Lived on Guam 5 years and some people there did worry about tidal waves. The Northern end of the island is 700+ ft above sea level and the reef offers good protection. It's one of the safer islands compared to most others.
Five years, huh? Almost a native.
When I talked to my son in law I asked him just how high he thought they were and he said at least a couple hundred feet above sea level. Resting easier even though the chance of a big wave hitting there are pretty slim. Thanks.
FGS