Diurnal Cultural Noise
Diurnal Cultural Noise is noise from human activity repeated on a daily basis.
In addition to recording the movement of the ground caused by earthquakes, seismometers measure ground motion from many other sources. Human activity can be a significant source of ground motion.
This spectrogram is a 24 hour record from station JSF, located near Interstate 280 on the Stanford University campus in California. The record starts at the bottom at 5:00pm local time. Low frequency noise declines through the evening and remains at a minimum throughout the night. Between 5:00am and 6:00am, there is an abrupt increase in low frequency noise which is sustained throughout the day.