The 1975 Kinnaur earthquake occurred in the early afternoon (local time) (08:02 UTC) of 19 January. It had a magnitude of 6.8 on the surface wave magnitude scale and a maximum perceived intensity of IX (''Violent'') on the Mercalli intensity scale, causing extensive damage in

Himachal Pradesh Himachal Pradesh (; ; "Snow-laden Mountain Province") is a state in the northern part of India. Situated in the Western Himalayas, it is one of the thirteen mountain states and is characterized by an extreme landscape featuring several peaks ...

, in northern

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

. Its epicentre was in

Kinnaur district Kinnaur is one of the twelve administrative districts of the state of Himachal Pradesh in northern India. The district is divided into three administrative areas (Kalpa, Nichar (Bhabanagar), and Pooh) and has six tehsils. The administrative h ...

in the southeastern part of Himachal Pradesh and caused 47 casualties. Landslides, rock falls and avalanches caused major damage to the Hindustan-Tibet Road. The earthquake affected many monasteries and buildings in the state and led to an extensive restoration work in the late 1970s and early 1980s in Himachal Pradesh. The

Spiti Spiti (pronounced as Piti in Bhoti language) is a high-altitude region of the Himalayas, located in the north-eastern part of the northern Indian state of Himachal Pradesh. The name "Spiti" means "The middle land", i.e. the land between Tib ...

and Parachu valleys in particular suffered the greatest damage being on the north–south Kaurik-Chango fault, causing damage to landmarks such as

Key Monastery Kye Gompa (also spelled Kyi, Ki, Key, or Kee - pronounced like the English word ''key'') is a Tibetan Buddhist monastery of the Gelugpa sect located on top of a hill at an altitude of above sea level, close to the Spiti River, in the Spiti ...

and

Tabo Monastery Tabo Monastery (or Tabo Chos-Khor Monastery) is located in the Tabo village of Spiti Valley, Himachal Pradesh, northern India. It was founded in 996 CE in the Tibetan year of the Fire Ape by the Tibetan Buddhist ''lotsawa'' (translator) Rinche ...

Tectonic setting

The state of Himachal Pradesh lies towards the southern boundary of the Himalayan mountain belt, which was formed by the

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

between the

Indian Plate The Indian Plate (or India Plate) is a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the other fragments of Gondwana , began ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

. The mountain building that formed the Himalayas is an example of

thrust tectonics Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...

and is dominated by

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

ing. There is however, a significant amount of extension along the length of the mountain belt, possibly related to its arcuate form, with the extension accommodating the bulging out of the frontal part of the Himalayas. However, the faulting in the NW Himalayas demonstrates west–east extension, which is at a fairly high angle to the trend of the main thrust structures and may be better explained as partly accommodating the eastward spreading of the

Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the ...

. One of the most significant extensional structures in Himachal Pradesh is the Kaurik-Chango Fault Zone. This is interpreted to be seismically active from the presence of thermal springs and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...

deposits and from studies of soft-sediment deformation structures thought to be

seismite {{Earthquakes Seismites are sedimentary beds and structures deformed by seismic shaking. The German paleontologist Adolf Seilacher first used the term in 1969 to describe earthquake-deformed layers. Today, the term is applied to both sedimentary ...

s. These seismites have been used to suggest eight earlier earthquakes of magnitude greater than 6 in the Sumdo area affecting these Late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

sediments. The estimated recurrence interval for earthquakes along this fault zone is about 10,000 years.

Earthquake

The earthquake rupture is estimated to be about in length and in area, with a displacement of about . The mainshock was preceded by a major

foreshock A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full se ...

Ground rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where the ...

was observed in the form of a series of small vertical faults, with downthrow to the west, offsetting part of National Highway 22 between Sumdo and Kaurik, with displacements up to 50 cm. The isoseismal lines for the earthquake are elongated in a north–south direction, parallel to the strike of the Kaurik-Chango Fault Zone. The focal mechanism of the earthquake indicates normal faulting along with a north–south-trending, west-dipping fault.

Damage

The areas most strongly affected by the earthquake were the districts of Kinnaur and Lahaul-Spiti. The worst-affected villages were in the Parachu and Spiti river valleys. The village of Karauk showed the greatest degree of damage, with no building being unaffected. Buildings sited on slopes or at the base of slopes were not only affected by the shaking but by boulders falling from the hills above them. The performance of the different types of residential buildings varied greatly. Houses made from mud, either directly or as sun-dried bricks showed damage over a wide area (up to from the epicentre) and those in the epicentral area were often severely damaged. Unreinforced masonry structures were also badly affected, particularly those made of "random rubble stone masonry" (RRSM) with mud mortar, some of them have collapsed completely. The best performing buildings were barrack type houses constructed from

corrugated iron Corrugated galvanised iron or steel, colloquially corrugated iron (near universal), wriggly tin (taken from UK military slang), pailing (in Caribbean English), corrugated sheet metal (in North America) and occasionally abbreviated CGI is a ...

covering a timber frame, which generally showed little or no damage. The many monasteries and temples in the area were mostly badly damaged. They were often constructed with mudbrick or RRSM walls and had heavy roofs. Strong vertical motion during the earthquake led to excessive loads on the upper part of the supporting walls causing them to bulge outwards. There were many landslides, rockfalls and avalanches triggered by the earthquake. One landslide dammed the Parachu river to a height of , forming a lake that caused flash flooding when it burst two months later.

Aftermath

Damaged temples and monasteries were repaired or rebuilt immediately after the earthquake. The Guru Ghantal monastery at Tupchiling, which was completely destroyed in the earthquake, was rebuilt using stone masonry and cement mortar. The roof, which was originally wooden, although it had already been replaced by slates by 1975, now consists of corrugated iron sheets. The original design of these earthen buildings had already evolved to contain elements of earthquake resistance before the damage in 1975. The walls were reinforced using ring beams around the whole structure to prevent outward displacement during an earthquake. Further reinforcement was in some cases provided by buttresses of stone or brick at each corner of the building. Initial repairs after the earthquake by the local people involved additional corner buttresses, replacement wooden roofs and repair of the upper walls with stone masonry. Most of these repairs, however, have either caused further problems or may do so in the future.

References

External links