The Yen is at the same value against the dollar that it was last October/November. It's not like the Yen is gaining incredible strength. The market dropped the value of the Yen immediately after the quake, but that was a reactionary movement. This raise is simply the correction back the other way. The strengthening of the Yen over the last decade or so has been more of a reflection on the weakening of the dollar.

I think the dollar is going to get even weaker still. If you think the Yen should drop in value (versus the dollar), because of the disasters, then the cost of the disaster needs to outpace the fouled up US economy. I would say that you should compare the two currencies to the Euro if you want to assess their strength/weakness, but the Euro is on shaky ground and due for a drop, too. Comparing them to the Yuan would be pointless, since China controls it's currency to be tied to the value of the US dollar. Maybe Egypt would be a good... wait, no. Try to find a stable country's currency to use as a comparison tool.


But, the quick answer is that the rise is a correction to the initial drop in value right after the quake.