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

Home , Chungthang, Dikchu, Jorethang, Lachung, Melli, Pelling

EERI Special Earthquake Report — February 2012

Learning from Earthquakes

Several teams from India investigat- Introduction shaking; a small number of these ed the effects of the Sikkim earth- collapsed or suffered irreparable quake between September 25th and An Mw 6.9 earthquake struck near the structural damage. Poor perfor- November 10th, 2011. This report is Nepal-Sikkim border on September 18, mance and widespread damage based on observations of the follow- 2011, at 18:10 local time. The earth- are of concern in important govern- ing contributors: C.V.R. Murty, S.T.G. quake triggered a large number of ment buildings, such as the sec- Raghukanth, Arun Menon, Rupen landslides and caused significant retariat, police headquarters and Goswami, A.R. Vijayanarayanan, damage to buildings and infrastruc- legislative assembly, perhaps some S.R. Gandhi and K.N. Satyanaray- ture. Sikkim was the most affected of the few engineered buildings in ana of the Indian Institute of Tech- state of India, followed by West Ben- Gangtok. The total loss of life in nology (IIT) Madras; Alpa Sheth of gal and Bihar. Neighbouring countries India is reported to be 78, 60 in VMS Consultants Pvt. Ltd., Mumbai; of Nepal, Bhutan, Tibet (China) and Sikkim, and the rest in West Bengal Arvind Jaiswal of EON Designers, Bangladesh sustained damage and and Bihar. The total loss has been Secunderabad; Hemant B. Kaushik losses to varying extent (Figure 1a). estimated at around US $500 mil- and Kaustubh Dasgupta of IIT Gu- The maximum shaking intensity is lion. wahati; Ajay Chaurasia of CBRI, estimated to be around VI+ on the Roorkee; Colonel Shashi Bhushan MSK scale. The earthquake was fol- Sikkim has a total population of of the Indian National Disaster Man- lowed by a series of aftershocks, two about 600,000 people (Figure 1b). agement Authority (NDMA); Deba- of which were M4.5 and M5.0 and hit Gangtok is the densest region in sis Roy of IIT Kharagpur; and R. within 75 minutes of the main shock. Sikkim, with a density of about Pradeep Kumar of the Indian Insti- 98,700 persons in an area of 77 sq tute of Information Technology, Hy- The landslides, rock falls, and mud- km (as per 2011 Census of India). derabad. Keya Mitra of Bengal En- slides were responsible for most loss This contrasts sharply with the gineering, Kolkata, and Durgesh C. of life and damage to infrastructure, density in North District of Sikkim, Rai, Goutam Mondal, Vaibhav Sing- as well as associated economic which has the smallest, at just about hal, Neha Parool, and Tripti Pradhan losses. There was also extensive loss 10 persons per sq. km. In the past of IIT Kanpur also reported on the of Buddhist monasteries and temples; decade, Sikkim has recorded an damaged sites. Eleven of the con- these heritage structures are built astounding 153% growth in its urban tributors were supported by the in random rubble masonry with mud population and a 5% decrease in NDMA. VMS Consultants and EON mortar. Most multi-story reinforced Designers sponsored the visits of concrete (RC) buildings were non- their members. The Building Materi- engineered and sustained consid- als and Technology Promotion Coun- erable damage due to earthquake cil, New Delhi, supported the visit of one contributor from IIT Mad- ras. IIT Guwahati supported the visit of its two faculty members. The IIT Kanpur team received support from the Poonam and Prabhu Goel Foundation at IIT Kan- pur. The reconnaissance teams together covered all four districts of Sikkim, with greater focus on the most affected region of North Sik- kim and the capital city of (a) Gangtok, and parts of North Bengal. Figure 1. ▲(a) key earthquake-affected areas; and ► (b) areas covered during the reconnais- This report is edited by sance, location of epicenter, and the rivers (b) C.V.R. Murty and Alpa Sheth. Teesta and Ringit.

1 EERI Special Earthquake Report — February 2012

(a) (b) 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/).

