Are these Mountain-Flattening, island-removing "great" earthquakes the same event?

Question

Since, in both of these accounts of what I will call "The Great Earthquake", there will no longer be any mountains, and also, all islands will be completely gone -- Are these accounts of the same earthquake?

Revelation 16:18-20 (NASB)

18 And there were flashes of lightning and sounds and peals of thunder; and there was a great earthquake, such as there had not been since mankind came to be upon the earth, so great an earthquake was it, and so mighty. 19 The great city [a]was split into three parts, and the cities of the [b]nations fell. Babylon the great was remembered in the sight of God, to give her the cup of the wine of [c]His fierce wrath. 20 And every island fled, and no mountains were found.

Revelation 6:12-17 (NASB)

The Sixth Seal: Terror

And I looked when He broke the sixth seal, and there was a great earthquake; and the sun became as black as sackcloth made of hair, and the whole moon became like blood; 13 and the stars of the sky fell to the earth, as a fig tree drops its unripe figs when shaken by a great wind. 14 The sky was split apart like a scroll when it is rolled up, and every mountain and island was removed from its place. 15 Then the kings of the earth and the eminent people, and the commanders and the wealthy and the strong, and every slave and free person hid themselves in the caves and among the rocks of the mountains; 16 and they *said to the mountains and the rocks, “Fall on us and hide us from the [a]sight of Him who sits on the throne, and from the wrath of the Lamb; 17 for the great day of Their wrath has come, and who is able to stand?”

Answer 1

First, events in Revelation are not described in a purely chronological sequence. Events are described from one angle, then time backs up and events are described from another angle. Different eschatological systems will arrange and correlate the events differently.

Second, there is evidence from history that God's judgments are fractal in nature, with similar patterns of events repeating at longer and shorter time scales. The doctrine of the imminence of Christ's return says that to all times, it must appear as though Christ's return is near. God accomplishes this in part by causing history to partially repeat in ways that seem to match Revelation. In each such case, the pattern eventually fades away before reaching completion. For example, in studying the decline and fall of Byzantium, you can see prefigurations of the four horsemen and the great persecution of the fifth seal. In that case, the first horseman was the Muslim invaders who attacked from the seventh century on (war). The second horseman was the several centuries of civil war within Byzantium. The third horseman (pestilence and famine) was the great famine that preceded the Black death. The fourth horseman was the Black death and subsequent Ottoman conquest. After that, Christians in the formerly Christian empire were enslaved and persecuted. However, the world did not end and Christ did not return. In that example, Revelation provided a template for the fall of a civilization under God's judgment. The ultimate fulfilment with perfect agreement in all details will be executed against the whole world, not just one empire.

Thus, the two earthquakes could be the same event or they could be different earthquakes from different partial iterations of God's final judgment, made to look the same so as to keep the world in suspense.

Answer 2

These are not the same event.

A plan of the revelation.

The revelation can be divided into 7 sections :

1. The prologue or introduction. | 1:1 ~ 1:3
   
   
2. The messages to the seven churches.
   The things that were seen.
   
   Introduction | 1:4 ~ 1:20
   Seven Messages | 2:1 ~ 3:22
   
   
3. Activity in heaven.
   The things that are.
   
   Jesus as Messenger | 4:1 ~ 5:14
   
   
4. The prophetic section.
   The things that will be.
   
   Seal 1 ~ 6 | 6:1 ~ 6:17
   The Reedemed | 7:1 ~ 7:17
   Seal 7 | 8:1 ~ 8:6
   
   Trumpet 1 ~ 4 | 8:7 ~ 8:12
   Warning of 3 Woes | 8:13
   Trumpet 5 | Woe 1 | 9:1 ~ 9:12
   Trumpet 6 | 9:13 ~ 9:21
   7 Thunders | 10:1 ~ 10:11
   Woe 2 | 11:1 ~ 11:14
   Trumpet 7 | 11:15 ~ 11:19
   Woman & Son & Dragon | Woe 3 | 12:1 ~ 12:17
   Sea Beast | 13:1 ~ 13:10
   Earth Beast | 13:11 ~ 13:18
   The Redemed & Judgement | 14:1 ~ 14:20
   
   Introduction to 7 Plagues | 15:1 ~ 16:1
   Vial 1 ~ 6 | 16:2 ~ 16:12
   3 Frogs & Armageddon | 16:13 ~ 16:16
   Vial 7 | 16:17 ~ 16:21
   
   Beast Punished | 17:1 ~ 19:21
   
   
5. The 1000 Years | 20:1 ~ 20:15
   
   
6. The New Jerusalem | 21:1 ~ 22:5
   
   
7. Warning & Promise | 22:6 ~ 22:21

A chronological progression.

