Spatio-temporal evolution of induced seismicity at Açu reservoir, NE Brazil

Abstract

S U M M A R YWe present the spatio-temporal evolution of seismicity recorded by eight three-component digital seismographs in operation continuously during a 3 yr period (1994 August to 1997 at Açu reservoir, NE Brazil. The Açu dam is a 34 m high earth-filled dam constructed in 1983 May on an area of Precambrian shield. Based on seismic monitoring between 1987 and 1989 using single-component analogue seismographs, previous workers concluded that the seismic activity was a case of reservoir-induced seismicity (RIS) associated with diffusion of pore fluid pressure beneath the reservoir. The digital data presented here reveal the seismic activity in remarkable detail with vertical and horizontal location errors ≈0.1 km. A total of 286 events were recorded by three or more stations and all occurred at a depth of <5 km. Using these data we demonstrate that the majority of the earthquake activity is clustered within several well-defined zones and that individual zones are active over discrete periods of time. Over the entire period of seismic monitoring between 1987 and 1997 there is no simple correlation between reservoir level and number of seismic events. Lateral migration of the locus of seismic activity in an unpredictable fashion is shown to be partly responsible for the poor correlation, as event detection is not uniform through time. We also show that the time delay between maximum water level and a subsequent increase in seismic activity varies systematically; longer time delays correspond to activation of an earthquake cluster with a greater average hypocentral depth. However, within any one cluster there is no correlation between time delay and depth. The 3-D distribution of seismic activity through time may only be explained in terms of triggering by the diffusion of pore fluid pressure if the rock properties (e.g. permeability, strength) are heterogeneous.

Increase of order in seismic processes around large reservoir induced by water level periodic variation

“…Namely, the increase of seismic activity is related to the complex impact of the water lake on the earth crust under the reservoir and is explained by the changes in ambient stress conditions due to the load (unload) of the water or, respectively, to the increase of interstitial pore pressure in the rock matrix beneath the reservoir due to downward percolation of fluid. It is also known that the water reservoir related changes in the seismicity of surrounding area -RIS, decreases after several years down to the level when even lesser earthquakes may occur with lower magnitudes compared to the basic level of the local seismic activity [1,15]. At the same time, the underlying dynamics of the mentioned decrease of seismic energy release, following the initial RIS activity is still an open problem.…”

“…Generally, the scientific and practical importance of investigation of possible mechanisms related to the dynamics of influence of high dam water reservoirs on local earthquakes generation is well acknowledged [1,15,22,23,25,26]. Since the mid of the past century, the RIS has been observed at many reservoirs and their geological, hydrological, and physical features remain subjects of intense investigation.…”

Investigations related to scientific deep drilling to study reservoir-triggered earthquakes at Koyna, India

“…The occurrence of reservoir-triggered seismicity (RTS) has been associated with a number of potential factors including the rate of loading, highest water level reached and the duration of retention of high water levels (Kaiser 1953;Gupta et al 1972a, b). Other studies have investigated the role of reservoir loading (e.g., Gough and Gough 1970a, b;Bell and Nur 1978;Roeloffs 1988) and the influence of pore fluid pressure (Snow 1972;Talwani et al 1999;Do Nascimento et al 2004). While major advancements have been made towards elucidating the role of individual parameters in triggering earthquakes, an integrated model that explains the genesis of RTS is unavailable.…”

Water resource developments in Ethiopia: potential benefits and negative impacts on the environment, vector-borne diseases, and food security

“…A study by Devi et al (2008) of the Gilgel-Gibe reservoir predicted that if no action is taken, it would be silted up within 24 years. They estimated the total amount of sediment deposited in the reservoir at 4.50 × 10 7 tons/year.…”

“…Eutrophication was demonstrated by Devi et al (2008) in the Gilgel-Gibe reservoir (south-western Ethiopia) by the presence of water pollution, particularly increased nitrogen and phosphorus concentrations. The authors concluded that pollution in that man-made lake was apparently due to fertilizers, decomposition of organic waste (erosion and (or) sedimentation), and detergents in waste water emitted in upstream towns.…”