Some Characteristics of Seismic Activity in the Song Tranh 2 Reservoir, Quang Nam, Vietnam by Local Seismic Network Data

The Song Tranh 2 hydropower construction is located in the Quang Nam province (central Vietnam), it has a reservoir volume of 740 million cubic meters of water and a dam height of 96 m. The reservoir was filled to capacity for the first time in February 2011 to about 160m, then it dropped to 140 m in July 2011. The filling of reservoir started again in August 2011 and the maximum water level of 175 m was reached in October 2011. Song Tranh 2 and its surrounding regions suffered from earthquakes in March 2011, it also suffered from a higher magnitude earthquake in October and November, 2012 of M=4.6 and 4.7 respectively. By the end of 2012, a seismic network including 6 stations was set up around the Song Tranh 2 reservoir area and a full network of 10 stations was set up by August 2013. The final seismic network is capable of detecting and locating weaker seismic earthquakes. It is also possible to calculate the extended source parameters like focal mechanism, slip direction etc. In the period from August 2013 to May 2014 about 2000 seismic events were detected, and 359 of them were localized and magnitudes were calculated. Seismic analysis and update catalogues are currently being conducted. The LocSAT application was used to locate events, to perform hypocentral inversion of the phase arrival data, to estimate the origin time, epicentral location, and depth by registered data from the VERIS network. Mechanism solutions with P-wave amplitude inversion of three events were determined. It suggests that reservoir construction is a major factor in the seismogenic process.