The 4.2 magnitude earthquake experienced in and around Delhi on Wednesday night was felt more strongly than its reading on the Richter scale suggested because of the fact that the origin of the waves lay in close proximity to the city and not very deep below the earth’s surface, scientists say. The epicentre of the earthquake was barely a few kilometres outside of Delhi, near Sonepat, and just eight km below the surface of the earth. “Had the epicentre been 100 km below, for example, it would not have been noticed in the same way as it did,” said Dr Shailesh Nayak, Secretary in the Ministry of Earth Sciences. Even within Delhi, areas around the Yamuna river, like Mayur Vihar and Noida, felt stronger tremors. “That area is all built on reclaimed land. Surface waves get trapped in the softer land and produce large amplitudes. In addition, there are a number of high-rise apartments in those areas which would have experienced greater vibrations,” Dr S S Rai of the Hyderabad-based National Geophysical Research Institute said. Earthquakes of magnitude 3 to 3.5 are not uncommon around Delhi which has been categorised as seismic zone 4. In the past, there have been occasional instances of Delhi being jolted by earthquakes of magnitudes between 6 and 6.5.