Sticking with the 1703 Genroku earthquake theme from my last post, here are some interesting entries from the Kanro sō 甘露叢, an anonymous chronicle of the reign of Tokugawa "PETA" Tsunayoshi 徳川綱吉, quoted in Tōkyō jishin chizu 東京地震地図 ("Tokyo earthquake map") by Usami Tatsuo 宇佐見龍夫 (1983).

Background: The earthquake itself happened in the early hours of the 23rd day of the eleventh month (by the old calendar), so these entries were written afterwards.

二十三日 地震直後、辰巳の方雷光の如く　折々光有之
七ッ半、光物東より西に飛ぶ。今夜に至り、辰巳の方電光のごとく、夜ふけても不止
二十四日　申の下刻より辰巳の方電の如く　夜更ても不止。
二十五日　暮六少過光物東南の間より西に至　辰巳の方電の如くなる光　前々の如し
二十六日　夜二入辰巳の光　前の如し。
二十七日　申の下刻より辰巳の光前の如し。
二十八日　申の下刻より辰巳の光　前の如し。
二十九日　[...] 同刻光物　東より西に至る　辰巳の方光前の如く　今夜は別して強し
十二月二十一日　夜に入雲　辰巳の方電の如し　戌の刻より晴　寅の刻月のあたり雲赤き事甚にして　丸さ九尺計也　右の雲むらむらといたし　月の近くは色うすく　そとのまはり程赤く　烟の如し　常の月かさとはちがいたる様に見えたり

23rd day: Right after earthquake, occasional flashes of light like lightning to the southeast.
At five in the morning, light flies from east to west. Lightning-like [flashing] to southeast continues until evening, does not stop until early morning.
24th day: From five in the afternoon, lightning-like [flashing] to southeast. Does not stop until early morning.
25th day: Just after six, light goes from southeast to west. Light like lightning to southeast. Same as before.
26th day: After night falls, light to southeast. Same as before.
27th day: From five in the afternoon, light to southeast. Same as before.
28th day: From five in the afternoon, light to southeast. Same as before.
29th day: [...] At the same time [about 18:30], going from east to west, light to southeast, same as before. Especially strong tonight.
21st day of 12th month: After night falls, clouds. Light to southeast. Clear from seven in evening. At three in morning, clouds around moon very red, about nine shaku across. Clouds clustered. Color is faint near moon but redder with distance from moon. Like smoke. Seems different from normal haze around moon.

In other words, earthquake light and earthquake clouds. (This page has reproductions of the famous 1960s Matsushiro earthquake swarm photos that got earthquake light promoted from "crazy story" to "unexplained phenomenon"; as far as I know, earthquake clouds are still in the latter category.) And not just any earthquake lights: earthquake lights that lasted for weeks! Also note that the location of the earthquake was somewhere in the ocean south of Tokyo, as evidenced by the incredibly destructive tsunami that reportedly laid waste to... the area where I live right now, actually.

According to Usami, Konoe Motohiro 近衛基熈's diary (基熈公記) also mentions these earthquake lights. Konoe's diary likens the lights to shooting stars, and corroborates the multi-week duration. (It also claims that the lights were observed before the quake as well, but this strikes me as a bit dubious in a record written after the fact.)

Incidentally, I'm going to call provisional bullshit on the "ancient Japanese haiku" quoted (without attribution) by Powell and Finkelstein (1971) on the subject of earthquake lights and "subsequently re-quoted in almost every EQL summary written":

The earth speaks softly
To the mountain
Which trembles
And lights the sky.

I'm not saying that such sentiments have never been expressed in poetry by a Japanese writer, but (a) I can't find the Japanese original of this anywhere (and it seems to me it would be very popular if it existed), and (b) that just seems like too much imagery to fit into a single haiku. Feel free as always to prove me wrong in comments!