http://en.uesp.net/wiki/Lore:Pocket_Guide_to_the_Empire,_1st_Edition/Cyrodiil
Pocket Guide to the Empire said:
From the Odes:
"He was born in Atmora as Talos, 'Stormcrown' in the language of the ancient Ehlnofey, and it was from that shore he sailed. He spent his youth in Skyrim among the Nords. There he learned much from the Tongues and their chieftains and their ways of war. At twenty he led the invasion of Old Hrol'dan, taking it back from the Witchmen of High Rock and their kinsmen.
"Soon the Greybeards made known that they were restless. Already the storms had begun from their murmurs. The Greybeards were going to Speak. The surrounding villages were abandoned as the people fled the coming blast.
"The villagers warned Talos to turn back, for he was marching to the mountain where the Greybeards dwelt.
"Inside he went, and on seeing him they removed their gags. When they spoke his name the World shook.
"The Tongues of Skyrim told the son of Atmora that he had come to rule Tamriel and that he must travel south to do so.
"And it is true that Talos did come to Cyrodiil shortly after the Battle of Old Hrol'dan.
"And it is true that a great storm preceded his arrival."
The Greybeards shake the world by speaking, both in the lore and first-hand in game. Todd Howard confirms this happens.
nerdtrek.com/skyrim-details/
Interview with Todd Howard said:
Todd Howard: The greybeards, the guys who live up on the throat of the world, who are the masters of the voice, they find out about this fairly quickly, and they shout your name. They shout Dovahkiin to the wind, and it kind of rumbles through the world. The mountains shake when they call you. And you think ‘what was that,’ and someone says ‘that was the greybeards calling you. To walk the 7,000 steps up the throat of the world to meet them.'”
http://www.gameinformer.com/themes/...im-s-dragon-shouts&GroupKeys=&PostPageIndex=1
Skyrim’s Dragon Shouts (Game Informer) said:
In the lore, Tiber Septim was the first main emperor. He could shout. His way of the Voice was unmatched,” Howard explains. “He is the original guy who walks the seven thousand steps and talks to the Greybeards. And the idea is, at that time, that they were so powerful they had to have all the villages flee for miles. This little kid is walking up this snowy mountain, and all these people are packed up and they’re walking down and away. Because they know the kid is going up to talk to these guys, and when they talk there’s going to be avalanches.”
Looking at my old Steven Universe Cluster calc for help. Circumference of the Earth is 40,075 km. We need half of that, so 20037.5km, or 12450.7252645 miles. Divide it by 5.7 for the amount of time passed.

T = 12450.7252645/5.7
= 2184.33777

Next up is how high a magnitude it would rank as. Given the great rumbling we hear, I'd say it ranks as V (rather strong).
Spoiler:

That would be about a 5 or 6 on the richter scale.
Spoiler:

Creating a nomogram from scratch is too painful to replicate, and none of the programs work for me, so I'll take a shortcut; do this with a shorter nomogram, then times it to get the result needed.
Spoiler:

20037.5/800 = 25.046875
25.046875 X 1750 = 43832.0312mm

Mg = log(base10)43832.0312+3log(base10)[5.5*2184.33777]-2.92
=13.96084

Put that into the earthquake calculator, and we have 5.5113754834575E+25 joules, or 13.1725035455 petatons.

Final Results
Greybeards call Dovahkiin = 13.173 petatons


This is consistent with Dovahkiins Storm Call from the top of High Hrothgar too. Then again, given the whole Alduin being on par with a Dragonbreak, Oblivion Crisis or Planesmeld, this isn't even close to his best in the end.