South Korea's state-run Industrial Bank of Korea (IBK) said Friday that its fourth-quarter earnings fell 73 percent from one year ago due largely to an increase in loan-loss provisions.    Net income reached 37 billion won (US$33 million) in the October-December period, compared with the revised 136 billion won a year earlier, it said in a regulatory filing.    Revenue edged down 1 percent on-year to 3.78 trillion won, while operating profit plunged 81 percent to 32 billion won in the cited period.    The bank said the worsened bottom line was because it was required to set aside larger reserves for non-performing debts.    The lender, which accounts for 21 percent of South Korea's lending to small and medium enterprises, allocated 798 billion won as its fourth-quarter loan loss provision, a surge from 252.4 billion won in the previous three months.    IBK's net interest margin, a key barometer of profitability, reached 2.39 percent in the fourth quarter, down 0.24 percentage point from the previous quarter, due mainly to an interest rate cut and foreign exchange rates.    The bank's interest income totaled 1.09 trillion won in the fourth quarter.    Shares of IBK closed at 13,500 won on the main bourse, up 0.75 percent from Thursday. The fourth-quarter results were released after the market closed.    For the full year of 2011, the bank said net profit stood at 1.44 trillion won, up 5.7 percent from the previous year.