‘Science shows a major earthquake is overdue’

Civil Society News, Gurugram

From imploding glaciers to landslides, floods and torrential downpours, natural disasters have been happening one after the other in the Himalayas in recent times, making life in the mountains seem more vulnerable than ever before.

These unsettling episodes have made news by leaving a trail of destruction in their wake.  But a yet bigger disaster is in the making — invisibly so because it involves a tectonic shifting of plates deep within the earth at 5cm a year. The outcome is expected to be a devastating earthquake on a scale the Himalayan region hasn’t witnessed since 1950.

Earthquakes happen periodically as the earth releases pent-up energy. They can’t be precisely predicted but they can be foretold. Scientists believe that a massive one is overdue in the Himalayan region and could happen anytime.

N. Purnachandra Rao spoke to Civil Society about what the scientific concerns are. Dr Rao is a seismologist of high standing who in his last job was chief scientist at the National Geophysical Research Institute (NGRI). in Hyderabad. He insists that as a scientist he is merely creating awareness — not spreading panic.

Awareness is important because, as with floods and landslides, the real danger to human beings is the form of development that has been foisted on the terrain of the Himalayas. Over-construction of buildings, thoughtless carving out of mountainsides for roads and deforestation have ushered in innumerable uncertainties.

While an earthquake cannot be avoided, it can be prepared for by retrofitting buildings and reducing congestion. A wake-up call is in order.    

 

Q: You have been warning about a tectonic shift happening in the Himalayan region which could lead to a devastating earthquake. What exactly is this tectonic shift?

Tectonic activity in the Himalayas is an ongoing process. It has been happening for millions of years. It was the Indian continent that travelled from Antarctica and collided with a landmass called Eurasia. After this collision, the mountains started building.

When two plates constantly collide, there’s a lot of stress built up. And earthquakes are nothing but release of this stress from time to time. Otherwise, the stress accumulates.

Now, the point of worry is that after 1950 we have not had a great earthquake. And according to our calculations, since these plates are converging, the Indian plate is actually going below the Eurasian plate, or subducting, at the rate of about 5 cm per year.

The Himalayan region has witnessed some of the world’s greatest earthquakes of magnitude 8 and above. We have already had four such great earthquakes in our recorded history: the 1897 Shillong earthquake, the 1904 Kangra earthquake, the 1937 Bihar-Nepal earthquake and, lastly, the 1950 Assam earthquake, also called the India-China or Assam-Tibet earthquake. These were all extremely devastating earthquakes.

It is a matter of huge concern that, since 1950, we have not had a great earthquake. Scientists believe that this earthquake is overdue. It can happen anytime. We know for sure from GPS readings that these two plates are converging. There is movement between these two plates. And each day the stress keeps building all along the Himalayan foothills.

I’m referring to the Jammu and Kashmir (J&K) sector on the western side, right up to the Arunachal sector on the eastern side, basically the Himalayan belt. The region of Uttarakhand and western Nepal has not experienced very great earthquakes. We therefore call it the seismic gap, which means that this is the potential region that might want to release the stress that is getting accumulated because the other regions have already released a lot of energy. Each 8-magnitude earthquake releases so much energy you can expect the next one to happen after several decades.

But that has not happened in Uttarakhand and western Nepal. It is a matter of concern. We expect a giant earthquake — it could be 8 or even 8.5 or more. The impact of such an earthquake can be devastating particularly since the Uttarakhand area is highly populated and is also a major spot for tourism and pilgrimage. Joshimath and Badrinath are very crowded and there is so much construction work going on. It’s an environmental issue.

 

Q: There’s no way of really predicting specific earthquakes, right? The standard, scientific response is to just be alert and aware?

Yes. What you said is right — earthquakes cannot be predicted. But let me define the meaning of a prediction. A prediction means you are able to give the exact date, time and location of a great earthquake. Small earthquakes happen every day. But when we talk about a very big earthquake, we cannot pinpoint the date and time but location is possible. We can always pinpoint which areas are potential areas for future earthquakes.

