1

THE DHUBRI EARTHQUAKE OF THE 3RD JULY 1930 E.R. GEE (1934) MEMOIRS OF THE GEOLOGICAL SURVEY OF INDIA, VOLUME LXV, PART 1, PAGE 1-106 [Selected & Edited Transcription] A large portion of northeastern India was, during the early hours of the morning of 3rd July, 1930, affected by seismic activity. Centering near the northwestern end of the Garo hills and adjoining valley of the Brahmaputra river, this earthquake was attended with disastrous results in northern Bengal and in western Assam, and was felt very distinctly over a wide area, extending from Dibrugarh and Manipur in the east, to Chittagong and Calcutta in the south, to Patna in the west, and beyond the frontiers of Nepal, Sikkim and Bhutan in the north. The sensible zone of the earthquake includes widely contrasting types of topography and geology. The epicentral tract, in the vicinity of the town of Dhubri adjoining the Brahmaputra river, and the areas badly affected to the northwest, west and south, comprise a portion of the alluvial plain country which is traversed by the lower courses of the Brahmaputra and Ganges rivers and by their numerous tributaries. To the north, in the outer part of the sensitive zone, rise the outer ranges of Nepal, Darjeeling, Sikkim and Bhutan Himalayas. To the NE and ENE of Dhubri, the higher reaches of the Brahmaputra river traverse a wide alluvial valley, narrowing eastward and dotted by a number of prominent hills, whilst the more distant southeastern areas include the alluvial plains of Mymensingh and Sylhet. Between these two latter tracts, east of the Brahmaputra, are the jungle-clad ridges of the Garo hills rising to well over 4,000 feet; these continue eastwards to link up with the Khasi and Jaintia hills of the Shillong plateau. Fortunately, from a point of view of estimating the intensity of the earthquake shock, a large portion of the epicentral and adjoining tract is traversed by the Eastern Bengal Railway line, the stations and railway cantonments along which, being built wholly of brick masonry of a fairly standard type have afforded very useful data in demarcating the isoseists of the main shock. These populated areas comprise the alluvial tract lying between the Ganges and Brahmaputra rivers. To the south and east of the Brahmaputra, however, within the jungle-covered uplands of the Garo hills, the town of Tura, lying a short distance outside the epicentral tract, and the still more distant station of Goalpara, are the only places of sufficient size and type from which the intensity of the shock can be gauged. With the exception of Rowmari and Manikarchar, where several brick buildings exist, the villages are mainly constructed of light bamboo or ikra (a reed grown in the locality) upon which the vibrations of the earth’s crust, resulting from

2

the main shock, would have left few recognizable imprints. The mapping of the isoseists within this southern area was therefore based on rather scanty information. In delineating these isoseismal lines, the scale originally adopted by Dr. R.D. Oldham in the case of the Great Indian earthquake of 12th June 1897, and later used by Dr. Murray Stuart in his description of the Srimangal earthquake of 8th July 1918 has been followed. In these earlier investigations, seven degrees of intensity lying within their isoseists, were defined as follows:

1) The first and innermost isoseist includes all places where the destruction of brick and stone buildings was practically universal.

2) Those places where damage to masonry or brick buildings was universal, often serious, amounting in some cases to destruction.

3) The third, those places where the earthquake was violent enough to damage all or nearly all brick buildings.

4) Places where the earthquake was universally felt, severe enough to disturb furniture and loose objects but not severe enough to cause damage, except in a few instances, to brick buildings.

5) The fifth, those places where the earthquake was smart enough to be generally noticed but nor severe enough to cause any damage.

6) All those places where the earthquake was only noticed by a small proportion of people who happened to be sensitive and being seated or lying down were favourably situated for observing it.

The corresponding shock intensities as represented in the Rossi- Forel scale have been previously suggested by Oldham:

Scale adopted by Oldham Rossi- Forel scale

Isoseist 1 Isoseist X

Isoseist 2 Isoseist IX

Isoseist 3 Isoseist VIII

Isoseist 4 Isoseist VII and VI

Isoseist 5 Isoseist V and IV

Isoseist 6 Isoseist III and II

Isoseist 7 Isoseist I

The evidence collected in regard to the recent disturbance, however, suggest that at no place within the epicentral tract was the shock of an intensity equal to that experienced within Isoseist 1 of the earthquakes of 1897 and 1918. At no point was the destruction of brick and stone buildings practically universal. Within the epicentral tract, however, including the town of Dhubri, the intensity appears to have been equal to that represented within Isoseist 2 of Oldham’s scale, an

3

intensity corroborated in this instance by the overthrow of certain pillars and statues within the epicentral region. An additional Isoseist No. 3a, which roughly corresponds to Isoseist VII of the R-F scale has been demarcated largely on the evidence brought forward by Dr. Krishnan in his report. The Epicentral Area [Isoseist No. 2] The only places of importance lying within the epicentral tract are the town of

