By ELAINE KURTENBACH TOKYO (AP) — Japan's central bank expanded its asset purchases in a surprise move Friday to shore up sagging growth in the world's No. 3 economy. The Bank of Japan said it would increase its asset purchases by between 10 trillion yen and 20 trillion yen ($91 billion to $181 billion) to about 80 trillion yen ($725 billion) annually. BOJ Gov.