its rural population. There may be a (Main Boundary Thrust [MBT] and The acceleration time history of further push for urban agglomera- Main Central Thrust [MCT]) crossing the main shock was recorded at tions in the future, which may make the state. A great earthquake of Mw Gangtok and Siliguri (Figure 2); the it easier for governance and disaster 8.1 struck in January of 1934 along PGA was 0.15g at Gangtok. The management in the challenging the Bihar-Nepal border along the inter- stochastic seismological projection terrain. plate boundary; other significant earth- is presented of the estimated mean quakes in this area in the last 50 years peak ground acceleration (PGA) Some parts of North Sikkim (Lac- include the September 2009 Bhutan contour in Figure 3a. The axi- hung and Lachen) and the hills of earthquake of Mw 6.1, the February symmetric contours are attributed Darjeeling in West Bengal are im- 2006 Sikkim earthquake of Mw 5.3, to the shallow focal depth of the portant international tourism desti- the August 1988 Bihar-Nepal earth- earthquake. The projected PGA in nations and have seen a growth of quake of Mw 6.5, and the November the meisoseismal region is as high multi-story RC buildings. Addition- 1980 Sikkim earthquake of Mw 6.0. as 0.35g; at Lachen, Ravangla, ally, North Sikkim shares a border Teesta, Chungthang and Mangan, with China and, for strategic rea- The Gangtok and Teesta lineaments, it is in the range 0.25g-0.29g, and sons, it is expedient for the Indian transverse to the Himalayas, are at Gangtok in the range of 0.15- government to maintain excellent responsible for many earthquakes in 0.20g. Sikkim lies in Seismic Zone roads and connectivity, even if it the region. Other prominent tectonic IV as per the Indian Standard may focus on a few key tourism and features in and around Sikkim include (IS:1893-Part 1, 2007) Criteria for strategic villages. These villages the Arun lineament and Dhubri fault in Earthquake Resistant Design of need to be better equipped for dis- the southeast, and the Kanchenjunga Structures, in which the design aster management and as tactical and Purnea-Everest lineament in the peak ground acceleration is 0.24g outposts. north. The focal mechanism solution for this zone. Pseudo-spectral for this event (as reported by USGS) accelerations of the ground motion Seismological Aspects indicates strike slip faulting and the recorded at Gangtok are similar to nodal plane coincides with the Teesta that of the code spectrum for the The state of Sikkim is spread on the and Kanchenjunga lineaments. The zone; code design spectral accel- Himalayan mountain range, also strike, dip, and focal depth of the fault erations at lower frequencies are known as the “Alpine-Himalayan plane have been reported as 313°, higher than those generated in this belt,” with the two main thrust faults 73°, and 35 km, respectively. event (Figure 3b).

2 EERI Special Earthquake Report — February 2012

In general, the maximum intensity of ground shaking in the entire affected area was VI+ on the MSK scale, but some poc- kets had higher shaking owing to site-specific amplification of ground motion on a hillock,e.g., at the ITBP quar- (a) (b) ters at Pegong in Chungthang (Fig- Figure 3. (a) Surface level peak ground acceleration (g) generated from stochastic seismological ure 4). Falling model. Black dots indicate location of landslides; (b) Comparison of recorded spectral accelera- rocks caused sig- tions during the earthquake and Indian Seismic Code design response spectrum at Gangtok. nificant damage to buildings and locations north of Dikchu; this is pos- reactivation in some cases was hydropower tunnel mouths in the sibly due to proximity to the epicenter not co-seismic, but developed over town of Chungthang. and steeper relief in the mountainous several days after the earthquake terrain. In the Chaday–Sankalang– because of heavy rainfall in area. Poor building performance was Dzongbu area, often these failures On-the-ground inspection revealed prevalent in towns sited on soft soil were found to have affected the signs of continual distress that layers of relatively flat river terraces highly weathered mica schists and indicated the post-earthquake land- and gradually sloping mountain phylites. The left bank of Lachung slides were inducements of already meadows, probably due to sus- chu in Chungthang was particularly ongoing slow mass movements. tained amplification of ground affected by several slope failures. Enquiry with the locals in Tukdah- shaking. Mudslides originating from Rangolikhola also corroborated mountain springs led to damage to Some incidents of reactivation of the landslide to be episodic, with buildings in Lachung (Figure 5). older landslides were reported, for a large event taking place several Even now, large boulders of fragile example, the Teendharia (Figure 8) decades back. sedimentary rocks are precariously and Balason landslides of the Dar- balanced along hill slopes at many jeeling district and the Health Sec- Site-specific scientific approaches locations. retariat landslide in Gangtok. The are required for studying relatively

Geotechnical Impacts

While landslides are frequent in this region during rainy seasons, an Figure 4. estimated 354 new landslides were Classic dam- caused by the event and 48 old age in lower ones reactivated (Figure 6). These stories of RC slides damaged roads and bridges frame build- and disrupted relief operations to ing with large towns and villages that were com- block masonry pletely cut off, some for over three infill panels at weeks (Figure 7). Subsidence at ITBP quarters Ranipool near Gangtok resulted in at Chungthang 180 mm settlement of a part of the (photo: Arvind National Highway, slowing vehicle Jaiswal). movement and causing traffic jams.

Landslide density in Sikkim increased approximately five-fold in

3 EERI Special Earthquake Report — February 2012

Figure 5. Damage to buildings due to rock slide at Lac- hung (photo: DC Rai). Figure 6. Landslides in Sikkim during the main event; soft mountain slopes along the relief operations and red dots indicate those mapped by National Remote Singalila range and in the Teesta for keeping all areas Sensing Centre (India), black dots by NASA satellite im- Valley, and assessing the landslide connected by roads age, and star the epicenter (source: STG Raghukanth). potential of in critical areas, for even in the aftermath example, near the Leprosy Hospital of earthquakes. soils with retaining walls, as has in Kalimpong (Figure 9). In addition been done in Sikkim. In addition, to the above, alternate road net- The Border Roads Organisation the inner edges of cuts along the work routes should be developed (BRO) is responsible for developing mountains are often not provided to bring redundancy for rescue and most mountain roads in the upper with seepage/rainwater drains. reaches of Sikkim, usually by cutting The construction techniques are hill slopes. When cuts are made in not scientific and of good qual- mountain slopes to widen or form ity; generally, only heuristic and roads, they are safe when the entire experience-based methods are road width is made on the native cut; employed, compromising safety of not so, however, when made on fill the construction. A review of the quality of engineering in hill road construction in the region indicates that, in many cases, local soil data is not being used for assessing the stability of the mountain slopes, and structural geologists are not consulted.