Dhubri (26° 06′: 90° 00′), the headquarters of the Goalpara district, and the village of Gauripur a short distance to the west. Opposite Dhubri, to the southeast of the Brahmaputra, it is possible that the jungle-clad tract of the northwestern corner of the Garo hills was subjected to a shock of almost equal magnitude. The town of Dhubri, at the rail-head of the branch-line from Golakganj

(26° 12′: 89° 54′), is situated largely on the fine micaceous alluvial sand which borders the Brahmaputra, though outcrops of gneissic rock occur along the right bank of the river in that vicinity. Within the town the following types of houses are included:

(a) Brick masonry, one or two-story buildings, the bricks being often of a relatively inferior, sandy type.

(b) Semi-pakka buildings of which the lower 3 to 4 feet are of brick masonry, and the upper portions of bamboo or ikra covered with mud plaster, and usually supporting a light galvanized iron roof.

(c) Structures of split bamboo or ikra, covered with mud plaster, and supported on a wooden framework with posts driven into the masonry plinth or alluvial foundation.

(d) A few types similar to (b) and (c) but with the framework merely resting on a masonry plinth so that the structure was free to move as a whole.

Of the former (a) few escaped undamaged; the majority was badly damaged and partially collapsed, whilst in at least one instance the almost total collapse of the structure took place immediately after the main shock. Of the semi-pakka type, a number were more or less badly affected, though in the case of a few recently constructed, well built houses, including the Girls High School, situated on more stable ground, practically no damage resulted. In most instances, where the supporting posts had been carried down into the plinth or into the ground (type c), the structures were badly affected, large cracks occurred in the plinths, decayed posts were often sheared near the base, large fall of plaster and of ikra took place, and the general vibration of the wall was sufficiently intense to cause the overthrow of heavy almirahs standing nearby. On the other hand, the few buildings in which the wooden framework merely rested on the plinth were, with the exception of slight plaster cracks, undamaged. The intensity of the shock at Dhubri might also be judged by the evidence of several overthrown monuments and gate pillars. A massive white marble statue of Queen Victoria, (about 16½ feet in height including the pedestal) which faced

4

south was overthrown to the NW, whilst the Shiva temple, a cone shaped brick-masonry structure over 20 feet high, cracked across within a few feet of the ground and toppled over in a N70E direction. All buildings located on made-up ground, in-filled tanks, ditches, etc, suffered acutely. In several instances, where the structure was founded partly on the natural alluvium and partly on old excavation that had been refilled with earth, a large crack occurred along the junction of the infilling and the alluvium, and that portion of the building located on the former subsided to the extent of over a foot. Amongst the brick-masonry structures, the four walls of the house of Rai Bahadur Biraj Mohan Dutt suffered partial or total collapse; the tilted roof however remained supported at certain points by pillars enabling the owner to escape unhurt. The old rectangular treasury building situated near the river was badly cracked and condemned. A tall conical shaped Observatory located on the river bank was also badly cracked in the upper portion. Near the center of the town the two-storey house and compound of Mr. Rabindra Narayan Chaudhuri suffered considerably; several brick walls and the brick-masonry pillars at the gate-entrance collapsed. Another two-story house of Mr. Sourindra Narayan Chaudhuri, was badly fissured, portions of the window and door arches were dislodged, while a brick-masonry partition in the upper story of the building collapsed. Several E-W cracks along with dislodged bricks were noted in the recently constructed extension of the Dhubri Charity hospital; two old pakka quarters in the hospital compound were also badly damaged. The Bara Musjid, a brick building with galvanized iron roof, suffered partial collapse. The railway station buildings, constructed of somewhat better quality materials, escaped with a few cracks. The police lines cracked in several places and walls collapsed. Of the Semi-pakka structures, the Bar Library, situated on the river bank, suffered considerable damage; the lower brick portion was badly cracked and partially collapsed, while the upper split bamboo with plaster was severely affected, particularly at the river end. The floor of the old buildings of the Government High School for boys was badly cracked; the ikra superstructure and supporting posts being in places shattered and shaken out of the vertical. N-S crack along with partial subsidence occurred in the new nearby school buildings. Several open N-S cracks across the floor noticed in a Government Hostel for criminal tribes. Of several houses situated in Dufferin road, the floor and basal three-foot masonry portions were badly damaged; here houses founded partly on in-filled tank subsided up to 3½ feet, the superstructure being badly damaged. Buildings situated in Keshugaon road, being founded on an old in-filled ditch, the front portions resting on the made-up ground had sunk considerably, resulting in large fissures across the lower pakka portions and distortion of the upper. The plinth and masonry floor of Dhubri Charity hospital was traversed by a number of WNW trending cracks.

