Cristiano Chimpliganond

Reservoir-induced Seismicity in Brazil

Abstract — A compilation of 16 cases of reservoir-induced seismicity in Brazil is presented with maximum magnitudes ranging from 1.6 ML to 4.2 mb. The compilation includes: location of the main epicentral area with respect to the reservoir (inside the lake, at the margin, or outside), predominant geology, and the temporal distribution of the main phase(s) of activity (initial or delayed in relation to impoundment). Data on the regional stress field for some reservoirs is also included. Four recent cases are discussed in more detail: Tucuruí, Nova Ponte, Miranda, and Serra da Mesa. A comparison with all other reservoirs deeper than 30 m and 50 m suggests that the hazard for induced-seismicity varies within Brazil: the NE part of the intracratonic Paraná basin has higher hazard as compared with the southern part of the same basin. No correlation of the induced hazard with variations in natural seismicity can be observed.

Influência de estruturas brasilianas na sismicidade desencadeada por reservatório na Usina Hidrelétrica de Irapé, Minas Gerais, Brasil

Inaugurated in 2006, the Irape Hydroelectric Plant has the highest dam in Brazil, with 210 m. The Seismological Observatory of the University of Brasilia is monitoring this structure since the beginning of its reservoir filling. The reservoir triggered seismicity caused by the increase of crustal tension just after the start of the remains like an important object of study for understanding this phenomenon. This paper aims at studying the seismicity recorded from January to May 2006, as well as to characterize the geology around the Hydroelectric Plant Irape in order to identify and describe the structures that help for better understanding the seismic events. The spatial orientation of the seismic events obtained by analyzing polarity and waveform is consistent with the guidance of prominent relief lineaments. These faults can be found attached to a larger structure with main NE/SW direction and tens of kilometers, which would be responsible for capturing Jequitinhonha and Aracuai rivers. This great lineament is interpreted herein as a structure related to a late stage of the Brasiliano-Panafrican event. The solution of focal mechanism, created using an inversion method of the waveform in the time domain, indicates that the direction of the possible plans are correlated to main failure of brittle structures targeting the area of work.

Estudo das vibrações geradas por detonações feitas na obra civil da Eclusa 2 de Tucuruí (PA)

The construction of the Tucurui dam in the decade of 80, situated in the River Tocantins, interrupted the navigation in this stretch of the watercourse. To give continuity to the passage of the fluvial transports the Eletronorte and Camargo Correa S.A., initiated the construction of two canals in the neighborhoods of the city of Tucurui/PA. Floodgate 1 is connected to the axis of the dam, and Floodgate 2 will be situated near the city of Tucurui, in the left edge of the Tocantins River. The dismounting of the rocks caused discomfort to the population which complained about damages in the residences. In this way, the Seismological Observatory of the University of Brasilia monitored the vibrations generated by blasting, with the aim to make a diagnosis and see if there is a relation between the detonations and the residences cracks. The velocity records of the particle vibration were obtained by engineering seismometer installed near the damaged residences. Records of 27 distinct points were analysed, and these information were intercorrelated with geological, pedological and geotechnical data, to understand its effects and to obtain the equation of seismic attenuation for this region. The 42 values of the particles velocity obtained were below the recommended value of 15 mm/s defined by the Brazilian norms as the upper level to avoid damages to the nearby residences. Regarding the sound pressure only one single measured value was beyond the intensity established by the Brazilian norms.

A look at global seismicity during 1999 in the longer-term time frame

An analysis and discussion of the main features and effects of the 1999global seismicity based especially on the inferred patterns of strong(Mw ≥ 7) earthquakes using NEIC/USGS data is presented.Based on the above data and their statistical features (see also Table 1)one may state that from the point of view of occurrence rate (number/yr)the 1999 global seismicity was fairly regular, but from the moment (orenergy) release standpoint it is well under the long-term average. The spacepartition was again rather typical and time distribution was quasi-Poissonian,noteworthy, the 1999 worldwide seismicity had an anomalously high deathtoll, to be discussed later. Two main new insights are brought by ouranalysis: (i) a (mega)quiescence along the whole south American segmentof circum-Pacific earthquake belt, which was inferred and rated asanomalous while it was underway and which, in retrospect, ended with thegreat (Mw = 8.4 HRV) 2001 Arequipa (Peru) event; (ii) an intriguingmonotonous rate decrease within only magnitude class 5.0 to 5.9 duringthe analyzed period (i.e., 1990–1999).