Buildings

Damage. Damage and losses were sustained by houses in the severely Figure 7. Landslide at the mouth shaken areas owing to of the cable-stayed bridge across three main reasons: Figure 8. Scouring of the permanent way underneath the Rangit River at Jorethang- of the heritage railway line at the Teendharia landslide slides on weak mountain Nayabazaar in West Sikkim district along NH 55 between Siliguri and Darjeeling (photo: slopes, rolling boulder (photo: C.V.R. Murty). Debasis Roy). impacts, and ground

4 EERI Special Earthquake Report — February 2012

public domain) prepared by the Department from time to time. The current map divides the city into six categories on the basis of lithol- ogy, hill slope, seismicity and other aspects. A maximum of 5½ stories may be built in Zone 1, 4½ stories in Zone 2, and so on, with no construction allowed in Zone 6. UDHD regulations prohibit construction on slopes exceeding 70 degrees (but see Figure 11).

Regulations explicitly assign the responsibility of ensuring structural stability to the owner of the plot, Figure 9. Lateral spreading of the soft soil hillock on which is located the Lep- but do not specify how this may rosy Unit of the Sub-Divisional Hospital of Kalimpong (photo: C.V.R. Murty). be ensured. Booming tourist villages of Lachen and Lachung, and shaking-induced damage (Figure Building codes. In Gangtok, build- towns such as Chungthang and 10). In some cases, the latter type ing permits and town planning are Jorethang, do not appear to follow of damage may have been exacer- controlled by the Urban Development any building laws even though the bated by the 2006 event (if the and Housing Department (UDHD). Gangtok Building regulations are structure was not retrofitted). Sci- All buildings are required to follow the applicable across the state. There entifically based land use zoning Sikkim Building Construction Regula- is no implementation mechanism should be undertaken to demarcate tions of 1991 (amended 2000). These for these regulations in any town obviously unsafe sites in the state regulations define maximum set- other than Gangtok, and no geo- of Sikkim. backs, ground coverage and height logical zoning maps for the rest of the buildings. While it is obligatory of Sikkim. And the UDHD has no Many instances were observed of to submit architectural plans, there system for punishing defaulters. soil movement under buildings on is no requirement to submit struc- hill slopes largely made up of meta- tural drawings, implicitly promoting In the district of Darjeeling in morphic and sedimentary rocks non-engineered buildings. There is neighbouring West Bengal, the covered with soft soil. In areas close no requirement for conducting soil situation is similar; effectively, there to tunneling works for hydropower investigation either. An engineer from is no techno-legal regime regulat- projects, local people ascribe this the Department of Mines and Geol- ing construction. In the three major creeping to vibrations arising from ogy of Sikkim inspects the site and towns of Darjeeling, Kalimpong, tunnel blasting, but the earthquake’s determines the number of floors that and Kurseong, diploma holders are higher levels of ground shaking may be allowed on the plot based given the license to design build- initiated a number of landslides. on the land-use zonation map of the ings, but designs are not verified at area (which is not available in the the municipal office.

Housing types. The state of Sikkim has been adopting three dominant construction typologies: (1) traditional wood frame construction with ekra/bamboo-matting walling, or wooden plank construction (Shee Khim); (2) reinforced concrete (RC) construction with Figure 10. Damage to houses due to rolling boulder at Lingzya and Chungthang (photos: Arun moment frame type Menon and Rupen Goswami). configurations; some

5 EERI Special Earthquake Report — February 2012

The highly satisfactory performance of this housing validates its appro- priateness in the Himalayan region and makes a compelling case for its sustenance. This traditional style (including hybrid varieties with structurally designed basements) should be encouraged in the state of Sikkim and neighbouring states.

