Detailed study of the recent seismicity of the Nesjavellir (Iceland) geothermal production area.

Amoroso O., Napolitano F., Convertito V., De Matteis R., Hjörleifsdóttir V., Scafuro M.R., Capuano P.
  Giovedì 14/09   15:10 - 19:30   Aula F3 - Maria Telkes   IV - Geofisica e fisica dell'ambiente   Presentazione
The Nesjavellir geothermal field is located in South West Iceland, in the northern section of the Hengill central volcano. OR-Reykjavik Energy now produces electricity and hot water for district heating at two power plants in the Hengill area. Seismicity in the area has been interpreted as a result of volcano-tectonic processes, natural geothermal activity, and geothermal operations. The goal of the study is to achieve a better knowledge of the mechanisms that cause seismicity by studying the properties of the medium and the kinematic characteristics of earthquakes. At shallow depths below Nesjavellir, low $V_p/V_s$ ratios and low $b$-values are estimated. Between 3.5 and 6 km depths, high $V_p/V_s$ ratios and high $b$-values are detected in correspondence of the deepest seismicity, which is characterized by a higher number of small events. Our results point to the coexistence of various processes that regulate seismicity. We are able to observe the space-time evolution of seismicity and the related variation in elastic media properties, through 4D analysis. This work has been supported by PRIN-2017 MATISSE project, No. 20177EPPN2, funded by Italian Ministry of Education and Research.