An earthquake with exceptionally strong higher-mode surface waves

Summary An earthquake in the Northern Sinkiang Province, China, on November 13th, 1965, produced exceptionally strong higher-mode surface waves recorded at the Swedish seismograph stations, especially by the Galitzin seismographs at Kiruna. Group-velocity dispersion curves are deduced for the second Rayleigh and the second and third Love wave modes. The energy content of the second Rayleigh and Love modes is computed, and it is found that the former amounts to about 70 times as much as in average. Various reasons for this exceptional behaviour are discussed, such as depth extent of focus, focal mechanism and properties of propagation path.