Site Response Study of Jammu City using Micro-tremor Measurements

Abstract

Micro-tremor measurements are one of the most commonly used methods for site response studies and have been widely used by most of the researchers because of its cost effectiveness. This method gives a realistic estimate of the natural ground frequency and can be applied in the areas where large earthquakes do not occur often. Due to the close relation between the nature of micro-tremors and the fundamental dynamic behavior of the surface soil layer, they are frequently used in the field of hazard estimation. The results of micro-tremor analysis are used as an important input for seismic microzonation studies around the world. Himalayan region is one of the most active seismic zones of the world. As such Jammu city lies in Zone IV on Seismic zoning map of India. It has been rocked by 25 earthquakes in between 1828 to 2005 of magnitude 6.0 or more. Jammu, the winter capital of Jammu & Kashmir state is a fast growing city. The micro-tremor data has been collected from locations covering almost every part of Jammu city using Altus K2 SMA. The data were collected by keeping SMA at each site for few hours. On the basis of natural frequency (Nf) the entire study area has been divided into four zones. The natural frequency Nf value shows that the central part of the city is less vulnerable zone, as compared to other parts of the Jammu city. An attempt has been made to compute the vulnerability index (Kg), which could be considered as the indicator of higher damaged areas. The results are in good agreement with the past damaging history of the city.