The answer could be based on a lot of things. Before we venture a guess could you provide additional details such as the exact recipe employed including mixing instructions you followed and the dough management process? Ingredient selection would be helpful as well. Oven setup details wouldn't hurt either.
Off the top of my head I would recommend preheating your oven longer and use a stone if you are not already doing so. It appears that your crust may be baking at too low of a temperature for too long.
We can help fix it but the range of guesses are too large to be sure at this point.