Effects of the 2005 Muzaffarabad (Kashmir) Earthquake on Built Environment
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Effects of the 2005 Muzaffarabad (Kashmir) earthquake on built environment Studying the effects of earthquakes has widespread destruction in POK, Paki- VIII at Uri, VII at Baramulla and Kupwara long been recognized as a necessary step stan’s North-West Frontier Province and V at Srinagar on MSK scale3. How- to understand the natural hazard and its (NWFP), and western and southern parts ever, the collapse of stone walls of random risk to the society in the long term. A of the Kashmir on the Indian side of rubble types was a surprise even with rapid assessment of general damage survey LoC. This earthquake is associated with much lesser shaking. It has been well es- and documentation of initial important the known subduction zone of active tablished that the local soil site and to- observations, not only help management thrust fault along the Himalayan moun- pographical conditions play a significant of emergency response and rehabilitation tain ranges in the area where the Eurasian role in modifying the nature of ground activities, but also help to assess the need and Indian tectonic plates are colliding motion which leads to varying degree of of follow-up areas of research1,2. The and moving northward at a rate of 40 mm/yr response to similar structures. Structures Muzaffarabad earthquake of 8 October (Figure 1). located on ridges and along steep slopes 2005 which caused major devastation on The worst affected major towns on the were subjected to a greater degree of both sides of the Line of Control (LoC) Indian side of LoC are Tangadhar in Kup- damage in comparison to those located in in Kashmir, presented another opportunity wara district and Uri in Baramulla dis- valleys, during this earthquake as well. to further our understanding of earthquake trict. Significant damages have also been The affected region lies in the top two risk in the region. reported from the Poonch and Rajouri high risk seismic zones of IV and V of The Mw 7.6 earthquake on 8 October district further south from the epicentre Indian seismic code IS:1893 (ref. 4) with 2005 was a major earthquake at a depth on the Indian side of LoC. During the re- an expected intensity of IX or more in of 26 km from the surface with its epi- connaissance survey we visited places the zone V and of VIII in the zone IV. centre located at 34.493°N, 73.629°E, along National Highway NH1A during The region affected by the Muzaffara- 19 km northeast from Muzaffarabad, the 14–19 October 2005 from Srinagar to Uri bad earthquake is mountainous terrain capital town of the Pakistan Occupied and along Sopore, Durgwilla, Kupwara, where the settlement is dense in valleys Kashmir (POK) and 170 km west-north- Traigaon on the road to Tangdhar. and sparse on hill slopes. Major civil en- west of Srinagar, Jammu & Kashmir, India Damage to buildings and other struc- gineering projects in the area are high- (USGS). The event which was similar in tures in general agreed well with the in- ways, bridges, small dams and micro magnitude to the 2001 Gujarat earthquake tensity of ground shaking observed at hydro-electric projects and a few RC framed and the 1935 Quetta earthquake caused various places, with the maximum of buildings. The housing units are largely 1066 CURRENT SCIENCE, VOL. 90, NO. 8, 25 APRIL 2006 SCIENTIFIC CORRESPONDENCE low rise brick and stone masonry load mary lateral resistance against the earth- ing masonry is quite different from typi- bearing types often in association with quake forces is provided by the membrane cal brick masonry and their performance timber. The diaphragms vary from pitched action of the diaphragms (floors and in this earthquake has been once again flexible roofs to mixed flexible and rigid roofs) and bearing walls. The seismic shown to be superior with no or very lit- concrete floors and roofs. performance of load-bearing masonry tle damage. No collapse was observed in Structures need to have suitable earth- structures depends heavily on the struc- such masonry even in the areas of higher quake-resistant features to safely resist tural characteristics (strength, stiffness shaking. This timber-lacing of masonry, large lateral forces that are imposed on and ductility) of surrounding walls to resist which is locally referred as dhajji-dewari them during infrequent earthquakes. Or- in-plane and out-of-plane inertia forces (meaning patch quilt wall) has excellent dinary structures for houses are usually and of the diaphragms (floors and roofs) earthquake-resistant features. Presence of built to safely carry their own weight and to not only safely resist the shear forces timber studs, which subdivides the infill, low lateral loads caused by wind and but also to distribute the forces to verti- arrests the loss of the portion or all of therefore, perform poorly under large cal