Corner frequency ratios of P and S waves and strain drops of earthquakes recorded by a tight network around the Karadere segment of the North Anatolian Fault Zone: evidence for non-classical source processes

We present a method for estimating ratios of P and S waves corner frequencies (Rcf) and earthquake strain drops by joint analysis of P and S source spectra of neighbouring groups of events. The method is applied systematically to data generated by similar to 9000 earthquakes around the Karadere segment of the North Anatolian Fault Zone. The results indicate several regions that produce consistently Rcf values higher (e. g. > 2) than expected from classical earthquake source models. These are associated generally with fault sections having strong geometrical heterogeneities, shallow depth sections and/or locations without large pre-existing surface trace. Earthquake ruptures in such regions are likely to generate significant rock damage and tensile components of faulting. To assess whether the observed high Rcf values are produced by enriched high frequency P waves, reduced high frequency S waves or both, we compare the associated P and S spectra with mean/median results. The analysis suggests that the high Rcf values of shallow events (depth < 4 km) are generated primarily by reduced high frequency S radiation, and that the contribution from elevated high frequency P radiation increases with depth and proximity to geometrical complexities. The results highlight the importance of considering carefully the existence of some volumetric source components in earthquake rupture processes.