Numerical Tests to Evaluate the Effect of Constraining the Spectral Shape of Reference Events on Source Parameter Scaling

ABSTRACT Extracting source parameters from recorded spectra requires correction for attenuation effects. In consideration of the trade-off between source and propagation effects, various strategies have been proposed to constrain the inverse problem with a priori assumptions. The objective of this study is to assess the impact of constraining the source spectra of reference earthquakes in an attempt to remove a common unknown term from the spectral decomposition results. We perform numerical analyses to simulate the outcomes of the decomposition by generating source spectra for different stress drop versus seismic moment scaling, considering a large population of earthquakes with moment magnitudes between 1.8 and 6.5. Following the strategy of constraining the corner frequency of reference events, we evaluate the error of the retrieved source parameters when the applied constraint shows different levels of discrepancy with respect to the assumption used to generate the synthetics. The numerical tests show that an assumption that differs from the correct one can introduce a magnitude-dependent bias that could alter the scaling of the corner frequency with earthquake size. Furthermore, the source spectral shape for large events is also influenced by the constraints applied to the reference earthquakes. As a consequence, inferences about the self-similarity of the rupture process across the scales, or the selection of the most appropriate source model based on the goodness of the spectral fit, may be strongly biased by the constraint imposed on the reference earthquakes.