Effects of three-dimensional crustal structure and smoothing constraint on earthquake slip inversions: Case study of the Mw6.3 2009 L'Aquila earthquake
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Environmental Science and Engineering Program
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AbstractEarthquake slip inversions aiming to retrieve kinematic rupture characteristics typically assume 1-D velocity models and a flat Earth surface. However, heterogeneous nature of the crust and presence of rough topography lead to seismic scattering and other wave propagation phenomena, introducing complex 3-D effects on ground motions. Here we investigate how the use of imprecise Green's functions - achieved by including 3-D velocity perturbations and topography - affect slip-inversion results. We create sets of synthetic seismograms, including 3-D heterogeneous Earth structure and topography, and then invert these synthetics using Green's functions computed for a horizontally layered 1-D Earth model. We apply a linear inversion, regularized by smoothing and positivity constraint, and examine in detail how smoothing effects perturb the solution. Among others, our tests and resolution analyses demonstrate how imprecise Green's functions introduce artificial slip rate multiples especially at shallow depths and that the timing of the peak slip rate is hardly affected by the chosen smoothing. The investigation is extended to recordings of the 2009 Mw6.3 L'Aquila earthquake, considering both strong motion and high-rate GPS stations. We interpret the inversion results taking into account the lessons learned from the synthetic tests. The retrieved slip model resembles previously published solutions using geodetic data, showing a large-slip asperity southeast of the hypocenter. In agreement with other studies, we find evidence for fast but subshear rupture propagation in updip direction, followed by a delayed propagation along strike. We conjecture that rupture was partially inhibited by a deep localized velocity-strengthening patch that subsequently experienced afterslip.
SponsorsObserved waveforms were provided by the Italian Strong Motion Database (ITACA, http://itaca.mi.ingv.it/). The displacement waveforms obtained from HR-GPS stations were kindly provided by A. Avallone [Avallone et al., 2011]. Map figures were prepared using the Generic Mapping Tools package (http://www.soest.hawaii.edu/gmt/). Financial support: Grant Agency of Czech Republic 14-04372S and Charles University project UNCE 204020/2012. This study was supported by the King Abdullah University of Science and Technology (KAUST), and numerical simulations were run on the BlueGene-P "Shaheen" of the KAUST Supercomputing Lab.