‘Intense Construction Activities Are Weakening Himalayan Region’

Noted seismologists Dr CP Rajendran and Dr Kusala Rajendran have embraced earthquake studies as their area of research. Their interest was triggered while doing their post-doctoral research at the University of South California where a mysterious earthquake in 1886 had destroyed the historic town of Charleston. Returning to India, they have focused on the enigmatic mysteries associated with earthquakes in a country where one quake occurs every 1-3 days.

Their research during the past three decades has seen them publish `The Rumbling Earth- the Story of Indian Earthquakes’ (published by Penguin) which explores the history of earthquakes as also raises the question of how prepared we are to face another big earthquake in the country given that during the last decade, 274 seismic events with a magnitude of 4 occurred within 300 km of our borders. Dr CP Rajendran talks exclusively to Newsclick. Edited excerpts:

Rashme Sehgal: This (the book) is probably the first scientific documentation of earthquakes in the country which highlights how India has witnessed some of the most violent earthquakes in the world. Why is that?

CP Rajendran: Perhaps, it is the first of its kind reviewing most of the earthquakes that have occurred in India in recent and historical times. There are individual reports and scientific papers on many of these earthquakes. Ours happens to be the first book that collated the information. Perhaps our joint work for the past three decades provided a favourable platform -–for a first-time attempt to compile the science and the impact of a natural force for public understanding.

RS: The largest documented earthquake in history occurred in Northeast India on August 15, 1950. It was called the Assam earthquake. What kind of fallout did this have?

CPR: The Assam earthquake demonstrated that large earthquakes can significantly change the landscape, especially with a large river system. Of course, it was the largest earthquake in Independent India that pushed the idea of studying earthquakes as a part of scientific discipline.

RS: The first historically known large earthquake occurred in the Rann of Kutch on June 16, 1819. You have studied it at some length. What were some of your and Kusala’s findings?

CPR: Ours was the first study that excavated the area to find relics of past earthquakes. The most important finding was that the 1819 earthquake had predecessors of similar sizes and physical impacts, with a recurrence interval of about 1,000 years. These earthquakes raised a low-lying ocean creek and converted it into land. The other contribution was that we could physically map the Allah Bund – generated by the 1819 earthquake -- which was never surveyed before using modern equipment. This is the first modern study of the 1819 earthquake.

RS: Bhuj (Gujarat) was also witness to a deadly earthquake. Was this linked to the earlier Rann of Kutch earthquake?

CPR: In some ways, the 2001 Bhuj earthquake was a surprise as the region where it occurred has not experienced any earthquakes in the historic past. With one earthquake in 1819, which is quite far from Bhuj, no one expected an earthquake in less than 200 years, near Bhuj The most important fallout of our study was the recognition that there are multiple earthquake sources in the Kutch region (which hosted the 1819 earthquake and the 1956 Anjar earthquake) which may have different repeat intervals, of the order of a few thousands of years. The 1819 source seems to have a recurrence period different from the 2001 source near Bhuj.

RS: Did the Koyna dam (in Maharashtra) trigger the massive Killari earthquake in 1993. We are building huge hydro projects along the Himalayas without keeping in mind the ecological consequences in terms of earthquakes, landslides and the formation of glacial lakes. Can you elaborate on the consequences of large-scale construction?

CPR: The Koyna Dam did not trigger the 1993 Killari earthquake. The dam did trigger a similar earthquake in 1967 and it continues to trigger smaller earthquakes near the Koyna Reservoir. Usually, the reservoir-triggered earthquakes occur in response to the filling/recycling cycles and they are confined to a few kilometres, adjoining the dam (maybe about 30 km in the case of Koyna, mostly to the south, extending to the Warna Reservoir). The source of the Killari earthquake is more than 350 km away from the Koyna reservoir and that would not affect this region.

Building large dams in the Himalayan region has several consequences. It is anyway seismically very active and earthquakes are bound to happen. The real threat would come from landslides that can breach the dam, and cause flooding.

The intense construction-related activities are already weakening the Himalayan region. The vulnerability of the region is already high, and construction activities are increasing the risk. So, it is not just the dams, it is the environmental, ecological and structural stress (weakening the slopes etc.) that are creating multiple risks.

The complex relationship between the glacial lake outburst, floods and destruction of dams was evident in the disaster that occurred in Sikkim last year. A major earthquake in the upper reaches of the Himalayas can also result in glacial lake outbursts. Combined with unregulated constructions, hydroelectric projects and related anthropogenic activities, these events lead to massive disasters.

