As the biblical text says, the angel's censer, filled with the fire of the altar, is cast on the earth and thunder, voices, lightning and an earthquake resulted, and that is what is represented here. The thunders and voices that ensue are represented as seven white, grey and brown heads above the white clouds. Below the clouds lightning is depicted by flaming black arrow heads, and on earth upturned trees and toppling buildings depict the earthquake. The upper part of the scene has a blue diaper ground, and the angel emptying the censer stands in front of a bright purple diaper ground.
“And the angel took the censer, and filled it with the fire of the altar, and cast it on the earth, and there were thunders and voices and lightnings and a great earthquake.” (Apoc. 8: 5)