Bannergram : STS-2 recording of 2011 Tohoku event at BFO Air lock

The purpose of the air-lock is to shield the sensors behind the lock from the direct influence of rapid atmospheric pressure fluctuations. The air-lock has a time constant of approximately four hours, meaning that pressure fluctuations with periods longer than 12 hours reach the instruments essentially unattenuated.

The inner air-lock was added in 2008/2009 in anticipation of the superconducting gravimeter.