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. ¿ 1998 American Geophysical Union