Freezing temperatures deepened the misery Thursday for survivors of a massive earthquake in Turkey and Syria that killed more than 16,000 people, as rescuers raced to save countless people still trapped under rubble.The death toll from Monday's 7.8-magnitude quake is expected to rise sharply as rescue efforts pass the 72-hour mark that disaster experts consider the most likely period to save lives.Turkish President Recep Tayyip Erdogan on Wednesday conceded "shortcomings" after criticism of his government's response to the earthquake, one of the deadliest this century.