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Focal depth and mechanism of mid-ocean ridge earthquakes

1973; American Geophysical Union; Volume: 78; Issue: 11 Linguagem: Inglês

10.1029/jb078i011p01818

2156-2202

Donald J. Weidner, Keiiti Aki,

High-pressure geophysics and materials

Rayleigh wave phase and amplitude spectra are used to determine the focal depths and mechanisms of mid-ocean ridge earthquakes. The effect of propagation on the spectra is removed by analyzing the differential phase and the amplitude ratio of the Rayleigh waves from a pair of close events with different focal mechanisms. This analysis preserves the difference between the source spectra. By matching the observations with theoretical models, a best description of the source is derived. The two mid-Atlantic ridge dip slip events that we have studied have a focal depth of only 3 ± 2 km beneath the ocean floor. Two dip slip events in the northeast Pacific have depths consistent with these results but with an uncertainty of 20 km. The depths of two mid-Atlantic ridge strike slip events are 6 ± 3 km. Two strike slip events in the northeast Pacific are shallower than 25 km. The phase analysis greatly aids the amplitude analysis and, for these events, is indispensable.