Download Seismology of Nepal: An Overview

Seismology of Nepal:
An Overview
Lok Bijaya Adhikari
Contents
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Introduction
Geology and tectonics
National Seismological Network
Seismicity
Introduction
• Nepal is a mountainous country within Latitude
260 22’ to 300 27’E and Longitude 800 4’ to 880
12’E. 83% of the area is covered by mountain
peaks.
• Remaining 17% is covered by alluvial plains
called ‘Terai plains’.
• The total area is 147181 sq.km.
• Altitude varies from 50 m to 8848 m. (msl)
• The population of the country is about 25
million.
• Climate varies from subtropical to alpine
type.
• Rich in biodiversity. Many types of plants,
birds and wild animals.
• Nepal is country of Mt. Everest and birth
place of Buddha.
Geology and Tectonics
• Nepal lies within 2400 km long active Himalayan
mountain belt with 800km coverage.
• Himalaya mountain is the product of continuous
collision between Indian and Eurassian plate since
early Tertiary.
• Himalaya is divided into four main tectonic region
- Higher Himalaya
- Lesser Himalaya
- Sub- Himalaya
- Indogangetic alluvial plains.
• Three major longitudinal faults divide
Himalaya in 4
major tectonics zones.
- Main Central Thrust (MCT).
- Main Boundary Thrust(MBT).
- Himalayan Frontal Thrust (HFT)
• These are formed due to underthrusting of
Indian plates during different epochs.
• Gangetic plain- Pleistocene to recent alluvial deposits
over 1000m thick.
• Sub-Himalaya – Consists of about 5 km thick
Neogene molasse sediments of Siwaliks overthrust
by older Lesser Himalayan rocks along MBT.
• Lesser Himalaya- Consists of intensely folded
metasedimentary rocks between MBT and MCT.
• Higher Himalaya- thick sequence of higher
Himalayan crystalline and overlying Tethyan
sedimentary rocks.
National Seismological Centre
• The centre was established in first in 1978 with a
vertical component seismometer at the periphery
of Kathmandu valley.
• By 1999 the total number of vertical component
short period seismic stations increased to 21, Plus
two strong motion seismograph in the Kathmandu
valley.
• Among them signals from 9 seismic station are
recorded in digital form at autonomous Regional
Seismological Center, Birendranagar.
• This year one BB STS2 is installed in RSC and
one Long Period seismometer is installed in NSC.
National Seismic Network
Seismic Vault
Seismic Station
Seismic Data Acquisition System in
Surkhet
Record of Local Earthquake
Seismicity
• West Nepal seems more active than the east.
• The major cause of seismicity in the Himalaya
is continuous collision between Indian and
Eurassian plates.
• The seismicity in
Nepal Himalaya
is
concentrated E-W along the narrow belt
between MBT and MCT.
• The depth of most of the earthquake lies
between 10-20 km.
Epicenter Map of Nepal Himalaya
(1994-2005)
• In the last 100 years 4 major earthquakes accommodate
the slip of Indian plate towards Tibet , but in the area
between 1905 and 1934 earthquake there is no large
earthquake since1255 earthquake(??). So this area of
seismic gap is seems to be most vulnerable area for the
large future earthquake.
Historical Earthquakes of Nepal
Date
Magnitude
(Intensity, MMI)
Death
Houses
destroyed
1255 (IX-X)
King was also killed 1/3 of kingdom
of Nepal
Perished
1408
Innumerable people
killed
1833 7.8 (VIII-IX)
500
1934 8.2 (IX-X)
10500
80000
1980 6.5 (VIII-
178
40000
1988 6.7 ( VIII-IX)
721
100000
All big temples
were collapsed
Geology of Nepal Himalaya
• Building
damaged in
1988
Udayapur
earthquake.