Sikkim EQ Report 02 07

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EERI Special Earthquake Report February 2012

Learning from Earthquakes

The Mw 6.9 Sikkim-Nepal Border Earthquake of September 18, 2011

Several teams from India inves-

tigated the effects of the Sikkim

earthquake between September

25th and November 10th, 2011.

This report is based on observa-

tions of the following contributors:

C.V.R. Murty, S.T.G. Raghukanth,

Arun Menon, Rupen Goswami,

A.R. Vijayanarayanan, S.R. Gandhi

and K.N. Satyanarayana of the

Indian Institute of Technology (IIT)

Madras; Alpa Sheth of VMS Con-

sultants Pvt. Ltd., Mumbai; Durgesh

C. Rai, Goutam Mondal, Vaibhav

Singhal, Neha Parool and Tripti

Pradhan of IIT Kanpur; Arvind Jais-wal of EON Designers, Secundera-

bad; Hemant B. Kaushik and Kaus-

tubh Dasgupta of IIT Guwahati;

Ajay Chaurasia of CBRI, Roorkee;

Colonel Shashi Bhushan of the

Indian National Disaster Manage-

ment Authority (NDMA); Debasis

Roy of IIT Kharagpur; and R. Prad-

eep Kumar of the Indian Institute of

Information Technology, Hyderabad.

Eleven of these contributors were

supported by the NDMA. The IIT

Kanpur team received support fromthe Poonam and Prabhu Goel foun-

dation at IIT Kanpur. VMS Consul-

tants and EON Designers spon-

sored the visits of their members.

The Building Materials

and Technology Pro-

motion Council, New

Delhi, supported the

visit of one contributor

from IIT Madras. IIT

Guwahati supported

the visit of its two fac-

ulty members. The re-connaissance teams

together covered all

four districts of Sikkim,

with greater focus on

the most affected re-

gion of North Sikkim

and the capital city of

Gangtok, and parts of

North Bengal.

Introduction

An Mw 6.9 earthquake struck near theNepal-Sikkim border on September 18,2011, at 18:10 local time. The earth-quake triggered a large number oflandslides and caused signicant

damage to buildings and infrastruc-ture. Sikkim was the most affectedstate of India, followed by West Ben-gal and Bihar. Neighbouring countriesof Nepal, Bhutan, Tibet (China) andBangladesh sustained damage andlosses to varying extent (Figure 1a).The maximum shaking intensity is

estimated to be around VI+ on theMSK scale. The earthquake was fol-lowed by a series of aftershocks, twoof which were M4.5 and M5.0 and hitwithin 75 minutes of the main shock.

The landslides, rock falls, and mud-slides were responsible for most lossof life and damage to infrastructure,as well as associated economiclosses. There was also extensive lossof Buddhist monasteries and temples;these heritage structures are built

in random rubble masonry with mudmortar. Most multi-story reinforcedconcrete (RC) buildings were non-engineered and sustained consid-erable damage due to earthquake

shaking; a small number of thesecollapsed or suffered irreparablestructural damage. Poor perfor-mance and widespread damageare of concern in important govern-ment buildings, such as the sec-retariat, police headquarters andlegislative assembly, perhaps someof the few engineered buildings inGangtok. The total loss of life inIndia is reported to be 78, 60 inSikkim, and the rest in West Bengaland Bihar. The total loss has beenestimated at around US $500 mil-lion.

Sikkim has a total population ofabout 600,000 people (Figure 1b).Gangtok is the densest region inSikkim, with a density of about98,700 persons in an area of 77 sqkm (as per 2011 Census of India).This contrasts sharply with thedensity in North District of Sikkim,which has the smallest, at just about10 persons per sq. km. In the pastdecade, Sikkim has recorded anastounding 153% growth in its urban

population and a 5% decrease in

Figure 1. (a) key earthquake-affected areas; and

(b) areas covered during the reconnaissance, lo-

cation of epicenter, and the rivers Teesta and Ringit.

(a)

(b)


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its rural population. There may be afurther push for urban agglomera-tions in the future, which may makeit easier for governance and disastermanagement in the challengingterrain.

Some parts of North Sikkim (Lac-hung and Lachen) and the hills ofDarjeeling in West Bengal are im-portant international tourism desti-nations and have seen a growth ofmulti-story RC buildings. Addition-ally, North Sikkim shares a borderwith China and, for strategic rea-sons, it is expedient for the Indiangovernment to maintain excellentroads and connectivity, even if itmay focus on a few key tourism and

strategic villages. These villagesneed to be better equipped for dis-aster management and as tacticaloutposts.

Seismological Aspects

The state of Sikkim is spread on theHimalayan mountain range, alsoknown as the Alpine-Himalayanbelt, with the two main thrust faults

(Main Boundary Thrust [MBT] andMain Central Thrust [MCT]) crossingthe state. A great earthquake of Mw8.1 struck in January of 1934 alongthe Bihar-Nepal border along the inter-plate boundary; other signicant earth-quakes in this area in the last 50 yearsinclude the September 2009 Bhutanearthquake of Mw 6.1, the February2006 Sikkim earthquake of Mw 5.3,the August 1988 Bihar-Nepal earth-quake of Mw 6.5, and the November1980 Sikkim earthquake of Mw 6.0.

