Determination of source, path and site parameters based on non-linear inversion of accelerometric data in Greece

Abstract

Source, propagation path and site conditions are the factors affecting seismic ground motion. Consequently, recordings acquired at a seismic station are formed by the convolution of these three factors. In this work S-wave acceleration Fourier spectra of earthquakes recorded at local and regional scale, by the ITSAK accelerometric network for the period 2010–2016, are modeled as a product of source, propagation path (including geometric and anelastic attenuation) and site effects. The data set consists of 136 crustal earthquakes occurred in the broader Aegean area, with magnitudes 4.2 ≤ Mw ≤ 6.5 and epicentral distances 20 km ≤ R ≤ 350 km, recorded at 112 broadband accelerometric stations installed at sites with various geologic conditions. Based on this data set, an iterative Gauss–Newton inversion method to solve the non-linear problem and retrieve the different terms of source, propagation path and site, is applied. This method uses an initial input model trying to find the best and at the same time a stable solution for the inverted parameters, which are, moment magnitude (Mw), corner frequency (fc), attenuation quality factor (Qs = Qofα), slope of the geometric attenuation (1/Rγ) and site transfer function (S(f)). The initial values of the starting model can be either known from other studies or inferred within a reasonable range. Depending on the level of knowledge on these input parameters, the associated standard deviation can be adjusted (large values for unknown parameters or small values for parameters which are well constrained). Results of the analyses exhibit satisfactory agreement of estimated source parameters with those proposed by seismological centers in Greece and propagation path properties similar to the ones determined in relevant previous studies for the same region. In addition, the site transfer functions obtained by the non-linear inversion are comparable with those calculated for the same sites using either standard spectral ratio or horizontal-to-vertical spectral ration (HVSR—receiver function) techniques. The aforementioned results are encouraging for reliable earthquake source parameters, propagation path properties and site effect assessment, in areas of intermediate to high seismicity.