Don, No, you need something 600 km long and very wide to get a M9. By rare, I mean it could not happend very often-the thrust component might only be, as an educated guess, 2 mm/yr. Subduction earthquakes in Japan, for example, occur at relative plate motions of something like 80 or 100 mm/yr. I M9 earthquake might have 20 or more m of slip, which would take only 200 years to build up in Japan. It would 10,000 years to build up on Santa Rosa-Cortes Ridge. But, you could not have a M9 because the structure is not big enough. So, instead you might have 5 m of slip and a M7.5 or 8 (depending on how much of it ruptured. It would be 2500 years between such slip events. But, we have not even proved that the structure is active, or even mapped the faults yet. Chris