The Gangtok and Teesta lineaments,transverse to the Himalayas, areresponsible for many earthquakes inthe region. Other prominent tectonicfeatures in and around Sikkim include

the Arun lineament and Dhubri fault inthe southeast, and the Kanchenjungaand Purnea-Everest lineament in thenorth. The focal mechanism solutionfor this event (as reported by USGS)indicates strike slip faulting and thenodal plane coincides with the Teestaand Kanchenjunga lineaments. Thestrike, dip, and focal depth of the faultplane have been reported as 313,73, and 35 km, respectively.

The acceleration time history ofthe main shock was recorded atGangtok and Siliguri (Figure 2); thePGA was 0.15g at Gangtok. Thestochastic seismological projectionis presented of the estimated meanpeak ground acceleration (PGA)contour in Figure 3a. The axi-symmetric contours are attributedto the shallow focal depth of theearthquake. The projected PGA inthe meisoseismal region is as highas 0.35g; at Lachen, Ravangla,Teesta, Chungthang and Mangan,it is in the range 0.25g-0.29g, andat Gangtok in the range of 0.15-0.20g. Sikkim lies in Seismic ZoneIV as per the Indian Standard(IS:1893-Part 1, 2007) Criteria for

Earthquake Resistant Design ofStructures, in which the designpeak ground acceleration is 0.24gfor this zone. Pseudo-spectralaccelerations of the ground motionrecorded at Gangtok are similar tothat of the code spectrum for thezone; code design spectral accel-erations at lower frequencies arehigher than those generated in thisevent (Figure 3b).

Figure 2.Acceleration time histories for the main shock of 18th September 2011 Sikkim event recorded at

(a) Gangtok, and (b) Siliguri (http://pesmos.in/2011/).

(a) (b)


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In general, themaximum inten-sity of groundshaking in theentire affectedarea was VI+ onthe MSK scale,but some poc-

kets had highershaking owingto site-specic

amplication of

ground motionon a hillock,e.g.,at the ITBP quar-ters at Pegong inChungthang (Fig-ure 4). Fallingrocks caused sig-nicant damage

to buildings andhydropower tunnel mouths in thetown of Chungthang.

Poor building performance wasprevalent in towns sited on soft soillayers of relatively at river terracesand gradually sloping mountainmeadows, probably due to sus-tained amplication of ground

shaking. Mudslides originating frommountain springs led to damage tobuildings in Lachung (Figure 5).

Even now, large boulders of fragilesedimentary rocks are precariouslybalanced along hill slopes at manylocations.

Geotechnical Impacts

While landslides are frequent in thisregion during rainy seasons, anestimated 354 new landslides werecaused by the event and 48 oldones reactivated (Figure 6). Theseslides damaged roads and bridges

and disrupted relief operations totowns and villages that were com-pletely cut off, some for over threeweeks (Figure 7). Subsidence atRanipool near Gangtok resulted in180 mm settlement of a part of theNational Highway, slowing vehiclemovement and causing trafc jams.

Landslide density in Sikkim in-creased approximately ve-fold in

locations north of Dikchu; this is pos-sibly due to proximity to the epicenterand steeper relief in the mountainousterrain. In the ChadaySankalangDzongbu area, often these failureswere found to have affected thehighly weathered mica schists andphylites. The left bank of Lachungchu in Chungthang was particularlyaffected by several slope failures.

Some incidents of reactivation ofolder landslides were reported, for

example, the Teendharia (Figure 8)and Balason landslides of the Dar-

jeeling district and the Health Sec-retariat landslide in Gangtok. The

reactivation in some cases wasnot co-seismic, but developed overseveral days after the earthquakebecause of heavy rainfall in area.On-the-ground inspection revealedsigns of continual distress thatindicated the post-earthquake land-slides were inducements of alreadyongoing slow mass movements.Enquiry with the locals in Tukdah-Rangolikhola also corroboratedthe landslide to be episodic, witha large event taking place several

decades back.

Site-specic scientic approaches

are required for studying relatively

Figure 3. (a) Surface level peak ground acceleration (g) generated from stochastic seismological

model. Black dots indicate location of landslides; (b) Comparison of recorded spectral accelera-

tions during the earthquake and Indian Seismic Code design response spectrum at Gangtok.

Figure 4.

Classic dam-

age in lower

stories of RC

frame build-ing with large

block masonry

inll panels at

ITBP quarters

at Chungthang

(photo: Arvind

Jaiswal).

(a) (b)


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soft mountain slopes along theSingalila range and in the TeestaValley, and assessing the landslidepotential of in critical areas, forexample, near the Leprosy Hospitalin Kalimpong (Figure 9). In additionto the above, alternate road net-work routes should be developedto bring redundancy for rescue and

relief operations andfor keeping all areasconnected by roadseven in the aftermathof earthquakes.

The Border Roads Organisation(BRO) is responsible for developingmost mountain roads in the upperreaches of Sikkim, usually by cuttinghill slopes. When cuts are made inmountain slopes to widen or formroads, they are safe when the entireroad width is made on the native cut;not so, however, when made on ll

soils with retaining walls, as hasbeen done in Sikkim. In addition,the inner edges of cuts along themountains are often not providedwith seepage/rainwater drains.The construction techniques arenot scientic and of good qual-

ity; generally, only heuristic andexperience-based methods areemployed, compromising safety ofthe construction. A review of the

quality of engineering inhill road construction inthe region indicates that,in many cases, local soildata is not being used forassessing the stability ofthe mountain slopes, andstructural geologists arenot consulted.

