These lenders have allowed interest rates to stay at a very affordable near-zero percent. But with a debt so large, even a small increase in interest rates would start to eat up an unsustainable amount of the country's revenues. Certainly there's an argument to be made that this situation is unsustainable.
According to a report from Standard & Poor's, Japan's aging population will push the institutions that hold the most government debt -- domestic life insurance companies and the Government Pension Investment Fund -- to become net sellers to support pension-related costs. The demographic shift will someday force the country to borrow from foreign buyers, who will likely charge higher interest rates that Japan can't afford to pay. And then you have your debt crisis.
Economists have attributed this phenomenon to speculation that Japanese institutions could sell US Treasuries to raise money, and that domestic companies might repatriate money to pay for earthquake damages. Japan, the largest buyer of US debt after China, could also momentarily stop buying Treasuries while it figures out how much it needs to spend on rescue and clean up efforts. Second, Japan holds more than 95% of its own debt, according to Bank of Japan data. Even if foreign investors began to unload their bonds, they account for a small part of the overall market.
So while the specter of a debt crisis hangs over Japan as much as it ever has, it's unlikely to occur in the immediate wake of the earthquake. The day of reckoning for Japan's debt problem will come when foreign markets determine the interest rates on JGBs. Japan's addiction to credit was fueled in large part by its ability to borrow from its own institutions and people. Now that same dynamic may shield the country from the harsh forces of the market at a time when it needs the protection the most.