cataclysmic beneath the earth. Tectonic plates that form the outer hard layer
of the earth always move, often said to be how fast your finger nails grow—33
millimeters or 1.3 inches a year; they dive under or slide past each other,
deform their edges, creating zones of smashed and cracked rock—faults—that span
a few feet to kilometres and building strain, akin to a rubber band wound
tightly. When the strain is no longer containable, the plates slip along the
faults, in a violent fling and rebound; rock comes apart; the earth shifts and
shakes. Earthquake researchers listen to the rumbles beneath the earth like
doctors listen to the patients’ hearts for telltale signs of impending slips.
Vineet Kumar Gahalaut, director of the National Centre for Seismology, has a network of GPS stations to clue in on the noise the plates make. In his graduate years, he wanted to do a masters in physics. A friend suggested applying for geophysics too. He got call letters for physics and geophysics from IIT Roorkee (then the University of Roorkee). A memory, stamped in when he was in class 8, of an earthquake in the Hindukush, that even shook his native Uttar Pradesh (now Uttarakhand), made him choose geophysics. After his Ph.D. he worked at IIT-Roorkee for a few years, did a brief stint with the Department of Science and Technology, and moved to the National Geophysical Research Institute (NGRI) where he could combine his passion for understanding geodynamics and proclivity for footloose travel.
Often in the field, exploring, he is fascinated by the Karakoram fault zone in Ladakh. “It’s so distinct, so visible; the features on the earth it created; the stream offsets it created,” he says. One block of the Karakoram fault moves horizontally in the opposite direction to the other block. If a river or stream passes on it, one part of it is on one block, and another part on the other block. With both blocks moving in opposite directions, one part of the river or stream moves in one direction and another part in another direction.(Imagine putting your hands in front and pushing one forward and dragging the other back.)
“You can see this beautiful river offset because of the strike-slip fault,” he says.
One hundred and ten years ago, one such offset produced by the San Andreas fault, a magnitude 7.8 earthquake near San Franscisco, revolutionised seismology and gave rise to the Elastic Dislocation Theory. At that time, theory of plate tectonics was not formulated. According to the famous “Lawson Report”, a fence sitting across San Andreas at right angles was torn in half in the quake, one truncated branch of it shifting nearly eighteen feet apart from the other.
It’s in such gob-smacking wonders of the earth that geologists revel. In a place near Mohand, further south of Dehra Dun, 50-year-old Gahalaut says, you suddenly see mountains and hard rock. The Indo-Gangetic plains, composed of alluvial soil, abruptly end and hard rock begins. “That’s due to the presence of a fault,” he says.
In a wide-ranging conversation with Fountain Ink, he evokes the world beneath our feet.
How did plate tectonics shape India? What are the processes that keep areas like the Himalayas and J&K seismically active?
The fertile land in the Indo-Gangetic plains (right from Punjab to Bihar and beyond) is the outcome of plate tectonics. Plate tectonics drove India towards north and caused the collision with the Eurasian plate. This led to the development of the magnificent mountain chain, the Himalaya. They control the precipitation and the rainfall drains into the Indo-Gangetic plains. The sediments brought down by the rivers because of erosion of the mountains make the land fertile. These sediments also form the aquifers where majority of the water gets collected for use in agriculture. So your bread and sugar basket is due to plate tectonics!
Similarly, the beautiful Andaman island belt is the result of plate tectonics. The subduction process raised these islands above the sea level and made them inhabitable.
In long term, plate tectonics does all this but in the short term it causes earthquakes. Because that’s how it actually works. The Indian plate underthrusts beneath the Eurasian plate and earthquakes occur at the contact surface between the two under the Himalayas, because of the friction. It is kind of stick and slip motion, so for most of time, the Indian plate which keeps moving north, gets stuck (locked) with the Himalayan wedge rocks and tries to drag it along with it but when the frictional forces exceed the material strength, it gives way (slips) and earthquakes occur. This keeps happening all the time and over various segments of the Himalayan arc. This also makes them seismically active. So a long term gain (mountains, climate) is actually achieved through short term losses (earthquakes).
Could you please give a brief overview of active faults in India?
Large and frequent earthquakes occur in the plate boundary regions of the Indian plate, the Himalayan arc, the Indo-Burmese arc, Andaman-Sumatra arc. That’s where we have most active faults. But then there are regions/faults within the Indian plate which are active, e.g., the faults in the Narmada Son area, Kachchh and Godavari basins. They are the results of early geological processes which wanted to further segment the Indian plate but could not succeed. We call them failed (or aborted) rifts. Nothing is perfect and homogenous and hence we have a few isolated regions within the plate which are seismically active.
What’s the scientific consensus on the Main Himalayan Thrust (MHT)? Everybody is predicting a big-zipper of an earthquake there. What’s the present state of Indian geologists and seismologists work there?
