Espessura crustal da parte norte dos Andes usando precursores de pP e sS para telessismos

Abstract

In this work we studied the crustal thickness in northern Andes and northern central Andes (between 10 • N and 9 • S). We analyzed the reflections from the underside of the Moho for six intermediate earthquakes occurred in the study area to estimate the crustal thickness at the bounce point. The pmP and smS phases (reflections at the Moho) are identified as precursors to the depth phase pP and sS, respectively, when recorded at teleseismic distances. This method require events of magnitude > 6 and depth > 100 km.In order to better identify those two reflections, it was necessary to stacking traces from different stations. The study area was divided in three sections: northern area between 6 • N -0 • (Colombia), in this area we analyzed two earthquakes and the crustal thicknesses in four bounce points were found; central area between 2 • S-5 • S (Ecuador), in this area we studied one earthquake and the crustal thicknesses in three bounce points were found; southern area between 6 • S -9 • S (Peru-Brazil border), where we analyzed three earthquakes and the crustal thicknesses in seven bounce points were found. Crustal thickness found in the southern area varied from 35 to 40 km, from 40 to 63 km in the central area and from 26 to 56 km in the northern area. We estimated a V p /V s ratio of 1.79±0.16 for the northern Andes using the time differences sS-smS and pP-pmP relation. Our analysis complements the data base of Moho depths in the Northern Andes and also, it allows a comparison with the model of crustal thickness estimated by Assumpção et al. (2013) confirming the Moho depth on both studies.