Source areas of midocean microseismic noise

Abstract

Comparison of microseismic noise data collected at the ocean‐bottom Hawaii‐2 Observatory (H2O), located midway between Hawaii and California, with wind and wave data shows three frequency bands having different source locations. At frequencies from about 0.3 to 0.5 Hz, the noise spectrum shows a strong correlation with overhead wind speed and direction, implying that this energy is generated locally. Correlation of swell height above H2O with microseism energy at frequencies below 0.3 Hz is generally poor, implying that these signals originate at distant locations. The highest noise levels observed occur in the 0.2‐ to 0.3‐Hz band, apparently resulting from the interaction of waves forced by pre‐ and postfrontal winds from relatively large coincident storms in the same vicinity. Correlation of the H2O microseism levels with NOAA buoy data, with hindcast wave height data over the North Pacific, and with seismic data from mainland and island stations, defines likely source areas of the 0.1‐ to 0.2‐Hz signals. Most of the microseism energy at H2O between 0.08 and 0.2 Hz appears to be generated by high‐amplitude storm waves impacting long stretches of coastline nearly simultaneously. [Work supported by the California Department of Boating and Waterways.]