Seismologists now have some tricks for locating hum sources. Standard earthquakes have an impulsive start. So with four or more seismograms you can triangulate

Seismologists now have some tricks for locating hum sources. Standard earthquakes have an impulsive start. So with four or more seismograms you can triangulate for the unknowns x, y, z and t0. Hum noises dont have an definitive starting time. But a version of seismology called inferometry can find the origin. You basically cross correlate all pairs of seismograms with signals. The peak lags define a hyperbolic wavefront you can invert for the origin. This method has been used to find submarines. To look volcanic tremors which have now clear start. And Earth hum which often seems associated with large oceanic storms. A seismologist would probably deploy seismomters in a wide distribution near the hum area. Then record continuously for about a week. And finally use inferometry to locate the source(s).