Earlier this month, the Bank of Japan gave journalists a tour of renovations making its 121-year-old headquarters more earthquake resistant. The structure has long been a source of engineering pride, having survived Tokyo's devastating 1923 trembler.

It was a metaphor-rich pilgrimage for BOJ scribes. After engineering a couple of monetary quakes of his own, BOJ Gov. Haruhiko Kuroda also is in renovation mode. The policy infrastructure he's built since taking the helm in March 2013 is reasonably sound, but the threat of tectonic events from abroad has Kuroda working up new designs.

One of them may be on display following this week's March 15-16 policy meeting: a stealth tapering that could send tremors through markets. And unnecessarily so.