Método morfo-estructural para la identificación de paleoeventos tecto-sísmicos: Aplicación a la zona costera de San Lorenzo, norte de Ecuador

Abstract

Se presentan evidencias de cambios morfológicos que implican la ocurrencia de movimientos relacionados con la actividad sísmica de la zona. En particular se enfoca en esta publicación un método de identificación de los eventos extremos que pueden ocurrir en estas áreas.

The identification of paleo events of sismo tectonic activity along active margins is difficult under wet tropical climate, for the bad preservation of tectonic morphology such as active fault scarps, and the rough conditions to get to the places where some observation can be made. Considering that these areas are generally characteristized by a dense drainage network under conditions where active deformation can apply, we set up a method combining three set of data: 1- The analysis of the drainage network at regional and local scale, 2- The identification of tectonic lineaments and their analysis as potential elements of active fault deformation, and 3- The analysis of the coastline variability as a determing element to date tectonic deformation, but also to provide complementary data for to analyze the active deformation. In the San Lorenzo area where no active deformation was previously identified, but strong sismic activity was known, we identify significant changes of the drainage pattern related to one or several tectonic events that happened during the period 3200-2800 BP. In relation with these events the La Boca uplift occurred between the San Lorenzo and la Boca faults, resulting in the deviation of several rivers toward the Santiago River and finally the Cayapas River. The discharge increase opened a new estuary. The geographic and human implications are important. The new drainage network made easier the communication between the Andes and the coast, short-cutting the previous wide area of mangrove, and giving the suitable conditions for the further development of the la Tolita culture few time later.