Seasonal patterns of seismicity and deformation at the Alutu geothermal reservoir, Ethiopia, induced by hydrological loading

Yelebe Birhanu, Matthew Wilks, Juliet Biggs*, J. Michael Kendall, Atalay Ayele, Elias Lewi

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

6 Citations (Scopus)
281 Downloads (Pure)

Abstract

Seasonal variations in the seismicity of volcanic and geothermal reservoirs are usually attributed to the hydrological cycle. Here, we focus on the Aluto-Langano geothermal system, Ethiopia, where the climate is monsoonal and there is abundant shallow seismicity. We deployed temporary networks of seismometers and GPS receivers to understand the drivers of unrest. First, we show that a statistically significant peak in seismicity occurred 2–3 months after the main rainy season, with a second, smaller peak of variable timing. Seasonal seismicity is commonly attributed to variations in either surface loading or reservoir pore pressure. As loading will cause subsidence and overpressure will cause uplift, comparing seismicity rates with continuous GPS, enables us to distinguish between mechanisms. At Aluto, the major peak in seismicity is coincident with the high stand of nearby lakes and maximum subsidence, indicating that it is driven by surface loading. The magnitude of loading is insufficient to trigger widespread crustal seismicity but the geothermal reservoir at Aluto is likely sensitive to small perturbations in the stress field. Thus we demonstrate that monsoonal loading can produce seismicity in geothermal reservoirs, and the likelihood of both triggered and induced seismicity varies seasonally.
Original languageEnglish
JournalJournal of Volcanology and Geothermal Research
Early online date13 Mar 2018
DOIs
Publication statusE-pub ahead of print - 13 Mar 2018

Keywords

  • Critically stressed reservoirs
  • Geothermal power
  • Hydrologic loading
  • Pore-fluid pressure
  • Seasonal seismicity
  • Vertical GPS

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