Reinforced concrete. As men- tioned above, there are about 13,000 RC buildings in Gangtok alone, almost 65-70% of which were built after 1995. Almost all of these buildings are nonengineered (there are only two qualified structural engineers resident in Sikkim). RC residential or hotel buildings are built on steep hill slope sites Dense unregulated RC construction on slopes in Gangtok Figure 11. on tight plots abutting each other. city (photo: C.V.R. Murty). Only a few institutional buildings are engineered, such as government RC construction mimics traditional matting infill wall panels, and a light buildings, educational institutions wood frame construction type; and roof. The matting is plastered on both and large hotels. RC construction (3) unreinforced masonry (URM) sides with mud or mud with fine river performed poorly during the earth- construction with masonry units of sand in earlier times, and by cement quake, even though the maximum stone, burnt clay brick or cement mortar in recent times. Another var- intensity of ground shaking was blocks, mud or cement mortar, with iation to this is the use of wood only around VI+ scale on the MSK NO earthquake-resistant features. planks in construction by the rich. scale in most of the affected areas. Of the above three typologies, the When made on flat ground, it rests third (URM) is less prevalent in re- on a relatively shallow and uniform Nonengineered RC buildings cent construction, and the second masonry plinth (made of stone and across Sikkim typically have a grid (RC) most prevalent. However, most mud mortar), and when made along of beams and columns in both of the RC construction in the last two hill slopes, it rests on a tapered stone plan directions. The buildings are decades is largely nonengineered. plinth. Four varieties of stone mason- 3-8 stories high, except in villages Most buildings built in recent times ry plinths are observed in Sikkim and like Lachen and Lachung, where in Gangtok, Chungthang, Pelling, the hills of Darjeeling: random rubble they are dominantly of two stories. Jorethang, Naya Bazaar and other masonry (RRM) with and without mud Despite a large number of deficien- larger towns in Sikkim are of RC. mortar; dry dressed stone masonry; cies in the RC buildings in Gangtok, dressed stone masonry; and dressed one feature that may have saved Earlier, especially before the 1975 stone masonry with pointing. In re- them from more damage is the use accession of Sikkim to India, build- cent times, the plinth has been con- of a uniform grid in most buildings. ings were of the traditional ekra and structed with RC. During the earth- The spans vary from 3m to 4.5m, Shee Khim style of up to two stories. quake, this type of housing was sha- depending on the site. As these However, RC is now the dominant ken to varying degrees, but with the structures are on sloping ground, form in response to the boom in exception of distress in some plinths heights of columns vary, with some tourism and the hydropower indus- (especially those made of RRM with- of them short columns and some try, and the pressure for more built out any mortar), the houses performed slender columns. Further, because space in the limited flat areas avail- exceptionally well. In instances where buildings are on hill sides. the width able for development. Now there are the cross-woven wood matting was of the building is smallest at the multistory buildings of up to eight replaced by clay-brick masonry in ce- base due to the topography. The stories in Gangtok and up to five ment mortar, damage was sustained roof of the building is partially or stories elsewhere. in the masonry infill walls, including wholly in steel roof trusses or joists out of plane collapse (Figure 12a and and metal sheets. The concrete for Ekra construction consists of a b). construction is hand-mixed, with wood frame with cross-woven wood

6 EERI Special Earthquake Report — February 2012

(a)

Figure 12. ▲ (a) Typical ekra house at Gangtok (photo: Alpa (b) Sheth); ► (b) Typical house with wooden planks (Shee Khim) with damaged rubble masonry plinth (photo: AR Vijayanarayanan). and around openings. Unreinforced neither control of the water-cement city. Buildings that had a sudden masonry (URM) was used to con- or aggregate-cement ratio, nor any change in the stiffness pattern of the struct a large number of government systems for cube testing of con- infill panel walls suffered significant schools and primary health centres. crete or testing of reinforcement. damage or collapse (Figures 13a and This stock sustained dilation of No vibrators were being used for 13b). Buildings experienced torsion masonry starting from the upper compaction in construction ob- and collapsed when distribution of stories (Figure 14). served during the reconnaissance. stiffness was poor in plan (Figure 13c). Buildings with large appendages After it was damaged in the 1988 The performance of RC frame (such as Telecom towers) also be- Bihar Nepal quake, the Archive buildings with unreinforced mason- haved poorly. A four-story RC building Building in Gangtok was retrofitted ry (URM) infills would have been at Dikchu bazaar (Figure 13d) con- using steel flats all around in the better if one-brick-thick URM infills structed about 10 years ago was con- form of bands around window open- walls were used instead of half- structed on slope over a RC retaining ings. The two-story building per- brick-thick URM infill walls, since wall and the slope started failing formed extremely well during the the half-brick walls either collapsed after the main shock. This resulted in 2006 earthquake, but significant out-of-plane or were severely dam- severe tilting of the building along the damage was observed in the lower aged in-plane. In cases where in- slope, which prompted occupants to stories after the recent event (Figure fills were absent or poorly built vacate the building before it collapsed 15a and b). (with too many openings), the dam- completely during an aftershock two age was significant. In RC frame days later. Another two-story RC Heritage structures. Sikkim and buildings where URM infill walls building constructed on slope and the hills of Darjeeling have many were made of large-sized thin ce- located near the Dikchu dam site Buddhist monasteries, some of ment concrete block units (350mm suffered partial collapse; however, which date back to the early 16th × 200mm × 75mm) masonry walls, it had not been used for residential century. These historical monaster- the performance of the building purposes and therefore losses were ies are masonry structures, primar- was poor. minimal. Also, three stories of a resi- ily constructed with random rubble dential house pancaked in the town of masonry (RRM) walls and timber Due to a boom in tourism, a lot of Naya Bazaar (Figure 13e). floor slabs and roofs. Some have residential buildings are now con- masonry walls with timber frame- verted into hotels with the owner Masonry. Masonry construction is work. Monasteries constructed in living on the uppermost floor. With found especially in the British colonial the recent decades are reinforced such multiple uses, there is some- government buildings in Sikkim and concrete (RC) structures with infill times a change in the layout of the Darjeeling. This type has very thick masonry panels. Structural repairs partition walls and some walls are walls made in random rubble stone in recent years — mostly ad hoc completely removed to make room masonry; dressed stone masonry and nonengineered — have intro- for a conference hall or restaurant. was used in some government struc- duced RC elements (columns, The Gangtok Building laws have tures. No earthquake-resistant fea- beams and slabs) into the struc- no well-defined land use zoning, tures are found in these structures — tures. Some monasteries were ret- and it is possible to have any type no bands, no through stones, and rofitted after the 2006 Sikkim earth- of occupancy in any area of the no vertical reinforcements at corners quake, but were damaged in the

