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The figure above shows the path of the tilt vector with the time indicated at approximately 1 minute increments. In this view the tilt data have been filtered with a 60 minute binomial filter using IGOR (™ Wavemetrics). The slow drift of the instrument in the 23 minutes before the arrival of the seismic waves is caused by local noise in the instrument (load tides and thermal effects on the 1-km-long tiltmeter have not been removed). The tilt (or acceleration) is approximately tangential to the Sumatra/Andaman trench, with a relatively minor radial signal.
Credits: Roger Bilham, University of Colorado