Crustal and upper mantle structure in the Amazon region (Brazil) determined with broadband mobile stations

Abstract

Three broadband stations operated from March 1997 to September 1998 in the Amazon region north of Manaus, Brazil, which, including the IRIS station PTGA (Pitinga), covered an area of roughly 60 × 200 km. Applying the receiver function technique to determine the crustal structure, there is evidence for an increase of the Moho depth from about 38 km below the Amazon Basin to approximately 48 km north of the basin. In addition, we analyzed the polarization of SKS‐waves to determine anisotropy. The observed splitting parameters in a majority of the data set can be accounted for by a layer of axial symmetric anisotropy with the fast direction oriented roughly N110E. This direction cannot be associated with the present‐day plate motion of the South American plate. However, the anisotropy may be related to a lithospheric fabric that was generated during the early tectonic history of the Amazonian Craton.

Basement depths in the Parecis Basin (Amazon) with receiver functions from small local earthquakes in the Porto dos Gaúchos seismic zone

“…The receiver function technique has been used successfully in Brazil for modeling deep structures such as the Moho discontinuity (Ammon et al, 1990;James et al, 1993;Assumpção et al, 2002Assumpção et al, , 2004Krüger et al, 2002;França and Assumpção, 2004;Dourado et al, 2007;Julià et al, 2008), discontinuities of 410 km and 670 km in the upper mantle transition zone (Liu et al, 2003;Bianchi, 2009) as well as shallow features like sediment thickness, particularly in the Paraná basin (An and Costa et al, 2006;Silva et al, 2008;Zevallos et al, 2009). …”

Crustal thickness map of Brazil: Data compilation and main features

“…We compiled crustal thickness estimates from all recently published receiver function studies including stations in South America, especially those from the Brazilian Lithosphere Seismic Project (BLSP) in Brazil (Bianchi, 2008;Julià et al, 2008;Lloyd et al, 2010). Crustal thickness estimates from other stations in central and northern Brazil were also compiled from Krüger et al (2002), Rosa et al (2012), Albuquerque et al (2011) and unpublished monographs such as Pedreschi (1989) and Costa (2005). The compiled studies report both crustal thickness (H) and Vp/Vs ratio (k) estimated with different techniques, such as the Hek stacking procedure of Zhu and Kanamori (2000), the waveform matching technique of Meijde et al (2003) and Lloyd et al (2010), the phase- (2004) and Assumpção et al (2004), and the joint inversion of receiver functions and surface-wave dispersion velocities of Julià et al (2000Julià et al ( , 2003.…”

Receiver function study in northern Sumatra and the Malaysian peninsula

“…Classical receiver function methods for single stations include picking of difference traveltimes for direct conversions and multiples and estimation of the corresponding discontinuity depth with an average background model (e.g. Krueger et al, 2002); estimation of discontinuity depth and V P /V S ratio by stacking direct Ps conversion and multiple waveforms in a gridsearch procedure (Zhu and Kanamori, 2000); inversion of stacked receiver functions for 1D shear wave models (Ammon, 1991). The retrieval of absolute shear wave velocities from receiver functions is still a major challenge.…”