Simulated ground motion of the earthquake on Octorber 22nd, 2012, M4.6 at Song Tranh 2 dam area
Records of ground motion by strong earthquakes are important documents used in earthquake-resistant design, particularly for key construction projects. In reality, there are few records of ground motion caused by maximum earthquakes at major infrastructure facilities, even at locations where strong earthquakes frequently occur with adequate monitoring facilities such as those in Japan, US and Taiwan. To overcome the shortage of raw seismic records at these facilities, there are many simulation studies to model strong earthquake records. This research has been conducted by developed countries to apply to seismic hazard assessment in the important facilities such as hydropower, thermal or nuclear power plants.
By the end of 2010, Vietnam has obtained 24 records of ground acceleration of 21 earthquakes (mostly recorded at Tuan Giao and Dien Bien seismic stations). Of these, there are 17 records of earthquakes and the rest are aftershocks of the Dien Bien earthquake on 19 February 2001 with M = 5.3. Song Tranh 2 Hydropower was built in 2010 with a seismic design of the dam of M = 5.5. In reality, the collection of strong motion records above is not enough to select a design ground acceleration for the seismic design of the Song Tranh 2 hydropower plant. In November 2010 Song Tranh 2 hydropower reservoir began water filling. From then to the end of March 2011, the people of North Tra My felt slight tremors and explosive noises, this phenomenon occurred on an increasing frequency. According to the Earthquake Observation Room of the Institute of Geophysics, from 03 November 2011 to March 2014, there were more than 468 earthquakes with magnitude M ≥ 1 occurred near Song Tranh 2 area. Among these, there were 5 earthquake with magnitude greater than M = 4.0 and one M = 4.7; 19 earthquakes with M ≥ 3; 36 earthquakes with M ≥ 2.5. Collection of these records has been very valuable for us to simulate an earthquake of M = 4.6 and compared with observed results. This result confirms that simulation strong ground motion can fully apply in seismic hazard assessment in Vietnam. Song Tranh 2 area we applied the empirical Green’s function method to predict broadband ground motion of earthquake M = 4.6 base on observed records of earthquake M = 3.5. We can also use the recorder earthquake M = 4.6 to simulation design earthquake M = 5.5.
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