Subduction zones are able to produce m9 earthquakes (unlike transform or divergent) plate boundaries becausea) the volcanic activity at subduction zones makes the fault plane stickier and therefore they release more energy when they reach their elastic limit. b) many people live along the coast of subduction zones, making a large segment of the population vulnerable. cc) the length of the rupture can be so large (up to 1200 km in a megathrust event) and the amount of slip is large. d) these types of faults typically have frequent earthquakes (every year or so), just so there isn't a lot of stress that builds up along the fault contact zone.