EERI Special Earthquake Report -July 1999 34°NW -rr

~ the youngest, appears to be seis- Strike 282. micalfy more active. Several damag- 9. <> <><>19<65 <> Dip Slip 95. ing earthquakes have occurred along <>~angsa 33 p these thrust faults, and there are con- ~ Strike 97" tinuing debates on the current O 81. Dip seismogenic potential of these fault Slip 89. systems. The M6.5 earth- 32 ~--O g>"V I Fau/t-P/aneSo/utlon (source: USGS) quake of 1991 I centered about 70 km northwest of Chamoli, is considered ~O I OU to be associated with this fault, as is 1991 O the Chamoli quake. Observations of 31 rkQshlo recent deformation in the epicentral 'Okhlmath 8 8 ~USGS Epicenter region also support this association. MBT TehrQ 0 .0 . o .IMD Epicenter o Dehra Dun .-~ <> An Active Fold? 30 1803 <> The Lesser Himalayan sequence ~~G lying between the MCT and the MBT OI\O~O \' shows stacking of various groups of 291 ...~- 01 75 76 77 78 79 80 81 82°E rocks characterized by south-vergent Figure 2: Spatial pattern of seismicity in Garhwal Himalaya during 1684- thrusts, which were later folded into 1985 with respect to two of the major thrusts MCT and MaT [Khattri et al., major scale synforms and antiforms. 1989, Proc. Indian Acad. Sci. (Earth. Planet. Sci.), 91-109]. The subsets The geologic maps of the area MCT -I, II, III are not marked. Shaded circle indicates the maximum felt area indicate the presence of an anticlinal structure very close to Chamoli. of the 1803 earthquake. Insert: Fault-plane solution of the main shock at During the postearthquake field Chamoli. investigation, signatures of recent deformation associated with this Kanpur (440 km southeast of the Geologic and Tectonic anticline were observed. A sharp epicenter), Shimla (220 km north- Setting contact of MCT I with recent deposits west) and Delhi (280 km southwest). The Himalayan mountain range, an is identified near Chamoli on the Maximum death and damage oc- outcome of the compressional pro- southern flanks of the anticline along curred in the district of Chamoli, cesses ensuing from the -Asia the . Thick deposits where about 63 persons died and collision (70-40 Ma), has been under- of colluvium (boulders and pebbles over 200 were injured. About 2,595 going extensive crustal shortening intercalated with coarse sand) occur houses collapsed and more than along the entire 2400-km-Iong north- at the foot of the steeper limb of the 10,850 were partially damaged. In ern edge of the Indian plate. A series fold. The colluvium may have been all, about 1,256 villages were af- of thrust planes is known to have remobilized on an incipient slope due fected. A few buildings at the distant formed as a result of these processes. to the development of the growing city of Delhi sustained nonstructural Three principal thrust planes in the fold. This contact is interpreted to be damage. No instances of liquefac- Himalayan region are the Main the surface expression of an active tion were reported. Linear cracks in Central Thrust (MCT), the Main fold. the ground were seen in some loca- Boundary Thrust (MBT) and the Main tions in the affected area. Frontal Thrust (MFT). Two of the major These observations are significant The earthquake was followed by thrusts and the regional seismicity are because the contact of the thrust intense aftershock activity; this in- shown in Figure 2. plane occurs close to the epicentral zone of the Chamoli earthquake. Al- Gluded at least three events of M >5 The MCT is believed to have resulted though the models for many earth- Most of the aftershocks were 10- from an intra-crustal thrust that quakes, including that at Uttarkashi, Gated to the east of Chamoli. The brought up the mid-crustallevel rocks suggest the rupture along MCT I , fault plane solution obtained from of the Higher Himalayan Crystallines geologic evidence for active faulting USGS (Figure 2, insert) indicates a to the Lesser Himalaya. Tectonically, it in this region is sparse. Observations pure thrust mechanism with two represents a ductile shear zone at in the epicentral region of the Cham- nodal planes striking at 282° and depth, comprising a duplex zone with oli earthquake may provide guide- 97°. The first one is preferred three distinct sub-thrusts: MCT I, MCT lines to identify active faults and folds because it conforms to the field II and MCT Ill, from south to north. Of in the Himalaya. observations. these, MCT I,the southernmost and

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potential area for a great earthquake (Figure 1). An alternate view is that the strain in this stretch was partially or totally released by the moderate earthquakes in the past. In this con- text, the mechanisms of large earth- quakes in the region and their relation to strain accumulation on the MCT need to be understood in greater detail.

