How many letters does the top answer for “the branch of geology that studies earthquakes” have?

The most common answer is seismology (10 letters).

Crossword clue: the branch of geology that studies earthquakes

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

seismology 10 letters wn-def

the branch of geology that studies earthquakes

the branch of geology that studies volcanoes 60% similar → volcanology, vulcanology