Description: We study the underside reflections of precursors to SS waves at the lithosphere and the upper mantle beneath eastern Asia. By analyzing the SS bounce points we have been able to investigate the upper mantle discontinuities along a corridor that extends from the Aleutians to the Tibetan plateau passing through Kamchatka, the Japanese subduction zone and the North China craton. One of our aims was to investigate the interaction between the lithosphere and the mantle transition zone beneath different geotectonic units along this corridor and the interaction of geodynamic processes at different depths. In the analysis, we have used the short period content of SS waveform data and methods like CMP stack and migration techniques to acquire high resolution lithosphere and upper mantle images and to improve the lateral and depth resolution for the upper mantle discontinuities. By using a newly developed method we have been able to detect the presence of the continental Moho at different depths along this corridor. We show that the SS precursors provide high resolution images of upper mantle discontinuities such as the 410 and 660 km and the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zone. Furthermore, we show for the first time, that it is possible to create new possibilities to study shallower structures such as the Moho by using the SS precursors.

Description: We make use of S receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the South American continent and adjacent areas. The Moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the Andean region. The depth of the lithosphere-asthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km. The identification of this phase becomes more difficult when the stations are located near subduction zones. We also observed the base of the subducted oceanic lithosphere down to depths of 220 km.

Description: We have used the S wave receiver function (SRF) technique to investigate the crustal thickness beneath two seismic profiles from the CHARGE project in the southern central Andes. A previous study employing the P wave receiver function method has observed the Moho interface beneath much of the profiles. They found, however, that the amplitude of the P to S conversion was diminished in the western part of the profiles and have attributed it to a reduction of the impedance contrast at the Moho due to lower crustal ecologitization. With SRF, we have successfully detected S to P converted waves from the Moho as well as possible conversions from other lithospheric boundaries. The continental South American crust reaches its maximum thickness of ~70 km (along 30°S between 70°W and 68.5°W) beneath the Principal Cordillera and the Famatina system and becomes thinner towards the Sierras Pampeanas with a thickness of ~40 km. Negative phases, possibly related to the base of the continental and oceanic lithosphere, can be recognized in the summation traces at different depths. By comparing our results with data obtained from previous investigations, we are able to further constrain the thickness of the crust and lithosphere beneath the central Andes.

Description: While the Andean cordillera grab most of the seismological attention due to it’s active tectonics, the stable platform is of mainly importance in understanding what could be considered the normal, out of anomaly earth and, may help to understand what are the final and long term results from such a dynamic process like subduction and other types of convergent and divergent plate boundaries interaction. During the last 15 year the Brazilian Lithospheric Seismological Project (BLSP) has been operating more than 60 temporary three-component broadband seismological stations, collecting seismological data mainly in the Brazilian part of the platform. The stations are mainly distributed from 35°W to 60°W and from 10°S to 25°S, covering most of the Parana basin, Tocantins fold beld, Ribeira fold belt and the San Francisco craton. Beyond this central region, there are still some stations distributed over the northern Brazilian margin, covering parts of the Amazon craton and the Parnaiba basin. To complement our dataset we use data from the GT/CPUP station (Vila Florinda/PY FDSN/IRIS). The processing steps included event selection, rotation to LQT coordinate system using an automatic algorithm based on diagonalization of the coherence matrix (for P-wave receiver function only) and deconvolution of the Q by L component for P-wave receiver function and L by Q for S-wave receiver function. The profile images were made by stacking the resulted receiver functions by piercing points locations following pre-defined lines crossing the main tectonic units. At each profile we highlighted the desired Ps and Sp conversion phase for each of the discontinuities and its time readings and errors were estimated by bootstrapping the traces during the stacking procedure. For drawing the conclusions we compared the times each other and with theoretical times computed from the IASPEI91 model and models that presented a ± 5% change in the P- and S-wave mantle velocities. The most important results observed are: 1) A clear cratonic signature, consisting of higher wave velocities for the mantle under the cratons and normal (410km and 660km) depths for the discontinuities 2) Strong presence of the Nazca subducted plate near 410 and 660 km discontinuities under the Southern part of the Parana basin 3) Lack of variation in the Transition Zone thickness and in the mantle velocities due to the presence of the possible plume proposed in 1995 by Vandecar at the Northern Parana basin region and 4) A possible transition zone thinning near the Matiqueira complex, at the Ribeira fold beld, near the Atlantic passive margin.