Buildings

Damage. Damage andlosses were sustained byhouses in the severelyshaken areas owing tothree main reasons:slides on weak mountainslopes, rolling boulderimpacts, and ground

Figure 5. Damage to buildings due to rock slide at Lac-

hung (photo: DC Rai). Figure 6. Landslides in Sikkim during the main event;

red dots indicate those mapped by National Remote

Sensing Centre (India), black dots by NASA satellite im-

age, and star the epicenter (source: STG Raghukanth).

Figure 7. Landslide at the mouth

of the cable-stayed bridge across

the Rangit River at Jorethang-

Nayabazaar in West Sikkim district

(photo: CVR Murty).

Figure 8. Scouring of the permanent way underneath

of the heritage railway line at the Teendharia landslide

along NH 55 between Siliguri and Darjeeling (photo:

Debasis Roy).


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shaking-induced damage (Figure10). In some cases, the latter type

of damage may have been exacer-bated by the 2006 event (if thestructure was not retrotted). Sci-entically based land use zoning

should be undertaken to demarcateobviously unsafe sites in the stateof Sikkim.

Many instances were observed ofsoil movement under buildings onhill slopes largely made up of meta-morphic and sedimentary rockscovered with soft soil. In areas closeto tunneling works for hydropowerprojects, local people ascribe thiscreeping to vibrations arising fromtunnel blasting, but the earthquakeshigher levels of ground shakinginitiated a number of landslides.

Building codes. In Gangtok, build-ing permits and town planning are

controlled by the Urban Developmentand Housing Department (UDHD).

All buildings are required to follow theSikkim Building Construction Regula-tions of 1991 (amended 2000). Theseregulations dene maximum set-backs, ground coverage and heightof the buildings. While it is obligatoryto submit architectural plans, thereis no requirement to submit struc-tural drawings, implicitly promotingnon-engineered buildings. There isno requirement for conducting soilinvestigation either. An engineer fromthe Department of Mines and Geol-ogy of Sikkim inspects the site anddetermines the number of oors that

may be allowed on the plot basedon the land-use zonation map of thearea (which is not available in the

public domain) prepared by theDepartment from time to time. Thecurrent map divides the city into sixcategories on the basis of lithol-ogy, hill slope, seismicity and otheraspects. A maximum of 5 storysmay be built in Zone 1, 4 storys inZone 2, and so on, with no con-

struction allowed in Zone 6. UDHDregulations prohibit construction onslopes exceeding 70 degrees (butsee Figure 11).

Regulations explicitly assign theresponsibility of ensuring structuralstability to the owner of the plot,but do not specify how this maybe ensured. Booming tourist vil-lages of Lachen and Lachung, andtowns such as Chungthang andJorethang, do not appear to followany building laws even though theGangtok Building regulations areapplicable across the state. Thereis no implementation mechanismfor these regulations in any townother than Gangtok, and no geo-logical zoning maps for the restof Sikkim. And the UDHD has nosystem for punishing defaulters.

In the district of Darjeeling inneighbouring West Bengal, the

situation is similar; effectively, thereis no techno-legal regime regulat-ing construction. In the three majortowns of Darjeeling, Kalimpong,and Kurseong, diploma holders aregiven the license to design build-ings, but designs are not veried at

the municipal ofce.

Housing types. Thestate of Sikkim hasbeen adopting threedominant construction

typologies: traditionalwood frame con-struction with ekra/bamboo-matting wall-ing or wooden planks(Shee Khim); rein-forced concrete (RC)construction with mo-ment frame type con-gurations; some RC

construction mimic

Figure 9. Lateral spreading of the soft soil hillock on which is located the Lep-

rosy Unit of the Sub-Divisional Hospital of Kalimpong (photo: CVR Murty).

Figure 10. Damage to houses due to rolling boulder at Lingzya and Chungthang (photos: Arun

Menon and Rupen Goswami).


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traditional wood frame constructiontype; and unreinforced masonry(URM) construction with masonryunits of stone, burnt clay brick orcement blocks, mud or cementmortar, with NO earthquake-resis-tant features. Of the above threetypologies, the third (URM) is lessprevalent in recent construction, andthe second (RC) most prevalent.However, most of the RC construc-

tion in the last two decades is largelynon-engineered. Most buildings builtin recent times in Gangtok, Chun-gthang, Pelling, Jorethang, NayaBazaar and other larger towns inSikkim are of RC.

Earlier, especially before the 1975accession of Sikkim to India, build-ings were of the traditional ekra andShee Khim style of up to two storys.However, RC is now the dominantform in response to the boom intourism and the hydro-power indus-try, and the pressure for more builtspace in the limited at areas avail-able for development. Now there aremulti-story buildings of up to eightstorys in Gangtok and up to ve

stories elsewhere.

