From the edge of India’s deepest pit

In Gothane village near Pune, scientists are digging a 5 km hole that will go deep under earth in search of seismic answers

February 25, 2017 04:30 pm | Updated 05:28 pm IST

Search for seismic clues

Search for seismic clues

Koyna, Maharashtra. For the first time in its life, ‘Shivganga’, the 90-tonne, 80-feet-high drilling rig found itself perched on a hill. Used to combing India’s western coasts—sometimes inside the sea—for crude oil, this time it has an unusual task: to plumb depths, yet unachieved on mainland India, and in the process, bring seismologists nose-pressingly-close to watching an earthquake come to life. Were everything to go to plan, in the next three months, the Indore-based Shivganga drilling company will have managed to get its rig to burrow 3 km deep. If successful, this would pave the way for a future, deeper dive—this time 5 km—into India’s innards. That’s approximately like going from Connaught Place to Nizamuddin.

The Indian project, when done, will rival previous excursions by China and an earlier one by Germany to tunnel 6-8 km into the earth. Unlike commercial wells, the holes being dug in Maharashtra will be a permanent edifice to science in India and the proposed 5 km hole will retain that depth “for centuries”, say scientists involved in the project.

National record apart, several mysteries lurk in the soil here. Gothane village, where the holes are being dug, and the surrounding city of Karad, located roughly 150 km from Pune, have for long been known for their fertile soil and vast vistas of sugarcane. This fertility is partly due to volcanoes, which belched incendiary magma 66 million years ago and set the stage for a global winter that, along with the Chicxulub asteroid strike, snuffed out three-fourths of life, including that of dinosaurs. The scars of those eruptions, spaced out over 7,50,000 years, are visible in the form of layers of black, nutrient-rich soil, called basaltic soil, that alternate with lighter layers—from the years when the eruptions took a break—and make the landscape look like stairs (hence the name Deccan Traps for the region, which is Swedish for ‘stairs’).

Dam and double dam

Palaeontological marvels may be lurking below but what has piqued scientific curiosity lies above the ground: the 300 feet tall, 800 feet wide Koyna dam, built in 1962, and in grandeur, among adolescent India’s engineering marvels. Five years later, an earthquake with as much energy as the bomb that destroyed Hiroshima levelled the Koyna township, killing 200 and injuring 1,500. Since then, generations of geologists, seismologists and civil engineers in India have been engrossed in a sub-field of seismology called reservoir-triggered seismicity. Large reservoirs like the Koyna dam—the theory goes—that can hold more than a trillion litres of water can crack and fissure the insides of the surrounding earth when water levels wax and wane in their reservoirs. This can induce weaknesses in the surrounding rock mass and trigger earthquakes.

Drilling rig ‘Shivganga’ looms large at Gothane village, roughly 150 km from Pune.

Drilling rig ‘Shivganga’ looms large at Gothane village, roughly 150 km from Pune.

Of the 1,000-odd large reservoirs across the world, only a tenth have been implicated in triggering earthquakes. Of them, only about four have been known to trigger tremblers of magnitude greater than 6, and in Koyna, nearly 50 years after the great quake, earthquakes continue to tickle the region to this day. Moreover, unlike more powerful earthquakes that result due to squabbling continental plates and originate deep—sometimes 20 km to 30 km inside the earth—reservoir-induced quakes are born 5-7 km from the surface and can be viewed with the right instruments. “The scientific consensus is that Koyna is the best site anywhere in the world where an earthquake can be observed,” said Harsh Gupta, veteran seismologist, ex-chairman of the National Geophysical Research Institute (Hyderabad) and the driver of the deep borehole drilling experiment.

For over a decade now, Gupta has been working on a model that attempts to forecast the time, magnitude and precise location of earthquakes in Koyna, a region that has occupied his research agenda for about half a century. In 2009, the model accurately forecast, 15 days in advance, a Magnitude 4 quake in Koyna and this was one among “a dozen such forecasts that were made that all came true,” he added.