7 EERI Special Earthquake Report — February 2012

most recent quake. Extensive damage was observed in these monasteries, with partial to near total collapse in several structures. Typical damage included out-of-plane bulging or collapse of random rubble masonry walls; sliding of timber roofs relative to the masonry walls; out-of-plane collapse of orthogonal corners of (c) perimeter RRM masonry walls; and shear failure of interior RC columns (Figures 16a, b, c, d). Almost two months after the earthquake, no initiatives were yet underway to study the genesis of the damage or undertake seismic retrofit.

At least two colonial chapels were severely damaged during the (a) event. The chapel designs had their roots in Scotland and England (d) and no modifications were made on them to reflect the seismicity of the Himalayan region. At the MacFarland Memorial Church in Kalimpong the URM spires atop its bell tower are near collapse (Figure 17), and there is in-plane shear damage to the walls and gothic arches. The chapel on the estate of Dr. Graham’s Homes had been damaged during the 2006 event, (b) (e) and was retrofitted locally by tying the arches with a 20mm diameter Figure 13. (a) Pancaked nine-story steel rod with end plates. During Dzongpo House building in Gang- the recent quake, there was a tok; three intermediate stories col- much larger in-plane shear failure lapsed owing to sudden change in crack on the front wall and signifi- lateral stiffness (photo: Alpa Sheth); cant damage to the perpendicular (b) damage to storage facility build- wall and internal arches (Figure ing in Chungthang (photo: Ajay 18). Chourasia); (c) and (d) collapsed three-story RC frame building at Nonstructural damage. This mod- Singtam (photo: Alpa Sheth); (e) erate earthquake also highlighted (f) pancaking of three stories of RC the need to address nonstructur- frame residential building at Naya Bazaar (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. Graham’s Homes estate in Kalimpong (photo: C.V.R. Murty).

8 EERI Special Earthquake Report — February 2012

(a) (b)

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). al elements (building contents, ing in Gangtok suffered serious dam- Schools. Older schools are made systems, facades) formally while age to its RC elements and URM ma- of traditional Ekra construction, designing buildings. Many losses sonry infills (Figure 20). At the Gover- while the recent ones (including were incurred in hospitals, office nor’s estate in Darjeeling all dressed extensions and replacements struc- buildings, monasteries, and resi- stone masonry buildings (1-3 stories tures) are URM and RC. Ekra con- dential buildings. Should the next tall) had separation at wall junctions struction performed relatively better earthquake be of severe intensity, and in-plane shear failure. than RC buildings, and damage to it may result in much higher loss RC schools deprived the govern- due to nonstructural elements.

Critical Buildings and Lifelines

Many government buildings were affected, even recently built, engineered RC structures. At the Secre- tariat Building in Gangtok, made of RC frame with unreinforced masonry infills of cement-block units, there was extensive damage to the infills of lower stories, pounding damage in the false ceiling at construction (a) (b) joints, and delamination of tiles along the corridor in upper stories (Figure 19). The annex portion of the building had damage in two RC columns at the expansion joint. The entire building was abandoned along with the annex portion. The Legisla- tive Assembly Building in Gangtok, a RC frame building with URM infills, was retrofitted in 2010, but it had significant damage to internal and (c) external infill walls, in addition to increased subsidence at the plinth level. Police check-posts and offices Figure 16. (a) Collapsed masonry building made of RC with URM infill walls of the Ringin Monastery at Mangan (photo: (d) were damaged to the extent of being Arun Menon); (b) damage to Dubdi Mon- rendered unsafe for operations. Al- astery at Yoksum (photo: Alpa Sheth); so, the Police Headquarters Build- (c) damage to Chungthang Monastery at Chungthang (photo: C.V.R. Murty); (d) damage to Pemayangtse Monastery in Pelling (photo: Alpa Sheth).

