A study published in 2016 suggested a new parameter to determine a subduction zone 's ability to generate mega-earthquakes . By examining subduction zone geometry and comparing the degree of curvature of the subducting plates in great historical earthquakes such as the 2004 Sumatra-Andaman and the 2011 Tōhoku earthquake , it was determined that the magnitude of earthquakes in subduction zones is inversely proportional to the degree of the fault 's curvature , meaning that " the flatter the contact between the two plates , the more likely it is that mega-earthquakes will occur . " Outer rise earthquakes occur when normal faults oceanward of the subduction zone are activated by flexure of the plate as it bends into the subduction zone . The 2009 Samoa earthquake is an example of this type of event . Displacement of the sea floor caused by this event generated a six-meter tsunami in nearby Samoa
2009 Samoa earthquake
2009 Samoa earthquake and tsunami
Subduction