Bhubaneswar: Sept. 28: The National Highways Authority of India has issued a showcause notice to the contractor after a concrete slab weighing around five quintals fell off a flyover on National Highway No. 5.

The incident that occurred at Jayadev Vihar on September 23 was the second case of concrete slabs falling off the overbridge at Jayadev Vihar Square in three months.

The highways authority has said that vibration on the overbridge generated by plying of vehicles led to the stone slab dislodging, but geologists have said a “partially active seismic fault zone” passing through Jayadev Vihar might have caused it.

Much before work on the overbridge was taken up here, geologists had expressed concern about the existence of this fault zone at a seminar — Role of Architects Towards Seismically-Safe Built Environment — held in 2005.

Project director of the National Highways Authority of India (NHAI) Aditya Ray said: “Lack of proper maintenance of bridge by the contractor concerned is one of the reasons for the accident.”

However, the NHAI authorities have refused to comment on the fault zone theory. “We have no expertise in that field. However, we are sure that there is a fault in the structural design of the bridge,” said Ray. The contractor concerned, JSPL, is in charge of building and maintaining the bridge on NH-5 for another 26 years on a built-own-operate-and-transfer basis.

However, a close study of the fault zone has revealed that cracks have developed in many buildings. “There’s nothing to panic about. But utmost care should be taken while constructing any buildings or other structures along the fault line,” said the former deputy director general of Geological Survey of India, P.N. Nayak.

Officials sources in the revenue and disaster management said encroachment on a natural drainage channel might lead to seepage of groundwater into nearby areas, putting pressure on the fault zone. Encroachment on the nearby natural drainage channel has led to its shrinking.

A fault zone from Chandarsekharpur passes through Jayadev Vihar and goes up to Vani Vihar. Experts have observed that a temple and water tank in Chandrasekharpur have tilted.

“The state should follow the pattern of Maharashtra, where more than 80 well-equipped micro-earthquake stations are present to record earthquakes. Odisha only has a single recording station,” said an official.