Evidence is growing for the presence of the MHT. In early days it was a concept, which was required for India-Eurasia interaction. But now we have enough direct evidence for its presence. The 2015 Gorkha earthquake caused loss of lives and property but it also provided the evidence for the presence of MHT under the Himalayan region. It shows that a slip occurred on a gently northward dipping plane at a depth of 10-18 km, which is nothing but the MHT.
The ongoing process of convergence causes strain accumulation all along the Himalayan belt. So if somebody says strain is accumulating in a particular segment in the Himalaya or the fault is locked, it shouldn’t scare anybody, because this is what plate tectonics and earthquake process implies. But if somebody says the fault is loaded then, he means that required strains for causing earthquakes have actually accumulated and this is worth attention. If somebody says that the fault is overloaded and the earthquake in the region is overdue then he means that the strain accumulation has exceeded the required strain for an earthquake and hence the situation is scarier. So in all cases we need a thorough understanding and quantification. Unfortunately, majority of people do not follow this, whether in India or elsewhere.
Our knowledge of the Himalayan arc is quite limited. Data are limited. We need a complete and reliable history of earthquakes. We have started acquiring good quality data only recently.
Could you please give a brief profile on MHT—its shape, its quake history, how much strain is building up, how it might slip, how much of the fault might break and consequent shaking, and how far long the rupture might propagate and go?
MHT is the contact surface between the underthrusting Indian plate rocks and overlying Himalayan wedge. It is a northward gentle, dipping surface. It shows up at the Himalayan mountain front, in terms of Main Frontal Thrust but then in the north it lies at depth which gradually increases to 20 km under the Higher Himalaya. Majority of the earthquakes in past have occurred on this surface. Major and great earthquakes rupture a substantial portion of it.
The 2015 Gorkha earthquake (a major earthquake), ruptured an area of 50x150 sq. km, but only the deeper part of the MHT under the Lesser and Higher Himalaya of central Nepal was involved and the shallow part of the MHT under the Outer Himalaya (or Shivaliks) of central Nepal remained unruptured. A great earthquake can typically rupture the entire MHT (deeper as well as shallow) of a Himalayan segment (with an area of approximately 100x300 sq. km).
All along the Himalaya the strain is building up at a rate that varies from 12 to 21 mm per year. The majority of this strain will be released in earthquakes. Small earthquakes do not contribute to the release of this strain. The question is since when has the strain been underway in each Himalayan segment. The longer the period, more the accumulated strain. The size of future earthquake would depend upon the region of strain accumulation and heterogeneities in the region. It’s not easy to estimate the two and hence estimation of size of future earthquake is not easy either.
We should be focusing more on the consequence of earthquake occurrence. Which are the areas where more damage is expected?
Every great fault creates a world around it. From the first you knew about it to the present, how has your understanding evolved on it; as a seismologist, do you love MHT, and what attracts you to that. It seems hordes of people from different countries are in love with it.
You need to evolve continuously and accept the new findings. Earlier papers were more on explaining the geological evolution of the Himalaya and hence not much was known how those structures host earthquakes. With the new data accumulating, giving lots of emphasis on how earthquakes occur and how these structures support the geological evolution of the Himalaya, now we are certain the MHT is at the ‘centre stage’ of this ‘drama’. It attracts lots of people because (i) it is a rare setting, the continent-continent collision and (ii) it gives the opportunity to study it as it is subaerial. The accessibility in subduction zones is limited because the process occurs mostly under water.
I love to work in the Himalayas, because of all the above factors and additionally, I was born here, I feel responsible for the people living here. Besides all the above, travelling in the Himalayas is beyond any other adventure to me.
The 2011 Tohoku, Japan, earthquake jolted the seismology community. Seismologists thought M9 was a low-probability event, that the epicentre was a fixed location, which looks like maybe more widespread the stable zones along the fault may not always stop the rupture from ripping further along. Are we in some similar sort of situation anywhere in India.
The Tohuku earthquake was an eyeopener. The same is true with the 2004 Sumatra Andaman earthquake. It told us that the known history of earthquake occurrence in the regions is too short. The processes responsible for these giant earthquakes operate over hundreds or thousands of years, whereas, our knowledge spans only a few hundred years. They (giant earthquakes) may be missing from our data base, if they have not occurred in past few hundred years. But that does not mean that they did not occur or will not occur. They will, but we do not know when.
We talk about structural barriers which stop the earthquakes and thus they delimit the size of an earthquake. However, there have been cases when an earthquake did not respect them and they were breached. We need to look into these barriers. We have just realised that.
Whenever—which was always—he was asked when the next earthquake would happen, Charles Richter would always reply, ‘five o’clock tomorrow morning’. How do seismologists deal with this uncertainty when everybody’s first question is ‘when is it going to happen?’
