Seismic activity and stress tensor inversion at Las Tres Vírgenes Volcanic and Geothermal Field (México)

• Brittle-ductile transition zone delineated by seismicity at TVVGF
• Significant correlation between fluid injection and seismicity
• Injection process changes stress field.
• Stress inversion is correlated with the local and regional tectonic features.

We analyze local earthquakes occurring between 2003 and 2012 at the Las Tres Vírgenes Volcanic and Geothermal Field (TVVGF) to establish their temporal and spatial distribution, and relationships with local and regional fault systems, water injection, acid stimulation and steam production tests. We obtained focal mechanisms and inverted data for the stress tensor to understand the local and regional stress fields. We analyzed 423 local earthquakes with magnitudes between 0.1 and 2.9 Mc and hypocentral depths from 0.2 to 7.4 km b.s.l. The cutoff depth at ~ 7.4 km possibly delineates the brittle–ductile transition zone. We identified seven swarms (from 1 to 7). Swarms 1 (December 2009), 2 (May 2010), 3 (June–July 2010) and 7 (December 2012) are strongly correlated with injection processes; whereas swarms 5 (April 2012) and 6 (September 2012) are correlated with local tectonic faults. Stress inversion showed NW–SE, E–W and NE–SW extensional orientations (Shmin), in agreement with the local tectonic stress field; while NE–SW compressional orientations (SHmax) are correlated with the regional tectonic stress field.