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A PRELIMINARY NOTE ON THE PEGU EARTHQUAKE OF MAY 5TH 1930

Coggin Brown (1932); Records of the Geological Survey of India Vol. LXV, Part 2; Page

221-270

In an account of the Rangoon earthquakes of September and December 1927 (Rec

Geol.Surv. India LXII p.259, 1929), which were followed by further slight shocks in

January 1929, the question was asked ‘Are they the forerunners of a really disastrous

quake, or do they in themselves indicate a gradual release of pent-up forces by acting as a

kind of safety valve to growing earth pressure or strain?’ Unfortunately the first theory

has proved correct, for, at about 8-18 PM on the night of May 5th, 1930, a violent

shock occurred, which practically destroyed the town of Pegu with great loss of life,

caused many deaths and considerable damage to property in Rangoon and was

sensible to human beings, with continuously diminishing intensity, as far as the

Kyaukpyu and Mergui districts up and down the coasts of Burma respectively, as far

north as the Mongmit State in the Northern Shan States, and across the greater part of the

Southern Shan States and the Kingdom of Siam. The outer curve marking these

approximate limits passes into the Bay of Bengal, the Andaman Sea and the Gulf of

Siam, but the land area actually cannot be less than 220,000 square miles.

The earthquake was automatically registered by recording instruments at seismological

stations in every part of the world and there is little doubt that, had the epicentral area lain

in a populated tract where buildings were not of the flimsy bamboo and thatch type

prevalent in this country, its toll of destruction would have been far greater than was

actually the case.

[From page 271-278; Determination from World Records of the Zero Time and the

Epicentre of the Pegu Earthquake of May 5th 1930. S.W. Visser]

Fifty ‘P’ records give suitable results and a zero time of 13h 45m 41s GMT is derived.

The epicentral area of this earthquake was found by the Burma party of the Geological

Survey of India to be situated between longitudes 96° 30′ E and 96° 40′ E and latitudes

16° 40′ N and 17° 20′ N. From usual (S-P) method it has been impossible to locate the

epicenter satisfactorily; but by means of (P) method [explained in the paper] a position

was computed which lay exactly within the epicentral area. This position was at

longitude 96.7° E; latitude 17.2° N.

General Accounts of the Shock [p 223]

A striking feature of this earthquake was its appalling suddenness. It occurred in Pegu at

about 8-18 PM without any warning and within a few seconds a considerable portion of

the town was in ruins. Fire broke out at once and the official report gives a total death of

at least 500 and probably more. Most responsible observers agree that the quake has two

phases separated by a slight pause and that the second was the more severe. The total

duration does not appear to have been more than 30 seconds, the first phase only

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occupying between 3 and 4 seconds and the general direction of the greater shock being

NNW-SSE. The clock in the railway station stopped at 20-18.5 hrs (BST).There is no

doubt that the shock itself was accompanied by loud earth sounds, audible to most

observers. Large cracks appeared in the ground in parts of the town, from which in many

cases water and sand were extruded for some time. Portions of the river banks cracked

and slid into the stream. One witness records visible surface waves crossing a tennis

court, while the second phase was strong enough to fling people violently to the ground.

The famous Shwemawdaw Pagoda was seen to sway twice and finally fall half sliding

down its fractured base and crash southeastwards into the stalls at its foot, beneath which

many perished. The bazaar area on the north side of the Rangoon- Toungoo road

presented a picture of complete desolation in which fallen brick work, twisted iron

girders and charred woodwork lay in shapeless masses below a few burnt and leafless

trees. In the center of the town most of the buildings fell in a southeasterly direction; the

Thunpayagyi Pagoda was badly damaged. The massive minarets of the mosque were

thrown into the street. The Municipal building was perhaps the most striking ruin and a

ferro-concrete house at the eastern end of the bridge over the Pegu river was completely

wrecked. The Court House and the Office of the DC, a low, solid structure, were not

badly damaged; the Hospital and the Jail also escaped severe damage, but the Govt. High

School was practically destroyed. On the west bank of the river the damage, though

considerable, was not so great as on the eastern side. To the west of the railway the

damage was much less and it also appeared that only a short distance out of Pegu, along

the Rangoon road, the intensity of the shock must have been very much less than it was in

the center of the town. The Civil Station of Pegu lies on an inlier of Lower Delta

alluvium or of Irrawaddian rocks, which form a low ridge running north and south,

protruding through the newer alluvium that stretches for many miles on either side. This

ridge of sandy rock is lateritised and offers a much firmer foundation than the clay of the

alluvial plain. It is interesting to note that the houses on this ridge did not on the whole

suffer severely, though some of them were badly cracked.

