Hyderabad: The Sivaramakrishnan Committee has recommended to the state government to enforce building standards and seismic code in VGTM UDA, the proposed capital area of Andhra Pradesh, as the area falls in a vulnerable zone for earthquakes.
According to the committee, the non-engineered buildings and poor quality multi-storied constructions in Vijayawada and Guntur are at moderate risk. The Committee referred to the Bhuj earthquake in 2001, when distant locations like Ahmedabad in Gujarat had suffered the impact.
The committee quoted a Geological Survey of India’s seismic micro-zonation study of the Vijayawada region, reporting that potential earthquakes could result from four neo-tectonic faults located within a range of 150 km from Vijayawada.
“AP lies in the earthquake hazard Zone III and Zone II and is prone to moderate to low damage risk,” said the report.
The report also says that liquefaction during an earthquake may be a more significant risk, given the high groundwater table across this fertile region. There are a number of high liquefaction vulnerable zones that will need to be carefully avoided or significant steps be taken to strengthen building.
Akhila Manne of the Earthquake Engineering Research Centre of IIIT said there are around 22 seismic sources (faults) in and around Vijayawada in a radius of 300 km and among them, the prominent active fault is the Gundlakamma fault.
“Vijayawada city is located along the Krishna River and is covered by dominant amounts of silty clay with some amount of silty sands and sandy silts.
The surface acceleration values have been very high in RR Gardens, Bundar Road, KP Nagar, Nehru Nagar and Durgamalleswar Swamy Devasthama. These areas have a water table depth of more than four meter and predominant soil consists of sandy clays.
At Autonagar, Labbipet, Satyanarayanapuram, Muthylampaudu, Pakirgudem, Loyola College, Currency Nagar, RTC Colony, Governorpet, Autonagar, Brahimin Street, Jakkamdpui and Hanumanpet, the accelerations are 0.1g to 0.2g. Peak ground accelerations Is very low below 0.1 g in Bhavanipuram, Gollapudi, Kederaswarpet, PNT Colony, Kasturbibaipet, Gurunanka Nagar, Bank Colony, Suryarapet, Patamatalanka, Prasadampadu, Ayodhyanagar, Poornandapet, Chandramouli Colony,” observed Ms Manne.
Meanwhile, Experts of National Disaster Management Authority and National Geographical Research Institute say Vijayawada is on par with Mumbai, Pune, Chennai, Ahmedabad, Trivandrum, when it comes to earthquake safety as all of them fall under Zone -3 with 0.16 g seismic factor of Peak Ground Acceleration.
Vijayawada is safer than Delhi and Patna, which are more vulnerable as per Seismic Zone Mapping of India. Experts revealed that ‘worst case scenarios’ are rarest and if building seismic codes are followed properly, Vijayawada will be safe to have high rises.
NGRI chief scientist R.K. Chadha said, “Delhi is in Zone-4 and is more vulnerable in comparison to Vijayawada. If proper precautions are taken, there should be no problem.”
However, he suggested local micro zone studies be carried out, adding, “1g means 981 mm per second square acceleration. For instance, the worst case scenario in Vijayawada is 0.22g which means 200 mm per second square, which will occur only in the event of an earthquake of a magnitude of 7.5 to 8. According to seismic zone mapping code, Vijayawada will experience maximum earthquake of 6.5 magnitude on the Richter scale. The worst case scenario is one in a million case.”
Experts say that concentration of alluvial deposits in Vijayawada city ‘greatly influences’ the site during tremors. Liquefaction, a phenomenon when saturated or partially saturated soil loses strength and behaves like liquid due to quake, induces ground failure.
“Massive structures like as dams, bridges, suffer critical damage due to initiation of liquefaction during seismic ground shaking,” said Akhila Manne of IIIT.
No liquefaction has been observed in Indrakiladri, Gollapalem Gattu, Machavaram, Mohgalrajpuram and Gunadala Hills. Geological Survey of India suggested land-use zoning as effective means to reduce future liquefaction.
