Earth as Giant Gravitational Wave Detector

Gravitational wave (GW) detectors range from meter-wide test masses to kilometer-long laser interferometers. The Earth itself is also a potential GW receiver that outputs its signal in seismic waves. A new analysis of seismograph data constrains the amount of GW radiation in the Universe at frequencies just below 1 hertz (Hz). The derived upper limit, presented in Physical Review Letters, is orders of magnitude lower than the previous bound at these frequencies.