Estimate of Rayleigh‐to‐Love wave ratio in the secondary microseism by a small array at Piñon Flat observatory, California

Using closely located seismographs at Piñon Flat (PFO), California, for 1 year long record (2015), we estimated the Rayleigh‐to‐Love wave energy ratio in the secondary microseism (0.1–0.35 Hz) in four seasons. Rayleigh wave energy was estimated from a vertical component seismograph. Love wave energy was estimated from rotation seismograms that were derived from a small array at PFO. Derived ratios are 2–2.5, meaning that there is 2–2.5 times more Rayleigh wave energy than Love wave energy at PFO. In our previous study at Wettzell, Germany, this ratio was 0.9–1.0, indicating comparable energy between Rayleigh waves and Love waves. This difference suggests that the Rayleigh‐to‐Love wave ratios in the secondary microseism may differ greatly from region to region. It also implies that an assumption of the diffuse wavefield is not likely to be valid for this low frequency range as the equipartition of energy should make this ratio much closer. Key Points Seismic array allows clean separation of Love waves from Rayleigh waves Rayleigh‐to‐Love wave ratio in seismic noise in California (PFO) is different from a European station WET This large difference between WET and PFO suggests a failure of diffuse wavefield assumption for the frequency range of microseisms