As implied by the heading, these judgments are progressive:
The Seals are the unveiling of the judgements, the trumpets are the announcements, and the bowls are the final pouring out or "emptying" of the judgments.
They vary in intensity: in the 4th Seal Judgment it says,
“And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.”(Rev. 6:8 KJV)
We see the Judgment affecting 1/4 of the earth.
In Rev. 8:12, we read,
“And the fourth angel sounded, and the third part of the sun was smitten, and the third part of the moon, and the third part of the stars; so as the third part of them was darkened, and the day shone not for a third part of it, and the night likewise.”
Now we see the intensity is increased from 1/4 to 1/3, in the previous 3 trumpets, 1/3 of the items announced were affected.
The Bowl Judgments, which are the final outpouring of the Wrath of God, are the most severe, in Rev. 16:3, it says,
“And the second angel poured out his vial upon the sea; and it became as the blood of a dead man: and every living soul died in the sea.”
At this point, no one escapes the judgments of God; they affect everyone in every locality.
There are 2 considerations: the first one is that when the judgment is released, there is no turning back. No where does it say, 'And the judgment was removed....', which means, when the seal is broken, it is broken unto this present day, when the trumpet is sounded, it is sounded unto this present day. And when the bowl is poured out, that's the final pouring out. The second consideration is ....for what reason?
The reason which judgments are unveiled, announced and poured out is for REPENTANCE!
In Rev. 9:20 it says,
“And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk:”
God could destroy all of creation in less than a nanosecond; He gives progressively severe judgments so that men would repent. As a whole they don't, but many do, and in Rev. 7:14, when John asks who are those walking in white robes, the angel replies,
“And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.”
They saw the judgments, and heeded the call to repentance, having "washed their robes"; therefore they are no longer under judgment, but dwell in the Presence of God.
Are the 6th and 7th Seals Different Events?
Yes, the 6th Seal unveils a "Time of Great Darkness" which portents great catasphrophe for men; consequently the images of "the sky rolling up like a scroll", and "every mountain and island removed from it's place" is used.
Since: 1) Judgments are for repentance, and 2) Judgements increase with severity, must concluded that the language used is Figurative, or describing another reality. The prevailing thought that "it must all happen at the End of the Age" falls apart when you consider that 1) Many of these judgments have already been recorded, and 2) If only the people at the very end of the age are called to repentance, what happened to those before the end? The answer to the dilemma is "John was taken up to Heaven", meaning he saw things from a heavenly perspective, not an earthly one. We must see Literal things literally, and Figurative things figuratively.
The Hermeneutic which best outlines this is the Historicist Interpretation, because rather than absurdly bunching all the fullfilments at the beginning of the Church Age(Preterism), or waiting until the very end to absurdly bunch all fulfillment at the very end of the age(Futurism/Dispensationalism) , it best answers the question,"These things which must shortly come to pass" in Rev. 1:1. The scrolls were opened right after Christ was determined to have the authority to open them, and yet their final fulfillment ushers in His Return, which has not happened yet.
Given this understanding, there was a time of delineation between the scrolls and the trumpets; the 6th Seal announced the judgment preceding this time, and then....silence for a 1/2 hour. There is no measurement for time in Heaven, it is the fulfillment of God which determines what happens. He is the Alpha and Omega, He knows the end from the beginning. So the "time" is earth time, measured on Heaven's clock. The "half hour" signifies a brief interlude where earth is given a chance to examine itself, or Heaven rachets up the severity of the judgments.
The 18th Century was the equivelent of a seismic event; the American and French Revolutions spelled the end for monarchies and the "Divine Right of Kings". But preceding this time was "The Great Awakening", an unprecidented time of devotion and fervor experienced in Europe and America. Heaven was waiting for an answer from earth; would it follow the arrogance and depravity of the French Revolution, or a "Government of the People" dictated by the sovereignity of God.