Assessment of predominant frequencies in Dhaka city, Bangladesh using ambient vibration

Abstract

Bangladesh is a moderately seismically active region in the world. The 1897 Great Indian earthquake has caused about 1542 death and immense damage of properties. This earthquake has been located close to the main cities of Bangladesh. Poor earthquake awareness and inadequate construction practices are the main reasons for such destruction. An improvement in understanding and familiarity of seismic hazard is needed to alleviate damage due to an earthquake. Natural principal ground frequencies have been studied for the capital city Dhaka, Bangladesh using ambient vibrations. The principal frequency at 105 sites has been estimated through applying horizontal-to-vertical spectral ratio technique. The ambient vibration has been carried out for 30 min at each location. The sampling rate is 200 samples/s. The predicted principal frequency has been authenticated with earthquake data recorded at three accelerometer locations in the study area. It has been found that geological time period has a major effect on principal frequency of the ground. The obtained principal frequencies differ from 0.4 to 1.6 Hz for the fairly loose/soft Alluvium Valley Fill, Artificial Fill, and Holocene Alluvium, and for most of the Pleistocene deposit. The results imply that frequencies of different locations of the city confirm the site properties that can be proposed for studying the seismic risks to develop a plan for disaster risk reduction for the city.