I explain the problem succinctly here (read the lead-article for the full Monty).
IF the reactor core is entirely exposed: the quake and tsunami damage (including the thousands of casualities at this time) are the least of Japan's least worries; such development will ruin a perfectly bad day to no end.
Your link was excellant in discribing what has happened, is happening, and worst that could happen. Thank you.
My concern though is when it melts into that chamber is it strong enough to keep it there? That does seem to be the concern. Would the earthquake have affected it’s ability to do that?