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Geophysical assessment of peak accelerations

1976; Seismological Society of America; Volume: 66; Issue: 3 Linguagem: Inglês

10.1785/bssa0660030959

1943-3573

Thomas C. Hanks, Dennis A. Johnson,

Seismic Performance and Analysis

abstract Forty of the larger peak accelerations at source-site distances R ≃ 10 km for earthquakes in the magnitude range 3.2 ≦ M ≦ 7.1 are the basis of a geophysical interpretation of peak acceleration data. For 4 1 2 ≲ M ≦ 7.1 these peak acceleration data are essentially independent of magnitude; for 3.2 ≦ M ≲ 4 1 2 these data increase from 0.1 to 0.2 g at M = 3.2 to about 1 2 g at M ≃ 4 1 4 . A qualitative argument is advanced to attribute the observed dependence on magnitude in the range 3.2 ≦ M ≲ 4 1 2 to the effects of faulting duration, anelastic attenation, and instrumental response. If this argument is valid, physical processes in the source region responsible for generating these high-frequency acceleration amplitudes at R ≃ 10 km are independent of magnitude. A simple theoretical argument predicated on the basis that high-frequency ground accelerations reflect isolated and localized bursts of faulting, suggests that this should be the case if the dynamic shear-stress differences gs accompanying localized failure in the source region are magnitude-independent. The peak acceleration data at R ≃ 10 km suggest that σ ˜ ≃ 2 2kb, a value nearly coincident with the maximum shear-stress differences likely to be sustained by active crustal fault zones at depths ≦ 10 km. If 5 kb is a more reasonable limit to the shear strength of crustal rocks at 10-km depth, 1.8 g is a more reasonable limit to ground accelerations caused by sources of faulting at R = 10 km.