However, recent advances in seismology indicate the possibility of detecting geohazards like rockslides, landslides, glacial avalanches, and associated floods as well as earthquakes using dense seismograph networks.

Also, real time monitoring and data transmission using satellite connectivity provides us an opportunity to put in place an Early Warning System (EWS), vital for the Himalayas which are vulnerable to a range of geohazards.

NGRI scientists demonstrated this after the February 7, 2021, catastrophic flood in Uttarakhand where a cascade of rockslide, debris and flooding events resulted in over 100 casualties at the Tapovan hydropower plant. The work was published in Science.

An artificial intelligence-based algorithm was developed for automatic identification and location of different geohazards from the continuous seismic data streaming in from all field stations. Accurate computation and quick dissemination of warning could certainly help minimize loss of life and property in the future.

 

Q: Currently, you do expect a major earthquake happening in this Himalayan belt?

I mean, I know for sure that Uttarakhand is going to have a great earthquake but I cannot say when exactly. Our calculations show that it’s overdue and it has to happen sometime. I often hope that it will release energy in the form of several smaller earthquakes, but nature doesn’t work like that.

 

Q: Does the building of infrastructure like big dams and massive highways have any impact on the tectonic plates? Does it result in earthquakes? Is there any correlation?

No, building of dams is not going to create great earthquakes. Big earthquakes happen at great depths of, say, 20 km or 30 to 40 km. Whereas anthropogenic activity, like the construction of dams and infrastructure projects, are just scratches on the surface.

Great earthquakes are caused only because of plate movements or tectonics. But, yes, dams can cause smaller earthquakes to happen. And this is called reservoir-triggered earthquakes. A classic example worldwide is the Koyna dam in Maharashtra. I was the project leader there for about ten years. We did a lot of studies there.

We noted that small earthquakes happen every day because of the loading and unloading of the dam on an annual basis. These small earthquakes can be related to the dam, its water levels and change of water levels, especially when you’re releasing water or due to heavy monsoon rain when the dam suddenly gets filled up.

So, let’s not say that dams are causing great earthquakes. That’s not true. But, yes, they are capable of releasing some energy in the form of smaller earthquakes. That’s possible.

 

Q: How can we be prepared for a great earthquake? What mitigation measures should we be looking at?

First, I would like to make it very clear that earthquakes don’t kill. It is buildings that kill. Take the earthquake in Turkey recently. We saw some disturbing visuals.

Essentially, when buildings cannot withstand these great earthquakes, they tend to collapse. And that’s how people die, by getting buried under the debris.

If you are standing in an open field with no buildings around, and if there’s a great earthquake, the worst that can happen is you just sway and fall down. Nothing more. It’s not a very dangerous situation. So please remember that earthquakes don’t kill, it’s the buildings that do. Especially the faulty ones.

The big problem is that people don’t construct buildings as per norms. I’ll give you another example, the 1993 Latur earthquake. The magnitude was just 6.3, which is not a very big earthquake. But almost 30,000 to 40,000 people were killed. People who visited the site will tell you that all the houses were made with mud and stone. In the monsoon season, the houses get wet and they simply fall like a pack of cards. The only building that stood in the village of Killari was the government school building, which was made with cement.

This is a big lesson for us: even a small earthquake can kill a lot of people if the buildings are not right.

Another example is the Muzaffarabad earthquake in Kashmir where again 30,000 to 40,000 people died. The point is we need to build as per norms. We have the Bureau of Indian Standards (BIS) which has issued clear guidelines on the kind of construction, construction codes, the engineering practices that need to be adopted for constructing various types of buildings. The guidelines are available and vary from region to region.

For example, you have four zones in India, depending on the severity of their earthquake hazard potential. The highest hazard zone is Zone 5. Here you can expect an earthquake of magnitude 8. It comprises the entire Himalayan belt, northeastern India, the Andaman Islands. It includes, in the west, Gujarat and the Kutch region. The guidelines for Zone 5 are more stringent.

