An overview of seismic ground response methods over the world and their applications in Vietnam

The estimation of the impact of earthquakes on buildings and mega structures in large urban areas is of extremely importance. That is why it always gets attentions from construction planners and policy makers who are concerned about construction rules. When earthquake occurs, the vibration is transferred to sites. Although the vibration intensity is at first not too strong, the motion probably becomes stronger and lasts longer under special conditions of the local site. Two famous examples for these effects occurred in Mexico City in 1985 and in Taiwan in 1999. There are a number of approaches to this problem, such as evaluations based on seismic field observations, the microtremor method, the method using the weak motion data, the method using the strong motion data, the one-dimensional wave propagation method or the three dimensional wave propagation method with simulation etc. In this paper, we will give an overview and discuss about the advantages and the disadvantages of the methods that have been commonly applied in the world. We also present the application of these methods in studies carried out in Vietnam in general and in particular, in Hanoi city. We found that the studies for Hanoi city were mainly carried out in the western areas of Hanoi and a few positions in the urban districts. In addition, the authors only gave comments about and assessments of the shear wave velocity, and classified the ground type without a detailed map of local site effects for the entire area of Hanoi. In order to obtain a full site effects evaluation for Hanoi city, future studies should focus on the application of 1D analysis for the central area of Hanoi city and combining 1D analysis with 2D or 3D to give a better picture about the impact of local site effects. This hybrid approach is necessary in order to compare and verify the data obtained by the empirical and the analytical methods. On the other hand, many problems need to be addressed, for instance, the construction of a detailed 3D geological model for Hanoi, the calculation of the dominant periods and the amplification of the local soil conditions for the urban areas.

Influence of Local Site Effects on the Typological Fragility Curves for Class-Oriented Masonry Buildings in Aggregate Condition

Background: The Municipality of Baranello, located in the province of Campobasso, is considered as a reference case study for implementing a systematic procedure for the assessment of local site effects. The territory is characterised by a heterogeneous soil, made of a basal interval formed in large part by outcrops found along with the middle-basal bands of the local slopes, which is particularly sensitive to geo-hazard effects. Aims: The present work aims to investigate the influence of local site effects on the seismic vulnerability of an oriented- class of masonry building compounds. The historical buildings surveyed are mainly made up of rough stone masonry, particularly vulnerable to seismic phenomena. The buildings are appropriately grouped in typological classes based on the CARTIS form and then subdivided into different categories according to the EMS-98 scale based on their geometrical and structural characteristics. Methods: The performed vulnerability analysis is based on a vulnerability-index method conceived for buildings grouped in aggregate condition. Moreover, the expected damage scenario is properly evaluated based on a specific attenuation law to take into consideration the effect produced by a reference scenario event. Furthermore, the local site conditions have been evaluated based on a 1D half space approach in order to predict the possible increment of the expected damage due to the soil stratigraphy. Results: The local site conditions provide a global increment of the expected vulnerability of 33% with respect to the case in which the geo-hazard effects are neglected. In this activity framework, typological fragility curves are derived for comparing the exceeding probability thresholds for the examined building classes. Conclusion: The proposed research represents an important starting point for large-scale vulnerability assessment since it provides a simplified and comprehensive method for predicting seismic damage scenarios of historic center considering local site effects.