9 EERI Special Earthquake Report — February 2012

ment of safe havens for post-earthquake relief camps and emergency services. Over 600 school buildings are said to have suffered extensive damage or collapse. One complete collapse of a school building was observed (Figure 21). A recently constructed school extension with (a) RC frame and roof, without masonry infill walls, had critical damage to RC columns and beams; poor design and quality of construction seem to be the causes. A school in Chungthang had a floor pancake due to movement of the boulder on which a column was founded (Figure 22). Many of these Figure 17. Collapse of unreinforced (b) masonry spires of the bell tower of buildings were abandoned and school the MacFarland Memorial Chapel in is now being held in makeshift tempo- Kalimpong (photo: C.V.R. Murty). rary tents. These will not be adequate in imminent winter. Figure 20. (a) and (b) Damage to three-story RC frame building with Some of the school buildings had masonry infills of the police head- suffered damage in the 2006 earth- quarters in Gangtok (photos: Alpa quake, but were not retrofitted. For Sheth and AR Vijayanarayanan). instance, the old building of Govern- ment Secondary School at Sichey is a 3-story RC building with brick masonry infill walls constructed in 1969. Minor damage was observed in this building during the 2006 earth- Figure 18. Crack initiating from the quake; however, it suffered extensive central arch and propagating to- damage during the recent quake and wards the right top through the cen- the entire school building had to be tral glass windows at the chapel abandoned. The adjacent new build- in Dr. Graham’s Homes estate in ing of similar construction suffered Kalimpong (photo: C.V.R. Murty). extensive cracking in floors due to ground movement, cracks along the staircases, and separation of brick Figure 21. Collapse of masonry masonry infill panel along the edges building of the primary school at of beam and columns (Figure 23a). Theng (photo: Arvind Jaiswal). RC columns in both buildings were damaged, especially those located near the door openings and in the corridor (Figure 23b). The walls of Ekra rooms in the terrace of the new building also suffered damage in the form of out-of-plane collapse and spalling of cement plaster (Figure 23c).

Medical facilities. Regional government hospitals are located in bigger towns like Gangtok and Gezing, and smaller primary health centers are Figure 22. Pancaking of one inter- spread out throughout the state of Figure 19. Structural damage at mediate story in five-story RC frame Sikkim and the Darjeeling hills. These expansion joint of Secretariat build- building of the Moonlight School at structures range from traditional Ekra- ing in Gangtok (photo: Alpa Sheth). Chungthang (photo: Arun Menon).

10 EERI Special Earthquake Report — February 2012 type to unreinforced masonry struc- Communications structures. tures, and recently to reinforced Communication systems failed in concrete. In most of these struc- towns like Chungthan, Lachen, and tures, pounding damage was no- Lachung after the earthquake shak- ticed at construction joints (Figure ing causing general power failures 24a); frame-infill separation, crack- and/or severe damage to RC build- ling of plaster and diagonal crack- ings with communication towers on ing of infill walls were observed in their roofs (Figure 26). Telephone RC frame buildings (Figure 24b), (a) connectivity had not been restored as was damage due to incorrectly even a month after the earthquake detailed seismic joints. in North Sikkim.

Some government buildings and Dams and water structures. Wat- hospitals in the state sustained nom- er networks were damaged from inal damage and could have been sources to treatment plants, and used after the earthquake, but were from treatment plants to distribution “declared” unsafe and ordered to nodes. The city of Gangtok lost its be demolished without professional water supply due to landslide dam- (b) inputs of engineers conversant with age to the distribution network. In safety assessment protocols. This Lachen and Lachung, the water caused severe disruption to medical pipes bringing spring waters were service, relief operations, and gov- damaged due to failure of concrete ernance continuity. Post-earthquake or rubble masonry pipe supports damage assessment teams that (Figure 27). The supports of water are trained to assess the safety of penstocks from mountain springs at buildings should be commissioned Lachung are made of plain concrete; in the state of Sikkim. This will en- these penstocks were damaged sure that critical hospital buildings (c) due to landslides and rock falls. are examined by personnel with expertise and allowed to stay open Along the Teesta River, 32 hydro- Figure 23. Damage to government power projects are being devel- if only slightly damaged. secondary school at Sichey: (a) oped; information is not available annex building, (b) RC columns, on the performance of structures Bridges. Bridges in the region are and (c) Ekra walls on top floor recently completed and in progress. built with wood, concrete, and steel; (photos: Hemant B. Kaushik and Seventeen employees of Project similarly, many designs are used: Kaustabh Dasgupta). deck slab and girder, arch, truss, Teesta III lost their lives due to suspension and cable-stayed. One collapse of access tunnels. The dominant concern with most bridges National Hydroelectric Power Cor- is their exceptionally poor mainte- poration (NHPC) has constructed nance; corrosion was noticed in RC elements, in particular. In general, no significant loss to bridges was apparent due to earthquake shaking; damage was various: loosening of abutments, pounding of spans, falling of lamp posts on deck, minor distress to anchor blocks of suspension bridges, distress to masonry piers and abutments, pounding (deck-deck and deck-abutment), (a) and residual displacement in deck/ abutment (Figure 25). Landslides, (b) rolling boulders, and flash floods Figure 24. (a) Pounding damage caused the most serious damage, at expansion joints in five-story with two bridges washed away by RC frame building of SMIMS boys’ hostel, Tadong (photo: Alpa Sheth); landslides and subsequent flash (b) frame infill separation in Primary Health Centre at Passingdang (photo: floods. Rupen Goswami).

