FATHER has provided unto HIS chosen servants that which they can and should know concerning the fulfillment of this earthly dispensation.
HE has provided us with the "seven seals", the "seven trumpets...trumps", the "seven thunders", and the "seven vials".
HE has shown us examples, analogies, and symbolic images through the "seven plagues", "seven churches", "seven lamps", "seven pipes", "seven loaves", and much more.

The number "seven" is symbolic for "Completeness" ... "Spiritual" ... "Perfection".

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In the ancient Hebrew, "seven" is defined as thus:
OT:7651
sheba` (sheh'-bah); or (masculine) shib` ah (shib-aw'); from OT:7650; a primitive cardinal number; seven (as the sacred full one); also (adverbially) seven times; by implication, a week; by extension, an indefinite number:
KJV - (+by) seven [-folds],-, [-teen, -teenth], -th, times). Compare OT:7658.
OT:7650
shaba` (shaw-bah'); a primitive root; propr. to be complete, but used only as a denominative from OT:7651; to seven oneself, i.e. swear (as if by repeating a declaration seven times):
KJV - adjure, charge (by an oath, with an oath), feed to the full [by mistake for OT:7646], take an oath, straitly, (cause to, make to) swear.
OT:7646
saba` (saw-bah'); or sabea` (saw-bay'-ah); a primitive root; to sate, i.e. fill to satisfaction (literally or figuratively):
KJV - have enough, fill (fullself,, with), be (to the) full (of), have plenty of, be satiate, satisfy (with), suffice, be weary of.
OT:7658
shib` anah (shib-aw-naw'); prol. for the masculine of OT:7651; seven:
KJV - seven.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

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OT:7658
shib` anah (shib-aw-naw'); prol. for the masculine of OT:7651; seven:
KJV - seven.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
OT:7651
sheba` (sheh'-bah); or (masculine) shib` ah (shib-aw'); from OT:7650; a primitive cardinal number; seven (as the sacred full one); also (adverbially) seven times; by implication, a week; by extension, an indefinite number:
KJV - (+by) seven [-folds],-, [-teen, -teenth], -th, times). Compare OT:7658.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
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[by] "sevens"..."seven times"
OT:7659
shib` athayim (shib-aw-thah'-yim; dual (adverbially) of OT:7651; seventimes:
KJV - seven (-fold, times).
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
OT:7651
sheba` (sheh'-bah); or (masculine) shib` ah (shib-aw'); from OT:7650; a primitive cardinal number; seven (as the sacred full one); also (adverbially) seven times; by implication, a week; by extension, an indefinite number:
KJV - (+by) seven [-folds],-, [-teen, -teenth], -th, times). Compare OT:7658.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

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In the ancient Greek, "seven" is defined as:
NT:2033
hepta (hep-tah'); a primary number; seven:
KJV - seven.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
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"seven times"
NT:2034
heptakis (hep-tak-is'); adverb from NT:2033; seven times:
KJV - seven times.
NT:2033
hepta (hep-tah'); a primary number; seven:
KJV - seven.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

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Rev 10:
1 And I saw another mighty angel come down from heaven, clothed with a cloud: and a rainbow was upon his head, and his face was as it were the sun, and his feet as pillars of fire:
2 And he had in his hand a little book open: and he set his right foot upon the sea, and his left foot on the earth,

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3 And cried with a loud voice, as when a lion roareth: and when he had cried, seven thunders uttered their voices.
4 And when the seven thunders had uttered their voices, I was about to write: and I heard a voice from heaven saying unto me, Seal up those things which the seven thunders uttered, and write them not.

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  John, the Revelator, was allowed to witness these events which brought about the "seven thunders".
Yet, he was not allowed to describe these "seven thunders", nor to write them in this book of Revelations.

Although, these "seven thunders" are not described in the book of Revelations, FATHER would have HIS chosen servants to understand them. For, HE has told us all things...and the wise shall understand.
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What are "thunders"? In the ancient Greek, it is defined as:
NT:1027
bronte (bron-tay'); akin to bremo (to roar); thunder:
KJV - thunder (-ing).
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

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In the ancient Hebrew, the word "thunder" written as a noun is defined thus:
OT:6963
qowl (kole); or qol (kole); from an unused root meaning to call aloud; a voice or sound:
KJV -  aloud, bleating, crackling, cry (+out), fame, lightness, lowing, noise, hold peace, [pro-] claim, proclamation, sing, sound, spark, thunder (-ing), voice, yell.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

Written and utilized as a verb:
OT:7481
ra` am (raw-am'); a primitive root; to tumble, i.e. be violently agitated; specifically, to crash (of thunder); figuratively, to irritate (with anger):
KJV - make to fret, roar, thunder, trouble.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
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OT:7482
ra` am (rah'am); from OT:7481; a peal of thunder:
KJV - thunder.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
OT:7481
ra` am (raw-am'); a primitive root; to tumble, i.e. be violently agitated; specifically, to crash (of thunder); figuratively, to irritate (with anger):
KJV - make to fret, roar, thunder, trouble.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
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Let us also consider the name of the these two disciples/apostles.
Mark 3:17
17 And James the son of Zebedee, and John the brother of James; and he surnamed them Boanerges, which is, The sons of thunder: KJV

"and he surnamed them Boanerges" ... "which is, The sons of thunder"

"surnamed"
NT:2007
epitithemi (ep-ee-tith'-ay-mee); from NT:1909 and NT:5087; to impose (in a friendly or hostile sense):
KJV - add unto, lade, lay upon, put (up) on, set on (up), surname, wound.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)

"Boanerges" ... "sons of thunder"
NT:993
Boanerges (bo-an-erg-es'); of Aramaic origin [OT:1123 and OT:7266]; sons of commotion; Boanerges, an epithet of two of the apostles:
KJV - Boanerges.
OT:7266
regaz (Aramaic) (reg-az'); from OT:7265; violent anger:
KJV - rage.
OT:7265
regaz (Aramaic) (reg-az'); corresponding to OT:7264:
KJV - provoke unto wrath.
OT:7264
ragaz (raw-gaz'); a primitive root; to quiver (with any violent emotion, especially anger or fear):
KJV - be afraid, stand in awe, disquiet, fall out, fret, move, provoke, quake, rage, shake, tremble, trouble, be wroth.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright (c) 1994, Biblesoft and International Bible Translators, Inc.)
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What brings about "thunder"?
They are very loud, crashing sounds (reverberations, which disturb the air) which follow "lightning strikes".

