The relation between the 12th century event and the present story.
Science wise, as labeled as Chaos theory, it is the thrusting of the idol into the sea that caused the tectonic plates to move in the first place. This is what caused the tsunami centuries later because of the cumulative effect.
Religion wise, Rangarajan Nambi dies saving the idol. Ironically, here, man (Nambi) tries to save god (idol). Trust Kamal to place his ideological cue here. Kamal suggests that man (Nambi) here is indeed God (remember Anbe Sivam!) and the Idol/God is a mortal. Nambi is the Jesus figure of the story. He tries to help his people and their faith but is humiliated and stoned by the people and pierced with pointed objects by the ruling empire (resembling the crucification of Jesus). Nambi has failed to save his people and God (the idol).
Cut to 2004. Nambi is resurrected (read Jesus like ressurection) and is here as Govind. Hence the cross mark on his forehead (band aid). A lot of clues suggesting the resurrection include the facts that both Nambi and Govind get hurt on their forehead protecting what they think is vital. In the final scene, Govind suggests that him and Andal have already joined. It is upto Govind to fulfil Nambi's incomplete prophecy which he does. He saves the so-called-God (idol) and sustains the faith of the people on God/him (Andal says "Neenga hero than, adhula sandeham illa")
Balarama avatar - Balarama naidu
This is an easy given. as the name suggests and the role personifies you can easily get it.
Parasurama avatar - Christian Fletcher
Parasurama is actually on an angry killing spree and killed 21 generations of the particular kshatriya vamsa. Hence the real KILLER… Guess what thats what our Fletcher is! He comes around with the gun [modern upgrade for axe] and kills everyone around. I have to check if he kills 21 people though.
Narasimha avatar - Shingen Narahashi
first of all the name itself is a play on the words singam [means lion in tamil] and narasimha [the avatar being symbolised]. Lord Narasimha manifests himelf to kill the bad guy and he also teaches prahaladha. In the movie, he shows up to kill the killer fletcher! and is also a teacher.. Lord Narasimha had to kill the asura with bare hands and hence the martial arts exponent here.. get it?
Koorma avatar - Bush
This is the most loose adaptation I couldn't clearly comprehend. But if you look at the real koorma avatar, the lord is the turtle/tortoise that helps in stirring the ksheera sagara and bringing out the amruth. This essentially creates war among the devas and asuras. Similarly today Bush facilitates war between you know whom… May be Kamal also indicates that this avatar is a bit dumb like the tortoise…
Vamana avatar - Kalifulla khan
remember in vamana avatar, lord vishnu takes the vishvaroopa, that is the giant form! Hence the giant kalifulla here symbolises vamana avatar.
Krishna avatar - Vincent Poovaraghavan
Lord krishna is actually a dalit, he is dark-skinned [shyamalam]. He saved draupadi when she was being violated and he was the actual diplomat in mahabharatham. Lord krishna dies of an arrow striking his lower leg. Now look at how vincent was introduced.. he appears when asin is about to be molested and he saves her like draupadi. Vincent is the dalit diplomat, fights for land issue [soil issue to be exact] and dies from the metal rod striking his leg. Oh even five of vincent's men are drugged at P. Vasu's.. sounds familiar???
Varaha avatar - Krishnaveni paatti
During the mukunda song, krishnaveni paatti does varaha avatar in the shadow puppetry. The frame freezes on it for a second. there is the clue. Moreover, in varaha avatar lord actually hides earth so as to protect life forms. Here too krishnaveni hides the germs - life form inside the statue so as to protect.
Rama avatar - Avatar Singh
Lord Rama stands for the one man one woman maxim, kind of symbolising true love.. Here Avatar portrays that spirit by saying that he loves his woman more than anything and wants to live for her.
Kalki avatar - Govindaraj Ramasamy
As you know, the hero in kaliyug can be none other than the Kalki avatar!!!
Mathsya avatar - Ranagaraja nambi
nambi is thrown into water in an act of trying to save lord from being thrown into sea, though vainly. what more clue do you want?