5

Of undamaged structures, the settling tank for the municipal water-supply, built of reinforced concrete, of diameter of 19 feet and 15½ feet in height, was unaffected. It was full of water at the time of the earthquake. The pumping station nearby, including a brick-masonry engine house, was not damaged, though the pipe leading underground to the river had in someway been affected so that the supply was temporarily curtailed. At Gauripur, about 4 miles west of Dhubri, the railway station was seriously affected by the main shock, the ground up-heaving in the vicinity of the booking-office, resulting in large cracks in the floor and walls of the building. At Gauripur village a number of buildings were severely damaged. ‘Statesman’ on 11th October, 1930 reports: There are 5 reinforced concrete structures in Gauripur, of which 4 are 2-storied and one single-story. One, built on a small hillock about 20 years ago, has suffered to some extent, narrow cracks appearing along the iron posts. All heavy furniture in this building fell down; all electric pendants were broken and the papering on the walls and decorated ceiling pealed off, but still the building was not materially damaged. The other four buildings were undamaged though in one of them a big fissure with sand and water spouting was formed in the base. In the vicinity of Dhubri and Gauripur, the railway line was seriously affected; embankments were fissured and partially collapsed, resulting in the subsidence and distortion of the tracts. Cracks were also formed in the masonry culverts and bridges. At the time of the main shock numerous fissures were formed in the alluvial ground, mainly in an approximately E-W direction. Sand and water spouted upwards to height of several feet. Wells in the locality overflowed and were silted up by the sandy alluvium brought up from below. In the vicinity of Dhubri, the level of the Brahmaputra river was reported to have temporarily risen from two to three feet. The main disturbance was apparently preceded and attended by a low rumbling sound which continued during the major oscillations. A number of clocks in the town were reported to have stopped, the time registered varying from 3-05 to 3-07 local time (2-35 to 2-37 AM IST). The duration of the main shock was variously estimated by local observers at from three to five minutes. It is perhaps somewhat remarkable that no loss of life occurred in the epicentral tract; only a few instances of slight injury due to the collapse of brick-masonry walls were reported. This is perhaps explicable when one remembers that at least a large number of the houses are built of a flexible superstructure, supporting light often galvanized iron roofs. At the time of the year also, a number of people were sleeping in the open or on their verandahs.

6

The Area enclosed by Isoseist No. 3 Within the isoseismal zone 3, the shock was of sufficient intensity to damage, to some extent, all or nearly all brick buildings. To the west and northwest of

Brahmaputra river, this area includes the town of Rangpur (25° 48′: 89° 18′),

Lalmanirhat (25° 54′: 89° 24′), Cooch Behar (26° 24′: 89° 30′), and Alipur Dooars

(26° 30′: 89° 35′), together with other smaller stations, all situated along the Eastern Bengal railway line. East of the river, among the Garo hills, the town of

Tura (25° 30′: 90° 12′) is included in this zone. The main shock within this tract appears to have been of intensity almost as great as that at Dhubri. Certain ‘gaps’ occur, however, where the damage was of a less serious character. As in the epicentral tract, distinct low rumblings, resembling the passing of a distant train or lorry, preceded and accompanied the main shock which, working rapidly up to a maximum, continued to be felt over duration of at least four minutes. The time of the main disturbance as given by the majority of observers, ranged from 2-30 to 2-40 AM (IST). Within the alluvial plain country west and north of the Brahmaputra, in addition to the general oscillation of the ground, the main shock appears to have traveled at the surface as a distinct wave or succession of waves, along the crests of which fissures were developed at intervals; from these fissures, sand and water spouted intermittently. Masonry buildings, situated along these crests, were severely affected, the floors of the buildings being forced upwards into low anticlinal curves causing the walls and roofs to open out along wide cracks above the lines of the crests, whilst numerous secondary cracks developed in conjunction with these principal fractures. In the case of the older buildings, partial collapse often took place. Well-built, recently constructed houses, sited on stable foundations, however, in some cases escaped undamaged. The lighter, wood and ikra houses prevalent at Tura, were often badly shattered and distorted, the amount of damage varying considerably according to the type and soundness of the foundations. In the case of railways, a large number of bridges and culverts were cracked and the displacement and slight subsidence of piers and abutments often took place. Throughout a large part of the area the track runs on the level of the surrounding alluvial country or on embankments; fissures in the ground, attended by sinking of the embankments, often resulted in the distortion of the line. A marked

exception is however observed between Golakganj (26° 12′: 89° 54′) and

Sapatgram (26° 18′: 90° 06′); here the line runs in a general NE to E direction to a large extent through forests, often in shallow cuttings made in the deposit of red and yellow clay that covers this area. Within these cuttings, practically no damage had resulted.