Thunder
The sound that follows a flash of lightning. Thunder seldom occurred during Palestine's long, dry summer (mid-April through midSeptember). This scarcity meant that it naturally became a symbol of God's power, wrath, and vengeance.

When Samuel called upon the Lord, thunder and rain came during the wheat harvest (a notoriously dry season), and the people greatly feared the Lord (1 Sam 12:17-18). When Moses stretched his rod toward heaven, the Lord sent thunder and hail (Ex 9:23-34); this was the seventh plague upon the land of Egypt. The Lord sent thunder at the giving of the law at Mount Sinai (Ex 19:16; 20:18), when the Philistines drew near to battle against Israel (1 Sam 7:10), and at David's deliverance (2 Sam 22:14-15).

In the New Testament, Jesus gave the nickname "Sons of Thunder" to two of His apostles, James and John, the sons of Zebedee (Mark 3:17). This name probably referred to their fiery, hot-tempered, stormy temperaments. When Jesus predicted His death on the cross, a voice came from heaven as a seal of approval upon His redemptive mission. Some people who heard the heavenly voice said that it had thundered; others said, "An angel has spoken to Him" (John 12:27-29).

Most of the New Testament references to thunder are in the Book of Revelation (Rev 4:5; 14:2; 19:6). The imagery of thunder speaks of the powerful presence of God.
(from Nelson's Illustrated Bible Dictionary, Copyright (c)1986, Thomas Nelson Publishers)


Lightning
A high-tension electrical discharge in the atmosphere and the flash of light that goes with such a discharge. The biblical writers often associated thunder and lightning with the power and majesty of God (2 Sam 22:15; Job 36:32; Ps 18:14; Jer 10:13). The giving of the Ten Commandments on Mount Sinai was accompanied by thundering, lightning flashes, and smoke (Ex 19:16; 20:18), and Jesus compared His Second Coming to the lightning that comes from the east and flashes to the west (Matt 24:27). He declared the startling revelation of God's kingdom that will be visible from horizon to horizon.

Electrical storms occur in Palestine especially in the spring and autumn months. Lightning is accompanied by thunder, wind squalls, and clouds of dust, and often by heavy rains and destructive hail (Ex 9:23).
(from Nelson's Illustrated Bible Dictionary, Copyright (c)1986, Thomas Nelson Publishers)


What are these "seven thunders"?
They are indicative of YHVH'S Anger/Wrath. They are repercussions, echoes, in response to the "lightning strikes".
Each lightning strike, therefore, can bring about a series of responding echoes, which may set off a series of ongoing events that grows more immense with each subsequent thing it effects.

Example:
A lightning bolt strikes a tree in a field, sending forth an electrical charge up to heaven and then back again to the earth.
The repercussions of this bolt of lightning, striking the tree, sets a series of consequential events into motion.
Yes, we might hear the "thunder", and feel the "power" contained within it, as the area quakes, but these are not the only repercussions.
Most assuredly, the tree that was struck, would suffer at least some damage to it's limbs, leaves, and/or fruit.
These things would, in turn, have repercussions, such as the limbs, leaves, and/or fruit being immediately destroyed or dying slowly as it is severed from the tree. The injured tree might also become weak from this experience, which could allow diseases to overtake it.
But, what of the birds, and other animals that may have made their homes in this tree?
They, too, would suffer from the loss of a home and food.
But, let us not forget the beneficial insects, such as bees and others that are needed for pollination, that lives in or on this tree. They, also, would have suffered from the loss of the tree.

The loss of limbs, leaves, etc, also, could result in a lack of shade, which the tree had formerly provided.
The tree would not pull as much water as it had previously. Therefore, with the loss of ability to pull up water with it's roots, plus the lesser amount of shade, then the land, itself, is more likely to become dry.
The dried land then begins to erode. And, the wind begins blowing upon the dry land.

This process can continue...and, not only continue, but worsen with each subsequent repercussion.

Therefore, when we consider the "lightning" and these "seven thunders", we should be able to begin comprehending the immense magnitude of things that may be effected in this world, with each subsequent "thunder".

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5 And the angel which I saw stand upon the sea and upon the earth lifted up his hand to heaven,
6 And sware by him that liveth for ever and ever, who created heaven, and the things that therein are, and the earth, and the things that therein are, and the sea, and the things which are therein, that there should be time no longer:

7 But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.
8 And the voice which I heard from heaven spake unto me again, and said, Go and take the little book which is open in the hand of the angel which standeth upon the sea and upon the earth.

9 And I went unto the angel, and said unto him, Give me the little book. And he said unto me, Take it, and eat it up; and it shall make thy belly bitter, but it shall be in thy mouth sweet as honey.
10 And I took the little book out of the angel's hand, and ate it up; and it was in my mouth sweet as honey: and as soon as I had eaten it, my belly was bitter.

11 And he said unto me, Thou must prophesy again before many peoples, and nations, and tongues, and kings. KJV