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The husband-and-wife seismologists have toured the world together for 35 years, mapping faults, decoding ancient clues, searching for the signatures that earthquakes leave behind. All in an effort to answer the questions: How do tremors work, and how should we prepare for the next big one? Their new book, The Rumbling Earth, recounts some of these adventures. ‘It can feel a bit like Sherlock and Watson, chasing leads and piecing it all together,’ they say

They are one of Earth’s most destructive forces, earthquakes. CP Rajendran and Kusala Rajendran would like to offer a reminder that they are one of Earth’s most creative too. There would be no mountains without earthquakes; rivers would flow straighter; sea floors, valleys and deserts would look vastly different.

“Tremors caused by plate tectonics are one of the most fundamental dynamic motions of our planet,” CP says.

It’s kept them together too, the Rajendrans like to say. The geologist and geophysicist, both 69, have been married for 43 years, in what is an unlikely pairing. “People from our fields tend to only disagree,” Kusala says, laughing.

Instead, the duo has travelled the world together, scanning bare ground, digging into the edges of ravines, and wading through crocodile-infested marshlands, seeking the signatures that earthquakes leave behind.

Their research has helped map fault zones, and offered insight into earthquake recurrence in vulnerable regions and in regions once considered safe from such activity (such as Latur).

They now have a book out. The Rumbling Earth: The Story of Indian Earthquakes

KUSALA RAJENDRAN,

(March; Vintage) traces their decades of research into how major earthquakes have altered India over centuries.

It explores how seismic activity in this country shaped the early years of study in this field (a giant quake in Assam in 1897 was among the first to be registered on a seismic recorder).

The book examines what ancient structures reveal about tremors of the past, and it looks forward, to estimate where the country’s next great seismic event will likely occur (by all accounts, deep in the Himalayas).

“Because our life is all about working on earthquakes, the book is also about our experiences, our travels, and the people who have helped us,” Kusala says.

C

P and Kusala met in 1980, while conducting research at the Centre for Earth Science Studies (now the National Centre for Earth Science Studies). In a year, they were married. Two years on, they had a son, Rahul Rajendran (now 41, an IT executive).

In 1988, Kusala was invited to pursue a PHD at the University of South Carolina, where CP and Rahul joined her, the former to do a stint of post-doctoral research.

CP soon became fascinated by the nearby site of the 1886 Charleston earthquake, which flattened the town, in a time just before the science of seismology took off. CP began to search the swamps for evidence of exactly how this quake unfolded.

“He began calling himself the Sherlock Holmes of geology,” says Kusala, laughing.

In a sense, he is, she adds. Because the field he was immersing himself in, palaeoseismology, studies earthquakes that occurred before instruments came about to record them.

Instrumentation, in this field, only dates to about the early 1800s. Back then, a lot of data came from India, which has the two massive plates crashing into each other in the Himalayas, and had meticulous recordkeeping by British surveyors based here at the time.

“The 1897 Assam earthquake produced what is called liquefaction, where intense pressure below the surface causes something like a volcano of mud, which can turn into a river of mud and flood an entire region,” says Kusala. “This was documented by the Geological Survey of India then, and helped scientists understand something new about what earthquakes could do.” L etters, diary entries, survey records and paintings are among the historical sources that help palaeoseismologists in their field.

The records of the British show, for instance, how an 1819 seismic event in the Rann of Kutch, now estimated to have been about an 8.2 on the Richter scale, lifted the earth into a mound that was 90 km long and about 4 metres high, blocking the Nara river and altering its course.

Going further back, one can study archaeological structures, though these are harder to decode. The Qutb Minar in Delhi, built between 1199 and 1509, has served as something of an earthquake recorder. The fourth section (from below) is made of white marble, a departure from the red sandstone, and was likely reconstructed after the 1341 earthquake in the region.

“Even the topmost floor is a reconstruction,” CP says. “British surveyors’ records indicate that an 1803 earthquake near Uttarkashi impacted some of the plains, and caused the top of the minar to topple.”

When Kusala, who was purely a datacruncher (as geophysicists tend to be), first accompanied him on his field trips in Charleston, she says she was mesmerised by the evidence he gathered. “It is actually like being a detective at a crime scene,” she says.

“You tap into your scientific intuition and collect samples that need to be dated. Essentially, you look at the circumstantial evidence and put it into context.”

Sometimes, for instance, a root system will remain intact, but the tree is long gone; a palaeoseismologist will study the roots to estimate the size of the tree and then estimate the seismic intensity it would have taken to separate it from the ground.

Kusala brought her expertise at crunching geological data to bear, and in this way, they began to research quakes together.

Five years on, in 1993, the little family returned to India, just months before a quake flattened 67 villages in Maharashtra’s Latur district, not typically a seismic zone. The central government’s department of science and technology asked the couple to investigate how this quake could have occurred with no pre-quake tremors.

It turned out that there had been warnings; a series of low-magnitude tremors in areas around the epicentre, the village of Killari. But because this region, like a lot of peninsular India, was considered continentally stable, it didn’t ring any alarm bells.

The Rajendrans further concluded that Latur’s was indeed an out-of-the-blue event; no earthquake of such magnitude had likely occurred there in at least 1,000 years.

T here is now a big quake building in the Central Himalayas, they say.

These massive mountains are, of course, the result of the fault line on which they sit. The fault line was caused when a floating India, having broken away from Gondwana and spent millions of years at sea, finally docked into Eurasia.

The Indian tectonic plate continues to push against the Eurasian, at the rate of about 5 cm a year. “The movement of the plate is almost uniform across the Himalayan arc,” says CP, ominously, “and yet the Central Himalayas haven’t had an earthquake in at least 600 years.”

Surrounding regions in the Eastern and Western Himalayas have registered five great earthquakes with magnitudes of around 8 or more, over the past two centuries: at Garhwal in 1803, Shillong in 1897, Kangra in 1905, Bihar-nepal in 1934, and Assam in 1950.

“So this is a missing event in the region. The stresses are building up, the rocks are getting weaker, and energy is accumulating. It will eventually have to be released along the fault,” Kusala says.

Meanwhile, the built environment across the Himalayas has expanded without taking into account the risks involved, CP adds.

“With all the advances in digital technology, AI models and warning systems, we should be offering incentives for buildings that can withstand earthquakes, educating the public, building awareness, putting an action plan in place for how to rehabilitate people when a major quake does occur. We should be better prepared than we were 20 years ago,” says Kusala.

That is exactly how Taiwan manages to keep its quake tolls low. Thirteen people died in the recent April 3 earthquake, down from about 2,500 deaths in a quake of similar magnitude in 1999.

“There are a lot of things that we should be doing in the region,” CP says, “but I’m not sure that we are.”

There is a missing event in the Himalayan region. The stresses are building up, the rocks are getting weaker, and energy is accumulating. This energy will eventually have to be released along the fault.

she and her husband are among the seismologists who expect the next big quake to be deep in the Himalayas

P

There are a lot of things that we should be doing in the Himalayan region, but I’m not sure that we are. CP RAJENDRAN, on India’s preparedness