If you take Zone 2, like Hyderabad, where I am right now, it is one of the safest places in India as far as the earthquake hazard is concerned. Therefore, construction guidelines are less stringent. We don’t expect very big earthquakes here.

There is complete understanding on how buildings need to be constructed, what are the precautions to be taken, the types of materials to be used and so on. They’re all available but, unfortunately, nobody uses them.

It’s only major government projects that are forced to use these guidelines because unless they have seismic certification, construction cannot proceed, whether these are dams or nuclear plants or bridges. In that sense, dams are actually built to withstand earthquakes. Dams follow BIS guidelines. No dam can be constructed just like that.

 

Q: People should be aware of such guidelines. Do we need an awareness campaign?

Absolutely. Basically, most people are either ignorant of such guidelines or they don’t care. I have myself campaigned in various earthquake-prone areas and I find that people don’t seem to be very interested because they feel that they end up paying a lot more money for safe construction.

This has been a problem because the guidelines are not mandatory for the public. They’re only mandatory for government buildings and government constructions.

 

Q: What is the reason for this lack of regulatory will to implement these guidelines?

My personal opinion is that, you know, we are a democracy and we always talk about our rights. Maybe no government wants to, you know, make it mandatory and offend the people, perhaps.

But let me add that you can also opt for retrofitting. If your building is, let’s say, 100 years old or whatever, you can consult a structural engineer and ask him to make certain modifications so that the building can be strengthened without having to pull it down. I strongly recommend retrofitting to strengthen buildings. We need to make people aware of the importance of such things, especially in the Himalayan region.

In the Himalayas, you have another issue. The region is not on hard rock. A building in Hyderabad is very safe because the city is situated on a plateau. So, you don’t have a lot of loose soil sediment sitting on the rock. We have a granitic basement. It’s a stable continent.

 

Q: You mean a strong flat surface?

Yes. But in the Himalayas and some other areas, where you have thick piles of alluvium or loose soil or loose sediment, there is a process called seismic amplification that takes place. You’re constructing tall buildings essentially on loose soil. So obviously the foundation is not strong. That’s one problem. The second problem is that when seismic waves travel through the earth, they get amplified when they encounter a layer of loose soil.

This problem is not limited to the Himalayan region. Take Delhi, for example. You have the Yamuna river and all along it you have loose alluvial soil several metres thick. Now, even a small earthquake, when it travels through the earth and reaches this loose soil, gets amplified. This is called site amplification. When such loose soil encounters earthquake waves, the amplitude of the seismic wave can increase two or three times, or more, depending on several factors.

We have undertaken micro zonation studies, in various cities in the country. We have identified the alluvial thickness, its implications and the kind of amplification that is possible when there’s an earthquake.

Our very first micro zonation study in India, of which I was the project leader, was carried out in Jabalpur in the 1990s. We could delineate 30-m-thick alluvium soil near the Narmada river. And we actually mapped the thickness of such soil in different places in Jabalpur city.

We submitted a report to the government stating what it meant, how waves could amplify, what were the precautions to be taken. For example, if you have a very thick layer of alluvium, then you are not supposed to make tall buildings because tall buildings resonate with thick alluvium and this resonance can cause the buildings to collapse.

If your alluvial thickness is less, then it is shorter buildings that are affected.

These studies have been done, reports have been submitted and valuable recommendations have come from the scientific community. An important issue is how best these results are utilized in future construction activity. You know what to expect. It is better to avoid disaster. Whether it’s the government or the public, they are not very serious. They don’t seem to understand the gravity of the situation.

 

Q: Are you saying, given the nature, character of the Himalayan region, an earthquake would have far greater intensity because of this kind of loose soil? You also have deforestation in the Himalayas. And we have a legacy of poor construction. Does all that add up to a really huge disaster?

