Locally generated tsunami along the Kaikoura coastal margin: Part 1. Fault ruptures

Tsunami are generated by sudden movements of the ocean bed or by objects such as subaerial landslides and bolides falling into the ocean. An examination of the geophysical setting for the northeast coast of the South Island, New Zealand, identified a substantial potential for submarine fault ruptures and submarine landslides. To examine possible effects of a tsunami, a numerical model was applied to calculate runup and inundation arising from locally-generated tsunami along this section of the coast. The specific events considered were fault ruptures on the Kekerengu Bank Fault and two lesser faults, and a submarine landslide in Kaikoura Canyon. The model is based on the Reynolds-averaged Navier-Stokes (RANS) equation and used a finite element spatial approximation, implicit time integration, a semi-Lagrangian advection approximation, and a simple method for treating non-hydrostatic pressure variations. The results indicate that the different generation events have significant effects on different parts of the coastal margin. For the fault-rupture events, the northern coast of the study area is very exposed to damage from a potential rupture of the Kekerengu Bank Fault. A concern is that the highest waves near Kaikoura would be a result of late arrival of coastally-trapped waves and would be delayed by up to 1.5h after the fault-rupture event.