Location of Love‐to‐Rayleigh conversion due to lateral heterogeneity or azimuthal anisotropy in the upper mantle

Abstract

Love waves can be converted to Rayleigh waves, which are sometimes called quasi‐Love waves, in laterally heterogeneous or azimuthally anisotropic mantle. A local four‐station network of broadband seismometers in Hokkaido, Japan, records the quasi‐Love waves from the earthquakes located in and around Oregon and California, USA. We infer that these quasi‐Love waves are generated by lateral heterogeneity or azimuthal anisotropy beneath the Aleutian or Kuril trench. We attempt to locate the Love‐to‐Rayleigh conversion areas for the August 17, 1991, off coast of northern California earthquake by using the group velocities of the observed surface waves. The locations of the Love‐to‐Rayleigh conversion areas concentrate near the Kuril trench. The concentration is the most clear at a low frequency of 8 mHz. This successful location of the conversion areas provides us with an important constraint on the generation of the quasi‐Love waves.