In Rangoon over 50 persons were killed and many injured as a result of falling

masonry. People found it difficult to stand and a few were thrown to the ground. A

rumbling noise is said by some to have preceded the shock. Fire broke out and water

mains burst. There is evidence of two distinct movements, beginning with gentle tremors

from east to west and followed by north and south vibrations during the main shock.

Estimates of duration vary from 30 seconds to 1.5 minutes. The southern portion of the

city is built on alluvium and ‘made-ground’ and most of the damage was done in this area

rather than on the higher ground composed of Tertiary rocks further south. The majority

of observers describe the shock as a violent rocking motion, which caused hanging

objects to crash into walls and ceilings, overturned light furniture and threw bottles and

crockery from shelves.

In Dalla, which is opposite Rangoon on the other side of the river, the earthquake is

described as commencing with an even tremor for about 6 to 8 seconds, followed

suddenly by a second shock of much greater severity, with no pause between. The

Superintendent of the Dalla Dockyard thought that he was being thrown over a balcony

towards the north while the house appeared to be skidding about more or less from east to

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west. The Chimneys of rice mills from Kanounghto district were thrown down. In

Syriam, which lies to the east of Rangoon on the opposite side of the Pegu river, the

buildings are mostly wooden structures and the damage was not very serious. The

comparative escape of Syriam from serious damage was probably due to the fact that the

town is built on the more solid, lateritised, Irrawaddian rocks which make up the Syriam-

Kyauktan ridge, for the effects were much more serious a few miles away to the

southwest on the recent alluvium at Seikkyi and Thilwa. Some walkers were thrown to

the ground, others kept their feet with difficulty; the duration is estimated at about a

minute. Heavy almirahs were thrown over, stationary motor cars moved like boats in a

heavy sea. Water in the Kanzoung lake moved north and south; a 35.5 feet water cooling

tower in the oil refinery overturned. Beyond cracking in a few masonry buildings no

damage appears to have been caused at Insein, an industrial and residential town 10

miles NNW of Rangoon; walls and hanging objects sway in north-south direction with

overturning of a few lightly balanced objects.

The intensity of the shock appears to have died away rapidly to the north of Pegu. In

Toungoo, which is 120 miles away and the headquarters of the adjoining district, two and

three distinct phases were reported by some observers, while others describe it as a single

shock which swung hanging lamps from north to south, but was so slight that it was

unnoticed by many people. Tharrawaddy, the headquarters of the district of the same

name, 68 miles by railway to the NNW of Rangoon and 48 miles, as the crow flies,

approximately to the NW of Pegu, the whole thickness of the Pegu Yoma lying in

between. The first phase had now become little more than a gentle swaying motion of

short duration, followed after a slight pause by the severe shock, which seems to have

lasted much longer. No damage was caused; hanging objects swung in various directions,

doors rattled violently, trees swayed and birds disturbed.

Turning now to the headquarters of the district that adjoins Pegu on the east, but which is

separated from it by the Sittang river and the head of the Gulf of Martaban, we find that

in Thaton (68 miles SE of Pegu) there was one strong series of vibrations of 11 to 12

seconds duration; the populace was thoroughly alarmed and most of the residents of the

town rushed out into the streets. A few brick houses were cracked and some plaster fell.

The top of the main pagoda in the town was slanted over towards the east. Another

pagoda cracked and collapsed from its south side at a later date.

THE ISOSEISMALS [p 227]

A map (Plate 10) shows the disposition of isoseismal lines, as we have been able to

outline for this preliminary study. The Rossi- Forel scale has been used and we are of the

opinion that even within the epicentral tract, the intensity of the earthquake nowhere

exceeded degree IX of this scale, which involves partial or total destruction of some

buildings.

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Isoseismal IX

The region of maximum intensity included within isoseismal IX, measures approximately

375 square miles. It lies within the Pegu and Hanthawaddy districts and stretches in an

elongated pear-shaped area south from the town of Pegu to beyond Thongwa, in the

Hanthawaddy district, in the south, a distance of 45 miles as the crow flies, increasing

from a breadth of four miles near Pegu to a maximum of 12 miles in the south.

Pegu is situated at the extreme northern end of the above region. In addition to the effects

of the earthquake already described, many cracks appeared in the ground in and about the

town. The most striking of these was one along which the alluvium had been thrust

northwestwards against the eastern foot of the ridge on which the Civil Station stands.

