Andhra Pradesh

‘Ongole most quake-prone in AP'

The revised map of seismic zones in Andhra Pradesh has identified Ongole area as the most earthquake-prone in this part of the country, instead of the Bhadrachalam belt as was believed earlier.

The map has been revised following fresh research inputs from national institutions like National Geophysical Research Institution and Geological Survey of India. Based on this map and accompanying report, the Disaster Management Department is expected to formulate an action plan for vulnerable areas in tune with the A. V. S. Reddy Earthquake Manual.

Five seismic zones

While India is divided into five seismic zones depending on the degree of their vulnerability, the entire north from the Himalayas down to Koyna in Maharashtra, barring a few patches, are rated as susceptible to quakes with a very high damage risk and accordingly listed in Zone V and IV.

Andhra Pradesh lies on the Peninsular Indian Shield (PSI) long considered as stable and not vulnerable. The earthquakes of Koyna (1967), Latur (1993) and Jabalpur (1997), however, demolished this theory, according to the report. Subsequently, a few zones of faults in the crystal layers of the Peninsular region causing quakes, had been identified, it said.

Many northeast-southwest trending fault-bound basement ridges and depressions traversed by transverse features like cross-trends have been found, especially in Ongole, Vizianagaram and other areas. These are likely to cause reactivation with a progressive build up of stress.

The geographical areas of AP fall in Zone I and II where both vulnerability and damage risk is held low. Ongole area spread over as many as 30 mandals which faced 12 earthquakes in the past 30 years, including two big ones in 1967 and 1959 with magnitude of 5.4 and 5 on Richter scale, is held as the most active zone in the State.

Tectonically active

Eastern Ghats belt and Godavari Valley are found to be tectonically active. A reference is made to the State's biggest earthquake (5.7) that occurred in Bhadrachalam area of the Godavari Valley in 1969 when the nearby Kinnerasani reservoir was disturbed. Vizianagaram area of the Eastern Ghat belt experienced a series of quakes, including one with an intensity of 5.5 in 1917. The report says if an earthquake with a magnitude of 5 occurs in PSI, it may take even a century for the stress to build up again.

Seismically active areas

Pinapaka, Gundala, Kothagudem, Manuguru, Yellandu and six other mandals in Khammam district where Bhadrachalam lies, and 10 mandals in Vizianagaram district, including Garividi and Nellimerla, are listed as seismically very active.

In Hyderabad, Jubilee Hills and Banjara Hills are included in this category along with the neighbouring areas of Medchal, Shamirpet, Shankarpalli, Serilingampalli, Rajendernagar and Moinabad.

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Printable version | Dec 6, 2021 6:19:51 PM |

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