Tremors lasted almost a minute: IISc study

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It is official.

The ground beneath Bengaluru shook for nearly one minute on Wednesday afternoon. Even while the final calculations on the magnitude of Wednesday’s tremor in Bengaluru are under way, the initial calculations showed that the city experienced tremors measuring 3 on the Richter scale.

The ‘Broad Band Centre’ (digital seismic activity monitoring centre) at the Indian Institute of Science (IISc) recorded the seismic activity in Bengaluru when the 8.7 magnitude earthquake hit Indonesia. The Centre is capable of recording seismic activities in any part of the world. The recordings made available to Deccan Chronicle show the effect of the tremors felt in Bengaluru.

“The seismic activity has been recorded and calculations are under way. We have got the signature of tremor over Bengaluru which lasted for about 60 seconds. But mostly, we will not feel that tremor all the 60 seconds, but only for a few seconds during the peak,” said Dr K.S. Vipin, Post-Doctoral Fellow, Department of Civil Engineering.

Dr Vipin also noted that depending on the structures on the ground, the effect of tremors can vary. For instance, the seismology centre inside IISc is situated on hard rock.

“The ground motion will not be recorded in higher magnitude if it is standing on rock. But if you are living close to a lake bed or unstable ground, the tremors are felt. That is why some areas in city reported tremors and some did not,” Dr Vipin added.

“We have been recording different earthquakes in our centre and we are currently analysing the cause and after-effects of the Indonesian earthquake. In the last three years, we have recorded many earthquakes for the purpose of study. The idea is to monitor the seismic zones around Bengaluru in a radius of 300 km since the ripple effects of any earthquake are felt even in areas situated far from the epicentre,” said Prof. M.R. Sitaram of the civil engineering department at IISc.