Over most of the considerable length of this particular crack, the alluvium was piled up to

the height of approximately one foot. The crack was remarkably straight and crossed

several low spurs at N5°E without much deviation. Near the Thanatpin road it opened out

to a width of 2 feet and was several feet deep. The iron piping of the tube well was

involved in this movement and bent over at a depth of 54 feet. Solid concrete foundations

for a pump house alongside the tube well were tilted diagonally and turned over to the

NW. Beyond the tube well the crack deepened, turned to N15°E and split into several

subsidiary branches. To the southeast the ground was flooded owing to the blocking of

various small streams, presumably by the raising of the local ground level and perhaps

also partly on account of the eruption of water from fissures. Other cracks appeared on

the western side of the ridge. Three, which ran approximately north-south, crossed the

Thanatpin road. The largest was traceable for 350 yards, in a N4°W with a downthrow of

six inches to the east and a maximum breadth of two feet. Cracking of this kind was

evident in other parts of the town and in some places the ground between two parallel

cracks had subsided in amounts varying between a few inches and one foot. Part of the

damage caused in Pegu was undoubtedly due to this cause, particularly in the vicinity of

the river, where the downward sliding motion of cracked blocks of alluvium wrecked

both masonry and wooden structure indiscriminately.

At Onhne there are no masonry buildings and little damage was caused yet we believe

that the shock was stronger than at Pegu. The Station Master described the ‘earth as

rolling up and down and from side to side as if I were in a small boat on a rough sea’. The

cement flooring of a hut was badly cracked and raised in places and a heavy safe thrown

off its stand and flung s distance of eight feet towards E10°N. A heavy water tank was

flung from a tall iron framework on the railway line and a truck loaded with 150 bags of

rice was overturned towards the east. Many large earth fissures and sand vents appeared

around Onhne. The line between Onhne and Thongwa was badly damaged; bridges were

cracked and sheared, piers moved out of the perpendicular, abutments were sunk, and

lines displaced and twisted. At Tawa village, on the edge of the most severely affected

area, two buildings were completely destroyed and seven persons reported killed. The

upper portions of mill chimneys and pagodas were dismantled while the road to the

railway station two miles to the west was badly cracked and in places sank. At Kayan the

Court House was leveled to the ground and only a few wooden posts left standing, while

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part of the hospital completely collapsed. Except the western, other walls of the bazaar

building fell; the mosque was very badly damaged and various other masonry buildings

were shattered. The death toll was variously reported as 12 and 16. Cracks opened in

the ground and reached a width of two feet seven inches in one place with a depth of six

feet. Water extruded from the crack caused flooding in the vicinity. Water and sand

spouted from various vents, for some time after the earthquake in sufficient quantities to

cover roads and fill small reservoirs. The floor of the Thongwa railway station building

was cracked and platform fissured. At 93 mile fissures one foot across opened up in the

embankment. The wing walls of the railway bridge in the vicinity were cracked from top

to bottom. Abutments sank and moved out of position and in places the line itself had

been dropped. In Thongwa town eight out of a total of eleven masonry buildings were

rent and some of them collapsed into heaps of debris. The posts of certain wooden

buildings were smashed and pushed out of position while several timber houses sank on

their foundations. In the surrounding area numerous sand vents opened up and several

block fissures were formed, people were thrown to the ground and heavy almirahs and

most smaller objects were overturned.

Isoseismal VIII

The area enclosed within the curve approximates 700 square miles and encloses part of

townships of Kyauktan, Thongwa, Kayan and Kawa in the Hanthawaddy district and

small portions of the Thanatpin and Pegu townships of the Pegu district in the north. At

Kyauktan a few houses partially collapsed while many were damaged. The ‘hti’ of the

Minkyaung Pagoda bent towards the NE and both it and other pagodas were cracked.

Most moveable objects in houses were overturned and appear to have fallen either to the

north or south. The hospital compound was traversed by many earth cracks. Heavy

almirahs in the hospital and the police station were flung to the ground. In Pandaw,

Kyaubin and Ywathit villages to the east of Kyauktan, ground is reported to have slipped

into the river, walls of houses to have collapsed, sand vents and earth fissures to have

been formed and loose objects to have been thrown over. In Kawa the shock commenced

with a tremor lasting about two seconds and was followed almost immediately by a

severe shock which seemed to last a minute. A brick house fell and killed one woman.