Ekra construction consists of awood frame with cross-woven wood

matting inll wall panels, and a light

roof. The matting is plastered on bothsides with mud or mud with ne river

sand in earlier times, and by cementmortar in recent times. Another var-iation to this is the use of woodplanks in construction by the rich.When made on at ground, it rests

on a relatively shallow and uniformmasonry plinth (made of stone andmud mortar), and when made along

hill slopes, it rests on a tapered stoneplinth. Four varieties of stone mason-ry plinths are observed in Sikkim andthe hills of Darjeeling: random rubblemasonry (RRM) with and without mudmortar; dry dressed stone masonry;dressed stone masonry; and dressedstone masonry with pointing. In re-cent times, the plinth has been con-structed with RC. During the earth-quake, this type of housing was sha-ken to varying degrees, but with theexception of distress in some plinths(especially those made of RRM with-out any mortar), the houses performedexceptionally well. In instances wherethe cross-woven wood matting wasreplaced by clay-brick masonry in ce-ment mortar, damage was sustainedin the masonry inll walls, including

out of plane collapse (Figure 12a andb).

The highly satisfactory performanceof this housing validates its appro-priateness in the Himalayan regionand makes a compelling case forits sustenance. This traditionalstyle (including hybrid varieties withstructurally designed basements)should be encouraged in the state

of Sikkim and neighbouring states.

Reinforced concrete. As men-tioned above, there are about13,000 RC buildings in Gangtokalone, almost 65-70% of whichwere built after 1995. Almost all ofthese buildings are nonengineered(there are only two qualied struc-tural engineers resident in Sikkim).RC residential or hotel buildingsare built on steep hill slope siteson tight plots abutting each other.Only a few institutional buildings areengineered, such as governmentbuildings, educational institutionsand large hotels. RC constructionperformed poorly during the earth-quake, even though the maximumintensity of ground shaking wasonly around VI+ scale on the MSKscale in most of the affected areas.

Nonengineered RC buildingsacross Sikkim typically have a grid

of beams and columns in bothplan directions. The buildings are3-8 storys high, except in villageslike Lachen and Lachung, wherethey are dominantly of two stories.Despite a large number of decien-cies in the RC buildings in Gangtok,one feature that may have savedthem from more damage is the useof a uniform grid in most buildings.The spans vary from 3m to 4.5m,depending on the site. As thesestructures are on sloping ground,

heights of columns vary, with someof them short columns and someslender columns. Further, becausebuildings are on hill sides. the widthof the building is smallest at thebase due to the topography. Theroof of the building is partially orwholly in steel roof trusses or joistsand metal sheets. The concrete forconstruction is hand-mixed, with

Figure 11. Dense unregulated RC construction on slopes in Gangtok

city (photo: CVR Murty).


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neither control of the water-cementor aggregate-cement ratio, nor anysystems for cube testing of con-crete or testing of reinforcement.

No vibrators were being used forcompaction in construction ob-served during the reconnaissance.

The performance of RC framebuildings with unreinforced mason-ry (URM) inlls would have been

better if one-brick-thick URM inlls

walls were used instead of half-brick-thick URM inll walls, since

the half-brick walls either collapsedout-of-plane or were severely dam-aged in-plane. In cases where in-

lls were absent or poorly built(with too many openings), the dam-age was signicant. In RC frame

buildings where URM inll walls

were made of large-sized thin ce-ment concrete block units (350mm 200mm 75mm) masonry walls,the performance of the buildingwas poor.

Due to a boom in tourism, a lot ofresidential buildings are now con-verted into hotels with the ownerliving on the uppermost oor. With

such multiple uses, there is some-times a change in the layout of thepartition walls and some walls arecompletely removed to make roomfor a conference hall or restaurant.The Gangtok Building laws haveno well-dened land use zoning,

and it is possible to have any typeof occupancy in any area of the

city. Buildings that had a suddenchange in the stiffness pattern of theinll panel walls suffered signicant

damage or collapse (Figures 13a and

13b). Buildings experienced torsionand collapsed when distribution ofstiffness was poor in plan (Figure 13c).Buildings with large appendages(such as Telecom towers) also be-haved poorly. A four-story RC buildingat Dikchu bazaar (Figure 13d) con-structed about 10 years ago was con-structed on slope over a RC retainingwall and the slope started failingafter the main shock. This resulted insevere tilting of the building along theslope, which prompted occupants to

vacate the building before it collapsedcompletely during an aftershock twodays later. Another two-story RCbuilding constructed on slope andlocated near the Dikchu dam sitesuffered partial collapse; however,it had not been used for residentialpurposes and therefore losses wereminimal. Also, three stories of a resi-dential house pancaked in the town ofNaya Bazaar (Figure 13e).

Masonry. Masonry construction isfound especially in the British colonialgovernment buildings in Sikkim andDarjeeling. This type has very thickwalls made in random rubble stonemasonry; dressed stone masonrywas used in some government struc-tures. No earthquake-resistant fea-tures are found in these structures no bands, no through stones, andno vertical reinforcements at corners

and around openings. Unreinforcedmasonry (URM) was used to con-struct a large number of governmentschools and primary health centres.This stock sustained dilation of

masonry starting from the upperstories (Figure 14).

After it was damaged in the 1988Bihar Nepal quake, the ArchiveBuilding in Gangtok was retrottedusing steel ats all around in the

form of bands around window open-ings. The two-story building per-formed extremely well during the2006 earthquake, but signicant

damage was observed in the lowerstories after the recent event (Figure15a and b).

