Perhaps the most interesting evidence of the tsunami attack was observed on Sempu Island itself. The island is a nature preserve and is uninhabited, hence no loss of life or damage to dwellings were reported on Sempu. The survey team did observe significant shoreline erosion in a small cove lying to the northeast of the fishing village. A long, narrow depression was formed, cutting inland through a forested valley bordering the beach. Sandy topsoil had been removed to create the one-m-deep depression, which was roughly funnel-shaped, 15 m wide at the shoreline and extending 50 m inland. The extensive erosion and onshore sediment transport observed in the cove lead us to conjecture that this area may have been subject to wave splash-up; this phenomenon occurs at the point where two trapped wave fronts propagating around an island's perimeter meet. This speculation is corroborated by eyewitness accounts in the fishing village at the channel's southwestern end: the natives reported a first wave approaching from the southwest, and then a second wave following from the northeast. The two waves would have therefore met somewhere to the northeast of the fishing village, which is where the small cove lies.
This account has been adapted from Synolakis et al.