The ‘hti’ of the main pagoda was bent and the head of one large image fell off. A number

of almirahs tumbled over in the hospital and the police station was slightly cracked.

Large fissures appeared in the silt on the north bank of the river and sixteen cracks

crossed the road between Kawa and Tongyi. While Tawa village undoubtedly

experienced a higher intensity, at Tawa railway station, two miles to the west, crockery

fell and lamps thrown over but almirahs did not move. Cracks appeared in the Chetty,s

temple and other brick and plaster houses were cracked. The top of the pagoda near the

station fell due east. Part of the Pegu-Thongwa railway line crosses the area enclosed

within this isoseist. At Kamase and Yitkan there was no damage, but bottles, glasses and

small almirahs were overturned. The main railway line from Rangoon to Mandalay enters

isoseismal area VIII at Tongyi, 30 miles NE of Rangoon. Here the main station building

was pushed 5° from the vertical towards NW. Payagyi, a village on the main line 10

miles north of Pegu, appears to mark the approximate limit of the VIIIth isoseist in this

direction. Here a large pagoda and two houses collapsed. The station building was

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slightly inclined from the vertical and a stationary train was moved a few feet. Almirahs

were tumbled over and the railway embankment slightly cracked.

Isoseismal VI- VII

It includes the southern portion of the Toungoo district with a long tongue running north

as far as the hill station of Thandaung. Following the general trend of the western edge of

the Pegu Yomas it swells out in the south to include, after crossing the Rangoon river, the

whole of the southern part of Hanthawaddy, a portion of Maubin and the greater part of

the Pyapon districts. On the east it enters the very sparsely inhabited and densely wooded

hills of the Papum district in the Salween valley. In the south it includes the greater part

of Thaton district and a small portion of northern Amherst.

At first sight and judging alone from the damage caused in the flatter portions of the

Rangoon town it might be imagined that an intensity of VIII had been reached here.

Remembering however that in the suburbs and particularly on the ridge practically no

damage of any consequence was caused- an area in which the intensity of the shock

cannot be placed higher than degrees VI to VII- we are led to conclude that the intensity

in the city itself was not more than VII, but that its effects were naturally augmented both

by the alluvium and ‘made- ground’ on which this portion is built, and by the poor

construction of the buildings which did collapse. Several buildings collapsed bodily,

burying the inmates in their ruins, the worst case being in China Street where a five

storied pucca building crumbled inwards. The roof and walling of a three storied house at

the corner of Mogul and Fraser Streets collapsed, and a similar fate befell another at the

corner of Dalhousie and Sparks Streets. A portion of the roof and cross walls of the

Young Women’s Christian Association building fell. Several buildings were so

extensively fissured that they were rendered unfit for habitation. Amongst the

Government buildings the Secretariat fared the worst. No. 230, Dalhousie Street, which

houses the Burma Party of the Geological Survey of India, suffered severely. The

walls were cracked in many places; part of the ornamental parapet fell; bricks fell from

the inside walls; heavy library almirahs were thrown over and smashed, while bottles in

the laboratory and museum suffered severely. The General Post office was cracked at

many places; various buildings belonging to the Corporation of Rangoon received minor

injuries. The General Office of the Burma Railway in Montgomery Street sustained

cracked arches and a wall was pushed slightly out of plumb. None of the jetties of the

Port Trust were affected except two pontoon bridges which were wrenched from their

sockets at the shore end and dropped into the river. Several sheds were badly damaged by

the cracking of walls. Many brick chimneys of mills in the Pazundaung and adjoining

areas crashed to the ground. The jeweled ‘hti’ of the Shwedagon Pagoda was dislodged

and left dangling from its summit. The ‘hti’ of the Sule Pagoda, where the damage caused

by the 1928 quakes had barely been mended, was again bent over.

[At the northern end of the area] Railway stations along the main line north of Payagyi,

such as Paungdawthi, Daiku and Pyuntaza experienced the higher intensity of VII. In

Paungdawthi bricks fell from the walls of the police station and a pagoda collapsed. The

brick work of a well sank and the well became dry. Slight cracks appeared in a road and

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almirahs fell towards east. In Daiku the Court House partially collapsed. In Pyuntaza,

further north still, the intensity seems to have been diminishing as pagodas did not fall

and only a single masonry building was cracked. In Pyu [the scene of a disastrous quake

on 4th

December 1930] the only damage caused seems to have been to crockery. The hill

station of Thandaung appears to be near the limit of this isoseist in the northern direction.

