Tomografía de CODA – Q del piedemonte llanero, Colombia

Abstract

The space variation of the parameter of attenuation Q - Coda in a sector of the Piedemonte Llanero is studied using the Coda waves. The estimation of the attenu- ation of the amplitude of coda is calculated by means of the Model of simple Isotro- pic Dispersion of Sato (1977), from seismograms of earthquakes located in the region, between September of 1993 to June 2002. Following the methodology used by Aki and Chouet (1975) we analyzed seismograms in four bands centered to 1. 5, 3, 6 and 12 Hz with respective bandwidths of 1, 2, 4 and 8 Hz. By linear regression Qc value were calculated at 1 Hz. From the expression proposed by Puli (1984) to model the amplitude of the coda waves by means of ellipses, we extended this expression to calculate the space variation of the cQ − 1, for three-dimensional analysis (anelastic tomography). By means of a square minimum inversion the value of attenuation for each cell of the three-dimensional model was calculated. Their results were corre- lated with the regional tectonic frame and found that when the attenuation increases with the depth, it correspond to zones with Tectonics of thick layers and on the contrary, where the attenuation diminishes with the depth corresponds to zones with tectonics of thin layers.