Seismic Activity Induced by Water Wells, Paraná Basin, Brazil

Abstract

Shallow seismic activity has been observed in the Bebedouro rural area, Northeast of São Paulo State, Brazil, since 2004. A 6-station seismographic network, installed in March 2005, has recorded around 2,200 micro-earthquakes. The events with magnitudes up to 2.9 and intensities V MM (March-April 2005) are located near some groundwater wells (120-200m deep) drilled in early 2003 to extract water from a basalt fractured aquifer. The activity occurs as swarms of events mostly during the rainy season when the wells are not pumped. The third swarm occurred in April 2006 one month after four new wells were drilled. Migration of the epicenters away from the wells with the largest water flow, more than 150m3/h, was clearly observed in 2005 with a “seismic diffusivity” of about 0.3 to 0.6m2/s. The spatio-temporal evolution of the seismicity shows it was triggered by the drilling and operation of the water-wells.