Rangpur Area (25° 48′: 89° 18′): Within the town of Rangpur fissures following E-W or NNW- SSE direction, traversed the alluvium and were accompanied by

7

the spouting of sand and water. Within the bazaar area, a number of buildings partially collapsed. The Town hall running roughly E-W is located along the line of one of the prominent earth fissures; a slight upheaval of the cement floor took place along the length of the building resulting in the formation of large cracks and the collapse of a small brick dome above the entrance. Further east along the same line of fissure the brick building of King Edward Memorial Hall was up-heaved several inches; large fissures continued upwards through the end walls and ceiling, while other portions of the structure were traversed by numerous subsidiary cracks. Some distance to the west, Kakina Kothi was seriously affected in a similar fashion. The Collector’s residence, an old bungalow raised several feet above the ground was also affected. The railway station was traversed by several large cracks running E-W resulting fall of bricks in the ticket office and damage to the eastern end building. To the east and west of Rangpur, the railway track was disturbed in a number of places and several bridges were damaged. Apart from the Sadar Subdivion, damages were also reported from Kurigram and Nilphamari Subdivisions.

Lalmanirhat (25° 54′: 89° 24′): In this area a number of WSW-ESE to E-W fissures traverse discontinuously the open ground and also displayed among the station offices and railway quarters. Buildings situated along these fractures were usually badly cracked. One such large crack has affected the station building and further east accompanied by sand and water blowing. Water and silt flowed from majority of wide diameter and tube wells supplying water to the railway colony. Out of total of 242 buildings affected 140 were damaged more or less severely, of which five railway staff quarters were condemned and rendered temporarily uninhabitable. To the north and south of Lalmanirhat the railway track suffered distortion in several places while a number of culverts and bridges were slightly damaged.

Cooch Behar City (26° 24′: 89° 30′): In this area no fissures were formed in the alluvium. Old brick buildings were badly shattered and in some cases partially collapsed. The plaster cracked fell in many places from the Palace, a fine two storey building running N-S. Two main cracks closing upwards penetrated through the brickwork of the north and south arches but surprisingly the triangular portion between the cracks did not collapse, though a number of bricks dislodged. In other parts of the building damage was largely confined to the upper storey, the window and door arches being affected. A small marble statue in the palace courtyard collapsed in a northerly direction, while several small turrets and a number of bricks dislodged from the upper part of the building. Two masonry buildings in the palace grounds were also seriously damaged. The revenue and treasury offices all fairly old brick masonry structures were very seriously affected. Brick turrets were dislodged from the NW corner of the Judge’s residence and the bungalow seriously affected. The Lansdowne Hall, a large old brick building in the vicinity also suffered considerable damage. The Thakur Bari (temple) building, of poor quality brick and plaster, with its brick dome over the entrance gate was severely cracked and large fall of plasters. The

8

Vice-President’s house, a two storey brick building with four rounded towers at the corners was damaged particularly in the upper storey with cracks and large fall of plasters; the NE and SW towers also suffered damage. The NW tower at its junction with the main building was reported to have been damaged during the earthquake of 1897 and has since remained slightly inclined to the vertical. Minor damages were caused to other brick buildings including the post office and PWD office. The high, massive, well constructed brick and stone masonry water tower building escaped damage. The Circuit house, hospital, the Memorial building and certain new offices left unhurt with only a few slight cracks. With the exception of a bridge a short distance north of Cooch Behar station, the north abutment of which was severely cracked, this northern branch of the railway from Gitaldaha

(26° 06′: 89° 30′) junction escaped without serious damage. At Alipur Dooars

(26° 30′: 89° 35′), to the north of Cooch Behar, masonry structures including the Court building and offices were reported to have been badly cracked. On the

main Eastern Bengal railway line to Amingaon (26° 12′: 91° 42′), the railway

buildings at Gitaldaha (26° 06′: 89° 30′) and Golakganj (26° 12′: 89° 54′) junction

escaped without serious damage. At Sapatgram (26° 18′: 90° 06′), however, the results were more disastrous. The small club building at the eastern end of the station collapsed while several quarters on the north side of the line were badly cracked with fall of bricks and plasters.

Bilaspara (26° 15′: 90° 10′): About 28 miles from Dhubri, on the Gorang river, the sub-divisional town of Bilaspara was also badly shaken. Of the few brick buildings which exist, the front portion of one was reported to have partially collapsed while others were badly cracked. Wells became filled with sand while water and silt were discharged from fissures in the ground. At Bogribari, six miles from Bilaspara, four pakka buildings were said to have been badly damaged.

