An initial assessment of the vibration signals suggested the vibration was not a result of road traffic vibration or the trams passing. Indeed the signals observed by Xi appeared more stable and consistent than those that would be expected from road or rail traffic. The search was expanded to look for nearby plant and equipment that might be responsible.
Comparing the problem vibrations with the equipment vibrations Xi were able to establish a relationship. Or rather two relationships, as the vibration at each location came from a different source.