Empirical Green’s Function Simulations Toward Site-Specific Ground Motion Prediction in Vietnam

Abstract

Vietnam has a low-to-moderate seismicity, but the currently available strong ground motion data used as a basis for a seismic-resistant design are insufficient. Generally, to overcome this issue, strong ground motions recorded at other places around the world are used, which have similar seismic, tectonic and physical earthquake characteristics, such as earthquake magnitude, source model, distance to the source, tectonic geological conditions, and soil conditions. However due to different path effects and site effect, if applied to the site-specific studies in Vietnam, the above approach would generate certain errors. Therefore, it is important to obtain strong ground motion data that are applicable for seismic design of constructions in a particular region. Especially, it is important to adhere to strict seismic design requirements for facilities, such as hydropower, thermal, and nuclear power plants. One of the most interesting solutions is the theory of simulating the waveforms of strong earthquakes commonly known as the empirical Green’s function. The empirical Green’s function is a useful tool for estimating the ground motions produced by large earthquakes using small earthquake records. The basic idea of the method is that these small events data already incorporate the information of the propagation path and the local site effects. Ground-motion simulations essentially use these small events as an empirical Green’s function and add them following the scaling law based on the omega-square model. In this article, we simulate design basis ground motion for the Song Tranh 2 hydropower dam as an example. We have applied the empirical Green’s function method to predict broadband ground-motion time histories for several M5.5, one M5.7, and one M5.9 earthquake scenarios at the dam site based on M4.6 observed ground motions without/with considering radiation pattern corrections. The results confirm that strong ground-motion simulations are applicable to seismic hazard assessment in Vietnam. Once we obtain accurate source parameters, the site-specific synthetic ground motions of the earthquake scenarios can be used for seismic design safety in Vietnam.