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### O Sismo de Codajás - AM, de 05.08.1983

### Abstract

One of the largest known Brazilian earthquakes (mb: 5,5; Ms: 5,3; epicentral intensity Vll MM) occurred in the middle of the Amazon sedimentary basin, where no previous significant event had been recorded. An isoseismal map is presented showing that the event was felt over an area of about 500.000 km2. The focal depth of 23 km was well determined with pP phases. A preliminary focal-planes solution, using P polarity data, indicates a predominantly thrust fault with about NNE-SSW horizontal compressive axis. The basement in the epicentral area is covered by about 2 km of sediments and no major tectonic feature that could be clearly associated with the earthquake is known.

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Brazilian Journal of Geophysics - BrJGSociedade Brasileira de Geofísica - SBGfAv. Rio Branco 156 sala 2509Rio de Janeiro, RJ, BrazilPhone/Fax: +55 21 2533-0064E-mail: editor@sbgf.org.br

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