Japan 869 AD: "The sea soon rushed into the villages and towns, overwhelming a few hundred miles of land along the coast. There was scarcely any time for escape, though there were boats and the high ground just before them. In this way about 1,000 people were killed"

Blindsided by Ferocity Unleashed by a Fault

Excerpt:

In Japan’s history, there does seem to have been a precedent for the recent quake, but it took place more than a thousand years ago. A text known as “Nihon Sandai Jitsuoku,” or “The True History of Three Reigns of Japan,” described an earthquake in July 869 and a tsunami that flooded the plains of northeast Japan: “The sea soon rushed into the villages and towns, overwhelming a few hundred miles of land along the coast. There was scarcely any time for escape, though there were boats and the high ground just before them. In this way about 1,000 people were killed.”

These were the same plains that were submerged this month. Analysis of sediments left by the 869 tsunami led to an estimate that the earthquake had a magnitude of 8.3.

Comment: Interesting article about how little is known about "underestimated or unknown faults"