That’s a big question. We all live, thinking that we will not die. We know for sure that one day we will die, but nobody knows when! Earthquake processes operate over decades and centuries. In both cases there is a lot of uncertainty. But in both cases we know that it is going to happen one day. In case of earthquakes, we say that these are the regions which have higher seismic potential than other regions. We know that the Garhwal-Kumaun region has not produced a big one in at least 500 years and if the current estimates of strain accumulation are correct then there is enough strain in the region to be released in a big earthquake. Of course we don’t know the tipping point. But that should not hold people back to not take measures against earthquake forces.
Even as they study processes that have gone on for millions and millions of years, seismologists have that sense of urgency because they are listening through their instruments to the rumblings underneath their feet and predict when it may turn into a boom and issue warnings. Political and administrative set-up and even people, instead, respond on geological timescale because the threat feels distant. Does it frustrate you?
The problem is that things move slowly, whether it is the continent or the reforms. And nobody knows the tipping point! Making people understand about hazard they are living with and the consequences thereof, enforcing building codes and retrofitting measures, implementing the do’s and don’ts, take time.
General public expect us to predict earthquakes, which we can’t, at least at this point of time. Life is not just 0 and 1, there are lots of things between 0 and 1. People expect us to talk only 0 and 1, but we need to tell them what lies between 0 and 1. We need to tell them how to live safely in high hazard regions, by taking measures against earthquake forces. So let there be earthquakes but it should not impact the society.
Typical earthquake research looks into the hoary past of the earth’s process to understand the present and forecast the odds of a quake over long term. What are the plans of your centre to understand earthquakes in real-time and act on that understanding? What are your plans in shaping real-time seismology? Hiroo Kanamori is the father of real-time earthquake warning in Japan. Of course, it’s a fact that quake hazard is more a day-to-day life thing in Japan than here.
Our first objective is
to strengthen the network. For such a large country and with so much of
earthquake productivity, we need a strong network which can reliably locate
earthquakes in real time. The other objectives would be to understand the
earthquake processes, identify the regions of high seismic potential, undertake
microzonation of a few vulnerable cities. There is a general consensus that the
north-west Himalayas (particularly, the Garhwal-Kumaon region) has very high
seismic potential, we would like to focus in that region for next few years. We
need to understand the forces and the structures that may host large earthquakes.
The other region of priority is the Indo-Burmese arc, which is the least
Where are we in realtime seismology and forecasting capabilities?
We have a real time seismic network in India. We locate earthquakes in real time and disseminate the earthquake parameters via automatic emails and sms. But we need to strengthen this network.
What are the hurdles in rolling out real-time warning and implementing those systems as in Japan, at least in quake-prone zones. Obviously, seismometers cost, and they are required in vast numbers to have a huge and dense network.
We have just started in early warning and we are realising that communication is the biggest bottleneck. These systems require reliable, foolproof and faster communication. Communications in the mountainous regions is a challenge. Moreover, we need to train people on earthquakes, drills. We keep seeing people becoming very unruly while disembarking and embarking trains. We cannot afford that during earthquake evacuation.
How do you envision the future of seismology in our country—given the problems of poverty, strife and conflict in certain parts on the surface; given the distant threat vs day-to-day needs.
We live in a strange society. Our attitude towards disaster and accident is very strange. We have short memory, we tend to forget whatever happened in the last earthquake. It also has to do something with poverty. People talk about resilience of society to cope with earthquake disaster. It’s good to recover fast but not good to forget what we just witnessed. Working in some parts of the country is not easy, particularly because of socio-political situation in those parts. We are actually waiting to deploy instruments in Kashmir, everything is in place but we are not able to do it because of the current situation. Why can’t I go to a place of my choice in my own country? Of course I want to come back safely too.
Do you foresee your centre tapping into space research (a new study has said that gravitational tug between the sun and the moon caused some quakes on San Andreas fault and that there was some speculation about radiation coming out just before earthquakes) and Navy expertise and whatever it takes to somehow have an early warning system for quake-prone zones?
I am open to this. We seismologists work with the hope that after studying earthquakes and understanding their occurrence processes, there will be a day when we will be able to successfully predict/forecast them (though we never admit that in our proposals). And if it takes unconventional methods, or the methods which we abandoned, we will use them. The influence of sun and moon on earth has been discussed quite a number of times when it comes to earthquake generation. Similarly, some radiation (electromagnetic, acoustic or any other kind) has been discussed to be a possible earthquake precursor but we still do not know for sure.
An early warning system is doable. With communication taking a fast forward leap, it should be soon possible to install Early Warning systems for the Himalayan earthquakes to be early warned about their occurrence at places like Delhi, Lucknow, Kanpur, etc.