The character of scaling earthquake source spectra for Kamchatka in the 3.5–6.5 magnitude range

Abstract

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 Δσ and apparent stress σ_a. It is found that the parameter Δσ is almost stable, while σ_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 Δσ and σ_a do not show any noticeable magnitude dependence. It has been established that M_w ≈ 5.7 is the threshold value of the magnitude when the change in regimes described occurs for the conditions on Kamchatka.