Heritage structures. Sikkim andthe hills of Darjeeling have manyBuddhist monasteries, some ofwhich date back to the early 16thcentury. These historical monaster-ies are masonry structures, primar-ily constructed with random rubblemasonry (RRM) walls and timberoor slabs and roofs. Some have

masonry walls with timber frame-

work. Monasteries constructed inthe recent decades are reinforcedconcrete (RC) structures with inll

masonry panels. Structural repairsin recent years mostly ad hocand nonengineered have intro-duced RC elements (columns,beams and slabs) into the struc-tures. Some monasteries were ret-rotted after the 2006 Sikkim earth-quake, but were damaged in the

Figure 12. (a) Typical ekra house at Gangtok (photo: Alpa

Sheth); (b) Typical house with wooden planks (Shee Khim)

with damaged rubble masonry plinth (photo: AR Vijayanarayanan).

(a)

(b)


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most recent quake. Extensivedamage was observed in thesemonasteries, with partial to neartotal collapse in several struc-tures. Typical damage includedout-of-plane bulging or collapseof random rubble masonry walls;sliding of timber roofs relative to

the masonry walls; out-of-planecollapse of orthogonal corners ofperimeter RRM masonry walls; andshear failure of interior RC columns(Figures 16a, b, c, d). Almost twomonths after the earthquake, noinitiatives were yet underway tostudy the genesis of the damage orundertake seismic retrot.

At least two colonial chapels wereseverely damaged during theevent. The chapel designs had

their roots in Scotland and Englandand no modications were made

on them to reect the seismicity

of the Himalayan region. At theMacFarland Memorial Church inKalimpong the URM spires atop itsbell tower are near collapse (Figure17), and there is in-plane sheardamage to the walls and gothicarches. The chapel on the estateof Dr. Grahams Homes had beendamaged during the 2006 event,

and was retrotted locally by tyingthe arches with a 20mm diametersteel rod with end plates. Duringthe recent quake, there was amuch larger in-plane shear failurecrack on the front wall and signi-cant damage to the perpendicularwall and internal arches (Figure18).

Nonstructural damage. This mod-erate earthquake also highlightedthe need to address nonstructur-

Figure 13. (a) Pancaked nine-story

Dzongpo House building in Gang-

tok; three intermediate stories col-

lapsed owing to sudden change in

lateral stiffness (photo: Alpa Sheth);

(b) damage to storage facility build-

ing in Chungthang (photo: Ajay

Chourasia); (c) and (d) collapsed

three-story RC frame building at

Singtam (photo: Alpa Sheth); (e)

pancaking of three stories of RC

frame residential building at NayaBazaar (photo: Alpa Sheth), and

(f) collapsed four-story house at

Dikchu (photo: Hemant B. Kaushik).

Figure 14. Excessive dilation of the upper

story of the sandstone stone masonry student

cottage built in 1925 in Dr. Grahams Homes

estate in Kalimpong (photo: CVR Murty).

(b)

(c)

(d)

(e)

(f)

(a)


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al elements (building contents,systems, facades) formally whiledesigning buildings. Many losseswere incurred in hospitals, ofce

buildings, monasteries, and resi-dential buildings. Should the nextearthquake be of severe intensity,it may result in much higher lossdue to nonstructural elements.

Critical Buildings and

Lifelines

Many government buildings wereaffected, even recently built, engi-neered RC structures. At the Secre-tariat Building in Gangtok, made of

RC frame with unreinforced mason-ry inlls of cement-block units, there

was extensive damage to the inlls

of lower stories, pounding damagein the false ceiling at construction

joints, and delamination of tilesalong the corridor in upper stories(Figure 19). The annex portion of thebuilding had damage in two RC col-umns at the expansion joint. The en-tire building was abandoned alongwith the annex portion. The Legisla-tive Assembly Building in Gangtok, aRC frame building with URM inlls,was retrotted in 2010, but it had

signicant damage to internal and

external inll walls, in addition to

increased subsidence at the plinthlevel. Police check-posts and ofces

made of RC with URM inll walls

were damaged to the extent of beingrendered unsafe for operations. Al-so, the Police Headquarters Build-

Figure 15. (a) Damaged masonry building of the police check post at Lachung (photo: Alpa Sheth); (b) damage to

heritage building in Gangtok (photo: Hemant B. Kaushik).

(a) (b)

(c)

(d)

Figure 16. (a) Collapsed masonry building

of the Ringin Monastery at Mangan (photo:

Arun Menon); (b) damage to Dubdi Mon-

astery at Yoksum (photo: Alpa Sheth);

(c) damage to Chungthang Monastery at Chungthang (photo: CVR Murty);

(d) damage to Pemayangtse Monastery in Pelling (photo: Alpa Sheth).

ing in Gangtok suffered serious dam-age to its RC elements and URM ma-sonry inlls (Figure 20). At the Gover-nors estate in Darjeeling all dressedstone masonry buildings (1-3 stories

tall) had separation at wall junctionsand in-plane shear failure.

Schools. Older schools are madeof traditional Ekra construction,while the recent ones (includingextensions and replacements struc-tures) are URM and RC. Ekra con-

struction performed relatively betterthan RC buildings, and damage toRC schools deprived the govern-

(a) (b)


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Figure 17. Collapse of unreinforced

masonry spires of the bell tower of

the MacFarland Memorial Chapel

in Kalimpong (photo: CVR Murty).

