CRUSTAL STRUCTURE OF THE PARANÁ BASIN FROM AMBIENT NOISE TOMOGRAPHY

Abstract:

Conventional seismic tomography tends to have poor resolution in regions of low seismicity where good path coverage is not always possible. Previous studies carried out in South America did not map clearly some areas of the continent, such as the southern part of the Paraná basin, because of insufficient number of crossing paths. To describe the crustal structure of the whole Paraná basin, in addition to data obtained by the analysis of Andean earthquakes, we used dispersion curves from ambient noise correlation between pairs of seismographic stations, a technique known by Ambient Noise Tomography (ANT). The obtained group velocity maps for South America correspond well with the main geological provinces of the continent: low velocities under the Andes and sedimentary basins and high velocities in cratonic regions. Inversion of the group velocities for the Paraná Basin were carried out with the following results: a) crustal thicknesses tend to be 45 km; b) high velocity anomalies for the uppermost mantle, which agree with previous studies consistent with the presence of a cratonic nucleus in the basin, particularly beneath its northern part. However, our surface wave tomography had no resolution to say whether such a nucleus is intact.