Determination of intraplate focal mechanisms with the Brazilian Seismic Network: A simplified Cut-and-Paste approach

摘要

? 2022 Elsevier LtdThe feasibility of a simplified Cut-and-Paste approach (CAP) for routine determination of intraplate earthquake mechanisms in Brazil is demonstrated with data acquired by the Brazilian Seismographic Network (RSBR). Our approach models three-component seismic recordings through: (i) computation of synthetics seismograms with a single, average velocity model, and (ii) independent alignment of observed and synthetic waveforms through waveform cross-correlation. No partitioning of regional waveforms into their corresponding body- and surface-wave trains is considered. The empirical alignment successfully accounts for lateral variations along specific source-station paths, along with location uncertainties and timing errors, and effectively augments the number of waveforms available for inversion. The performance of the proposed approach is demonstrated through modeling of two recent intraplate earthquakes: the Mw 4.4 2017 Maranh?o earthquake and the Mw 4.1 2020 Amargosa earthquake. For the Maranh?o event, we obtain a strike-slip focal mechanism (340° ± 0°, 70° ± 0°, 0° ± 0°) and a centroid depth of 9 km with magnitude of Mw 4.4, fully consistent with previous studies. For the Amargosa earthquake, we obtain a normal-fault mechanism (20° ± 4.6°, 60° ± 16.9°, -30° ± 14.4°) with a preferred centroid depth of 10 km, which is in general agreement with P-wave polarity data and the orientation of the nearby Salvador Shear Zone. We thus conclude that our simplified CAP approach is an effective tool for modeling regional waveforms in Brazil and, most likely, in sparse networks in general.