EERI Newsletter, November 2011 Volume 45, Number 11

Learning from Earthquakes M 6.9 Earthquake of September 18, 2011 This report was contributed by EERI 4.6 within 30 minutes of the members C.V.R. Murty, Indian In- main shock. The region falls stitute of Technology (IIT) Madras; into the second highest seis- Alpa Sheth, VMS Consultants, Mum- mic zone of the Indian Seis- Figure 1. bai; and Durgesh Rai, IIT Kanpur. mic Code IS:1893, Epicenter An earthquake of magnitude 6.9 Zone IV, with an ex- of Sikkim pected shaking inten- earthquake occurred at 6:11 pm local time on EPICENTER September 18, 2011, with an epicen- sity of VIII. and route ter at the - border region As the region is mountain- of damage (Figure 1); the focal depth has been ous and rains preceded survey trip. estimated as 19.7 km. The region is the earthquake, the event known to be seismically active, lo- triggered massive land- (URM) infill cated in the Alpine-Himalayan seis- slides. Damage to build- panel walls mic belt characterized by two major ings and infrastructure due to weak fault systems (MBT and MCT) asso- caused by landslides masonry ciated with the collision of the Indian was more severe than and large and Eurasian plates. The event was damage due to direct unsupported located north of MBT in the eastern ground shaking in some length- or height- Nepal-Sikkim Himalayas, which has regions (Figures 2 and 3). to-thickness ratio. been a region of intense seismic Landslides cut off the severely af- Most buildings activity in recent times. Maximum fected areas, especially at higher had a symmetric and uniform grid of shaking was experienced in India’s altitudes, hampered rescue and re- beams and columns. Some buildings northeastern state of Sikkim, fol- lief work, and required the help of that had open stories collapsed, lowed by Tibet, Nepal, the Indian Army helicopters. usually at mid-height (Figure 4), or had severe structural damage. Like- states of Bengal, Assam, Bihar, and The affected area has a low popula- wise, buildings with asymmetry in Meghalaya, together with the neigh- tion density of an average of 88 per- placement of URM infill walls, caus- boring countries of Bhutan and sons/sq. km. The state capital of ing torsion, also were severely pun- Bangladesh. The maximum shaking is the biggest city in the ished. Single RC buildings collapsed intensity attributed to this earth- area. Much of the construction is of far from the meizoseismal area; e.g., quake is VIII in the North Sikkim dis- empirically constructed reinforced at in South Sikkim district trict in the regions of Chungthang concrete (RC) buildings of four to about 80 km from Gangtok (Figure 5). and Lachung. The total death toll is nine stories adjoining each other on Traditional Ekra housing made of about 112 persons, with 60 reported small plots, with buildings extending bamboo or wood framing with light- fatalities in the state of Sikkim alone. to the property lines. A majority of weight infill panels of straw and The earthquake was followed by these buildings exhibited extensive plaster behaved exceptionally well. aftershocks of magnitude 4.8 and damage to unreinforced masonry continued on next page

Figure 2. Landslide near the cable-stayed bridge at Nayabazar (South Sikkim District) restricted the use of the bridge for relief work after the earthquake (photo: Figure 3. Damage due to rockslide and mudslide at C.V.R. Murty). Lachung (photo: D. Rai).

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Figure 4. Pancaking of middle two stories in a Figure 5. Pancaking of three stories in five- Figure 6. All columns supporting roof of nine-story building at story house in Jorethang, South Sikkim Phudong Monastery, North Sikkim, failed. Gangtok, East Sikkim (photo: A. Sheth). (photo: A. Sheth). (photo: D. Rai). M 6.9 Sikkim Earthquake ings of the past few decades in- as the King’s monastery in Gangtok. clude those made in RC, with beams continued from previous page Sikkim is the second smallest state and columns infilled with URM infill in India; about 31 hydropower Heavy damage has occurred to walls. In this RC construction, there projects have been sanctioned in temple structures (shrine halls) of is no frame action; the RC construc- the past three years, some of which various Buddhist monasteries (Fig- tion mimicked the historic wooden are close to completion. No serious ure 6). Historic monastery temples construction. Both sets of monas- damage to these projects, which are made of thick (two to five feet teries were damaged; some had often involve long tunnels through thick at base) external load-bearing partially collapsed, and others mountains, has been reported to rubble masonry wall in mud mortar. showed extensive structural dam- date. The earthquake’s impact on The internal framing was of wooden age. Few monasteries escaped with these projects is currently being posts and beams. Monastery build- minor nonstructural damage, such investigated.

News of the Membership Publication ASCE Honors Gould, Hawkins, Prakash Printed FEMA 455 Three EERI members were recently Neil Hawkins, professor emeritus at The printed (in color) version of named Distinguished Members of the University of Illinois in Urbana, FEMA 455, Handbook for Rapid the American Society of Civil Engi- was recognized for his eminence as Screening of Buildings to Evaluate neers (ASCE). Only approximately a leader in developing codes and Terrorism Risk is now available from 200 of the Society’s 140,000 mem- standards for structural engineering the Applied Technology Council bers worldwide have achieved the practice, for his research on rein- (ATC). The primary purpose of the highest accolade of active distin- forced and prestressed concrete and screening procedure is to prioritize guished membership. The awards the transfer of his results into prac- the relative risk among a group of were presented during ASCE’s An- tice, and for his achievements in the buildings in a portfolio or community, nual Civil Engineering Conference education of engineering students. but it can also be used to develop in Memphis, Tennessee, October Shamsher Prakash, professor building-specific risk information. 20-22, 2011. emeritus at the Missouri University The procedure emphasizes the vul- Phillip Gould, professor at Wash- of Science and Technology in Rolla, nerability factor, due in part to the ington University, St. Louis, was was recognized for his pioneering relatively significant level of control recognized for developing innovative work on liquefaction of fine-grained that the owner has over this factor technology for the design and con- soils and seismic analysis of rigid compared with the other two factors struction of large cooling tower shells, retaining walls, revolutionizing use relevant to risk: threat and conse- for applying finite element technol- of geotechnical engineering case quences. The Handbook can be (1) ogy to the development of prosthetic histories in professional practice downloaded from the FEMA website heart valves, and for promoting and education, and authoring the (http://www.fema.gov/library), or (2) earthquake hazard mitigation world- first comprehensive text on soil purchased for $60 through the ATC wide through research, teaching, dynamics. Online Store at www.atcouncil.org/ and professional leadership. Online-Store/vmchk.html.

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