Medaram earthquake not unusual: Seismic experts

 Hyderabad: The moderate earthquake of magnitude 5 that occurred around 7.27 am on Wednesday at Medaram in Mulugu of Telangana is not an unusual event. These types of phenomena occur periodically in the peninsular shield region of the Indian tectonic plate, seismic experts have averred.

Dr Prakash Kumar, director of CSIR-National Geophysical Research Institute (NGRI) whose observatory has recorded the earthquake, described it as a shallow one with a depth of around 10 km. However, the tremors were felt across several parts in the two Telugu states, including Hyderabad and Vijayawada.

The strike-slip earthquake has occurred in the fault lines of The Godavari Rift Valley region, which has been described as a weak zone. In a typical strike slip earthquake, faults occur vertically when two blocks move horizontally releasing the accumulated stress. A network of seismic stations of NGRI in the region also has recorded the earthquake. NGRI has a network of 150-180 seismic stations all over the country.

Dr Prakash Kumar said that a team of seismologists would leave for the epicenter region and install a strong motion seismograph to record any aftershocks. An earthquake of 5 magnitude in the region has occurred after more than 50 years as a 5.7-magnitude with its epicenter at Bhadrachalam shook the region in 1969. A 4.3-magnitude earthquake occurred in the Medchalin 1983 and another one of 4.6 magnitude in Pulichintala area in 2021.

According to M Sekhar, Principal Scientist of the Seismology Group, NGRI, aftershocks can occur anytime and there is no specific timeline. They can occur within a few hours, few days or even few months after an earthquake.

Seismologist and former NGRI chief scientist, R K Chadha said it was normal and not unusual to have moderate earthquakes of 5 magnitude and above in the peninsular shield which falls in the Seismic Zone III of the Seismic Zoning Map of India. The Seismic Zone III is moderately active. These earthquakes occur as a result of the stress accumulated over the years due to the tectonic movement of the Indian plate. While the Himalayan region is considered as “high stress” area and falls in Seismic Zone V, the peninsular shield is generally low-stress regime, he added.

He said that earthquakes of magnitude 5 and above occur at longer intervals of many years in the low-stress region unlike the high-stress Himalayan region where earthquakes of magnitude between 5 and 6 occur with greater frequency. Also, larger earthquakes exceeding magnitude 8 have occurred in the Himalayan region—Shillong (1857), Kangra (1905), Bihar-Nepal (1934) and Arunachal Pradesh (1950).

Depending on the magnitude, shallow earthquakes like the recent one in the intra-plate regioncan be felt up to a distance of 200 km or more. They can be felt over a larger distance if they are of greater magnitude like theLatur earthquake (1993) which was of 6.3 magnitude and felt up to Hyderabad. Intra-plate earthquakes in the Peninsular Shield occur along the weak rift valley zones like Godavari Rift Valley and Narmada-Son Rift Valley.

Describing Wednesday’s earthquake as a natural phenomenon, Dr Chadha said that it has nothing to do with climate change.