elements (walls) and maintain the in- several masonry panels and resisted pro- lateral forces caused by even moderate tegrity of the structure. gressive destruction of the rest of the size earthquakes. In Kashmir, traditional timber–brick wall (Figure 2). Moreover, the closely The majority of buildings in the affected masonry construction consists of burnt spaced studs prevent propagation of di- region use the unreinforced masonry clay bricks filled in a framework of tim- agonal shear cracks within any single walls as bearing and enclosure walls. ber to create a patchwork of masonry, panel, and reduce the possibility of out- These masonry structures can be viewed which is confined in small panels by the of-plane failure of masonry of thin half- as box-type structures in which the pri- surrounding timber elements. The result- brick walls even in higher stories and ga- ble portion of the walls. Dhajji-dewari system is often used for walls of upper stories, especially for the gable portion of the wall, even when the walls in bot- tom stories could be made of brick or stone masonry (Figure 2 a). In older constructions, another form of timber-laced masonry, known as Taq has been practiced in which large pieces of wood have been used as horizontal run- ners embedded in the heavy masonry walls, which add to the lateral load re- sisting ability of the structure (Figure 2 b). The concept of Dhajji-dewari has also been extended to develop a mixed construction in which stones are used as filler hard material in wall panels created by a series of piers in softer coursed brick masonry of greater integrity under lateral loads (Figure 2 c). The masonry walls with stones confined in such a manner have performed quite satisfactorily, in contrast to usual brick or stone masonry. In the upper reaches of North Kashmir Himalayas, majority of houses use stone masonry in mud mortar for walls and flexible diaphragms for floors and roofs consisting of timber. Stone masonry is produced from a wide range of materials and constructed in many different forms that have shown varying degree of per- formance in this earthquake. Unreinforced stone masonry is very durable even in the hostile environment and can accommo- date movements and resist natural forces without becoming unstable and falling apart, especially when they are laid in even courses after proper dressing (Fig- ure 3). Figure 1. Location of epicentre of the earthquake and its aftershocks, Main Central Thrust However, some forms of stone masonry, fault, and the towns visited in the Indian side of Line of Control (LoC). especially Random Rubble (R/R) stone CURRENT SCIENCE, VOL. 90, NO. 8, 25 APRIL 2006 1067 SCIENTIFIC CORRESPONDENCE a b c Figure 2. Traditional masonry for proven earthquake resistance. a, Dhajji-dewari system of timber laced masonry for confining masonry in small panels; b, Taq system of embedding timber thick walls; c, Brick masonry piers for timbers in stone infilled wall. b a Figure 3. Examples of mixed construction involving dhajji-dewari and dressed/undressed stone masonry and brick masonry. a b c Figure 4. Out-of-plane collapse of stone masonry walls. masonry construction are extremely vul- built during the last 4 to 5 decades suf- Uri and Kupwara are a few examples. nerable to earthquakes. Undressed stones fered heavy damage especially when the Such out-of-plane failures arising from are laid in mud or cement mortar and structure is old. This was primarily due the dynamic instability of unsupported plastered in cement mortar to provide to the fact that the walls could not main- walls were also evident in collapsed tall finished surface. Most of government tain their integrity during the shaking. slender end wall in brick masonry as well. buildings, hospitals, schools, jails, etc., The collapsed walls of army buildings in Moreover, masonry walls are weakened 1068 CURRENT SCIENCE, VOL. 90, NO. 8, 25 APRIL 2006 SCIENTIFIC CORRESPONDENCE by openings for doors and windows (Fig- ings. However, there are many variants ing material. Corrugated Galvanized Iron ure 4). of pitched roofs with varying degree of (CGI) sheets have also been used as a Deficiencies of stone masonry walls seismic performance. In rural areas and roofing material in many cheaply built were more evident in R/R type masonry low cost houses, roofs are either com- school buildings. These roofs are inher- and were responsible for the majority of posed of wooden joists and planks or ently weak in shear and cannot tie the the observed damage in the earthquake- simple wooden trusses and rafters. In walls together even when they are prop- affected areas. Such deficiencies can government buildings, wooden planks erly connected to them. Most of roof render typical brick masonry buildings are placed on rafters to support the roof- failures can be attributed to a combination vulnerable to damage as shown in Figure of deficiencies such as loss of support of 5.