"By shining a laser through the fiber optics, the scientists could detect vibrations from above ground thanks to the way the cable ever so slightly deformed. As a car rolled across the subterranean cable or a person walked by, the ground would transmit their unique seismic signature. So without visually surveilling the surface, the scientists could paint a detailed portrait of how a once-bustling community ground to a halt, and slowly came back to life as the lockdown eased."

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