Reservoir-induced Seismicity in Brazil

Geophysical Research Letters

et al. 2016

Self Cite

The collapse of a mine tailings dam and subsequent flood in SE Brazil on 5 November 2015 was preceded by a small‐magnitude seismic sequence. In this report, we explore the spatiotemporal associations between the seismic events and the accident and discuss their possible connection. We also analyze the signals generated by the turbulent mudflow, as recorded by the Brazilian Seismographic Network (RSBR). In light of our observations, we propose as possible contributing factor for the dam collapse either ground shaking and/or soil liquefaction triggered by the earthquakes. The possibility of such a small‐magnitude earthquake contributing to the collapse of a tailings dam raises important concerns regarding safety and related legislation of dams in Brazil and the world.

Section: Discussionmentioning

confidence: 99%

The tailings dam failure of 5 November 2015 in SE Brazil and its preceding seismic sequence

Agurto‐Detzel

Bianchi

Geophysical Research Letters

et al. 2016

Self Cite

“…Seismicity maps using time-variable threshold magnitudes (e.g. Adams & Basham 1991;Engdahl & Rinehart 1991;Assumpção et al 2002) are useful for recognizing areas with different seismicity rates and better defining seismogenic zones.…”

Section: Seis M I C I T Y I N S E B R a Z I L I A N P L At F O R Mmentioning

confidence: 99%

Intraplate seismicity in SE Brazil: stress concentration in lithospheric thin spots

Geophysical Journal International

Schimmel

Escalante

et al. 2004

S U M M A R YIntraplate seismicity has generally poor correlation with surface geological patterns. Except for major extensional features, such as aborted continental rifts, which may act as weak zones, it is usually difficult to find simple geology based models to explain differences in seismic activity in stable continental regions. Seismicity in Brazil is clearly not uniform and a few areas of higher activity have been identified. However, the seismic areas show almost no correlation with the main geological provinces, which is typical of other intraplate settings. A recent uppermantle tomography study in SE and central Brazil, using approximately 8500 P-wave and 2000 PKP-wave arrivals recorded in 59 sites since 1992, has mapped P-wave velocity anomalies from lithospheric depths down to 1300 km. In this region, higher seismic activity occurs preferentially in areas with low P-wave velocities at 150-250 km depth. The low P-wave velocities are interpreted as shallower asthenosphere. In such areas, a hotter geotherm will reduce the strength of the lithospheric upper mantle causing most of the intraplate forces to be concentrated in the brittle upper crust. The low-velocity anomalies coincide with Late Cretaceous provinces of alkaline intrusions. The proposed ponding of the Trindade plume head beneath lithospheric thin spots is consistent with our tomography results, suggesting that plume effects may have helped to preserve lithosphere/asthenosphere topography. Although other factors are also important, the present data show that stress concentrations resulting from lithosphere/asthenosphere topography should play an important role in explaining the intraplate seismicity in the Brazilian platform.

“…This occurred in the Açu reservoir [Ferreira et al, 1995], where an annual water level variation of only about 3-5 m was enough to cause earthquakes with a delay of about 2 months. In Brazil, a total of 20 cases of RTS have been reported [Assumpção et al, 2002;Chimpliganond et al, 2007;Ferreira et al, 2008], many of them near the northeastern border of the intracratonic Paraná Basin (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Seismic activity triggered by water wells in the Paraná Basin, Brazil

Water Resources Research

Yamabe

Barbosa

et al. 2010

[1] Triggered seismicity is commonly associated with deep water reservoirs or injection wells where water is injected at high pressure into the reservoir rock. However, earth tremors related solely to the opening of groundwater wells are extremely rare. Here we present a clear case of seismicity induced by pore-pressure changes following the drilling of water wells that exploit a confined aquifer in the intracratonic Paraná Basin of southeastern Brazil. Since 2004, shallow seismic activity, with magnitudes up to 2.9 and intensities V MM, has been observed near deep wells (120-200 m) that were drilled in early 2003 near the town of Bebedouro. The wells were drilled for irrigation purposes, cross a sandstone layer about 60-80 m thick and extract water from a confined aquifer in fractured zones between basalt flow layers. Seismic activity, mainly event swarms, has occurred yearly since 2004, mostly during the rainy season when the wells are not pumped. During the dry season when the wells are pumped almost continuously, the activity is very low. A seismographic network, installed in March 2005, has located more than 2000 microearthquakes. The events are less than 1 km deep (mostly within the 0.5 km thick basalt layer) and cover an area roughly 1.5 km × 5 km across. The seismicity generally starts in a small area and expands to larger distances with an equivalent hydraulic diffusivity ranging from 0.06 to 0.6 m 2 /s. Geophysical and geothermal logging of several wells in the area showed that water from the shallow sandstone aquifer enters the well at the top and usually forms waterfalls. The waterfalls flow down the sides of the wells and feed the confined, fractured aquifer in the basalt layer at the bottom. Two seismic areas are observed: the main area surrounds several wells that are pumped continuously during the dry season, and a second area near another well (about 10 km from the first area) that is not used for irrigation and not pumped regularly. The main area displays cyclic annual activity, but the second area does not. We explain the earthquake swarms as being triggered by pore pressure diffusion in the fractured basalt layer due to additional pressure from the newly connected surface aquifer. This reaches critically prestressed areas up to a few kilometers away from the wells. During periods of continuous pumping, the reduction of pore pressure in the confined aquifer stops the seismic activity. Our study suggests that this kind of activity may be more common than previously thought and implies that many other cases of small tremors associated with the drilling of water wells may have gone unnoticed.