The Character of Scaling Earthquake Source Spectra for Kamchatka in the 3.5-6.5 Magnitude Range

摘要

The properties of the source spectra of local shallow-focus earthquakes on Kamchatka in the range of magnitudes M-w = 3.5-6.5 are studied using 460 records of S-waves obtained at the PET station. The family of average source spectra is constructed; the spectra are used to study the relationship between M-w and the key quasi-dimensionless source parameters: stress drop Delta sigma and apparent stress sigma(a). It is found that the parameter Delta sigma is almost stable, while sigma(a) grows steadily as the magnitude M-w increases, indicating that the similarity is violated. It is known that at sufficiently large M-w the similarity hypothesis is approximately valid: both parameters Delta sigma and sigma(a) do not show any noticeable magnitude dependence. It has been established that M-w approximate to 5.7 is the threshold value of the magnitude when the change in regimes described occurs for the conditions on Kamchatka.