Reservoir-Induced Seismicity at Castanhão (Ne Brazil)

Reservoir-induced seismicity (RIS) has acquired great attention of geoscientists mostly because of big destructive potential in structures and human loss. This kind of seismic events has been reported since 1945 at lake Mead (USA). However, the largest induced earthquake (M 6.3) took place at Koyna (India) in 1967. In NE Brazil, at least two cases of RIS were reported: one Açu reservoir (Ferreira, 1995; do Nascimento 2004a, 2004b, 2004c) and another one reservoir. The latter is the subject of the present paper. Our study shows the results of a campaign done in the period from November 19th, 2009 to December 31 at the Castanhão reservoir. We deployed six three component digital seismographic station net one of the areas of the reservoir. These data were used to estimate the velocity model and its parameters, hypocenters, focal mechanism, and carry out a temporal. We recorded and analyzed a total of 526 w were registered in at least three stations. To determine hypocenters and time origin, we used HYPO71 program assuming a half-space model with following VP (P-wave velocity) equal to 5.95 km/s and V to 1.73 – the later was estimated by the Wadati diagram. The earthquakes hypocentral distribution was observed in three main clusters activated in different periods and others spread over with depths varying up to 2km within the network. The focal mechanism determination made from a group of 8 selected earthquakes. The solution acquired with this polar distribution by visual was 217º for strike, 70º for dip and 45º for slip. A hypocentral distribution from this 8 events suggests 257º for strike and 57º for the dip.