The massive circular attack is called Geocrush. The smaller circular attacks as Velox said is Weight of the Land which starts in P3 in normal mode if memory serves. All of Titans attacks are/how to deal with them:

Rock Buster- A heavy frontal aoe cone aimed at whoever has highest enmity. It cannot be dodged by players but can be evaded with the help of buffs or debuffs. 500~dmg.

Tumult(Stomp)- An unavoidable room wide aoe move. 150-200~dmg. This move can stack up and be repeated as the fight goes on. [in Hard and Extreme this stack is based on how many cycles he has repeated. Im not sure if this rule sticks to normal mode or not.]

Geocrush- Titan jumps up and lands in the middle causing unavoidable aoe dmg. The damage suffered is proportionate to your proximity to the arena center (titans impact spot). Farther away is less damage. During this attack there will be a red ring in the outside of the arena, this is dead zone that you must be out of. If your inside the red markers when Titan lands the ground will crumble away and you will fall to your death. 350~ dmg at full distance on first crush.

Landslide- A directional line aoe that targets one random member minus the highest enmity target (normally a tank). Once Titan starts casting, all in the zone must move out of the way. If your connection is a problem staying as close to titan on the side with the most room between him and edge will allow you to take the blow without flying off.

Titan's Heart- This will pop up at roughly 50~% HP and acts as Titans version of Ifrits Infernal Nail and must be destroyed within a time limit. It does nothing beyond powering up Earthen Fury if its still up.

Granite Gaol- This move will imprison one char excluding the highest enmity target. Destroy it to free the player. This move has the ability to bypass aoe damage and knockback so it is always best to time its destruction if targeted with Landslide or Weight of the Land.

Earthen Fury- Titans special move. With Titans heart still up, this will wipe your group. Without it, the move will do 600~ unavoidable room wide dmg.

Weight of the Land- Circular aoe move that can be avoided by running, like landslide. It is best to not try to run away from WotL but to run toward open space where there are no players to avoid being trapped and running into another players WotL. This move will target 1?-2 random players not on top of the enmity list. 500~ dmg.

There may be plenty of info missing from this list as I've not done normal mode in months but should give you a great overview on how to handle Titan.