[In the eastern part of the area] at Thanatpin, two distinct tremors were felt, houses

were cracked and the top five feet of a 45 feet chimney shaken off. At Waw, the mosque

was cracked and almirahs were overturned. At Okpo the quake was described as three

large shocks and a pagoda on the Thaton side of the Sittang was thrown down. East of

Sittang river at Pa-an township three separate shocks are reported strong enough to crack

some buildings slightly and to cause lamps to swing in a north-south direction. From

Zingyaik and Mokpalin total duration of shock reported to be 1 to 1.5 minutes in NE-SW

direction. Small objects fell and three pucca buildings were cracked. In Moulmein two

distinct shocks were noticed which caused trival damage to brick buildings and general

alarm to persons walking or at rest. In the Chaungzon township, which lies to the

southeast of Moulmein, the ‘this’ of pagodas at Myitmodaung and Payagyigone were

bent towards the east, while small cracks appeared in their bases. Mudon reported the

shock as slight, while in Amherst two distinct phases are recorded causing hanging lamps

to swing, floor and beams of wooden houses to creak and some clocks to stop.

[The southern portion] West of the Rangoon river this isoseist includes the townships of

Twante and Kungyangon North and South. The shock caused general panic in them all

and was very distinctly felt as a noticeable to and fro movement. Lamps and photographs

hanging on wall were thrown down while in Kungyangon South one side of a masonry

pongyi kyaung collapsed. This isoseist includes the southeastern portion of the Ma-u-bin

district. All reports from the town agree that the shock had two distinct phases. It caused

hanging objects to swing in N-S dirction and slightly cracked the veranda of the District

Council Office and walls of DC’s office. The earthquake was felt throughout the whole

of the Pyapon district. The Bogale Township reported freedom from damage. At Pyapon

plaster fell from the hospital walls; while in Kyaiklat extensive cracks appeared in the

arches and masonry floor of the SDO’s house. In the Dispensary many cracks were made

over arches and in walls while masonry floors and one ceiling gave way. No damage

occurred in Dedaye though people outdoors had great difficulty in standing and various

loose objects overturned.

Acceleration of the Wave Particle

Using West’s formula for determining the acceleration of the wave particle and the

measurements of certain more or less suitable objects which were overthrown in Pegu,

Kayan, Ohnne, Tawa and Thanatpin, Mr Leicester has deduced the following results:

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f Place and Object

ft/sec2

mm/ sec2

Remarks

Pegu, gate pillars 7.0 2130 (IX-X)

Kayan, gate pillars 6.95 2120 (IX-X)

Onhne, loded

railway wagons*

10.45 3180 (X)

Tawa, factory

chimney

5.92 1800 (VIII-IX)

Thanatpin, factory

chimney

4.03 1230 (VIII)

The Roman figures refer to the

corresponding degree of

intensity on the Rossi-Forel

Scale

* Rather doubtful on account of

the springs.

Special Surface effects of the Earthquake [page 251]

Changes of level: It was reported that the Tawa lock of the Pegu- Sittang canal together

with the adjoining country had been raised by 0.77 feet. This was first noticed on the day

following the earthquake by comparison of the canal gauge readings at Tawa lock,

Kyaukpadaung and Pagannyaungbin. A circuit of levels was run from Tawa to Thanatpin

and Thanatpin to Pegu and these showed that the Tawa lock and the surrounding area had

been raised by 0.77 of a foot. No damage was caused to the lock itself and the guage,

which is fixed to the masonry, did not change its relative position. The whole movement

thus appears to have been rather a wide spread bodily uplift. Re-leveling operation

carried out within the limits of the Port of Rangoon revealed a settlement of the ground

amounting to an average of about 0.1 foot on the line of levels between Graham Smith’s

Bench Mark and Monkey point, though all the bench marks were equally affected.

Earth-fissures: In addition to those already described (page 5, 1st para) several block

fissures were observed near Thongwa. Near the headmen’s house four parallel ones

within a distance of 20 feet, extended north and south for about 200 feet. Two of them

were over three feet wide with subsidence of a foot in the center or at the side. Twelve

feet away from the fissures were numerous sand vents which erupted water and sand for

three days. Near the Okkanwa bridge, on the left bank of the Takaw chaung, numerous

parallel, long and wide fissures were visible. One end of the bridge had subsided by about

a foot. In Okkan village, fissures from four to five feet in width, trending ENE-WSW

were formed. The extrusion of sand and water from them caused several wooden houses

in the vicinity to subside, and in one case to leave some of the posts dangling in the air.

