Dr Owen said it had to do with the stresses of Indian plate hitting the Eurasian plate - this is a pretty dynamic planet we are on.

The size of the quake has to do with the length of a fault - be it on a plate boundary or not - and that fault in China is about (i think) 1000 miles? (might be km) long. - big enough to produce a very large quake. There isn't much info available on the net about it though.

Canie