Figure 18. Crack initiating from the

central arch and propagating to-

wards the right top through the cen-

tral glass windows at the chapelin Dr. Grahams Homes estate in

Kalimpong (photo: CVR Murty).

Figure 19. Structural damage at

expansion joint of Secretariat build-

ing in Gangtok (photo: Alpa Sheth).

Figure 20. (a) and (b)Damage to

three-story RC frame building withmasonry inlls of the police head-

quarters in Gangtok (photos: Alpa

Sheth and AR Vijayanarayanan).

Figure 21. Collapse of masonry

building of the primary school at

Theng (photo: Arvind Jaiswal).

Figure 22. Pancaking of one inter-

mediate story in ve-story RC frame

building of the Moonlight School at

Chungthang (photo: Arun Menon).

ment of safe havens for post-earth-quake relief camps and emergencyservices. Over 600 school buildingsare said to have suffered extensivedamage or collapse. One completecollapse of a school building wasobserved (Figure 21). A recentlyconstructed school extension withRC frame and roof, without masonryinll walls, had critical damage to RC

columns and beams; poor design andquality of construction seem to be thecauses. A school in Chungthang hada oor pancake due to movement of

the boulder on which a column wasfounded (Figure 22). Many of thesebuildings were abandoned and schoolis now being held in makeshift tempo-rary tents. These will not be adequatein imminent winter.

Some of the school buildings hadsuffered damage in the 2006 earth-quake, but were not retrotted. For

instance, the old building of Govern-ment Secondary School at Sicheyis a 3-story RC building with brickmasonry inll walls constructed in

1969. Minor damage was observed inthis building during the 2006 earth-quake; however, it suffered extensivedamage during the recent quake andthe entire school building had to be

abandoned. The adjacent new build-ing of similar construction sufferedextensive cracking in oors due to

ground movement, cracks along thestaircases, and separation of brickmasonry inll panel along the edges

of beam and columns (Figure 23a).RC columns in both buildings weredamaged, especially those locatednear the door openings and in the cor-ridor (Figure 23b). The walls of Ekrarooms in the terrace of the new build-ing also suffered damage in the form

of out-of-plane collapse and spallingof cement plaster (Figure 23c).

Medical facilities. Regional govern-ment hospitals are located in biggertowns like Gangtok and Gezing, andsmaller primary health centers arespread out throughout the state ofSikkim and the Darjeeling hills. Thesestructures range from traditional Ekra-

(a)

(b)


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type to unreinforced masonry struc-tures, and recently to reinforcedconcrete. In most of these struc-tures, pounding damage was no-ticed at construction joints (Figure24a); frame-inll separation, crack-ling of plaster and diagonal crack-ing of inll walls were observed in

RC frame buildings (Figure 24b),as was damage due to incorrectlydetailed seismic joints.

Some government buildings andhospitals in the state sustained nom-inal damage and could have beenused after the earthquake, but weredeclared unsafe and ordered tobe demolished without professionalinputs of engineers conversant withsafety assessment protocols. This

caused severe disruption to medicalservice, relief operations, and gov-ernance continuity. Post-earthquakedamage assessment teams thatare trained to assess the safety ofbuildings should be commissionedin the state of Sikkim. This will en-sure that critical hospital buildingsare examined by personnel withexpertise and allowed to stay openif only slightly damaged.

Bridges. Bridges in the region are

built with wood, concrete, and steel;similarly, many designs are used:deck slab and girder, arch, truss,suspension and cable-stayed. Onedominant concern with most bridgesis their exceptionally poor mainte-nance; corrosion was noticed in RCelements, in particular. In general,no signicant loss to bridges was

apparent due to earthquake shak-ing; damage was various: looseningof abutments, pounding of spans,falling of lamp posts on deck, minor

distress to anchor blocks of suspen-sion bridges, distress to masonrypiers and abutments, pounding(deck-deck and deck-abutment),and residual displacement in deck/abutment (Figure 25). Landslides,rolling boulders, and ash oods

caused the most serious damage,with two bridges washed away bylandslides and subsequent ash

oods.

Communications structures.Communication systems failed intowns like Chungthan, Lachen, andLachung after the earthquake shak-ing causing general power failuresand/or severe damage to RC build-ings with communication towers ontheir roofs (Figure 26). Telephone

connectivity had not been restoredeven a month after the earthquakein North Sikkim.

Dams and water structures. Wat-er networks were damaged fromsources to treatment plants, andfrom treatment plants to distributionnodes. The city of Gangtok lost itswater supply due to landslide dam-age to the distribution network. InLachen and Lachung, the waterpipes bringing spring waters weredamaged due to failure of concreteor rubble masonry pipe supports(Figure 27). The supports of waterpenstocks from mountain springs atLachung are made of plain concrete;these penstocks were damageddue to landslides and rock falls.

Along the Teesta River, 32 hydro-power projects are being devel-oped; information is not availableon the performance of structures

recently completed and in progress.Seventeen employees of ProjectTeesta III lost their lives due tocollapse of access tunnels. TheNational Hydroelectric Power Cor-poration (NHPC) has constructed

Figure 23. Damage to government

secondary school at Sichey: (a)

annex building, (b) RC columns,

and (c) Ekra walls on top oor

(photos: Hemant B. Kaushik and

Kaustabh Dasgupta).

