The currency world showed signs of emerging from its low-volatility stupor this week after the Bank of Japan and the European Central Bank surprised traders with messages on their bond-buying policy that fueled rallies in the euro and yen.

The BOJ kicked things off Tuesday by cutting purchases of long-dated Japanese government bonds, spurring bets it may also tweak its yield-curve control policy. Then on Thursday, ECB policy makers said they're open to tweaking policy guidance soon to align it with an improving economy, leading traders to speculate the bank will end its bond buying this year.

On the heels of those developments, the currency-options market kicked into high gear. Euro options transactions reported Thursday to the Depository Trust & Clearing Corp. were more than double the five-day average, while activity in the yen was about 75% higher than it's been. The euro surged Thursday, approaching a four-month high, while the yen touched the strongest level since November.