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Geodetic observations of crustal motions in the Tonga Lau system, using the Global Postioning System, suggest that the intense magnetic seismicity in the region can be attributed to high subduction and back-arc extension rates. The opening rate of the Lau basin increases northward up to nearly 60 mm per year. The northern Tonga ridge contains part of a rigid microplate, as suggested by the absence of straining in the region. Convergence rates across the Tonga increases northward up to nearly 240 mm per year.

Laboratory experiments indicate that the overpressuring of fluids in geological faults can bring on the slippage that results in earthquakes. These overpressured fluids could diminish the shear stress needed to make the faults slide through a two-step process: sealing and compaction. Sealing blocks the movement of fluids from the fault zone to the adjacent rock and compaction of the fault rock allows slippage by increasing pore pressure in the sealed fault.

Large earthquakes are possibly caused due to shearing of isolated mountains (seamounts) in subduction zones of the ocean. The position of seamount decapitation determines the magnitude of the earthquake. Asperities are strong areas of the plate interface that control earthquake occurrences. They are made from the subducted seamounts and are affected by sea floor roughness and style of sediment subduction. The size of earthquakes varies between subduction zones probably due to the absolute velocity of the overlying plate that affects the speed of subduction.

Some subduction zones are seismically active and cause earthquakes, while some others are quiescent. The Cascadia subduction zone, which extends along the coast from northern California to southern British Columbia, is one such area which has geological evidence of possible earthquakes. Tichelaar, Ruff, Hyndman and Wang attempted to discover the reason for the lack of earthquakes in this region in recent times. They suggest the narrow seismic zone as a possible reason.