Microseisms at Palisades: 2. Rayleigh wave and Love wave characteristics and the geologic control of propagation

The wave type of the microseisms recorded at Palisades, New York, is investigated to determine the Love and/or Rayleigh wave content. It is found that microseisms arriving from the southeast and northwest consist almost entirely of Rayleigh waves, while microseisms from the northeast and southwest have significant Love wave energy. The Love waves appear to be generated in the same source region as the Rayleigh waves. To account for the variation in Love wave energy as a function of source direction, the geologic structure along the various propagation paths is reviewed, and it is found that Love waves appear to be inhibited when propagating across the discontinuity surface between ocean and continental crust and when propagating across continental shield regions, both obstacles to a continuous surface layer. Observations from around the world are discussed, and we show that these two generalities appear to account for many of the reported discrepancies in microseism composition.