A Hybrid Inversion Technique for the Evaluation of Source, Path, and Site Effects Employing S-Wave Spectra for Subduction and Upper-Crustal Earthquakes in El Salvador

Abstract

We propose a hybrid inversion analysis (HIA) technique aimed at incorporating earthquakes from different seismogenic sources in one single inversion scheme. The application of this technique provides estimations of the source, path, and site effects at 23 strong-motion stations in El Salvador, Central America. The strong-motion dataset comprises 404 triaxial accelerograms corresponding to 63 subduction and upper-crustal earthquakes with M S magnitudes between 3.0 and 7.8. Application of the HIA technique reveals: (1) good matching of the estimated source spectra with those derived from the x 2 point source model; (2) rapid and low attenuation patterns characterizing the upper-crustal volcanic belt and subduction zone, respectively; and (3) soil transfer functions characterized by amplification ratios larger than those derived from spectral ratio techniques by a factor of two. Referencesite-dependent techniques yield similar soil transfer functions at all stations, whereas the horizontal-to-vertical spectral ratio technique yields similar results at sites characterized by clearly predominant peaks.

Separation of source and site effects by generalized inversion technique using the aftershock recordings of the 2009 L’Aquila earthquake

“…Castro et al, 1990, Salazar et al, 2007 and sometimes also of source spectral shape (e.g. Drouet et al, 2008).…”

Spectral models for ground motion prediction in the L'Aquila region (central Italy): evidence for stress-drop dependence on magnitude and depth

“…(1) can be performed either following a parametric approach, where the unknown functions related to source and propagation are expressed in terms of standard models (e.g. Kawase 2006;Tsuda et al 2006Tsuda et al , 2010Salazar et al 2007;Drouet et al 2008Drouet et al , 2011, or following a non-parametric inversion scheme (e.g. Castro et al 1990;Parolai et al 2000Parolai et al , 2004Oth et al 2008Oth et al , 2009.…”

Attenuation characteristics, source parameters and site effects from inversion of S waves of the March 31, 2006 Silakhor aftershocks

“…SVD and LSQR] [Andrews 1986, Menke 1989]. According to Andrews [1986] one undetermined degree of freedom exists in Equation (2) that can be resolved by assuming a predefined source spectral model [Boatwright et al 1991, Salazar et al 2007 or setting the site response of one or more rock sites in the dataset equal to one [Andrews 1986, Castro et al 1990, Parolai et al 2000.…”

“…In parametric scheme [e.g. Salazar et al 2007] a predefined function is considered for attenuation along the travel path while in the nonparametric approach [e.g. Oth et al 2009] the attenuation is constrained to be a smooth function of distance including all attenuation effects like anelastic attenuation or geometrical spreading that takes the value of 1 at the reference distance R0, which is set to 9 km in present work.…”

“…This method was firstly proposed by Andrews [1986] recasting the spectral ratios method into a generalized inverse problem, then decomposing the body-wave spectra into source, site, and path contributions, simultaneously. Several authors have used and developed this approach to earthquake ground-motion data worldwide [Castro et al 1990, Boatwright et al 1991, Hartzell 1992, Parolai et al 2000, Salazar et al 2007 among others]. For instance, Castro et al [1990] introduced a two-step nonparametric inversion method to isolate source, site and path effects along the Guerrero, Mexico, subduction zone.…”