BANGALORE, July 17: Mystery shrouds the cause of a muffled explosion which rattled window panes and set off vibrations in several areas of Bangalore city on Tuesday morning, causing people to panic. The blast was thought to be an earthquake by residents of areas like Indiranagar, Malleswaram, Majestic, J P Nagar and Koramangala, but the Mines and Geology Department Director said the Sesmological Centre at Gauribidanur had ruled out this possibility. The Defence sector has also disclaimed responsibility, and no reports have come in regarding any untoward incident. The mystery continues.