Tura (25° 30′: 90° 12′): Across the Brahmaputra, the town of Tura, the headquarters of the Garo hills, is situated at a height of about 1,400 feet. The strata which comprise these outer (western) ridges include relatively soft, red, yellow and white sandstones, grits, and pebbly conglomerate, alternating with bands of white and grayish clay. These sedimentaries appear to be faulted against the harder metamorphic rocks- feldspathic gneisses, etc, which constitute the high ridge overlooking the station from the west. The suggested fault trending roughly N-S, is exposed just behind Tura Inspection Bungalow, at which point a dyke of coarse dolerite crops out along or very near the line of fault. In the near vicinity of this fault, the sedimentaries are markedly crushed and the dips steep, though further down the slopes gentler inclinations are observed. Low spurs of these sandstone and clay strata run in a westerly direction from the line of the Inspection Bungalow fault. On these low ridges and the boulder-strewn slopes of the valleys between, the main civil portion of the station and the bazaar is situated to the south of the ridge which extends westward from the Inspection Bungalow, while on the slopes of the northern side of this spur are the bungalows of the American Mission and of the Forest Department.

9

The main earthquake shock, estimated to have lasted for five minutes, was accompanied by a loud noise; on account of the absence of masonry buildings similar to those in the plains, it is somewhat difficult to draw an accurate comparison regarding the intensity of the shock. Those houses situated on or near the ridge tops on solid grit or sandstone were less severely affected, though where the ends of the buildings overlooked the steep hill sides, owing to the formation of fissures within the soil and weather rock slopes, the foundations were often undermined and superstructures considerably distorted. A number of houses in the bazaar and below the hospital were shaken out of vertical and portions subsided down the slopes. Almost all the Government buildings are constructed of ikra or split bamboo, the wooden posts of the framework being embedded in the masonry plinth or carried down into the ground. Most of these suffered shearing of the wooden supports, distortion of walls, large fall of plaster, and overthrow of furniture inside the building. While the Forest bungalows with similar structure were seriously affected, the American Mission bungalows suffered only minor damages. On the low E-W ridge the Civil Surgeon’s, the Sub-Deputy Collector’s and the Extra Assistant Commissioner’s bungalows were severely affected. Other similarly constructed buildings, portion of which sustained material damage included the offices of the Sub-Deputy Collector (land & Revenue) situated higher up the same ridge; the Training School and Headmaster’s quarters on the northern slope of the ridge; the Post office, the office of the PWD, the Charitable Dispensary and the Hospital below the Rowmari road. The Deputy Commissioner’s bungalow, Treasury, Kutchary, Jail etc are situated on a southerly projecting sandstone spur. In the DC’s residence large fall of plaster took place; fissures in the sub-soil traversed the upper slopes in front of the bungalow. While the treasury building suffered no damage, cracks in floors, fall of plaster, shattering due to subsidence etc were observed in the Kutchary and Jail complex. PWD boundary pillar was displaced down the hill side while another was shattered. Up the south-eastern slopes above the town, the pipes from a small water reservoir which traverse the faulted junction between the sedimentary and metamorphic rocks, opened slightly in one or two instances without any serious damage. Below the Inspection bungalow, the Garo War Memorial, a massive structure about six feet in height, composed of blocks of soft sandstone, collapsed. Higher up the ridge the tombstones of the cemetery either rotated or bodily thrown out. A light bridge on the Rowmari-Tura road was damaged; the NNW dry masonry abutment partially collapsed. At the western foot of the Garo hills, in the vicinity of the Brahmaputra, a number of fissures, from which sand and water had previously spouted, were observed in the alluvium. A few pakka buildings which exist at Rowmari and Mankarchar were badly damaged.

10

The Area enclosed by Isoseist No. 4 Within the area damage to buildings was of minor nature, though furniture and loose objects were disturbed. The extensive area under the isoseist covers Gauhati and Cherrapunji on the east, Pabna on the south, Suri and Purnea in the west, and reaching to the borders of Sikkim and Bhutan in the north. Old brick buildings, included in the numerous towns of the Bengal plains within this tract, were in some cases severely damaged, though well constructed masonry houses suffered only slight, if any. In Assam, the ‘earthquake proof’ buildings of Gauhati and Shillong were, except in the cases of old structures, able to resist the shock. In the inner portion of this area, the Eastern Bengal and the Bengal Dooars Railway suffered in some instances appreciably particularly in the case of the former between Sapatgram and Bijni.

Buxa Fort (26° 48′: 89° 36′): Buxa Fort is situated on the foothills of the Himalaya at a height of about 2000 feet. This group of barracks and Government bungalows suffered considerably. The amount of material damage was however largely due to the type of structures; those buildings which had been seriously affected being built of untrimmed rectangular stones set in decayed sandy mortar. Projecting masonry chimneys cracked badly and in some cases partially collapsed. On higher spurs are several pickets or small block houses; these massive structures built with white and grey quartzite were built in 1898, the previous structures having collapsed during the great earthquake of 1897. Certain of these pickets had been considerably damaged; some cracked and other collapsed. The forest Rest House and other wooden structures however survived. At the foot of the hills the railway stations of Buxa and Jainti and the adjoining station of Raja Bhat Khawa suffered only minor damages, the railway line being unaffected. At Dalsinghpara, situated a short distance to the west, a two-storey brick-walled structure supported by a steel framework incurred a number of cracks and the chimney fell to the NW. Other brick buildings in the vicinity lacking steel support were reported to be badly cracked, while the walls of the doctor’s house collapsed. At Hamiltonganj, a short distance to the south, slight cracks were observed in railway buildings.

