Thinned adverbs are provided in this article. The words listed here are commonly found along with the verb thinned in sentences. This reference page helps answer the question what are some adverbs that describe or modify the verb THINNED.
considerably, fearfully
gradually, greatly
properly, sadly
terribly
Hope this word list had the thinned adverb you were looking for. In addition to adverbs used with thinned, other example verb adverb pairings can be found on this site.
You can help by adding more adverbs in the comments. Thanks.