Figure 1. Bathymetry around the Tonga–Kermadec trench along with the region's seismicity.

Seismicity with depth deeper than 60 km is obtained from Engdahl et al.⁵⁸ and indicated by coloured circles according to the focal depth. Plate boundaries are depicted by solid lines: orange and cyan lines represent ridges and trenches, respectively. Magenta lines indicate transform faults. Regions where Ocean Island Basalts (OIB; high He³/He⁴ ratio) with a signature of the Samoan plume are found³,⁴,⁵ are indicated by enclosed solid magenta lines. Other possible signatures of the Samoan plume are found in the regions represented by yellow enclosed lines⁶,⁷,⁸,⁹,¹⁰. Relative velocity of the Pacific plate to the Australian plate is depicted by the thick white arrow based on MORVEL by DeMets et al.⁵⁹ and velocities from GPS stations in an Australia-fixed reference frame are indicated by thin white arrows⁶⁰.