The old sediment layers would be interesting as well. Just remember that when you’re at the beach and the tide suddenly goes way, way out, run for high ground right now!
And remember that it’s important to not stop running, because the likelihood is the wave, when it starts in, will outrun you, even with a head start. If there’s a tall building with an elevator available, heading to a higher floor could be the best bet. Just a couple years ago I saw one of those alleged eyewitness vids of the Boxing Day tsunami, and it wasn’t the big grand sweep, it showed the rising water pnning people against railings and each other as they tried to climb the stairs, and was taken from a vantage point perhaps ten or fifteen feet above the stricken. Didn’t enjoy watching that very much.
On the less serious side, a Nat Geog tsunami vid included an interview with a couple who, in the early 1960s, heard one of the very first tsunami warnings after the system got established, and drove down to a park on the ocean “to watch the tsunami come in”. The water crossed the beach, filled the parking lot, and they panicked and tried to drive off, but they were (and this is the fun part) were in a VW Beetle, so the wheels weren’t on the ground. The tsunami started to recede, the car bumped up against the fence, finally settled back onto its wheels, and they then, finally, got out of there. Hippies.