Sunday's earthquake, 420 km south of Port Blair in the Andaman and Nicobar islands, was felt in certain parts of Chennai and others on the eastern coast. "It is very simple," said R.K. Chadha, scientist with the National Geophysical Research Institute, Hyderabad. "Feeling the tremors of a distant earthquake is mainly due to surface waves that are generated by it. Though attenuation of energy happens with distance, feeling it in distant areas is due to local conditions."