Azimuthal and Radial Anisotropy Models of West-Central Brazil using Ambient Seismic Noise

Classical teleseismic analysis provides important information about the upper Mantle structure in west-central Brazil, but it is challenging to obtain reliable crustal model at this semi-aseismic region because of the lack of local earthquake records. Calculated azimuthal and radial anisotropy, which is obtained by surface waves, gives the most direct information on the crustal structure in the Pantanal, Chaco, and Parana basins as a part of west-central Brazil. Ambient seismic noise methods are now well-established and used in different period bands for different scales. For this purpose, up to three-years of 3-component continuous data recorded by the five sub-networks are prepared in the period range of 4 to 80 sec and then are cross-correlated to retrieve inter-station empirical Green's function (EGF) signals. These sub-networks are including (1) XC with 35 stations, (2) BL with 19 stations, (3) BR with 15 stations, (4) ON with two stations, and (5) GT two stations. The radial anisotropy model indicate the thickness of the upper crust, with relatively positive radial anisotropy, varies from subsurface to maximum depths of 8 km, while middle crust with relatively negative radial anisotropy extends to a maximum depth of 25km. Whereas, the lower crust has relatively positive radial anisotropy. Also, the middle crust beneath the Chaco-Paraná basin is thinner than the Paraná basin. Moreover, the azimuthal anisotropic fast directions in the middle and lower crust are consistent with both regional magmatic anomalies in the Parana basin. While this direction consists of regional tectonic trends in the Chaco, Pantanal basins.