Understanding the very strong damaging Nepal/Sikkim earthquake (18/09/2011)

Last update: September 28, 2011 at 10:44 am by By

Earthquake information : A magnitude 6.9 earthquake hit Sikkim, India 12:40:48 UT (10:48 PM at epicenter) The depth of the hypocenter was at 20.7 km. The earthquake caused victims and huge damage in Sikkim (India), India and Nepal. It was also well felt in Bangladesh.

Read also: Very strong damaging earthquake in the Nepal / Sikkim (India) border area
Read also: “I Have Felt It” reports
Read also: Video selection showing the many faces of this cruel earthquake
Read also: Nepal / Sikkim experiences – 3 countries, 3 different stories
Read also: SEEDS Sikkim Early Recovery Plan
Read also: 20 minutes news compilation video
Read also: The most impressive Image series of the Nepal / Sikkim Himalaya earthquake so far

Tectonic explanation of what happened

The September 18, 2011 Sikkim, India earthquake occurred near the boundary between the India and Eurasia plates, in the mountainous region of northeast India near the Nepalese border.
Initial analysis suggest the earthquake was complex, likely a result of two events occurring close together in time at depths of approximately 20 km beneath the Earth's surface.

At the latitude of the September 18 earthquake, the India plate converges with Eurasia at a rate of approximately 46 mm/yr towards the north-northeast. The broad convergence between these two plates has resulted in the uplift of the Himalayas, the world's tallest mountain range. The preliminary focal mechanism of the earthquake suggests strike slip faulting, and thus an intraplate source within the upper Eurasian plate or the underlying India plate, rather than occurring on the thrust interface plate boundary between the two.

This region has experienced relatively moderate seismicity in the past, with 18 earthquakes of M 5 or greater over the past 35 years within 100 km of the epicenter of the September 18 event.
The largest of these was a M 6.1 earthquake in November of 1980, 75 km to the southeast.

Text and images : courtesy USGS

Country and location
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Your Email address might help us if we request for additional details about your experience. This field is NOT mandatory. It is up to you to give it or not.
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People :
Felt by persons at rest, on upper floors or favorably placed.
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People :
Felt indoors; hanging objects may swing, vibration similar to passing of light trucks, duration may be estimated, may not be recognized as an earthquake.
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People :
Generally noticed indoors but not outside. Light sleepers may be awakened. Vibration may be likened to the passing of heavy traffic, or to the jolt of a heavy object falling or striking the building.
Fittings :
Doors and windows rattle. Glassware and crockery rattle. Liquids in open vessels may be slightly disturbed. Standing motorcars may rock.
Structures :
Walls and frames of buildings, and partitions and suspended ceilings in commercial buildings, may be heard to creak.
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People :
Generally felt outside, and by almost everyone indoors. Most sleepers awakened. A few people alarmed.
Fittings :
Small unstable objects are displaced or upset. Some glassware and crockery may be broken. Hanging pictures knock against the wall. Open doors may swing. Cupboard doors secured by magnetic catches may open. Pendulum clocks stop, start, or change rate.
Structures :
Some large display windows cracked. A few earthenware toilet fixtures cracked.
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People Felt by all. People and animals alarmed. Many run outside. Difficulty experienced in walking steadily.
Fittings :
Objects fall from shelves. Pictures fall from walls. Some furniture moved on smooth floors, some unsecured free-standing fireplaces moved. Glassware and crockery broken. Very unstable furniture overturned. Small church and school bells ring. Appliances move on bench or table tops. Filing cabinets or "easy glide" drawers may open (or shut).
Structures :
Slight damage to buildings with low standard. Some stucco or cement plaster falls. Large display windows broken. Damage to a few weak domestic chimneys, some may fall.
Environment :
Trees and bushes shake, or are heard to rustle. Loose material may be dislodged from sloping ground, e.g. existing slides, talus slopes, shingle slides.
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People
General alarm. Difficulty experienced in standing. Noticed by motorcar drivers who may stop.
Fittings :
Large bells ring. Furniture moves on smooth floors, may move on carpeted floors. Substantial damage to fragile contents of buildings.
Structures :
Unreinforced stone and brick walls cracked. Low standard buildings cracked with some minor masonry falls. A few instances of damage to buildings of ordinary workmanship. Unbraced parapets, unbraced brick gables, and architectural ornaments fall. Roofing tiles, especially ridge tiles may be dislodged. Many unreinforced domestic chimneys damaged, often falling from roof-line. Water tanks Type I burst. A few instances of damage to brick veneers and plaster or cement-based linings. Unrestrained water cylinders (hot-water cylinders) may move and leak. Some common windows cracked. Suspended ceilings damaged.
Environment :
Water made turbid by stirred up mud. Small slides such as falls of sand and gravel banks, and small rock-falls from steep slopes and cuttings. Instances of settlement of unconsolidated or wet, or weak soils. Some fine cracks appear in sloping ground. A few instances of liquefaction (i.e. small water and sand ejections).
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People Alarm may approach panic. Steering of motorcars greatly affected. Structures : Low standard buildings heavily damaged, some collapse. ordinary workmanship buildings damaged, some with partial collapse. Reinforced masonry or concrete buildings damaged in some cases. A few instances of damage to buildings and bridges designed and built to resist earthquakes. Monuments and pre-1976 elevated tanks and factory stacks twisted or brought down. Some pre-1965 infill masonry panels damaged. A few post-1980 brick veneers damaged. Decayed timber piles of houses damaged. Houses not secured to foundations may move. Most unreinforced domestic chimneys damaged, some below roof-line, many brought down. Environment : Cracks appear on steep slopes and in wet ground. Small to moderate slides in roadside cuttings and unsupported excavations. Small water and sand ejections and localized lateral spreading adjacent to streams, canals, lakes, etc.
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Structures Many low standard buildings destroyed. Ordinary workmanship buildings heavily damaged, some collapse. Reinforced masonry or concrete buildings damaged, some with partial collapse. Buildings and bridges designed and built to resist earthquakes damaged in some cases, some with flexible frames seriously damaged. Damage or permanent distortion to some buildings and bridges, designed and built to normal use standards. Houses not secured to foundations shifted off. Brick veneers fall and expose frames. Environment : Cracking of ground conspicuous. Landsliding general on steep slopes. Liquefaction effects intensified and more widespread, with large lateral spreading and flow sliding adjacent to streams, canals, lakes, etc.
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Comments

  1. sonam says:
    November 27, 2011 at 2:37 am

    i pray god that let no one suffer such agony, as we did

    Reply
  2. Mausham subba says:
    September 19, 2011 at 2:21 pm

    We where not able to sleeep because of fear ……stl in midnyt it was shaking…..

    Reply

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