Fig. 7: Ensemble properties of the inverted source spectra for the two events (Mw4.5 in orange and Mw4.2 in blue).
From: Physics-based broadband characterization of weak earthquakes
Corner frequencies fc are obtained by fitting an omega-squared spectrum to the moment rate spectra of the individual models (i.e., indirectly through the finite-fault inversion result, see Fig. 4a). The Brune and Madariaga stress drops are calculated following Eq. (5) from the corner frequencies and scalar seismic moments, see text. Diamonds show estimates for the maximum a posteriori (MAP) models. Note the agreement between the stress drops of the dynamic models (Fig. 6) and the stress drop estimates using the Madariaga approach. Arrows denote respective results from the same spectral fitting applied directly to the observed station-averaged apparent spectra (AS). The overestimated values of fc and consequently stress drop for the directive Mw4.2 event likely result from averaging empirical AS over stations with limited coverage of the focal sphere, which biases their estimate (Fig. 1b).
