ALBERT

Description: . The Earth suffers deformations due to the gravitational attraction of the celestial bodies and the redistribution of water mass occurring by the action of the ocean tide. These effects are known as solid Earth tide and ocean tide loading, and can be estimated by observations of the amplitudes and phases of their tidal wave constituents. Considering that GNSS observations may be used to estimate these effects and that the solid Earth tide displacement is well resolved, this work estimated and analyzed the amplitudes and phases of the 11 principal constituents of ocean tide loading, using GPS observations. The methodology was applied to data collected from five stations in Brazil, and the amplitudes and phases of the tidal constituents were estimated and evaluated regarding their values and convergence times. The results showed that most of the estimated parameters converged during the analyzed period. In addition, after correcting the effects of ocean tide loading in each GPS solution, using the computed parameters and the existing models, the coordinates were compared and the results presented some local differences, allowing to recommend the use of GPS to estimate tidal constituents considering the local behavior of the point.Keywords: GPS, ocean tide loading, tidal constituents.RESUMO. A Terra sofre deformações devido à atração gravitacional de corpos celestes e também em função da redistribuição de massa d’água que ocorre por ação da maré oceânica. Estes fenômenos são denominados maré terrestre e carga oceânica, e podem ser estimados por meio das amplitudes e fases das componentes de onda de maré. Considerando que as observações GNSS podem ser usadas na estimativa destes efeitos e que os deslocamentos devido à maré terrestre são teoricamente bem resolvidos, este trabalho estimou e analisou as amplitudes e fases das 11 componentes principais de carga oceânica, utilizando observações GPS. A metodologia foi aplicada a dados coletados em cinco estações instaladas no Brasil, e as amplitudes e fases para as componentes de maré foram estimadas e avaliadas, considerando seus valores e tempo de convergência. Os resultados mostraram que a maioria dos parâmetros estimados convergiu durante o período analisado. Além disso, após corrigir os efeitos de carga oceânica em cada solução GPS, utilizando os parâmetros calculados e os modelos existentes, as coordenadas corrigidas foram comparadas e os resultados apresentaram diferenças locais, permitindo recomendar o uso do GPS na estimativa de componentes de maré considerando o comportamento local do ponto.Palavras-chave: GPS, carga oceânica, componentes de maré.

Description: We propose a local magnitude scale (ML) for Peru, based on the original Richter definition, using 210 seismic events between 2011 and 2014, recorded by 35 broadband stations of the National Seismic Network operated by the Geophysical Institute of Peru. In the solution model, we considered 1057 traces of maximum amplitude records on the vertical channel from simulated Wood-Anderson seismograms of shallow events (depths between 0 and 60 km) and hypocentral distances less than 600 km. The attenuation factor has been evaluated in terms of geometrical spreading and anelastic attenuation coefficients. The magnitude ML was defined as ML = Log10AWA+1.5855Log10(R/100)+0.0008(R−100)+3±S, where, AWA is the displacement amplitude in millimeters (Wood-Anderson), R is the hypocentral distance (km), and S is the station correction. The results obtained for ML have good correlation with the mb, Ms and Mw values reported the ISC and NEIC. The anelastic attenuation curve obtained has a similar behavior to that other highly seismic regions. Station corrections were determined for all stations during the regression analysis resulting in values ranging between −0.97 and +0.73, suggesting a strong influence of local site effects on amplitude. © 2017, Springer Science+Business Media Dordrecht.

Description: SUMMARY Based on new data from permanent and temporary networks, we present fundamental mode Rayleigh wave group velocity maps at periods of 10–150 s related to the lithosphere beneath South America. We analyse waveform data from 1043 earthquakes, from 2002 to 2019, which were recorded by 282 stations. To isolate fundamental mode Rayleigh waves, a phase-matched filter is applied, and the measurements of group velocity are obtained from multiple filter analysis techniques. Thus, we obtain 17 838 paths, covering most of the South American continent, which reach their maximum at the period of 30 s and decrease for both shorter and longer periods. We calculate average dispersion curves and probability density distribution of all measured curves to check the consistency of our data set. Then, regionalized group velocity maps are obtained by iteratively combining the fast marching method and the subspace inversion method. The resolution of our models is assessed by checkerboard tests, which show that the synthetic group velocities are well recovered, despite some amplitude and smearing effects in some portions of the model, probably owing to regularization and uneven ray path coverage. Compared to previous group velocity studies for South America, our models present better resolution, mainly for shorter periods. Our maps of 10 and 20 s, for example, show an excellent correlation with the sedimentary thickness (CRUST1.0) and topography density (UNB$\_$TopoDens). Regions of exposed basement and high-density are related to fast group velocities, while sedimentary basins and low-densities are observed as areas of slow group velocities. We identify small-scale fast group velocity heterogeneities that may be linked to the Rio Apa and Rio Tebicuary cratons as well as to the geochronological provinces of the Amazonian Craton. The most striking feature of our map at 40 s is a fast group velocity structure with the same NE trend of the Transbrasiliano lineament, a Neoproterozoic megashear fault that crosses a large part of the South American continent. Our long-period maps sample lithospheric depths, revealing that cratonic areas of South America, such as the Amazonian and São Francisco cratons, correlate well with fast group velocities. Another interesting feature is the presence of a strong group velocity gradient between the Paraná and Chaco-Paraná basins, which nearly coincides with the location of the Western Paraná Suture, a continental-scale gravity discontinuity. From our group velocity maps, we estimate 1-D S-wave velocity depth profiles at 10 locations in South America: Chaco-Tarija Basin, Borborema Province (BP), Amazonian Craton, Paraná Basin, Tocantins Province, Acre Basin (AcB), Altiplano-Puna Volcanic Complex, Mantiqueira Province (MP), Parnaíba Basin and São Francisco Craton. Most of our inverted S-wave velocity profiles show good agreement with the SL2013sv model at lithospheric depths, except the BP, AcB and MP profiles. Particularly for the BP, a low shear wave velocity, from about 75 to 150 km depth, is a feature that is not present in the SL2013sv model and was probably resolved in our model because of our denser ray path coverage. This decreased S-wave velocity may be due to a lithospheric thinning beneath the BP, as already pointed out by previous studies.