Seismic microzonation

[4] Microzonation maps can serve as a basis for evaluating site-specific risk analysis, which is essential for critical structures like nuclear power plants, subways, bridges, elevated highways, sky trains and dam sites.

[6] It has long been recognized that the intensity of ground shaking during earthquakes and the associated damage to structures are significantly influenced by local geologic and soil conditions.

Though the earthquake epicenter was located around 350 km from the city, the sites with soft clay deposits exhibited a huge amplification of ground motion resulting in severe damage.

Dynamic characteristics of site such as predominant period, amplification factor, shear wave velocity, standard penetration test values can be used for seismic microzonation purpose.

Shear wave velocity measurement and standard penetration test are generally expensive and are not feasible to be carried out at large number of sites for the purpose of microzonation.

Ambient Vibrations measurement (also called Microtremor) has become a popular method for determining the dynamic properties of soil strata and is being extensively used for microzonation.

Seismic microzonation map of Greater Bangkok prepared based on predominant period of site obtained from microtremor observations [ 1 ]
In the 1985 Mexico City earthquake , structures built on soft soil sediment sustained severe damage
Clay deposits around the perimeter of Oakland area amplified the ground motion tremendously in the Loma Prieta earthquake in 1989