Co-Seismic Phenomena

The Chamoli earthquake was accom- panied by severe ground deforma- tions. Fissures, landslides and changes in the groundwater flow were Figure 3: Ground fissure at Telcom Hill near Gopeshwar reported from several locations. Well- h I developed ground cracks, trending Historic and Current muc arger. roug hly In. th e eas t -wes t d 'Irec t 'Ion an d Seismicity The limited recorded data from this showing lateral movement of up to region suggest a northwest-oriented about 12 cm, were observed in Go- Historic and instrumental data sug- zone of moderate activity (Figure 2). peshwar, Chamoli and Bairagna. gest fewer large earthquakes in the Two M >6 earthquakes within a span Attempts were made to trench across region compared to the rest of the of eight years, a larger event 196 some of these ground fissures at Himalaya (Figure 2). One earth- years ago, and the clustered micro- Telecom Hill, Gopeshwar (Figure 3), quake, probably of M > 7, is report- seismicity indicate strain accumulation but none of the trenches could be ex- ed to have occurred in this region in the region, The 700-km-Iong seis- tended downward more than a meter on September l' 1803. Several mic gap between the rupture zones of because of debris and boulders, In villages are reported to have been two great earthquakes (the 1905 one of these trenches, a poorly de- buried by the rockfalls and land- Kangra [M8.6] and the 1934 Bihar fined thrust plane was detected. Ori- slides caused by that earthquake. M8.4]), generally referred to as the I entation of these discontinuous The temple located -40 "Central Gap," is considered to be a ground fissures conforms to the strike km north of Chamoli was severely I iO 8km damaged. Even though the earth- JPShi~ quake's location remains uncer- -Rock fall t Telecom Hill USG,:iCeneter tain, intensity reports suggest that the 1803 event may have been in D Okhimath . the same region affected by the 30~301 r O 0 current earthquake. Birahi ~ ;l/"1 c []J 0 sett!ements I The postearthquake survey of the Chamoli earthquake examines two ~- temples-one at Gopeshwar and 30"25' c MSK IntensitV1 the other at Makkumath, built dur- o V ~moli ing the 7 to12th centuries. These O \11 Qadi show evidence of severe damage O \111 c;;cr during the 1803 event. Many parts OWl/ D c c 3fJ'20' of these two temples have been Aftershocks a~dprayag I reconstructed, as indicated by the cM<3 I/MD EPiCe;e1 [J3~M<4 inscriptions on their wall stones. Gauchar """"""'- D' D4~M<5 ~ That these temples suffered only DM?5 / minor vertical cracks during the i,/ 30°15' current earthquake, in spite of 79"05' 79°15' 79°25' 79°35' being located in the meizoseismal Figure 4: Intensity variation during the main shock and location of aftershocks area, indicates that the magnitude in the affected area. Shaded portion shows the trend of the fault from the fault- of the 1803 event may have been plane solution, which is consistent with the damage distribution.

