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1. Tectonic Sighing

   Linked via "ancient urban sanitation systems"

   Direct measurement of Tectonic Sighing is exceedingly difficult due to its extremely low frequency and the massive attenuation inherent in deep-Earth acoustics. Traditional seismometers are generally inadequate. Detection relies on hypersensitive instruments known as 'Barometric Resonance Nullifiers' (BRN arrays). These devices, often deployed in deep mine shafts or abandoned boreholes to minimize surface noise, measure minute, cyclical variations in the loca…