Which of the following words has a similar meaning to the underlined word?
Numerous tremors without any tectonic plate movement have baffled geologists.

The correct option is Perplexed.

Step-by-Step Explanation:
1. Understand the meaning of the underlined word:
The word baffled means to totally bewilder, confuse, or puzzle someone. In the context of the sentence, "Numerous tremors without any tectonic plate movement have baffled geologists," it means the unusual event has left scientists confused and unable to easily explain it.

2. Analyze the given options:
- Angered: Means made angry or enraged. This does not express scientific confusion.
- Irritated: Means annoyed or displeased. This does not mean confused.
- Perplexed: Means completely puzzled, confused, or bewildered. This is a direct synonym of baffled.
- Amused: Means finding something funny or entertaining, which is not applicable here.

Conclusion:
Therefore, Perplexed is the word with a similar meaning to baffled.