Fault plane of the 1944 Tonankai earthquake remains unresolved

Determine whether the 1944 Tonankai earthquake in the Nankai Trough region ruptured the megasplay fault or the top surface of the subducting oceanic crust, recognizing that existing observational data lack sufficient resolution and that available evidence remains inconclusive regarding the fault plane involved.

Background

In the Nankai Trough, two structural interfaces are considered potential coseismic plate boundaries: the megasplay fault and the top of the oceanic crust. Rupture along a megasplay fault is particularly consequential because seafloor deformation associated with such rupture can generate larger tsunamis.

The paper notes that for the 1944 Tonankai earthquake, observational data did not have sufficient resolution to definitively identify which fault was ruptured. While tsunami inversion and interpretations of nearby subsurface structural information provide supporting evidence for slip along the megasplay fault, a definitive conclusion has not been reached.

References

Whether or not a large earthquake ruptures a megasplay fault is an important question as seafloor deformation owing to the rupture of megasplay faults may cause larger tsunamis. Although the observation data of the 1944 Tonankai earthquake did not possess sufficient resolution to determine which fault was ruptured, the tsunami inversion result and some interpretations of nearby subsurface structural information provide supporting evidence of the slip along the megasplay fault. However, no conclusions have been reached.

— Physics-informed deep learning quantifies propagated uncertainty in seismic structure and hypocenter determination  (2402.08854 - Agata et al., 2024) in Discussion (Section 5)