Goalpara (26° 12′: 90° 36′): Located on the left bank of the Brahmaputra between Gauhati and Dhubri. The bazaar portion of this town is located on the alluvium bordering the river, though outcrops of gneiss occur a short distance to the south. Comprising to a large extent small light ikra structures with galvanized iron, and a few brick buildings, this area appeared to have suffered only minor damage. Cracks and fall of plaster and occasional dislodgement of bricks are noted. The Treasury building, Court house, Circuit house, High School and Inspection bungalows were damaged. Several bridges on the Assam Trunk Road settled down and cracked including the bridge over the Krisnai; the west end span tension flat irons on both sides were bent.

11

Gauhati (26° 12′: 91° 48′): The main buildings of the town are constructed of ikra covered with plaster, though a number of semi-pakka type, with brick-masonry below are also met with. These, except in the case of old structures, either escaped without injury or suffered only minor damages in the nature of fall of plaster. Of the few brick buildings which exist, the older ones incurred numerous masonry cracks particularly over the window and door arches. The Judicial and Revenue record rooms were badly damaged in the form of cracks and separation of walls. The wall of the Jail was cracked. Singra Bridge and another timber pile bridge on AT road were damaged.

Shillong (25° 30′: 91° 54′): Since the 1897 disaster almost all the houses of Shillong have been constructed of light materials (wood, ikra and bamboo with plaster) on ‘earthquake proof’ lines, so that in spite of their location in many cases on steeply slopping hillsides, they were in great majority of cases, undamaged. The shock was fortunately of insufficient intensity to cause landslips of the soil and sub-soil though the vibrations were strong enough, in some cases to result in the dislodgement of vases etc within the buildings. In the cases of a few old structures, fall of plaster took place’ while at the Parsonage cracks were formed near the corners of the masonry plinth.

Cherrapunji (25° 18′: 91° 42′): On the southern edge of the Shillong plateau the small station of Cherrapunji is situated on the Tertiary grit and sandstone overlooking the plains of Sylhet. The badly constructed native quarters were damaged in a number of cases, partial collapse taking place in some cases. The Police Station, adjoining quarters and the Circuit House suffered minor fall of plasters. A number of stone pillars were cracked. Portion of 25-30 feet high monument collapsed while several smaller one rotated. At Mawflang (16 miles SW of Shillong), the Mission house was reported to have been badly damaged. The effect was similar to the Mission house at Misang, 16 miles from Mawflang.

Certain railway buildings between Sapatgram (26° 18′: 90° 06) and Amingaon

(26° 12′: 91° 42′), particularly chung quarters were affected. A number of places situated in the Bengal plain in the western half of this isoseismic zone, including the towns of Dinajpur, Saidpur, Parbatipur, Baura and Gaibanda were severely shaken. Old structures were badly cracked while newer structures suffered minor damages. Distant towns from the epicentral tract including Jalpaiguri, Siliguri, Domohani, Katihar, Malda, Rajshahi, Nator, Sirajganj and Bogra, only a portion of the older masonry structures was damaged. The Area enclosed by Isoseist No. 5 This area embraces the Ganges delta (including the city of Calcutta) and the Chittagong area to the south, and the Damodar valley coalfields, Monghyr, Patna and Darbhanga areas to the west. To the east the Sylhet, Cachar and Tezpur areas are included, together with the more distant tracts of Manipur, Sibsagar, the Digboi oilfields and the adjoining Makum-Lido colliery areas. Within this area

