Seismicity around Brazilian dam reservoirs |
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Authors: | P E F P Coelho |
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Institution: | (1) Department of Geology, N6A 5B7, University of Western Ontario, London, Ontario, Canada |
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Abstract: | More than 30 cases of seismicity associated with dam reservoir sites are known throughout the world. Despite the lack of data
in some areas, where seismicity occurred after reservoir impounding, there have been distinct seismic patterns observed in
seismic areas after dam projects implantation. This has demonstrated that reservoir loading can trigger earthquakes.
A mechanism of earthquake generation by reservoir impounding is proposed here with particular application to the Brazilian
cases and to areas subject to low confining stress conditions in stable regions. Six artificial lakes are described and the
associated earthquake sources are discussed in terms of natural or induced seismicity. Earthquake monitoring in Brazil up
to 1967, when Brasilia's seismological station started operation, was mainly based in personal communications to the media.
Therefore, there is a general lack of seismic records in relatively uninhabited areas, making it difficult to establish a
seismic risk classification for the territory and to distinguish natural from induced seismicity. Despite this, cases reported
here have shown an alteration of the original seismic stability in dam sites, after reservoir loading, as observed by the
inhabitants or records from Brasilia's seismological station. All cases appear to be related to an increase in pore pressure
in permeable rocks or fracture zones which are confined between impermeable rock slabs of more competent rock. It is apparent
that some cases show some participation of high residual stress conditions in the area. |
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