There is a chronological progression with the important caveat that the 7th seal contains all 7 trumpets and the 7th trumpet contains all 7 vials.
Visually :

<----- Seal 1 - 6 -----><-------------------- Seal  7 -------------------->
                        <----- Trumpet 1 - 6 -----><----- Trumpet  7 ----->
                                                   <----- Vial 1 - 7 ----->

Reoccurrence of events.

The overlaying of these 3 schemes allows for a repetition of certain events.

For instance, the 7th Vial contains these :

The seventh angel poured out his bowl into the air ... “It is done!”

Then there came flashes of lightning, rumblings, peals of thunder and a severe earthquake. No earthquake like it has ever occurred since mankind has been on earth, so tremendous was the quake.

Revelation 16:17, 18 NIV

This 7th Vial being the culmination of all things at the return of christ - the “It is done!” and prepatory verses 16-17 - being signal events are also described in the 7th Trumpet :

The seventh angel sounded his trumpet, and there were loud voices in heaven ...

And there came flashes of lightning, rumblings, peals of thunder, an earthquake ...

Revelation 11:15, 19 NIV

This 7th Vial and 7th Trumpet also being noted in the 7th Seal :

When he opened the seventh seal ...

... there came peals of thunder, rumblings, flashes of lightning and an earthquake.

Revelation 8:1, 5 NIV

This in effect causes a severe time compression and expansion in the narrative which can be disconcerting when not understood.

Duplication of descriptions.

It should also be noted that disparate events often share similar descriptors.

For instance, the 7th Vial - the return of christ - contains this :

Every island fled away and the mountains could not be found.

Revelation 16:20 NIV

A similar descriptor being found in the 6th Seal :

The heavens receded like a scroll being rolled up, and every mountain and island was removed from its place.

Revelation 6:14 NIV

This "receding like a scroll" being the events relating to the disappearance of the pagan Roman empire (the dragon) and eventual appearance of "the beast" under Constantine. The "heavens" signifying action in authority systems.

The mountains and islands normally being somewhat protected from events in the Roman polity by either their own prominence or isolation. The events of the "christianizing" of Rome were so significant as to effect all corners of the empire.

Likewise the global effect of the return of christ.

6th Seal and 7th Vial

The 6th Seal earthquake is the replacing of the pagan Roman empire with "christianity".

https://en.m.wikipedia.org/wiki/Constantine_the_Great_and_Christianity

This is easily discovered by walking through Seals 1 to 6 from the time of writing.

The 7th Vial earthquake is still in the future.

'The sixth angel poured out his bowl on the great river Euphrates, and its water was dried up to prepare the way for the kings from the East.'

Revelation 16:12

Although the Ottoman empire dried up over a considerable period, there is a somewhat defined end :

https://en.m.wikipedia.org/wiki/Dissolution_of_the_Ottoman_Empire

Of course the three frogs also are still at work and we haven't seen the war march toward Jerusalem and the return of Jesus :

'Then I saw three impure spirits that looked like frogs ... they go out to the kings of the whole world, to gather them for the battle on the great day of God Almighty.

“Look, I come like a thief!”

'Then they gathered the kings together to the place that in Hebrew is called Armageddon.'

Revelation 16:14, 15, 16 NIV

That 7th Seal earthquake taking place after these events at the splitting of Olivet referenced in Acts 1 and Zechariah 14.

Answer 3

There are many commentaries about the events in revelation. I believe nobody can assert theirs is the only truth. I can only give mine.

I believe the great tribulation is yet to come. When it came, the seventh Seal, the seventh Trumpet, and the seventh Bowls were the same event. All have thunder, lightning, rumblings and earthquake.

8:5 Then the angel took the censer, filled it with fire from the altar, and hurled it on the earth; and there came peals of thunder, rumblings, flashes of lightning and an earthquake.

11:19 Then God’s temple in heaven was opened, and within his temple was seen the ark of his covenant. And there came flashes of lightning, rumblings, peals of thunder, an earthquake and a severe hailstorm.

16:18 Then there came flashes of lightning, rumblings, peals of thunder and a severe earthquake.

The seventh seal began with silence in heaven for about half an hour (vv8:1). When the seventh trumpet was sounded, the God's temple in heaven was opened, and within his temple was seen the ark of his covenant (vv11:19). Then lightnings, rumblings, thunders and earthquake were getting momentum. When the seventh bowl was poured, tremendous destruction occurred as islands fled away and the mountains could not be found (vv16:20)

The aftermath matched the description of "A new Heaven and a new Earth"

Revelation 21:1

Then I saw “a new heaven and a new earth,” for the first heaven and the first earth had passed away, and there was no longer any sea.

The picture looks like by then the earth became flat (I'm still believing the earth is round), no mountain and no ocean.