12

the earthquake was almost generally noticed, punkahs and other hanging objects swing decidedly, but the shock was not sufficiently severe to cause damage. Report from Calcutta A series of slight but sustained earthquake shocks affected Calcutta for 3 minutes at 2-57 (2-33 hrs IST) this morning. Residents in many parts, awakened by tremors, left their houses until the danger had passed. Along Chowringhee Road and in the vicinity the shocks were particularly severe and panic-stricken people rushed outside and took refuge. Almost every road in the city was thronged with startled residents. Many rushed to the maidan. Telephone lines put out of order all round the city. Not for several years has Calcutta experienced such a severe shock. Dr C.S. Fox reports: Electric fan (flat No7 Loudon Court) swing NW-SE. Thacker Spink & Co’s building had been badly cracked by the joists working loose. Small cracks and stiffness in opening doors of Galstaun Mansions, Alexandra Court (above the 2nd floor E-W cracks across the building), Whiteaway Laidlaw and several other buildings. The shock was severely felt at a depth of 50 feet in the shaft being sunk in the Botanical Gardens for the subway under the Hooghly. A house collapsed in Harrison road but the damage is due to the weakness of the structure than to the intensity of the shock. The earthquake has weakened several old buildings and severely strained others of defective construction. At Calcutta the shock was strong enough to waken people and cause objects to swing but not to damage a well built structure. H. Crookshank reports: At 2-56 A.M. (Calcutta time) on 3rd July awakened by a strange cracking noise and got up. All hanging objects swing NNW-SSE. The strange noise was probably caused by the unusual strains affecting the building. Numerous minor cracks and serious damage to the Bishop’s palace and High Court reported. The former is a very old building and therefore easily broken; numerous irregular cracks could be traced upwards from the window arches. Apart from minor cracks there is a serious 6 inches wide horizontal crack at the base of one of the pinnacles flanking the main spire in the High Court building. This pinnacle would certainly have fallen through the roof had it not been supported by a steel core. Several minor cracks observed in the Reuters building. Though the main building was undamaged, all five blocks to the north of it was slightly cracked. M.S. Krishnan reports: Awakened by the rattling of doors and windows and rocking of the bed on the 2nd floor of 26A, Camac Street. A picture hung on a N-S wall was oscillating visibly along that wall. A hanging weighted cord swings in NNE-SSW direction. As the quake subsided the Cathedral clock struck the hour of three (2-36 IST). At Bengal Telephone Corporation a few plaster cracks observed.

13

Under ground disturbance: It is the experience of two men of Calcutta Electric Supply Corporation who were working on the shaft for their river tunnel in the Botanical Gardens. Four people were working on a staging in the shaft, eight feet internal diameter, about 50 feet below ground-level and in compressed air. The skip used for raising and lowering the men was suspended ready for the men to step into it in case of anything happening. At about 2-57 AM (Calcutta time) one of the men seized a bamboo ladder, which is attached to the side of the shaft, caught one of the other men, who might have fallen and held him. The other two men were thrown against the side of the shaft opposite……..When the quake started the skip began to swing. Geology of the Area The greater portion of the northwestern end of the Garo hills, in the vicinity of the epicenter of the main Dhubri earthquake, is composed of ancient metamorphic strata. These continue eastwards into the Shillong plateau and recur in the area east of Nowgong. These gneissic rocks are overlain by a variety of sediments ranging from Mesozoic to Tertiary in age. At the southern edge of the plateau these sediments are often inclined at steep angles and have been affected by numerous faults and thrusts. The low ground around the Brahmaputra river and to the south of the plateau tract, these beds pass beneath the soft alluvial deposits that spread westwards into the Indo- Gangetic plain. Similar alluvial deposits extend north of the Brahmaputra to near the foothills of the Himlayas, where the outermost strata include Tertiary and Gondwana sediments, steeply folded and striking in a general E-W direction. At Dhubri, and higher up this Brahmaputra valley, several inliers of the ancient metamorphic strata crop out among the recent alluvium. It appears that the Assam plateau topography originated in late Tertiary to sub-Recent times as a result of earth-movements—sharp flexures accompanied by faulting along its southern and western extremities. With the relative advance of the Himalayas towards the south, also during the late to post- Tertiary, lines of fracture were doubtless formed to the north of the present plateau, separating the ancient gneisses, from the more recent sediments of the Himalayan foothills. The low-lying areas immediately to the north, west and south of the Garo hills and the Shillong plateau are, therefore, in all probability zones of structural weakness, liable to earth-movement. The epicenter of the Dhubri earthquake lies near the junction of the northern and western of these zones, while the epicenters of certain of the more severe aftershocks appear to have been located further up the Brahmaputra valley within the northern zone of instability.

14

Seismograph Records etc

Station Arrival of P wave [2nd July,GMT]

∆ as calculated

from station

coordinates

Origin Time as deduced from P [2nd July, GMT]

H M S Km H M S

1. Agra 21 5 45 1199 21 3 13

2. Dehra Dun 21 6 29 1270 21 3 49

3. Hyderabad 21 6 58 1522 21 3 47

4. Phu-lien 21 7 24 1795 21 3 42

5. Oorgaum 21 8 22 1896 21 3 28

6. Colaba 21 7 56 1933 21 3 58

Excluding records from 1 & 5 (due to clock error), origin time ‘O’ calculated is 21 hours 3 minutes 49 seconds on 2nd July (GMT). Epicenter: From field observations it has been possible to fix the position of the epicenter of the main earthquake within narrow limits. This position, a few miles

