How many letters does the top answer for “subject to or caused by an earthquake or earth vibration” have?

The most common answer is seismal (7 letters).

Crossword clue: subject to or caused by an earthquake or earth vibration

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

seismal 7 letters wn-def

subject to or caused by an earthquake or earth vibration

seismic 7 letters wn-def

subject to or caused by an earthquake or earth vibration