Earthquake is instance shaking of the earth surface. The shaking is caused by movements in Earth’s outermost layer(lithosphere). There are four different types of earthquakes:
But most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes.
Actually ,what happens is two nearest tectonic plates (like Eurasia and Indian plate in context of Nepal) slides, bumps or hit everytime which raises friction and most of the times this friction will be small and we do not feel an earthquake,but sometimes this friction will be greater than critical value and due to that friction, energy gets releases and this energy creates seismic waves that travel through the earth's crust and cause the shaking and we feel it which is earthquake.
Some Basic Information:
- Seismology is the study of earthquakes and seismic waves that move through and around the earth.
- A real-time record of earthquake ground motion is done by the instrument called seismometer
, commonly called as a seismograph
- Fig: seismograph
- It consists of a mass attached to a fixed base. During an earthquake, the base moves and the mass does not.
The motion of the base with respect to the mass is commonly transformed into an electrical voltage.
The electrical voltage is recorded on paper, magnetic tape, or another recording medium.
- The recording they make is called a seismograms.
- The Richter scale is a standard scale used to compare earthquakes. It is a logarithmic scale, meaning that the numbers on the scale measure factors of 10. So, for example, an earthquake that measures 6.0 on the Richter scale is 10 times larger than one that measures 5.0.
- The place where earthquake origin is called hypocenter.
- The location directly above hypocenter on the surface of the earth is Epicenter
The junction of the India and Eurasia tectonic plates is the cause of earthquakes in the Himalayan region during April 2015
Actually, there are three types of Tectonic earthquakes.
1)Convergent Plate Boundary: It occurs when two tectonic plates move toward each other. Massive Himalaya is created in this way.
2)Divergent Plate Boundary: It occurs when two tectonic plates move away from each other. This type creates mid-oceanic ridges or rift valleys. Iceland is an example of a country undergoing a continental divergent boundary.
3)Transform Fault/Boundaries:Here two tectonic plate slip by each other.
EarthQuake in Nepal
The junction of the India and Eurasia tectonic plates is the cause of earthquakes in the Himalayan region during April 2015.
You can get updates of an earthquake in Nepal from sites: http://seismonepal.gov.np/home
Microseismic monitoring(It is a very fast and efficient tool to understand the seismotectonics of the region.) in Nepal started in November, 1978 by Department of Mines and Geology (DMG), Ministry of Industry, government of federal democratic republic of Nepal in collaboration with Laboratoire de Geophysique Appliquee, Paris University, France with the installation of first short period vertical seismic station Phulchoki (PKI) hilltop in the south of Kathmandu. The numbers of stations were augmented gradually to create the National Network consisting of 21 short period seismic stations in 1998 and 7 accelerometer stations in 2012. The network is operated in collaboration with the Department of Analysis & Surveillance of Environment (DASE), France. The 21 short period seismic stations and 7 accelerometer stations occupy the Lesser Himalaya and Sub Himalayan terrain of Nepal Himalaya uniformly.
The recording is carried out at two centres Birendranagar Regional Seismological Centre (RSC), Surkhet and National Seismological Centre (NSC), Lainchour, Kathmandu. RSC records 9 stations of mid-western and far-western Nepal while NSC records the remaining 12 stations from Pyuthan to Taplejung. The stations are operated in two sensitivity channels allowing a dynamic range of 110 dB. The signals are digitized centrally acquired using JADE software of DASE. The location is made with ONYX software of DASE since April 2001. Before this ISIS software of DASE was used for acquisition & processing.
Source : http://seismonepal.gov.np
It is interesting to note that only earthquakes of magnitude 6.5 or above are known to cause damage in Nepal
History of EarthQuake in Nepal
1.) 1255 AD(1310 BS)
The first recorded earthquake in the history of Nepal took place on June 7, 1255 AD. 2200 were killed including Abahya Malla( Malla Dynasty king of Nepal) Target Region: Kathmandu. The magnitude of the earthquake is said to be around 7.8 in Richter scale.
2. 1260 AD
This earthquake occurred during the reign of King Jayadev Malla. This is the next recorded big earthquake after 1255 AD.Target Region: Sagarmatha. The magnitude of the earthquake is said to be 7.1 in Richter scale where 100 were killed.
This is the next recorded big earthquake after 1260 AD. The magnitude of an earthquake is said to be 7.9 in Richter scale where 100 were killed. The epicentre of the earthquake was Mechi Zone.
4.1408 August (1463 BS)
This is the next recorded big earthquake after 1344AD was during the reign of King Shyam Singh. The earthquake of 1408 AD has been reported to destroy the Machhendra Nath temple of Patan. (Source) .Affected Area of the earthquake was near Nepal-Tibet Border, Bagmati zone. The magnitude of the earthquake is said to be 8.2 in Richter scale where 2500 were killed.
The magnitude of an earthquake is said to be 8.7 where 6000 people were killed. Epicentre:Near Saldang, Karnali zone.
This earthquake occurred during the reign of King Sri Niwas Malla, 4500 people where killed. The magnitude of the earthquake was 8.0
The targetted region was Northern Koshi zone.
Targetted Region: Northern Bagmati zone. The magnitude of the earthquake was 7.9 where 4000 were killed.
8)1833, 26 August
Occurred during the reign of Rajendra Bikram Shah. Epicentre:Kathmandu/Bihar. The magnitude of the earthquake was 8.0 Ms where 6500 were killed.
9)1869 AD, 7 July
Affected Area: Kathmandu
Magnitude: 6.5 Ms
10)1916 AD, 28 August
11)1934 AD (1990 BS )( 90 Salko Vukampa)
Affected Area: Nepal/India/Tibet
Magnitude: 8.0 Mw
12)1966 AD, 27 June
Epicentre: Nepal/India border
13)1980, 29 July
Affected Area: Baitadi, Bajhang, Darchula
14)1988 AD, Udaypur Earthquake
Affected Area: Eastern Development Region mostly affected and some parts of Central Development region
15)2011 AD, 18 September
Affected Area: Sikkim, India
The epicentre of an earthquake is in Nepal-India border at east and mostly Indian state of Sikkim was affected and has intense damage over there than on Nepal.
Magnitude: 6.9 Ms at 6.25 pm
At that time 6 were deaths and 30 were injured reported by Ministry of Home Affairs, Government of Nepal. Among 6, 4 were from eastern mountains and 2 were from Kathmandu valley.
16)2015, 25 April
Affected Area: Kathmandu, Gorkha district at Barpak
17)2015, 12 May
Affected Area: Nepal/China/Bangladesh
2. Chaulagain, H., Gautam, D., & Rodrigues, H. (2018). Revisiting Major Historical Earthquakes in Nepal. Impacts and Insights of Gorkha Earthquake in Nepal, 1–17.doi:10.1016/b978-0-12-812808-4.00001-8