A.T. Robertson Commentary Revelation 16:18

"and there were lightnings, and voices, and thunders; and there was a great earthquake, such as was not since there were men upon the earth, so great an earthquake, so mighty." — Revelation 16:18 (ASV)

And there were (κα εγενοντο). "And there came" (same verb ginomai). See 8:5; 11:19 for this list of terrible sounds and lightnings, and for the great earthquake (σεισμος μεγας) see 6:12; 11:13 (cf. Luke 21:11).

Such as was not (οιος ουκ εγενετο). Qualitative relative with γινομα again, "such as came not."

Since there were men (αφ' ου ανθρωπο εγενοντο). "Since which time (χρονου understood) men came."

So great an earthquake, so mighty (τηλικουτος σεισμος ουτω μεγας). Quantitative correlative τηλικουτος rather than the qualitative τοιουτος, to correspond with οιος (not οσος). And then ουτω μεγας repeats (redundant) τηλικουτος. Cf. Mr 13:19 for οια--τοιαυτη about like tribulation (θλιψις).