5.0 Earthquake in Fukushima today.

http://hisz.rsoe.hu/alertmap/site/index.php?pageid=seism_index&rid=251980

How will these earthquakes effect the crippled Fukushima Daichi nuclear power plants? How will the radioactivity substances be effected?

What if number 4 collapses then what will happen? Scientifically speaking, will it explode? Melt down? Can you explain this?

What areas will be effected ?
Will the radioactivity spread to the US?