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of the thrust front (MCT I). The higher elevation on the hill slopes. The well-developed. The Uttarkashi earth- majority of these east-west-oriented intensity VII observed at Makkumath, quake took place in October immedi- fissures, particularly those devel- located on a river terrace about 20 km ately after the monsoons, which lead oped in the well-consolidated debris, from the epicenter, is possibly another to a much higher incidence of slope may be a manifestation of the fault example of site amplification due to failure and foundation movement. movement. Ground cracks at several alluvial CoVer. Finally, construction practices in the places also developed as part of Chamoli area are much better than The area has a number of analog slope failure, and these pose threats those in Uttarkashi before 1991. to the down-slope settlements. strong-motion accelerographs oper- ated by the University of . Cracks were seen in asphalt roads Building Behavior at some locations, indicating the Strong-motion records were obtained possibility of failure due to ground at Gopeshwar (9 km from the epicen- Many of the villages in the affected slippage. At several sites, large- ter), (27 km), Okhimath (25 area are not connected by passable scale earthquake-induced landslides km) and Tehri (80 km). The peak roads and are accessible only after and rock falls were observed. Those ground accelerations in the two hori- considerable trekking. In addition to near Gopeshwar, Chamoli and Gadi zontal and the vertical directions at these villages. the area has several continued a fortnight after the event. these locations folloW: Gopeshwar small townships along the major Interestingly, these rockslides are (0.20g, 0.36g, and 0.16g), Joshimath roads. also confined to locations along (0.071g, 0.063g, 0.041g), Okhimath MCTI. (0.091g, 0.096g, 0.047g), Tehri The building stock consists primarily (0.054g, 0.062g, 0.034g). The accel- of rural dwellings, with some urban eration time history at Gopeshwar In many groundwater springs, flow houses and a few modern structures ShoWS a large pulse, typical of near- for office or commercial purposes. increased by as much as ten times, SoUrce ground motions. Load-bearing random rubble stone surpassing even the post-monsoon masonry in mud mortar formed the discharge. However, at Bairagna vil- ThoUgh the 1991 Uttarkashi and the predominant wall system employed in lage, the flow decreased and the present Chamoli events are of Compa- the area. Much of the construction of water became muddy, indicating rable magnitude and focal depth, dam- recent years has been in brick or possible fluidization and remobiliza- age was much less in Chamoli for tion of fine sediments. several reasons. The villages in Uttar- concrete block masonry using ce- kashi are located on well-developed ment mortar. The roofing system is Intensity Distribution, Site river terraces of the Bhagirathi River, usually thatch, corrugated galvanized Effects and Strong Motion making them more vulnerable to site iron sheets, slate tiles, or reinforced Records effects as compared with Chamoli, concrete (RC) slabs. In general, where the river terraces are not So most roofs are pitched. Figure 4 shows the intensity of shaking at some locations. Intensity showed rather abrupt changes from one location to another, because of site effects on river terraces com- posed of alluvial deposits of sand and boulders. For instance, the right bank of the Birahi Ganga River has two settlements: Upper and Lower Birahi, about 1 km apart. The inten- sity of shaking was VIII at Upper Birahi on the river terrace at a higher elevation, whereas it was VI at Lower Birahi on hard rock. A forest department checkpostjust across the river from Lower Birahi also showed higher intensity (VII) due to its location on the river ter- race. The intensity at Lower and Upper Chamoli was VIII, but at Gopeshwar, located 2 km away, it was V. While Chamoli is located on Figure 5: Collapse of one of the wythes in a traditional house in slate wafer the river terrace, Gopeshwar is at a masonry.

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~ EERI Special Earthquake Report -July 1999

