# A Site-Specific Response Analysis: A Case Study in Hanoi, Vietnam
## 1 Introduction  
The study of earthquake ground motions and associated earthquake risks plays an important role in the sustainable development of earthquake-prone countries. Site response analyses are usually performed to analyze ground amplification and to develop the design response spectra [1]. The northern part of Vietnam is located in the plate boundary between the South China plate and the Indochina plate. The plate boundary is the Red River fault zone that strikes in the NW-SE direction and extends over a length of 1000 km between the Gulf of Tonkin and Tibet [2]. It caused large scale displacement and major tectonic features in Vietnam, such as rifting and folding. Hanoi is located to the North and the capital of Vietnam lies in the center of the triangular basin of the Red River. The center of the city is placed on the south bank of the river. Most of the deltaic land lies on both sides of the Red River and its tributaries. Hanoi is also affected by many adjacent zones such as the Lai Chau-Dien Bien (LC-DB), Son La, Ma River, Lo River, and Chay River faults (Figure 1) [3]. A total of 1645 earthquakes with a local magnitude (M\({}_{\rm L}\)) of 3.0 and higher were recorded in Vietnam from 114 to 2003 [4]. There were three earthquakes recorded at Hanoi in 1276, 1278, and 1285 with M\({}_{\rm L}\)=5.5-6.0. In 1983, several moderate earthquakes happened in the northern provinces of Vietnam. However, even with a distance of approximately 300 km from these epicenters, the people of Hanoi experienced a strong vibration and a number of buildings were damaged. It revealed that amplification of seismic ground motion through soft soil caused a high amplification. Recently, earthquakes occurred in the neighboring provinces of Hanoi such as Dien Bien in 2001, Ha Giang in 2005, Ninh Binh in 2005, and Hoa Binh in 2010 with a M\({}_{\rm L}\) of 5.3, 4.7, 3.1, and 4.0, respectively. Site-specific ground response analysis is a usual practice to predict the local site condition effects. [PERSON] et al. [5] performed the site-specific one-dimensional (1-D) equivalent linear (EQL) site response analysis for the nuclear power plants in Japan. [PERSON] and [PERSON] [6] carried out the seismic response analysis on the Italian site conditions to develop a seismic microzoning map for Catania City. [PERSON] and [PERSON] [7] conducted the 1-D EQL site response analysis for Goa City in India using the data of the Bhuj earthquake 2001. Recently, [PERSON] et al. [8] performed 1-D nonlinear site response analyses for the Korean sites to investigate the effect of strength correction on the seismic site coefficients. [PERSON] et al. [9] implemented the 1-D EQL site response analysis for sites in Islamabad, Pakistan. Due to the recent earthquakes as well as the urban infrastructure development, the impact of the earthquake in Hanoi has also been considered and studied by performing site-specific seismic response analyses [10; 11; 12; 13]. [PERSON] et al. [10] and [PERSON] and [PERSON] [11] assessed the hazard and possibility of liquefaction of soil layers caused by earthquakes in the urban area of the city. [PERSON] et al. [13] concluded that the soil deposit in the Hanoi region may increase earthquake damage because of the amplification of ground motion after performing site response analysis from the microtremor survey. The current seismic design code of Vietnam, TCVN 9386:2012 [14], was constructed based on Eurocode 8 (EC-8) [15] with consideration of the Vietnamese seismic map. The above-mentioned studies revealed that there is limited literature available on the site-specific response analysis in Vietnam. The relative difference between the design spectra based on the site-specific amplification factors and the code-based spectra has not been investigated yet. Moreover, all the aforesaid studies did not consider a range of input motions to account for the variability in frequency contents of ground motions.