Analysis of tsunami earthquakes such as the 1946 Aleutian Islands earthquake shows that the release of seismic moment takes place at an unusually long period . Calculations of the effective moment derived from surface waves show a rapid increase with decrease in the frequency of the seismic waves , whereas for ordinary earthquakes it remains almost constant with frequency . The duration over which the seabed is deformed has little effect on the size of the resultant tsunami for times up to several minutes . The observation of long period energy release is consistent with unusually slow rupture propagation velocities . Slow rupture velocities are linked to propagation through relatively weak material , such as poorly consolidated sedimentary rocks . Most tsunami earthquakes have been linked to rupture within the uppermost part of a subduction zone , where an accretionary wedge is developed in the hanging wall of the megathrust . Tsunami earthquakes have also been linked to the presence of a thin layer of subducted sedimentary rock along the uppermost part of the plate interface , as is thought to be present in areas of significant topography at the top of the oceanic crust , and where propagation was in an up-dip direction , possibly reaching the seafloor
1946 Aleutian Islands earthquake
1946 Aleutian Islands earthquake
Tsunami earthquake