not have been good. Buildings with lin- (280 km from the epicenter) sus- tel bands that sustained damage had tained non structural damage. For serious flaws with continuity of the instance, Tarang Apartments (Figure band (Figure 8). 9), an eight-story building with an open ground story, sustained cracks 4. RC Frame Buildings. There are in infill walls and separation of infills many RC frame buildings with brick from the RC frame at the lowest infills in the affected area. Gopeshwar, story. This structure is located in the being the district headquarters. has Patpatganj area on the banks of the numerous such buildings up to four Yamuna River. Even though minor, stories high. Such buildings performed this damage underlines the disaster very well. even though most of these vulnerability of Delhi from both near- were not formally designed, and cer- by damaging earthquakes and large tainly not for seismic loads. The com- events in the far-off Himalaya. Addi- mon form of damage included separa- tionally, many buildings in tion cracks at the interface of the RC ( 125 km west of Chamoli) sustained . frame and infill panels, and cracking of damage. For example, in some old infills. This is in line with what was buildings of the Survey of India, the experienced in the 1991 Uttarkashi gable masonry collapsed and there (M6.5) and 1997 Jabalpur (M6.0) was severe cracking along the junc- earthquakes. These buildings have tions between the pitched roof and simple structural configurations and the masonry walls. are characterized by small spans and small openings. The masonry infills act Lifelines Figure 7: Two-story house at Pipal- more like shear walls and not as non- koti with no damage. Ground story structural elements. In fact. at times. There is no rail network in the region, in slate wafer masonry, upper story the construction of the masonry walls but there is a good road network added later in concrete block ma- and the reinforced concrete pro- along the mountains. Hence, there sonry. Both stories have an RC gresses simultaneously so as to save are numerous road bridges, mostly lintel band. on the form work for the beams and single span but in a few cases, multi- columns. Clearly, such buildings tend span. The superstructure is either a east corner, a room has been pro- to be more like load-bearing wall-type steel truss or a reinforced concrete vided for office space, making the structures. with columns acting as girder. The abutments are of stone building unbalanced from a torsion strong corners and beams acting as masonry, and intermediate piers in the multi-span bridges are of rein- aspect. The columns along the pe- roof bands. rimeter became short columns, com- forced concrete. The connection pared with the interior ones, and Interestingly. a number of such RC between the superstructure and sustained more cracking. Moreover, frame buildings were also found to substructure consists of rocker and the columns on the west side sus- have RC lintel bands. This is the result roller bearings. Though most bridges tained greater damage than those on of rather common confusion in some performed well, we cannot conclude the east side due to the torsional seismic regions of the country where that bridges as built in the area have effect. code requirements of lintel bands in adequate seismic resistance. The masonry buildings are assumed to intensity of shaking experienced by 3. Masonry Buildings with Lintel apply also to the RC frame buildings the bridges is much lower than what Bands. Numerous dwellings built in with masonry infills. is expected in seismic zone V. recent years in villages and towns have reinforced concrete lintel Many buildings were observed with 15 The area has numerous pedestrian bands. These include both stone to 30 cm of column steel reinforcement bridges across the rivers, some of masonry buildings and brick or con- projecting above the roof for future ver- which are suspension bridges with crete block masonry buildings (Fig- tical extension. Such buildings. if ex- spans ranging from 15 m to 60 m. ure 7). Often the rooms are provided tended vertically, can be a major prob- Lateral buckling of the bridge deck with an RC shelf (about 0.45 m wide) lem in future earthquakes due to this was observed at one of the pedes- projecting from the wall at the lintel inadequate lap length. trian suspension bridges located near Bairagna (Figure 10). The cables level th:at serves the dual purpose of Building Damage at a a storage slab and a lintel band. were found to have loosened, possi- Distance Most houses with lintel bands per- bly due to the shifting of the anchor formed very well, even though the An interesting aspect of this earth- block at one end where there was quality control in these dwellings may quake was thata few buildings in Delhi slope instability.

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quake numbered much fewer than ~ the nearly 800 in the 1991 Uttarkashi earthquake. In addition to the pos- sible technical reasons cited earlier, this may be due to some serendipity: at the time of the earthquake, a pop- ular movie was being screened by a 1V channel, so many people were awake and easily escaped their col- lapsing homes. Furthermore, the area has major Hindu shrines and draws huge tourist traffic from May to Octo- ber, but the timing of this earthquake was during the off-season. Hence, the task of search and rescue opera- tions was easier and carried out by "~~..:;:.;;" local people. Army and paramilitary .c,~..'~!'-- ,. personnel were called in to help in Figure 8: Partial collapse in a stone masonry house at Gadi village. The relief operations the very next day. lintel band, present in the front portion, does not continue along the side The state government provided some wall. cash compensation, food rations, and cloth tents. Since the winter is over by March, cloth tents were sufficient for temporary shelters. Food and oth- er supplies had to be air-dropped to numerous villages which were either normally inaccessible by vehicle, or were cut off due to landslides. Poor accessibility made relief operations challenging, and remote villages ex- pressed dissatisfaction over the length of time it took for aid to reach them. Headquarters for the is at Gopeshwar, 10 km by road from Chamoli. Since Gopeshwar did not experience major damage. the entire administrative machinery could func- tion effectively. However, frequent vis- its by senior politicians and admin- Figure 9: Tarang apartment in Delhi that sustained damage to infill walls istrators from the state and central governments may have significantly The area lost electrical power a few of Chamoli and Gopeshwar was dis- diverted the attention of the district seconds after the earthquake; in rupted because landslides damaged officials. Revenue officials initiated some areas it took as long as a week the pipes. It took about a week to re- damage assessment for individual to restore the power. The telecommu- store most of the water supply lines. houses immediately after the earth- nication system continued to function The affected area has a minor irriga- quake. This was also a difficult task after the earthquake. A 20 m-high tion network consisting of typically 0.4 due to the inaccessibility of many steel truss communication tower lo- m to 0.5 m-wide and equally deep con- villages, resulting in some complaints cated on Telecom Hill at Gopeshwar crete-Iined canals. The lining of the about fairness in damage assess- did not show any distress. canals cracked at several locations, ment. The water supply in the area comes but no major damage to the system Significant aftershock activity, which from collecting water from springs was reported. included a few events of M >5, cre- into tanks at higher elevations and ated fear among the people, and they Emergency Response distributing it through a network of hesitated to sleep indoors even when pipes. The water supply to the towns Fortunately, the fatalities in the earth- their dwellings had little or no dam-

