日本古籍提及西元794年在四國有海嘯

Recently the Yomiuri News on-line reported the following:
平安京への遷都が行われた７９４年（延暦１３年）に南海地震とみられる未知の巨大地震が起きていたことが、古文書の調査でわかった。 　
岡山大の今津勝紀准教授（日本古代史）が１７日、発表した。南海地震は１００年程度の周期で起きているとされるが、この地震の前後約２００年間の記録はこれまでに見つかっておらず、その「空白期間」を埋める地震だとしている。 　
今津准教授によると、日本の正史の一つ「日本後紀」などの内容を抜粋した「日本紀略」（平安時代に編纂）に、延暦１３年７月１０日、「宮中並びに京畿官舎及び人家震う。或いは震死する者あり」との記述があった。その２年後には、四国の海沿いを巡る古代の街道「南海道」を廃止し、後に新たに道を設けたと記されていた。 　
今津准教授は、街道の廃止は、巨大地震による大津波被害のためだったとし、その震源域が太平洋側と推定されることから、南海地震だったと判断した。
（2012年4月17日23時45分 読売新聞）
(試譯文)
An investigation into the ancient documents showed that the strange massive earthquake occurred in 794 (Enryaku 13th years) when the capital relocation to Heiankyo was carried out could be the Nankai earthquake.
Associate Professor Katsunori Imazu (Japanese ancient history) of the Okayama University announced this on the 17th (April). Although it was supposed that the Nankai earthquake had a  occurrence cycle of once in about 100 years, the record on this earthquake for about 200 years was not found  until now, there was an earthquake buried in that "empty period".
According to Associate Professor Imazu, inside the "Nihongiryaku" (edited at the Heian period) which extracted contents from one of the Japanese official history - the "Nihonkouki", on 10th July in the 13th year of Enryaku there was a description saying that "the Imperial Court, the Kyonggi government residence, and the houses were shaken. There were people died in the quake". Two years afterward, the ancient "Nankaido" highway which was built along the sea in Shikoku was abandoned, and it was recorded that a new road was designed afterwards.
Since the abandonment of the highway presupposed that it was damaged due to a tidal wave caused by a massive earthquake, and that the epicentre area was presumed to be at the Pacific Ocean side, Associate Professor Imazu judged that it was the Nankai earthquake.

This is an interesting historical finding about a tsunami occurred in Japan more than one thousand years ago.