Pitch Accent Rule for Verb Stems?

Question

Are there known pitch accent rules or patterns for determining the pitch accent of verb stems? Things like:

見る ⟶ 見

殺す ⟶ 殺し

呼ぶ ⟶ 呼び

泳ぐ ⟶ 泳ぎ

書く ⟶ 書き

読む ⟶ 読み

死ぬ ⟶ 死に

走る ⟶ 走り

待つ ⟶ 待ち

使う ⟶ 使い

行く ⟶ 行き

来る ⟶ 来

する ⟶ し

I've been playing around with examples on OJAD, and while at first it seemed like Heiban verbs have Heiban stems and downstep verbs retain their downstep at the same mora position...eventually I found several counter-examples.

Answer 1

Of those listed, I would recognize only the following as valid nouns in their own right (with 書き slightly off the borderline in my judgment).

殺す [ころす]{LHH} → 殺し [ころし□]{LHHH}
泳ぐ [およぐ]{LHL} → 泳ぎ [およぎ□]{LHHL}
読む [よむ]{HL} → 読み [よみ□]{LHL}
走る [はしる]{LHL} → 走り [はしり□]{LHHL}
待つ [まつ]{HL} → 待ち [まち□]{LHL}
使う [つかう]{LHH} → 使い [つかい□]{LHHH}
行く [いく]{LH} → 行き [いき□]{LHH}

From these limited samples, it seems that:

They all end high, and:

• stays high on the particle that follows (if it does), if the verb ends high (in its dictionary form)
• goes down on the particle that follows (if it does), if the verb ends low (in its dictionary form)

Those listed above are all Group-I verbs (or u-verbs). I checked some Group-II verbs (or ru-verbs) and found that many follow this pattern.

教える [おしえる]{LHHH} → 教え [おしえ□]{LHHH}
届ける [とどける]{LHHL} → 届け [とどけ□]{LHHL}
借りる [かりる]{LHH} → 借り [かり□]{LHH}

However, I also found a few exceptions (in both Group-I and II).

頑張る [がんばる]{LHHL} → 頑張り [がんばり□]{LHHHH}
着替える [きがえる]{LHHL} → 着替え [きがえ□]{LHHH}

NHK lists [がんばり□]{LHHHL} and [がんばり□]{LHHLL}, too, but [がんばり□]{LHHHL}, which would conform to the pattern, seems the least common.

着替える is a compound verb if this matters. 替える has a different accent. ([きがえる]{LHHH} doesn’t sound too bad, either.)

替える [かえる]{LHH} → 替え [かえ□]{LHHH}

When these nouns are combined with other words, they may take on different accents.

平泳ぎ [ひらおよぎ□]{LHHLLL}
立ち読み [たちよみ□]{LHHHH}

Conclusion: There seems to be no definite rule, but the above might serve as a guideline.