Tremors in Chincholi: what is in store?

The ground motions suggest that the Chincholi region could be a seismically active zone.

A few villages in Chincholi taluk of Kalaburagi district have been witnessing tremors for the last several weeks and it is disturbing to note that the villagers are sleeping outside their homes for fear of earthquake.

Though tremors are small (1.6 magnitude on the Richter scale), fear and agony of people are understandable. Amidst this fear-stricken atmosphere, scientists, officials and political leaders are assuring villagers that nothing will happen.

It is interesting to note that mild tremors (1.2) hit this area in 2008 and 2015 as well. The past and present ground motions thus suggest that it (the Chincholi region) could be a seismically active zone which may have something big in store.

Ground vibrations, ground deformation, rumbling and streaky sounds are regular features before most major earthquakes strike. The strange sounds are produced as the rocks undergo stress, friction and rupturing deep in the earth.

The Latur-Killari earthquake of September 30, 1993 on the Karnataka-Maharastra border too had similar, but still stronger quake compared to that of the Chincholi area. But sadly, scientists and administrators ignored them, only to pay a heavy price of 10,000 lives.

Chincholi and surrounding areas have more or less the same geological setting like Latur-Killari areas. In this region, 66 million-year old basaltic rocks sit over the much older granitic ro-cks. But at places, basaltic rocks lie over sedimentary or relatively soft rocks. Also, sometimes, they are inter-layered. This structural and compositional heterogeneity could trigger movement of earth blocks resulting in low-magnitude earthquakes. 

But, if the movement of the blocks is related to major rifts as happened in Latur-Killari, then the effect  will be deadly. So, th-ere is an urgent need to geophysically probe Chincholi area to ascertain the subsurface conditions for interpretation of tremors and their source. Till then, it is safe to treat the present tremors as related to some fault/rift rela-ted activity, but anticipate bigger trouble and be prepared for it.
It is often said that it is not the earthquake but the buildings which kill. A glaring example is again that of Latur-Killari earthquake of 6.3 magnitude, compared to a still higher magnitude (6.7) California earthquake in 1994 which was responsible for 57 deaths. The difference between the two was the buildings.

Most rural areas of Kalaburagi have houses built of mud and stones and roof covered with sla-bbing stones (Shahbad stones). Even a small earthquake of about magnitude 4 can be disas-trous, as these houses crumble and turn into death traps. But, the earthquake-proof houses in California made all the differen-ce. Hence, the dire necessity is the preparedness, and that can be effective if rural houses in sei-smic zones are made earthqua-ke-resistant through retrofitting.

A frequently asked question is “why earthquakes cannot be predicted accurately”. Unfortunately, in spite of the scientific advancement, the precise prediction is still a distant dream.

The only outstanding prediction in the history of earthquakes is that of Hicheng (China) earthquake of February 4, 1975. This earthquake was predicted months before on the basis of foreshocks and other forerunners. People slept outside their homes for that agonising month of predicted time.

As predicted, a 7.3 magnitude earthquake struck the Hicheng city. The prediction saved an estimated 2.5 lakh lives. Yet, about 2,000 people, who mostly ignored warnings, perished in the quake. But sadly, another major earthquake of 7.6 in magnitude in Tangshan city in 1976 which killed over 2.5 lakh people, could not be predicted. Extensive rese-arch is going on globally for real time prediction of earthquakes.

Plate movements

Over 10 lakh earthquakes occur every year. Of them, about a lakh have the magnitude of less than 2.5 and about 100 are large enough to cause damages. Plate movements and faulting are the two strong reasons identified for their occurrence. Earth is a mosaic of seven major plates of about 100 km thickness which slide past along their boundaries producing major earthquakes of less than 5 in magnitude.

Within these major plates, there are hundreds of small intra-plates and their contact bou-ndaries are also the sites of seismic activity. The linear structural break along which rocks move against each other which is referred to as faulting, also causes earthquakes. The Latur-Killari and Chincholi areas represent such intra-plate and/or fault boundary domains. Hence, the possibility of earthquakes in Chincholi area can’t be ignored.

Therefore, when people live in seismically active areas, they should be prepared to face the eventuality. Obviously, the wisd-om of the tremor-scared villag-ers here has come to fore as they are sleeping outside homes. But how long this can continue? It is high time that the government came to their rescue. The villagers need to be provided with makeshifts to sleep in the night.

Also, the government should initiate measures to provide them technical and monitory support to retrofit their homes so that they can withstand vib-rations, and people can live without the fear of earthquakes. Th-us, in seismic zones, prepared-
ness is the key against tremors.

(Prabhakar is Professor of Geology, Bangalore University and Radhika is Associate Professor of Geology, East West  Engineering College, Bengaluru)