In a recent paper entitled “Seasonal trends and relation to water level of reservoir-triggered seismicity in Song Tranh 2 reservoir, Vietnam” published in Tectonophysics, we addressed seismicity induced by the exploitation of artificial water reservoirs. Changes in water levels in such reservoirs can cause strong and sometimes tragic earthquakes. Song Tranh 2 is a reservoir in central Vietnam with a maximum water level of 35 meters. The capacity of the reservoir is 740 million cubic meters, and the water level varies from 140 to 175 meters. Seismic activity in the area of the reservoir began in 2011, shortly after it was filled. Previously, this part of Vietnam was considered nearly aseismic. In our work, we focused on the impact of a gap in reservoir filling during maintenance operations and the effect of seasonal water level changes after refilling on seismicity and the associated hazard.
We found that the one-year pause in reservoir filling is characterized by nearly twice as much seismic activity and a significantly higher seismic hazard determined during this period for magnitude 3.5 and above compared to the time before the reservoir was emptied and after it was refilled. We have shown a seasonality of seismic activity in the latter period (2013-2016), which is related to water changes during the dry season, when water is released from the reservoir after reaching maximum filling, and the wet season, when water is collected during the period of increased rainfall. The greatest increase in activity is observed with a two to three month delay relative to the onset of water filling and release during the annual cycle of reservoir water collection and release. Related to this is also a significant difference in the seismic hazard. In the dry season, a tremor of magnitude 3.5 or stronger is almost three times more likely to occur than in the rainy season. Based on these results and by analyzing the delay with which an increase in activity occurs, we inferred that the main factor influencing seismicity triggering is the change in rock pore pressure associated with changes in water levels during the year.
This work was produced as part of a project number 2017/27/B/ST10/01267 funded by the NCN in the OPUS grant, the data used in the paper is available through the EPISODES platform (https://tcs.ah-epos.eu) as part of the Song Tranh episode.
Link to the article (open access): https://www.sciencedirect.com/science/article/pii/S0040195121004030