Let me first clarify that deforestation has a severe impact on the environment, but not on earthquakes. Big earthquakes are only caused by plate movements. None of these anthropogenic activities can influence the occurrence of a large earthquake. But deforestation has an impact on other forms of hazards, like landslides, floods, glacial melting and avalanches.

Now, if you have visited Joshimath, you will be shocked to see not only deforestation, but a lot of construction activity and road widening. For instance, you have a mountain slope on one side and you have a narrow road below. Just to widen the road, they try to chop off these mountain ranges. In the process, the mountainside which was slanting is made steep because you have eaten into the mountain to widen the road. That’s dangerous because a vertical slope can easily collapse.

One of the reasons you are seeing landslides in the Himalayan region is road widening. The government is continuing construction activities and deforestation, just to support the tourism sector. I’m not against developmental activities. But we need to draw a line somewhere. It’s a huge disaster waiting to happen.

You see the route from Joshimath to Badrinath, and the kind of landslides, avalanches that we have been seeing in recent times is really enormous. The government should stop further activities, in my opinion. We have an ongoing project there so I’m quite familiar with that region.

In Joshimath, land has been sinking. As a result, several buildings developed cracks, a serious situation. Places like Joshimath are constructed over the debris of previous landslides. We are not talking of stable ground at all. So, any tectonic movement or any disturbance to the environment, including a heavy monsoon, will cause the land to simply sink.

Climate change due to global warming has also completely disturbed existing monsoon patterns, resulting in erratic rainfall.

Another big disaster in the Himalayas is GLOF, or Glacial Lake Outburst Flood. You have hundreds of glacial lakes sitting on mountain tops in the Himalayas. Basically, a glacial lake is a lake body that’s frozen. You have several craters in mountain regions, filled with water that gets frozen. In the past, that was never an issue because the lakes stayed frozen.

What’s happening now is that due to temperature rise and global warming, more glacial lakes are bursting. And a glacial lake, remember, is a huge body of water. When the lake bursts, the entire water in the glacial lake starts flowing down and flooding nearby areas. If there is a river, flooding is compounded since the river travels through various places.

GLOF has become a serious problem now.

We never bothered about glacial lakes earlier but now we need to monitor them, see which lakes are likely to burst in the near future so that we can take precautionary measures or begin evacuation programmes for people. But that is faraway. Currently we have not even started analyzing or studying these lakes.

Adding to Himalayan woes is the so-called cloudburst phenomenon, which has been on the rise recently. That is also a direct consequence of global warming. Let me explain. A cloudburst occurs because what happens is orographic lifting. If you have a mountain slope, then warm air has nowhere to go except along the slope because there’s an obstruction. It cannot travel horizontally. It’s forced to take a path upwards.

In the process, it goes up very quickly where you have a much lower temperature. The entire mass of warm air suddenly cools and turns into droplets which merge into a huge water body. And that water body just falls down.

It is similar to the glacial lake outburst, except that we call it rainfall. Technically it’s not rainfall but actually a cloudburst. A cloudburst is when a huge amount of water falls instantly at one place. This is also on the rise. Cloudburst is also due to global warming. We hadn’t heard this term much earlier but now we hear it often.

 

Q: But what can be done about that?

Unfortunately, there is no mechanism to record a cloudburst till date. The India Meteorological Department (IMD) has various sensors to monitor weather across the country. But a cloudburst is a very local phenomenon. Unless you have an instrument right at that spot, you have no possibility of measuring changes in the weather and thereby predicting a cloudburst or even recording it. We have no such technology at the moment.

 

Q: It’s a wake-up call for the entire Himalayan region.

Absolutely. It’s not only the big earthquake due. You have a series of hazards that are building up. Landslides are also due because of deforestation which weakens slopes and detaches soil.

People are also making buildings on hill slopes, another big problem. When I visited Joshimath, I was shocked to see how people constructed houses along deforested hill slopes. One big earthquake, and their houses will just slide down. It is really dangerous.