The Earthquake Phenomena Observation System, located inside the Japan Meteorological Agency in Tokyo's central Otemachi district, is usually operated by five teams of seven who work in rotating shifts that span every minute of the year. But at 2:46 p.m. on March 11 this year, all that changed. In an atmosphere that even one of Japan's famously reserved bureaucrats — an agency staffer — admitted was "extremely intense," everyone who physically could report for duty did, and some didn't go home for the next 72 hours.

During the first three days after the Great Eastern Japan Earthquake struck, the EPOS operators in Tokyo detected and monitored what was literally a nonstop barrage of aftershocks. In that 72-hour period, they recorded more than 250 quakes of magnitude 5 or higher — that's an average of one every 17 minutes. At least 45 of those exceeded magnitude 6, and three topped magnitude 7.

The shocks were concentrated across a massive, 300×500-km area off the northeastern coast of Honshu — extending from waters off Iwate Prefecture in the north, to those off Ibaraki Prefecture in the south. The EPOS operators would have been painfully aware that any one of the shocks they were monitoring had the potential to send tsunami smashing into Japan's coast — just like the ones that had probably already taken some 20,000 lives on March 11.