Analysis of the cross-correlation between water level and seismicity at Açu reservoir (Brazil)

• Correlation is studied between reservoir water level and seismicity at Açu.
• Monthly water level and earthquake counts show a yearly cycle.
• The evolution of seismicity is mainly due to pore pressure diffusion.

The main objective of the study is the analysis of cross-correlation between water level and seismicity recorded over 10 years at Açu reservoir (Brazil) to unravel the physical mechanisms driving the observed seismicity. The reservoir is a shallow (< 35 m deep) earth-filled dam, which is located in a rifted crystalline basement. Robust power spectral density of both monthly water level and earthquake counts show a significant yearly cycle, indicating the clear link between the two variables in terms of loading/unloading of the dam. The application of the singular spectrum analysis (SSA) has allowed to extract from both time series their significant component. The cross-correlation analysis confirms that the evolution of seismicity is mainly due to pore pressure diffusion and other processes due to fracture compaction (undrained response) are not strongly present in our data.