A break in self‐similarity in the Lunigiana‐Garfagnana region (northern Apennines)

Abstract

In this study, stable source parameters are determined for small earthquakes in the Lunigiana‐Garfagnana region using an empirical methodology based on coda envelope measurements that are significantly less affected by the source radiation pattern, directivity, and heterogeneous path variation, than traditional direct wave measurements. We find evidence that the scaled energy (=ER/M0) increases with moment and source spectra are not self‐similar for 3.0 ≤ Mw ≤ 4.6. The calibration procedure allows for an independent check of three important features: (1) that the empirical path corrections provide consistent amplitude measurements for the same event at different stations, distances, and azimuths; (2) that the long‐period levels of the source spectra are consistent with independent M0 derived from long‐period waveform modeling; (3) that small event spectra are flat below a conservative estimate of the corner frequency and thereby effectively accounting for near‐site attenuation.