Figure 24. (a) Pounding damage

at expansion joints in ve-story

RC frame building of SMIMS boys hostel, Tadong (photo: Alpa Sheth);

(b) frame inll separation in Primary Health Centre at Passingdang (photo:

Rupen Goswami).

(a)

(b)

(c)

(a)

(b)


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concrete gravity dams over theTeesta River near Dikchu and overthe Rangit River near Rangit Nagar.Though RC buildings in residentialcolonies for NHPC employees nearthese project sites suffered minor

to moderate damage in the form ofcracking in masonry inll walls and

minor cracking in RC members, nodamage due to earthquake shakingor landslide was observed in thebody of any of the dams. Both damswere instrumented to record strongground motions; however, all ve

strong-motion accelerographs werereported to have malfunctioned atthe time of the earthquake. Duringthe main shaking, a falling boulderdestroyed an electrical transformer

located on the Teesta V dam site,and severe landslides and ground

deformations were observed nearboth the dam sites that resulted inaccumulation of excessive debrisand silt in the reservoir and on thedownstream of the dam. The nailed/bolted slopes on the right abutment

of Teesta VI hydropower project sitenear Singtam were affected by massmovements seated deeper than thenailing/bolting.

Electrical power. The meisoseismalarea lost power immediately after theearthquake due to collapse of hightension towers along the distributionnetwork due to landslides (Figure 28).This also resulted in loss of landlineand mobile communications in theaffected area. High-tension towersand lines were damaged due to fall-ing debris from landslides, and evenlocal distribution poles were dis-lodged due to ground deformationgenerated by soft soil slopes. Powerwas not restored in worst-hit locationseven 12 days after the earthquake.

Post-Earthquake

Response

North Sikkim areasof Lachung, Lachen,and Chungthangremained cut off

from the rest of thecountry for overthree weeks dueto telecommunica-tions damage and

landslide-blocked roads. Foodpackets were air-dropped from heli-copters in these regions during theinterim period. Local village heads(Pipons) were appreciative of theimmediate response of the Indian

Army in providing medical assis-tance and supplying essential com-

modities such as food grains, butthey were critical of the role playedby the local administration (Govern-ment of Sikkim) and the NationalDisaster Response Force (NDRF)deployed by the central governmentwhich had come unprepared. NDRFon such deployments needs to beself-contained.

Locals bemoaned the lack of anymeans of communicating with theirfamilies elsewhere in the state or

out of it. Some locals lost their livestrying to walk across to other vil-lages or towns to check on children,only to be buried in a landslide.There was a feeling of abandon-ment as the Chief Minister of theState of Sikkim had not visited themost ravaged sites more than a

month after theevent.

Damage assess-

ment. Many build-

ings across the statesuffered damage ofvarying degrees.

One critical questionthat all governmentlevels in Sikkimfaced is how to de-cide whether a build-ing can be usedafter an earthquake

Figure 25. (a) Damaged abutment of bridge at

Ralom Phamtam [photo: Government of Sikkim)

and (b) pounding and residual displacement in deck in Jawaharlal Nehru

Bridge at Melli (photo: Rupen Goswami).

Figure 26. Damage in lower story

of RC frame building with telecom

tower on its roof at Chungthang

(photo: Arun Menon).

Figure 27. Damage to plain concrete pipe supports of

penstocks carrying water to town of Lachung (photo:

Alpa Sheth).

(a)(b)


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or not. There was no agency to dis-tinguish between dangerous andbenign cracks. Buildings were va-cated in panic, and many important

government les may have beenlost in the process. Some govern-ments constituted formal commit-tees for damage assessment, andplaced damaged buildings intothree categories: (1) those requiringminor repairs, (2) those requiringmajor repairs, and (3) those requir-ing replacement. In general, how-ever, the engineers in the state donot have the background to assessdamages. Residents have movedback into many damaged buildings,

even though some of these build-ings may not be capable of resist-ing strong aftershocks, and are unt

for occupation.

In the tense moments after theearthquake, many local administra-tions depended on visiting facultymembers and engineers from otherstates conducting post-earthquakereconnaissance of the affectedareas. Some of them managed tocontribute a days effort to identify

unsafe buildings, but decisions on alarge number of damaged buildingswere pending six weeks after thequake. This lack of decisive evalua-tion led to situations like the state-ordered demolition of the buildingthat serves as the Health and FamilyWelfare Unit of the main Sir ThutobNamgyal Memorial Hospital in Gang-tok. This order stands even when

the six-story RCframe building hasno damage (including even ne cracks

of frame-inll separation in the URMinll walls) except

for some distress in

the independentlybuilt four-columnporch at the en-trance.The Government ofWest Bengal haddeputed the Block

Development Ofcers (BDOs) to

report the number of houses dam-aged. In the District of Darjeeling,under extreme pressure from thelocals to seek government compen-sation meant for damaged buildings,the BDOs were coerced to post allhouses in some areas fully damaged.This resulted in the Government ofWest Bengal declaring about 37,000houses damaged, while the eld

reconnaissance suggests otherwise.

