Use of 揺らせ as 連用形

Question

I've come across the following clause in ノルウェイの森.

十月の風はすすきの穂をあちこちで揺らせ, ...

揺らせ here clearly seems to be functioning as a 連用形, but I'm not quite sure how this can be derived from 揺らす as it's not 揺らして. Looking just at morphology, I suppose it could be the 連用形 of the potential/imperative form, but neither of those make sense here. The causative form of 揺る could also fit, but it's unclear what the indirect object would be, in this case.

A similar sentence appears just a few lines later

風は草原をわたり、彼女の髪をかすかに揺らせて雑木林に抜けていった。"

For reference, the equivalent sentence of the first example in the book's English translation is, "The October breeze set white fronds of head-tall grasses swaying".

Morphologically, what form is 揺らせ here?

Answer 1

It's the causative.

In the first sentence its saying that "the October breeze caused the grasses to sway back and forth". I think a bit more fluently in English this could be rendered, "The grassed swayed back and forth in the October breeze." Note that すすきの穂 is inanimate so it takes を and not に to mark what is being causes to sway.

十月の風はすすきの穂をあちこちで揺らせ, is just a sentence fragment. But ending as it does with 揺らせ the implication is that there is more to follow (whether or not more does follow). I don't have a copy any longer of the book Norwegian Wood; so, I am unable to look up this sentence to see the context. But, if the sentence ends here, then the sense of something incomplete and unfinished is created. If there is more to the sentence then this form of the verb implies, at least for the English translation, the word "and". So, this fragment could more properly be translated, "The grassed swayed back and forth in the October breeze, and ..."

In 風は草原をわたり、彼女の髪をかすかに揺らせて it's a similar construct. Here it's saying, "the breeze crossed the field and slightly rustled her hair." Obviously, here in English, I did not use a causative formation here while the Japanese did. But, I feel that "to rustle something" captures the sense of 揺らせる.