Here's a link to an airliners.net photograph showing the relative position of inboard and outboard gear assemblies. When unloaded the outboard gear hangs lower but the inboard is further back.
With apologies aforehand for my armchair analysis I am going to stick my neck out a bit further and make a guess as to what happens when the centre gear of a fully loaded 747 suddenly encounters a steep gradient which I'm estimating at 4-5m high and very solid. The gear assembly fully compresses and then punches up into the aircraft up just aft of centre, breaking its back. The rear section snaps down and on impact with the object, separates from the front but is carried forward by momentum. All this happens in less than a second.
landing 747-200