Análise geoestrutural de colapso sísmico em trecho do Rio Amazonas e suas implicações para a comunidade da Costa da Águia, Parintins (AM)

Abstract

The present work addresses a complex phenomenon that occurred on the riverbed from the Amazon River, 30 km upstream from the Parintins city, on the extreme east of the Saracura Cove, where a seismic collapse inside the river would have caused a devastating effect on the riverside, causing serious damages to the local Riverside community. On the occasion, a wave with more than 6 meters tall could be seen rising in the middle of the river after a loud sound, that, followed by smaller waves, caused a big devastation on the right riverside. Simultaneously, occurred the slaughter of a big volume of sedimentary packages on the right riverside, forming a semicircular cove with 620 m on the front by 480 m on the back on the Eagle Coast, affecting directly 130 people and causing the death of a Farmer. The episode became known as The Saracura Event of the Eagle Coast. The stretch in question lies in a meandering concavity with an opening to the northeast, inserted in a seismologic zone, whose geological fault controls the river and his great flow system. According to the local residents, the region has been the stage of recurring events with great proportions, that, according to them, occurred in 1973, 1994, 1997 and 2007. So, the city hall and the civil defense concluded that the Eagle Coast should be immediately evacuated, what never happened because of the population's discontent with the reallocation suggested by the State. The research aimed to understand the complex phenomenon that occurred on the riverbed of the Amazonas River and his socioeconomic implications to the Eagle Coast community. For this, the procedures consisted of the mapping of the riverbed using bathymetric measurements; SRTM images interpretation; Interpretation of multi spectral images of the satellite Landsat 8; Colorful composition and overlay of images acquired through remote sensing made available by INPE; Material collection from the riverside for granulometry analysis; Information gathering from institutions, public agencies and residents. The sediment analysis and observations revealed that the stretch is composed by bundles of Holocene incohesive sediment belts, the right riverside is characterized by being a low floodplain, subside and conducive to slaughter. The interpretation of the geological structure revealed that the area of the Saracura Event lies on two structural trends (Saracura Fault and the Arari Lineament), subsidizing the hypothesis of the event being a reflex of a possible transcurrent movement with tilting to the south. In general lines, it is hoped that the present work contribute, even that in a simple way, to strengthen the debate about the influence of the structural geotechnical exercises on the Amazon river landscape.