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 412M7.1 these peak acceleration data are essentially independent of magnitude; for 3.2M412 these data increase from 0.1 to 0.2 g at M = 3.2 to about 12g at M414. A qualitative argument is advanced to attribute the observed dependence on magnitude in the range 3.2M412 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.

First Page Preview

First page PDF preview
You do not currently have access to this article.