11 EERI Special Earthquake Report — February 2012

Post-Earthquake Response

North Sikkim areas of Lachung, Lachen, and Chungthang remained cut off (a) from the rest of the country for over (b) Figure 25. ▲ (a) Damaged abutment of bridge at three weeks due Ralom Phamtam [photo: Government of Sikkim) to telecommunica- and ► (b) pounding and residual displacement in deck in Jawaharlal Nehru tions damage and Bridge at Melli (photo: Rupen Goswami). landslide-blocked roads. Food packets were air-dropped from heli- concrete gravity dams over the deformations were observed near copters in these regions during the Teesta River near Dikchu and over both the dam sites that resulted in interim period. Local village heads the Rangit River near Rangit Nagar. accumulation of excessive debris (Pipons) were appreciative of the Though RC buildings in residential and silt in the reservoir and on the immediate response of the Indian colonies for NHPC employees near downstream of the dam. The nailed/ Army in providing medical assis- these project sites suffered minor bolted slopes on the right abutment tance and supplying essential com- to moderate damage in the form of of Teesta VI hydropower project site modities such as food grains, but cracking in masonry infill walls and near Singtam were affected by mass they were critical of the role played minor cracking in RC members, no movements seated deeper than the by the local administration (Govern- damage due to earthquake shaking nailing/bolting. ment of Sikkim) and the National or landslide was observed in the Disaster Response Force (NDRF) body of any of the dams. Both dams Electrical power. The meisoseismal deployed by the central government were instrumented to record strong area lost power immediately after the which had come unprepared. NDRF ground motions; however, all five earthquake due to collapse of high on such deployments needs to be strong-motion accelerographs were tension towers along the distribution self-contained. reported to have malfunctioned at network due to landslides (Figure 28). the time of the earthquake. During This also resulted in loss of landline Locals bemoaned the lack of any the main shaking, a falling boulder and mobile communications in the means of communicating with their destroyed an electrical transformer affected area. High-tension towers families elsewhere in the state or located on the Teesta V dam site, and lines were damaged due to fall- out of it. Some locals lost their lives and severe landslides and ground ing debris from landslides, and even trying to walk across to other vil- local distribution poles were dis- lages or towns to check on children, lodged due to ground deformation only to be buried in a landslide. generated by soft soil slopes. Power There was a feeling of abandon- was not restored in worst-hit locations ment as the Chief Minister of the even 12 days after the earthquake. State of Sikkim had not visited the most ravaged sites more than a month after the event. Damage assessment. Many buildings across the state suffered damage of varying degrees.

One critical question that all government levels in Sikkim Figure 26. Damage in lower story faced is how to de- of RC frame building with telecom Figure 27. Damage to plain concrete pipe supports of cide whether a build- tower on its roof at Chungthang penstocks carrying water to town of Lachung (photo: ing can be used (photo: Arun Menon). Alpa Sheth). after an earthquake