Such a model, however, relies on detecting foreshocks, or tremors caused by smaller earthquakes, that may be acting as a build-up to a larger one in a process known as earthquake nucleation. It doesn’t reveal the deeper mechanism as to what has caused the earthquake and whether the surrounding mass of rock was strained enough that a slight trigger—such as water accumulating in a nearby reservoir—would be enough to set off a shaker. “So far, what can be studied from the surface has already been done… that is why we need to go down… beneath the basalt and observe what’s actually happening at the fault,” Gupta said over the phone.

Fault zone

Since 2011, a mix of international and Indian scientists have twice visited Koyna to discuss if digging a deep hole would be insightful to take forward the science of reservoir-triggered seismicity and if so, how deep this hole should be and where best to locate it. All earthquakes in the greater Koyna region have occurred within a 20x30 sq. km radius. The challenge was to zero in on a “fault zone,” or a location where a major rupture might occur that would also be relatively easy to access. After digging nine test holes since 2012, each no more than a kilometre and a half, Gupta and his colleagues zeroed in on this site, which is close enough to a fault zone, and can likely generate a strong enough earthquake that can yield myriad data on how the surrounding soil shakes and what kind of gases, water pressure and temperatures exist at the points where the earthquake births. Atop the hill, the Shivganga rig is surrounded by several white shipping containers, each half as big as a railway coach, and making up the temporary home, office space, dining room, kitchen and cyber-café for the 80-odd crew. Working continuously in two shifts, they are mostly seasoned oil-men (and they are all men) who’ve spent lifetimes teasing out petroleum crude in Bombay High and West Asia. Alongside them are fresh-faced researchers, some still in college and all of them flocked around the professorial Sukanta Roy, who’s spent two-and-a-half decades pondering the mysteries of geothermal vents and hot springs at NGRI.

A researcher studies soil samples at the dig site in Gothane village.

A researcher studies soil samples at the dig site in Gothane village.

Describing the Shivganga rig’s deep dive as a “24/7 activity”, Roy—who’s spent most of the last two years at Karad—has stopped counting the number of trips he makes from a makeshift laboratory in the city, up a muddy trail that only in December earned the right to be described as a road, to the hilltop drilling site. “All my research life has been around boreholes… I think I’ve seen most of them... Kerala, Gujarat,” said Roy, as he guided me past a windmill with a signboard at its base warning of snakes. “There’s a photograph of a scorpion at the heel of one my colleagues,” he said.

Unlike, say, a construction site where a gaping hole marks out the space being worked upon, here, the hole being dug is at a maximum width of 26 inches, not much bigger than an effluent pipe. As it tapers down near a potential earthquake epicentre, the bore will encounter increasingly hotter temperatures and unknown clumps of sand, stone and rock. “We were going along and suddenly, at 1,027 metres, we ran into water,” said Roy, “The whole operation then ceases and has to change to first seal off the water seepage.” Normal drilling that time could begin only after a hiatus of three weeks.

Too costly?

The complexities and risks involved in drilling are a window into the criticism that the Koyna drilling project faces from India’s wider geological community. While they may eventually be the country’s deepest boreholes, they are also the costliest. Deeper holes have been dug in India. Apart from dives in Bombay High or the oleaginous Cambay basin, the Oil and Natural Gas Commission once went an unprecedented 6 km deep in Himachal Pradesh looking for oil. However, all of these have involved tunnelling through soft, sedimentary rock and are naturally refilled with sand and gravel once commercially exploited. The deepest hole ever dug is in the Kola Peninsula of Russia and goes down a Hadesean 12 km. This one will cost about Rs. 470 crore—or a little more than India’s Mars Mission—and includes setting up a permanent research laboratory in Karad. The actual drilling will cost about 30% (or Rs. 150 crore).

