Seismic Activity in Nepal

Earthquakes can cause damage in more ways than just one. First, there's always direct damage or material damage that normally affects infrastructure: buildings, dams, powerplants, transportation ways, etc. But then there's also indirect damage including loss of lives, the impact on the socio-economic state of each country, as well as the way natural hazards influence the further mental condition of the people affected by them.

Natural hazards such as earthquakes continue to present a huge mystery on one hand and an opportunity on the other, as science is continuously exploring their occurrence and developing new theories as well as technology for a better understanding of their consequences. Advancements in seismology, of course, play a major role for the whole of humankind as there are many earthquake-prone regions, but are of utmost importance in those parts of the world where earthquakes truly represent a daily hazard, for example in Nepal.

Nepal's geological formation processes began about 75 million years ago with the drift of the Indian plate towards the northeast. Simultaneously, the Tethyn oceanic crust started its subduction under the Eurasian plate. Both processes contributed to the creation of the Indian Ocean as well as the uplift of the Himalayas. It's due to these geological processes that Nepal consists of three principal physiographic belts: the Himal mountain region, the Pahad mountain region whose mountains vary from 800 to 4000 meters in altitude, and the Terai lowland region.

Picture 1: Nepal's streets.

As a country in South Asia, Nepal is a land with diverse typography, complex geology, and a highly varying climate. For years, Nepal has been exposed to many human-induced and natural hazards and, according to the Global Climate Risk Index, ranks 4^th in terms of climate risk. Besides, the country also ranks 11^th in terms of global risk for earthquake occurrence and impact and is also in the top 20 of all the multi-hazard countries in the world, which doesn't only apply to earthquakes but also to landslides, floods, droughts, glacier lake outburst floods, and extreme temperature.

Earthquakes can cause damage in more ways than just one. First, there's always direct damage or material damage that normally affects infrastructure: buildings, dams, powerplants, transportation ways, etc. But then there's also indirect damage including loss of lives, the impact on the socio-economic state of each country, as well as the way natural hazards influence the further mental condition of the people affected by them.

Natural hazards such as earthquakes continue to present a huge mystery on one hand and an opportunity on the other, as science is continuously exploring their occurrence and developing new theories as well as technology for a better understanding of their consequences. Advancements in seismology, of course, play a major role for the whole of humankind as there are many earthquake-prone regions, but are of utmost importance in those parts of the world where earthquakes truly represent a daily hazard, for example in Nepal.

Nepal is of trapezoidal shape and covers an area of 147,516 km² with a population of approximately 29.3 million. Nepal's geological formation processes began about 75 million years ago with the drift of the Indian plate towards the northeast. Simultaneously, the Tethyn oceanic crust started its subduction under the Eurasian plate. Both processes contributed to the creation of the Indian Ocean as well as the uplift of the Himalayas. It's due to these geological processes that Nepal consists of three principal physiographic belts: the Himal mountain region, the Pahad mountain region whose mountains vary from 800 to 4000 meters in altitude, and the Terai lowland region.

As a country in South Asia, Nepal is a land with diverse typography, complex geology, and a highly varying climate. For years, Nepal has been exposed to many human-induced and natural hazards and, according to the Global Climate Risk Index, ranks 4^th in terms of climate risk. Besides, the country also ranks 11^th in terms of global risk for earthquake occurrence and impact and is also in the top 20 of all the multi-hazard countries in the world, which doesn't only apply to earthquakes but also to landslides, floods, droughts, glacier lake outburst floods, and extreme temperature.

The landscape itself is quite vast and diverse as Nepal varies from low-lying plains up to the Himalayan mountain range and hills, which makes the probability of the occurrence of various natural hazards even higher. Whereas the hilly and mountainous regions are more at risk of landslides, the monsoonal rains and river systems make the lower plains more exposed to seasonal flooding. Seismic activity, on the other hand, affects the whole country and is the greatest in the urban and mountainous regions.

The spatial distribution of earthquakes in Nepal shows “that earthquakes epicenters are not evenly distributed and demonstrate an approximately east-northwest trend in Nepal and the surrounding region. The uneven spatial distribution of earthquake epicenters depicts distinctly higher earthquake activity in the eastern and far-western parts of Nepal than the southern portion of the country¹."

According to the history and distribution of past earthquakes in Nepal, this natural hazard represents one of the nation's deadliest-ever disasters with an enormous socio-economic impact. According to EmDat 2019, earthquakes alone were the cause of death of more than 8900 Nepalese people between 1990 and 2019 and left total damage of over 5 billion USD. In the past, Nepal has experienced several frequent catastrophic earthquakes, especially in the Kathmandu Valley, which belongs to the world's most at-risk urban area for seismic activity, according to the Global Facility for Disaster Reduction and Recovery. The strongest earthquake in Nepal, for example, occurred not that long ago, in 2015, near the city of Kathmandu in central Nepal. The Gorkha earthquake with a magnitude of 7.8 and its aftershocks as well as accompanying landslides injured thousands of residents and killed about 9000 people. It not only caused a huge loss of lives but also destroyed buildings, crops, livestock, and agricultural tools.

Picture 2: Gorkha earthquake consequences.

Besides the Gorkha earthquake, there were also many other earthquakes causing severe damage to the country, whose effects and overall impact are often felt most by the poorest and the low-caste populations. While Nepal is known for its seismic activity, it can also be affected by earthquakes that often occur in its neighboring countries, for example in India, which can also cause substantial damage.

The strongest earthquakes over the past 50 years also include:

• The magnitude 7.3 earthquake in Dolakha occurred in 2015;
• The magnitude 6.9 Sikkim earthquake occurred in 2011;
• The magnitude 6.9 earthquake in Bihar occurred in 1988;
• The magnitude 6.5 earthquake in Pithoragarh occurred in 1980;
• The magnitude 6.5 earthquake in Pithoragarh in Uttarakhand occurred in 1980;
• The magnitude 6.3 earthquake in Doti occurred in 1966.

Picture 3: Consequence of an earthquake in Nepal.

Due to the instability of the country of Nepal, its poor infrastructure, socio-economic aspects, and overall multi-dimensional vulnerability, the consequences of strong earthquakes with accompanying natural hazards such as landslides, can be quite substantial. It basically affects every part of the infrastructure necessary for the well-being of the country and its population: large-scale hydroelectric power facilities, agricultural facilities, buildings (hospitals, schools, etc.), and transportation ways. Although there has been some progress in making the infrastructure seismically safe, there continues to be a lack of seismic technologies and trained masons and engineers. “To enhance seismic resilience, effective risk management – including risk assessments, building codes, zoning regulations, resilient building techniques and building back better – must be rapidly implemented and enhanced².”

Sources:
1) Thapa, D.R. 2018. Seismicity of Nepal and the surrounding region. Bulletin of Department of Geology, Tribhuvan University, Katmandu, Nepal. Vol. 20-21, pp. 83-86.
2) UNDRR. 2019. Disaster Risk Reduction in Nepal: Status Report 2019. Bangkok, Thailand, United Nations Office for Disaster Risk Reduction (UNDRR), Regional Office for Asia and the Pacific