12 EERI Special Earthquake Report — February 2012

the six-story RC Intermediate Shelters and frame building has Reconstruction no damage (includ ing even fine cracks The intensity of ground shaking of frame-infill sepa in the state of Sikkim and hills of ration in the URM Darjeeling during this earthquake infill walls) except was small — only V-VI+ on the for some distress in MSK scale — so damage to build- the independently ings and structures was limited. built four-column Persons with severely damaged porch at the en- houses moved to their relatives’ trance. houses as an interim measure. Figure 28. Damage to electrical power transmission Because some schools, primary tower at Lower Payong, South Sikkim (photo: Govern- The Government of health centres, and government ment of Sikkim). West Bengal had governance buildings were se- deputed the Block verely damaged, there is an urgent or not. There was no agency to dis- Development Officers (BDOs) to effort for construction of intermedi- tinguish between dangerous and report the number of houses dam- ate facilities (Figure 29). Consider- benign cracks. Buildings were va- aged. In the District of Darjeeling, ing the availability of bamboo in the cated in panic, and many important under extreme pressure from the state, a possible design for inter- government files may have been locals to seek government compen- mediate houses, schools, and lost in the process. Some govern- sation meant for damaged buildings, primary health centers could utilize ments constituted formal commit- the BDOs were coerced to post all that as primary construction mate- tees for damage assessment, and houses in some areas fully damaged. rial; the traditional wood-frame placed damaged buildings into This resulted in the Government of construction could be adapted with three categories: (1) those requiring West Bengal declaring about 37,000 bamboo mats as walling; this type minor repairs, (2) those requiring houses damaged, while the field of construction is already prevalent major repairs, and (3) those requir- reconnaissance suggests otherwise. in Sikkim. ing replacement. In general, however, the engineers in the state do This earthquake is demonstrating that The Government of Sikkim needs not have the background to assess post-earthquake building damage to firm up a comprehensive recon- damages. Residents have moved assessment is not just a technical struction strategy, even though the back into many damaged buildings, activity, but also an administrative effort required is smaller than re- even though some of these build- and legal activity, which needs prior quired by other recent large earth- ings may not be capable of resist- rehearsal by all stakeholders (techni- quakes. The challenge is made ing strong aftershocks, and are unfit cal, administrative and political lead- complex due to factors like acute for occupation. ers), promulgation of appropriate laws shortage of manpower within the to protect persons undertaking dam- state capable of undertaking earth- In the tense moments after the age assessment, and safeguards quake-resistant design and con- earthquake, many local administra- against misuse by political leaders. struction, shortage of construction tions depended on visiting faculty materials and members and engineers from other labor, and the states conducting post-earthquake remoteness of reconnaissance of the affected affected areas. areas. Some of them managed to The state may contribute a day’s effort to identify consider develop- unsafe buildings, but decisions on a ment of designs large number of damaged buildings for earthquake were pending six weeks after the resistant homes quake. This lack of decisive evalua- in line with the tion led to situations like the state- cultural aspirations ordered demolition of the building of the people in that serves as the Health and Family the region, and it Welfare Unit of the main Sir Thutob should establish Namgyal Memorial Hospital in Gang- Figure 29. Makeshift school in tents on river terrace at some form of reg- tok. This order stands even when Chungthang (photo: Alpa Sheth). ulatory framework

13 EERI Special Earthquake Report — February 2012

and implementation mechanism 2. No new URM structures should be quake. This is not acceptable to ensure conformance to seismic permitted in Sikkim, and existing by any standards in the modern safety construction procedures. ones should be retrofitted, espe- communications era. cially the critical, lifeline and gov- 9. There is an urgent need to study Community Impacts ernment structures. the strong ground motions in 3. Develop a comprehensive plan to order to incorporate reasonable Villages susceptible to landslides retrofit all heritage structures in expectations in the design were relocated to safer areas; how- Sikkim and West Bengal. When codes. There is a network of ever, as a result, one saw villagers, even basic earthquake-resistant ground motion instruments in especially women, walking between construction is not known by local the region operated by various their original and relocated homes architects and engineers, special national agencies and institutes, over miles of steep terrain in North assistance may be required from but it must function in the next Sikkim. The harsh living conditions outside these states to support earthquake. in the cold, steep and poorly acces- this culturally and historically criti- 10. There is no government engi- sible terrain, and annual landslides cal work. neering and architecture college during the rainy seasons, have 4. There should be an aggressive in the whole state of Sikkim or made inhabitants resourceful and promotion of traditional Ekra hous- in Darjeeling to provide regular able to deal with lesser disasters. ing by development of a manual advice to the governments of Numerous bamboo bridges made of good construction practices and Sikkim and West Bengal. There by villagers across streams were inclusion of this as a formal hous- are two structural engineers testimony to this. The continued ing construction typology eligible (with masters degrees) and presence of the Border Roads Orga- for bank loans. about 35 architects in the entire nization in the region is vital. There state of Sikkim, few trained in is an opportunity for engaging the 5. Post-earthquake damage assess- the subject of earthquake- military as they have a permanent ment teams need to be mobilized resistant constriction. The newly presence in the area. from out of state that have sound judgment on usability of damaged opened Sikkim-Manipal Institute of Technology should be en- Lessons Learned structures and no stake in the new construction. As well, technical in- couraged to engage with the formation needs to be disseminat- state of Sikkim to bring about This earthquake has brought into an environment of earthquake relief issues of disaster mitigation ed to professional architects and engineers on accepted methods safety in the state. Similarly, and management in the inhospitable an engineering college should region of the Himalayas which is for assessment and retrofit of damaged structures. be established in the hills of one of the most seismically active Darjeeling to support the local regions of the country. 6. Mandatory review of the safety of needs. 1. The extent and type of damage all ongoing and completed hydro- in newly built RC structures are power projects should be initiated and the information shared with The lessons learned can have not commensurate with the in- large benefits if they are acted on tensity of ground shaking. Most the community as a confidence- building measure. quickly — unlike the opportunity lost damage can be attributed to ir- after the 2006 earthquake in the regular structural configuration, 7. Document all losses incurred by same area. While local residents will improper design and detailing, nonstructural elements, and dis- remember this earthquake as one poor construction materials and seminate technical know-how to that caused landslides and de- practice, or complete absence architects and engineers on meth- stroyed heritage structures, earth- of regulatory framework from ods of protecting these elements. quake professionals see it as a the government side to ensure 8. The epicentral area was cut off for warning before the big one strikes. earthquake-resistance in the more than 12 days after the earth- built environment.