RS: At present, the Geological Survey of India has documented that we have 66 active fault lines, all of which can produce earthquakes. How serious can this problem be given rapid urbanisation and increasing population?

CPR: Most of the active faults are located in areas that have produced earthquakes either historically or in recent times -- like the Himalayas, Northeast India, Gujarat and the Andaman and Nicobar. Earthquakes are bound to happen in these regions, the only question is when.

Accelerated urbanisation, expanding built environment and population density are likely to amplify the effect of the earthquakes by causing more damage and death. Many engineered structures may not pass the stability test during an earthquake and are not designed to minimise the shaking effects. There must be a concerted effort from the disaster management authorities to create awareness among the people and facilitate better construction practices.

RS: While most of these fault lines occur along the Himalayas and in the Andaman- Nicobar region, why then did we witness a deadly earthquake on September 30, 1993 in Killari 42 km south of Latur (Maharashtra) which destroyed 67 villages and took over 10,000 lives, given that this is not regarded as a quake-prone zone?

CPR: It is well-known that most earthquakes around the world are confined to the plate boundaries where tectonic strain is felt most, like the Himalayas (the weak regions where the 100-km-thick plates that form the top part of the earth collide with each other). While the plate boundaries are subject to intense and more frequent earthquakes, regions away from the plate boundaries also produce earthquakes. These are usually moderate (magnitude less than 7.0 and far separated in time. Thus, a region like Latur, with no history of earthquakes, caused one in 1993.

Similar earthquakes have occurred in Australia, Canada and other places that are several thousand kilometres away from any active plate boundary. Because they are so infrequent, and their predecessors must have occurred much before recorded human history, they are unexpected and communities living in those areas are thoroughly unprepared to face such eventualities.

RS: Your book mentions how 90% of the world’s earthquakes occur along the rings of fire that are spread along the Pacific Ocean belt. But these earthquakes do not seem to have caused the kind of damage to lives and property caused by the earthquakes in India. Your comments.

CPR: The statement that 90% earthquakes occur along the plate boundaries (especially the Ring of Fire) includes all earthquakes, even those originating in the ocean. The real issue is that earthquakes kill more people in densely populated and economically backward countries, where preparedness is low.

The 2023 Turkey-Syria earthquake reportedly killed more than 50,000 people and levelled the cities. However, casualties and the level of destruction for a similar magnitude earthquake (magnitude 7.4) in Taiwan in April 2024 were limited. The low death toll is attributed to the country’s preparedness. Taiwan’s performance in reducing earthquake-related loss is a lesson for countries like India -- one of the most populous countries, but least prepared for natural hazards, including earthquakes, going by the previous performances.

RS: Earthquakes often result in dramatic changes to the earth’s structure. Please elaborate.

CPR: The changes are observed on the surface of the earth (not exactly the earth’s structure, which is a term used to describe the internal structure). One of the classic examples that demonstrate the changes caused to the earth’s surface is the 1906 San Francisco earthquake that occurred on the San Andreas Fault. It caused a lateral shift of about 6 meters visible on the railway tracks, fences and pavement.

RS: How far can seismology be considered a science when it cannot predict the occurrence of an earthquake?

CPR: Seismology is not just about predicting earthquakes. It is about imaging the interior structure of the earthquake, quantifying the size of earthquakes; predicting their effects and relating them to the causative faults, and much more. It is the study of the spatial distribution of global earthquakes that led to the theory of plate tectonics – a fundamental theory that provides the basis for all earth processes.

Unlike cyclonic storms, tornadoes and similar weather processes that can be monitored using measurable parameters, earthquakes originate several tens of kilometres below the surface, beyond the realm of observation and as the result of many emergent feedback processes that are not easily quantifiable or observable. Yet, there is hope that modern computational techniques will be able to take us closer to that goal.

RS: The earth’s mantle has two layers that are in constant motion and this provides the basic mechanism for the movement of the tectonic plates. How much is this movement affecting the Himalayas as a whole?

CPR: The Himalayas are the outcome of the collision of the India-Eurasia tectonic plates – an event that happened about 40 million years ago. The process is still ongoing. The grinding movement of these plates continues at about 20 mm per year along the Himalayas. This plate movement is what causes the build-up of tectonic stress along the Himalayas. When the strain increases on the fault to the point of failure to overcome the rock strength, it leads to the fault break and the earthquake. The strain release that causes the earthquakes occurs somewhat periodically and that also contributes to the rising of the mountain. Thus, the mountain owes its origin to the earthquake activities along the numerous faults.

Rashme Sehgal is an independent journalist.