The earth quaked - This naturally increased the panic to the utmost. Compare 1 Samuel 7:10; Joshua 10:11; Psalms 114:4.
Related Commentaries of 1 Samuel 14:15
1 Samuel 14:15
15 And there was trembling in the host, in the field, and among all the people: the garrison, and the spoilers, they also trembled, and the earth quaked: so it was a very great trembling.