CONICET | Buscador de Institutos y Recursos Humanos

A preliminary near-surface seismic survey was carried out at LlancaneloLake (Argentina) with the aim of mapping the quaternary layers, composed of sedi-mentary layers overlying basalt. A geological model has been obtained by interpretingthe events of a common-shot gather. Expressions of the traveltimes of the direct andrefracted waves versus oset provide means to evaluate the velocities of the layers andthickness of the upper layer. Moreover, the standard processing sequence is appliedto the data to obtain a stacked section. This procedure reveals the location of deeperinterfaces, although it is highly aected by the ltering of the direct and refractedevents, which have the same slope of the medium- and far offset reflection signals.The fact that the direct arrival has not a zero intercept time indicates the pres-ence of a very thin layer at the surface (shallow salt deposits). Further evidence ofthe near-surface layer is that the refracted and reflection events are ringing and thereare strongly dispersive Rayleigh waves. An interface has been found approximately be-tween 54 and 57 m depth. The P- and S-wave velocities of the shallow layer are 2000and 550 m/s, according to the slopes of the direct and Rayleigh waves, respectively,and rock-physics empirical relations, while the lower layer has a P-wave velocity of2800 m/s, obtained from the refracted event. A tentative interpretation of the apexof a reflection event locates the top of the basalt layer at 190 m depth approximately.A viscoelastic model has been dened, with quality factors of typical volcaniclasticsediments. We then compute a synthetic common-shot gather and snapshots by meansof full-wave pseudospectral methods. The synthetic gather resembles the real one, pro-viding additional support to the interpretation.