Higher-Mode Rayleigh Waves as an Aid to Seismic Discrimination.

摘要

Long-period records of surface waves from earthquakes in central Asia are often complex, with rapid amplitude fluctuations and apparent multiple arrivals of energy of the same frequency. Comparison of records from closely spaced earthquakes shows that the complexity is not caused by multipath propagation, but is associated with the seismic source geometry. The multiple arrivals are higher-mode Rayleigh waves traveling with group velocities faster than the fundamental mode. A relatively high ratio of higher-mode to fundamental-mode energy can be produced when an unusual combination of source depth and focal mechanism leads to poor excitation of the fundamental-mode Rayleigh wave, in which case, the amplitude of the higher mode yields a more reliable estimate of the size of the event than the amplitude of the fundamental mode.