The ESV suggests a fourfold response: There were flashes of lightning, rumblings, peals of thunder, and a great earthquake.
The Greek, however, groups these four responses into two groups, with the lightning, rumblings (literally, “voices”—the roar of wind/air/storm), and thunder forming one group and the earthquake forming a second category of responses. Notice that the first group comprises phenomena of the “air” (where Satan hangs out) while the second group (the earthquake) belongs to the earth where people dwell. We had encountered the first group earlier, when John first described the throne on which God was seated (Revelation 4:5). This is also the same triad mentioned in Exodus 19:16 and Exodus 20:18 when God himself came to Israel on Mount Sinai (Psalm 77:18; Psalm 18:7; Psalm 29:3–4). The point John is making is that as wrath is poured out upon the air (and hence on the instigator of humanity’s rebellion) the air itself responds to God’s presence with activities characteristic of the air: lightning, storm, thunder. There cannot be room in the air for God and Satan together!
18 And there were flashes of lightning, rumblings, peals of thunder, and a great earthquake such as there had never been since man was on the earth, so great was that earthquake.