south of Dhubri, is at 25°°°° 57′′′′ N: 90°°°° 00′′′′ E. Established on field-evidence alone, this point agrees quite well with that indicated by seismograph records. Depth of Focus: Regarding the depth of the focus, little evidence is apparent. No rapid decrease in intensity is observed in the vicinity of the epicenter, the area included within Isoseists 2 and 3 being of a varying radius of 35 to 50 miles. This might suggest a focus of very considerable depth; but the data are indeed very inconclusive. Foreshock: There appears to be no evidence of accessory shocks preceding the main Dhubri earthquake. Reports indicate that the disturbance took place suddenly after a considerable period of quiescence of seismic activity in the region. Aftershocks: During the 21½ hours that succeed the main earthquake, a total of 54 separate shocks were recorded. Almost all of these were experienced at Dhubri; a number were felt at Gauhati, while the one recorded at about 5-49 AM was felt at much greater distances from the Dhubri epicenter. On 4 and 5 July 1930, 37 and 34 shocks respectively were recorded. A large number of these appeared to have originated near the main earthquake others not registered at Dhubri suggest an origin higher up the Brahmaputra valley in the vicinity of Gauhati. After 5 July the number of aftershocks decreased very considerably from 5 shocks/day at the end if first week to 3 shocks/ day in the final week of July, 1930. This gave a total of 223 aftershocks during the month of July of which more than one-half occurred during the three days that followed the main shock. The shock that occurred about 12-37 on 11th July, 1930 was felt at such distant places as Calcutta in the south and Manipur in the east. 35 aftershocks were

15

recorded in August 1930 followed by 17 during September and only another 4 up to 2nd July 1931; a total of 294 events were recorded during the first 12 months. During the year 3rd July 1931 to 2nd July 1932 the monthly total varied usually up to 5, though in January 1932 nine shocks were reported. Several of these appear to have centered up the Brahmaputra valley to the east of the main epicenter. A fairly severe quake was experienced over a large area at about 21-36 on 24th March 1932. The total number of shocks reported during the second year was 35. In August 1932 there appears to have been a revival of seismic activity. A fairly severe shock occurred at about 11-35 on 1st August, and a still more acute one at about 10-10 on the morning of 14th. This latter shock may have originated high up the Brahmaputra valley in the vicinity of Dibrugarh or Digboi. Two less severe shocks also originating in the same locality occurred later on 14th August. The total for that month was 10. A second revival of seismic activity occurred on 10th November, 1932, when 12 minor shocks were reported from Gauhati and neighbouring stations. Others followed, principally around Gauhati, during the remainder of the month, bringing the monthly total for November up to 25. The total again fell during the next three months but rose again to nine during March 1933. During March to June 1933 majority of the aftershocks appear to have originated near the main Dhubri epicenter. Total number of aftershocks for the third year following the main disturbance was 68 almost double the number reported during the second year. REPORT CONCERNING THE LALMANIRHAT ENGINEERING DISTRICT, EASTERN BENGAL RAILWAY- Lister Jackson The earthquake was felt throughout the district. There are distinct belts, however, where its severity has been more pronounced, and where the extent of the damage has been consequently heavier. The belts more seriously affected were:

(i) Between Bonapara (25° 12′: 89° 30′) and Kaunia (25° 48′: 89° 24′) on the Santahar- Kaunia line.

(ii) Between Shampur (25° 42′: 89° 12′) and Bhutsara (25° 48′: 89° 25′) on the Parbatipur- Kaunia line.

(iii) Between Tista river and the Dharla river near Mogalhat (26° 00′: 89°

00′) on the Kaunia- Golakgang line, including Lalmanirhat colony. (iv) The Dhubri branch

(v) Between the Sankosh river near Sapatgram (26° 18′: 90° 06′) and the

Manas river near Bijni (26° 30′: 90° 42′) on the Golokganj- Amingaon line.

Between Santahar and Bonarpara piers of Bengali bridge were displaced about six inches and track thrown out of alignment. Between Bonarpara and Kaunia the track was disturbed in isolated places due to subsidence of bank, notably

between Bonarpara and Naldanga (25° 30′: 89° 30′). Masonry in several bridges cracked, accompanied by sinking of piers and abutments in many cases.

16

In the Parbatipur- Kaunia section masonry in several bridges cracked and pier sunk. Tracks buckled and kinked in many places between Tista- Lalmanirhat- Mogalhat. Masonry in culverts and bridges damaged to slight extent. Four piers at south end of Tista bridge sunk. Slips occurred in three places on the upstream guide bunds of the Sankosh bridge near Pateswari. Piers of Gangadhar bridge thrown out of alignment. Serious disturbances of bank and displacement of track occurred chiefly between Balajan and Dhubri. Masonry in culverts and bridges cracked. Piers sunk in bridges. A total of about 95 miles of track was affected in the Golokganj- Amingaon section, both by displacement and subsidence. Bridges affected include those over Hel river, Gourang bridge and several others. However none of the larger bridges such as Sankosh, Aie, Champamati, Monas and Beki suffered any damage.

17

18

19