According to many scientists, that’s an unacceptably high cost for a mission that will only incrementally improve our understanding of earthquakes. In terms of what the mission proposes, say critics, it isn’t very different from the San Andreas Faulty Observatory at Depth (SAFOD), an ambitious programme in the U.S. from a decade ago to bore 4 km deep into one of the most active faults on earth. That programme didn’t deliver on its goals because several of the instruments put into the borehole worked sub-optimally and the project had to wind up ahead of schedule.

“The chances that a Koyna-type earthquake (that occurred in 1967) will occur will be one in a 1,000 years,” said Shyam Rai, professor of earth sciences at the Indian Institute of Science Education and Research in Pune. “Anywhere in peninsular India we get a maximum Magnitude 6 earthquake in a 100-year span. Major Himalayan earthquakes are more likely and more serious.” The geological conditions in Koyna—namely the unusually thick layer of basalt, the location of a large reservoir—are so specific to the region that it would thwart any broader understanding of whether earthquake forecasts can be improved in order to understand greater threats such as Himalayan earthquakes.

So far, what can be studied from the surface has already been done… that is why we need to go down… beneath the basalt and observe what’s actually happening at the fault — Harsh Gupta, veteran seismologist

Another scientist said, on condition of anonymity, that “about 70% of Indian geologists, familiar with the programme, weren’t convinced of the scientific case for the experiment.” Programmes such as SAFOD had extensive consultations with nearly 200 scientists before a drilling decision was made and no comparable effort, in terms of having a disinterested review committee discuss its merits, was done in the case of Koyna. Rai added that much of the seismic monitoring data from Koyna, for the past seven years, was “under lock and key” and it was very likely that the information from the boreholes would also be made inaccessible. “I can download all the data from SAFOD, the Chinese and German borehole drilling programmes right away, but here our policy doesn’t permit such free access. How will the public money being spent here be of benefit?” Rai said.

Core of the issue

Gupta is emphatic that as far as Koyna goes, all that can be understood from surface observations have already been done. Getting below the basaltic layers is crucial because no earthquakes have so far been known to form in that layer. He sees the drilling programme akin to a “space mission” and as something that can spawn a generation of new scientists who can make fundamental contributions to geology. Himalayan earthquakes occur too deep in the ground and it would be hard to find suitable sites to design a drilling problem. About 60% of the accumulated strain in Koyna, according to Gupta, has dissipated and it was likely that most of it would peter out over the next few decades. However, earthquake forecasts weren’t only about timing. “What would you do if I told you that a Magnitude 8 earthquake would hit Delhi in the next four hours… it would be chaos and most people wouldn’t be able to escape,” said Gupta. More than time-based predictions, a firmer understanding of how geological processes were influencing the Indian landmass is critical to understand climate trends, future reservoir construction and building codes.

Indeed, one of the reasons guiding the Union Cabinet when it apportioned money for the programme in November 2013 was that it would “…provide crucial insights into Deccan volcanism and mass extinction; thermal structure and the state of stress in the lithosphere; the geothermal potential of the West Coast Belt as well as the geothermal record of climate change in the region.”

Later this year, microbiologists from the Indian Institute of Technology-Kharagpur will be looking for rare bacteria—known as extremophiles or those that can thrive in inhospitable conditions and hold clues to evolutionary history—in the rock-core dug out by Shivganga. Indian-American scientist Sankar Chatterjee has reportedly said that he is keen to examine samples from the Koyna boreholes to find evidence for the so-called ‘Shiva Crater’ hypothesis, which holds that the dinosaur-wiping mass extinction was catalysed by a 500 km wide asteroid strike whose impact is visible in the form of a huge crater in the Arabian Sea. “If we lined up all the cores that we have so far dredged up, it would be 10 km long,” said Roy. “We’ve learnt from the mistakes of others and I firmly believe this project will help us make some fundamental discoveries.”

jacob.koshy@thehindu.co.in

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