Spectral Evidence for Reservoir-Triggered Seismicity at Song Tranh 2 Reservoir (Vietnam)

The time dynamics of the instrumental seismicity (1 <= ML <= 4.7) recorded in the area of Song Tranh 2 reservoir (Vietnam) between September 2012 and March 2020 was analyzed in this study. The daily maximum of the water level was analyzed by means of the periodogram, while the earthquake sequence was analyzed by using the Schuster spectrum, which is a well-known statistical method to detect significant periodicities in a temporal point process. Our results indicate the presence in the water level of a significant periodicity lasting about 1 year, which seems to modulate the earthquake sequence, mainly closer to the center of the reservoir. These results might support in a rigorously statistical manner that the seismic process occurring in the Song Tranh 2 area may be triggered by the periodical loading-unloading cycle of the reservoir.