The Gulf of Guinea, specifically the Bight of Bonny, is up to ~20,000ft deep. Average ocean waves have a period less than 15s and the average ocean depth of the Atlantic is ~11,000ft. Oddly similar ratios! So it's plausible this 26s wave period is caused by the increase in depth [0]. The abnormally large seismic amplitude can be similarly attributed, as pressure patterns conditionally form along the bottom of the ocean (in either direction) due to combined features of both the wave and the ocean bottom topography.