7 EERI Special Earthquake Report -July 1999

age. Speculation about an impend- parable magnitude and focal depth, the g) The earthquake took place in an ing large earthquake added to the latter caused much less damage and area known for its seismogenic po- fear and panic. Massive forest fires, fewer casualties. It is postulated that tential, and yet appropriate plans to which are common during this time the extensive and well-developed river handle such an eventuality were not of year, drove some wild animals terraces on which the villages of available. The lessons of the Uttar- toward the damaged villages and Uttarkashi are located may have kashi and Chamoli earthquakes need added to the insecurity. Impending played a major role in ground shaking to be integrated into an earthquake monsoons in the next two months characteristics. disaster management plan for the en- raised concern over slope failures tire Himalayan belt. e) The earthquake clearly demon- and additional damage to already strated site effects at several locations h) This earthquake has provided an partially damaged houses. where the damage intensity was much excellent opportunity to carry out a Important Issues and higher on alluvial deposits than at near- significant seismic rehabilitation and by rock sites. In view of several M >5 strengthening project in the entire Recommendations aftershocks, quick deployment of mo- Garhwal area, not only in the most This earthquake caused moderate bile strong-motion acceler?graphs in affected villages. The fact that villag- shaking of intensity up to VIII on the large numbers could have provided ers on their own have been adopting MSK scale in an area that lies in excellent information on site character- lintel band construction shows that seismic zone V. The Indian code im- istics; unfortunately, this opportunity they may be receptive to a system- plies that areas in zone V are prone was missed. atic program in this direction. to shaking intensity of IX and above, f) This area seems to hav£! experi- Five moderate earthquakes of so this earthquake caused a lower enced a much larger and rnore damag- around 6.5 magnitude have occurred intensity of shaking than what is pos- ing earthquake in 1803; th ere is no in India since 1988; this leaves the sible. Even though the damage is room for complacency. Tv.o parallel country with no choice but to develop limited in its extent and nature, this initiatives are urgently needed: an strong initiatives in earthquake earthquake has taught severalles- earthquake disaster reduction program disaster preparedness, mitigation sons and raised some important to strengthen the existing housing and management. As a beginning, a issues. stock, and a better assess ment of the white paper on the status of earth- a) While the traditional stone houses earthquake hazard by wa~' of paleo- quake science and engineering in performed poorly as expected, the seismic and other studies. the country should be commissioned. satisfactory performance of struc- tures with lintel bands clearly estab- lishes an improvement. b) The performance of RC frame buildings with brick infills has once again demonstrated that brick infills may perform satisfactorily for ordi- nary buildings, without configuration irregularities, during M 6.6, MSK in- tensity VIII, events. This is important Figure 10: for building practices in many devel- Lateral buckling oping countries. Efforts are needed of the deck of a to develop suitable design proce- suspension dures for such buildings. bridge at c) Nonstructural damage to some Bairagna. buildings in far-off Delhi clearly un- derlines the potential for a major disaster there. Considering the politi- cal and social significance of such an eventuality, efforts should be di- rected towards effective earthquake disaster mitigation and management in the Indian capital. d) Although the Uttarkashi and Chamoli earthquakes were of com-