Modelo mejorado de velocidades unidimensional de corteza y manto superior en el transarco andino argentino entre latitudes 31.5° y 33.5° S

Abstract

Using a one-dimensional approach of the earth, a new P-wave velocity model (Vp) was determined for crust and upper mantle that improve hypocenter localization in the South-Central Andean foreland of Argentina. This region that shows intense crustal and deep earthquake seismic activity have been monitoring by appropriate seismic local network during a period of 3 month. A total of 12,841 first arrival P- wave were identified. This data set was produced by 1,262 intermediate deep earth- quake and 449 crustal earthquakes. Considering a pre-defined Vp model, a subset of well constrained earthquakes were selected as input data for inversion process. Tree layer crustal and one layer upper mantle Vp model was adopted. VELEST code was used for simultaneous inversion of velocity, hypocenter and station correction pa- rameters. Results for different damping parameters were evaluated at the end of process inversion. The final crustal model shows Vp of 5.95, 6.15 y 6.82km/s relat- ed to deep interfaces of 10, 32 and 45km below sea level. Root mean square (RMS) of residuals was 0.31s, 20.5% less than initial localizations. Vp for upper and mid- dle crust layer exhibit light changes related to the initial model. For upper crust, the final Vp was slightly bigger than the initial model suggesting a more participation of crystalline basement rock. In lower crust, resulting Vp was less than expected for determinations at north of our network suggesting a possible rock composition segmentation. Vp for upper mantle of 7.34km/s was very lower than previous works possible effect of poor conditioning. This Vp was finally defined as 8.04km/s. Sta- tions corrections result keep inside normal limits and they are consistent with de- 

terminations using data from other seismology network. The general pattern of seismicity has not strongly changed but more precise localizations could be able to illuminate new features and more reliable correlations with some tectonics and structural domains. The new velocity model here proposed reduces hypocenter localization uncertainty and it is defined as a new Vp local model for crust and upper mantle for precise and fast localization of crustal and intermediate deep earthquakes in the region where, Nazca plate is in flat subduction and transition to normal and also concentrates the most earthquake activity of Argentina.