This earthquake is demonstrating thatpost-earthquake building damageassessment is not just a technicalactivity, but also an administrative

and legal activity, which needs priorrehearsal by all stakeholders (techni-cal, administrative and political lead-ers), promulgation of appropriate lawsto protect persons undertaking dam-age assessment, and safeguardsagainst misuse by political leaders.

Intermediate Shelters and

Reconstruction

The intensity of ground shakingin the state of Sikkim and hills ofDarjeeling during this earthquakewas small only V-VI+ on the

MSK scale so damage to build-ings and structures was limited.Persons with severely damagedhouses moved to their relativeshouses as an interim measure.Because some schools, primaryhealth centres, and governmentgovernance buildings were se-verely damaged, there is an urgenteffort for construction of intermedi-ate facilities (Figure 29). Consider-ing the availability of bamboo in thestate, a possible design for inter-

mediate houses, schools, andprimary health centers could utilizethat as primary construction mate-rial; the traditional wood-frameconstruction could be adapted withbamboo mats as walling; this typeof construction is already prevalentin Sikkim.

The Government of Sikkim needsto rm up a comprehensive recon-struction strategy, even though theeffort required is smaller than re-

quired by other recent large earth-quakes. The challenge is madecomplex due to factors like acuteshortage of manpower within thestate capable of undertaking earth-quake-resistant design and con-struction, shortage of construction

materials andlabor, and theremoteness ofaffected areas.The state mayconsider develop-ment of designsfor earthquakeresistant homesin line with thecultural aspirationsof the people inthe region, and itshould establishsome form of reg-ulatory framework

Figure 28. Damage to electrical power transmission

tower at Lower Payong, South Sikkim (photo: Govern-

ment of Sikkim).

Figure 29. Makeshift school in tents on river terrace at

Chungthang (photo: Alpa Sheth).


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and implementation mechanismto ensure conformance to seismicsafety construction procedures.

Community Impacts

Villages susceptible to landslides

were relocated to safer areas; how-ever, as a result, one saw villagers,especially women, walking betweentheir original and relocated homesover miles of steep terrain in NorthSikkim. The harsh living conditionsin the cold, steep and poorly acces-sible terrain, and annual landslidesduring the rainy seasons, havemade inhabitants resourceful andable to deal with lesser disasters.Numerous bamboo bridges madeby villagers across streams were

testimony to this. The continuedpresence of the Border Roads Orga-nization in the region is vital. Thereis an opportunity for engaging themilitary as they have a permanentpresence in the area.

Lessons Learned

This earthquake has brought intorelief issues of disaster mitigationand management in the inhospitableregion of the Himalayas which is

one of the most seismically activeregions of the country.

1. The extent and type of damagein newly built RC structures arenot commensurate with the in-tensity of ground shaking. Mostdamage can be attributed to ir-regular structural conguration,

improper design and detailing,poor construction materials andpractice, or complete absenceof regulatory framework from

the government side to ensureearthquake-resistance in thebuilt environment.

2. No new URM structures should bepermitted in Sikkim, and existingones should be retrotted, espe-cially the critical, lifeline and gov-ernment structures.

3. Develop a comprehensive plan toretrot all heritage structures in

Sikkim and West Bengal. Wheneven basic earthquake-resistantconstruction is not known by localarchitects and engineers, specialassistance may be required fromoutside these states to supportthis culturally and historically criti-cal work.

4. There should be an aggressivepromotion of traditional Ekra hous-ing by development of a manualof good construction practices andinclusion of this as a formal hous-ing construction typology eligiblefor bank loans.

5. Post-earthquake damage assess-ment teams need to be mobilizedfrom out of state that have sound

judgment on usability of damagedstructures and no stake in the newconstruction. As well, technical in-formation needs to be disseminat-ed to professional architects andengineers on accepted methodsfor assessment and retrot of

damaged structures.

6. Mandatory review of the safety ofall ongoing and completed hydro-power projects should be initiatedand the information shared withthe community as a condence-

building measure.

7. Document all losses incurred bynonstructural elements, and dis-seminate technical know-how toarchitects and engineers on meth-ods of protecting these elements.

8. The epicentral area was cut off formore than 12 days after the earth-

quake. This is not acceptableby any standards in the moderncommunications era.

9. There is an urgent need to studythe strong ground motions inorder to incorporate reasonableexpectations in the design

codes. There is a network ofground motion instruments inthe region operated by variousnational agencies and institutes,but it must function in the nextearthquake.

10. There is no government engi-neering and architecture collegein the whole state of Sikkim orin Darjeeling to provide regularadvice to the governments ofSikkim and West Bengal. Thereare two structural engineers(with masters degrees) andabout 35 architects in the entirestate of Sikkim, few trained inthe subject of earthquake-resistant constriction. The newlyopened Sikkim-Manipal Instituteof Technology should be en-couraged to engage with thestate of Sikkim to bring aboutan environment of earthquakesafety in the state. Similarly,an engineering college should

be established in the hills ofDarjeeling to support the localneeds.

The lessons learned can havelarge benets if they are acted on

quickly unlike the opportunity lostafter the 2006 earthquake in thesame area. While the common manwill remember this earthquake asone that caused landslides and de-stroyed heritage structures, earth-quake professionals see it as a

warning before the big one strikes.

Sikkim EQ Report 02 07

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Transcript of Sikkim EQ Report 02 07