea/Brawley zone.
Chris