During the second half of 2002, a seismic swarm (more than 250 microearthquakes) was recorded at Las Pailas Geothermal Field (PGF) with local magnitude M L < 2.0 and depths between 1.0 and 5.5 km. 116 earthquakes were located and 86 were used to draw Poisson ratio (σ) maps. Using seismic distribution, structural data, polarization of the fastest S wave and field observations, I determined, identified and verified faults and fractures with NW and NE directions, where two of them are strike slip

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... ctive faults. Based on Poisson ratios, data field and seismicity analysis, I conclude that PGF is a high-pressure water domain reservoir controlled by fault systems and can be divided in sectors according to three different conditions or classifications. The first condition has low σ values (higher vapor amount) and low permeability, is located to the east and west limits of PGF, where the PGP-02 and PGP-05 wells are located. The second condition has high σ values (between 0.24 and 0.30) normally suggesting higher fluids amount, within this sector wells PGP-04 and PGP-06 are located. The third sector has intermediate or higher σ values (0.18-0.23) and can be related with phase shift areas along fault systems and where wells PGP-01 and PGP-03 are located.