One large fissure traceable for a quarter of a mile near the bank of the Okkan chaung was

ten feet wide in places and its bottom could not be reached by a 20 feet long bamboo.

Near its northern termination one side was three feet higher than the other. The roads in

Thongwa town, metalled with laterite, were traversed by longitudinal, transverse and

diagonal cracks. South of Thongwa near Nyaunglebin village, several block fissures up to

six to eight feet wide and about 150 yards in length ran parallel to the bank of the

Hmawun chaung. Sometimes they bifurcated and in one case a scarp two feet high had

been formed. Both the fissures and the smaller cracks followed this tidal stream. Many

sand vents had opened up in the vicinity.

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Sand vents and sand sloughs: Sand vents were a common occurrence within the

epicentral tract and especially so in the vicinity of Thongwa. In some cases regular

craterlets with a circular hole through which water and sand issued were seen; in others

the central crater was missing and small circular patches of sand had formed. Sand vents

also occurred within the deltaic portion of the affected area. ENE of Thayetkwin a large

sand blow measuring 48 by 42 feet seen. On the Thabyegan- Thongwa road sand vents

extended from 18th

mile at least as far as Thongwa. Between the village of Tinegwin and

the Pegu river, there were many NW-SE trending large and small cracks developed from

which water squirted for two hours after the eruption, forming elongated heaps of sand 15

to 36 inches high. Near the western bank of Pegu river, 1 mile south of Thayetpingaung,

50 to 60 such cracks observed with pile of sand extruded from these. Longer cracks were

about 70 yards long, zigzagged or wavy in detail though maintaining the overall NW-SE

trend, with tons of sand spread about the surrounding country. Mud and water spouted to

a height of 18-20 feet, like a fountain at the time of the earthquake and next day morning

the spout was 1.5 feet high and oozing continued for almost 17 hours after the

earthquake. On the eastern bank of Pegu river an even greater area was affected and

larger volume of sand ejected. Near Thabyegon village a 60feet square dry tank with a 10

feet deep well at its center spouted water to fill the tank South of Thongwa, the rice

fields around Nyaunglebin, Eikthaya and Sawechaung all bore evidence of similar events.

Effects on Water Supplies: Wells and tanks throughout the epicentral tract were

affected almost universally. In most cases the water levels appear to have risen soon after

the shock and then to have fallen, to lower levels than usual, later. In some instances

large quantities of silt were deposited in both tanks and wells. Of the five big tanks in

Thongwa, at the time of the earthquake, four were dry and the other contained a little

water. After the shock the latter overflowed its banks while the others filled up. Water in

a well of the Kangyi Kgyaung near Thabyegon was found to have risen six feet after the

shock, but it fell again the next morning.

Effects on Ships: A.S. Oxfordshire which was lying in Rangoon Harbour, felt a big bump

at the time of the earthquake as if the vessel’s moorings had given away. The whole ship

seemed to be lifted bodily 3 or 4 feet, once or twice, with jerky fore and aft movements.

The Commander of the S.S. Queda, whose ship was lying in ballast at No. 3 Strand fixed

moorings, stated that the vessel vibrated slightly at first and that the vibrations increased

in intensity for about 45 seconds. The S.S. Ekma was lying at Latter Street Wharf. Her

first movement was a violent roll to the port (northwards); at the same time the vessel

was thrown heavily against the wharf. She then surged along the jetty westwards with

such force that eight 1.5 inch bolts holding down a mooring lead were sheared in half.

The recoil was less violent. It is to be noted that in spite of these occurrences the tidal

gauge record for the day showed nothing abnormal according to authorities in

Dehra Dun. The pilot Vessel, which was at her station at the mouth of the Rangoon

river, reported that severe vibrations were experienced although the ship was in deep

water. The outward bound City of Carlisle heading roughly SSW with about 5 feet of

water under the ship, felt the vessel ‘buck’ as long and loaded ships often do when

approaching or leaving shoal water. This was followed by a hard bump as if the vessel

had struck something; she trembled and then proceeded normally. Oil- tanker S.S. Beme,

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drawing about 24 feet, felt severe vibrations although in deep water. Kyokai Maru, in

light draft, passing over Choki Shoal with six feet or more of water under the ship felt as

if the vessel was receiving several hard knocks underneath.

Aftershocks [page 257]

Confining attention to the Pegu and Toungoo districts, it is apparent that places in the

epicentral tract such as Pegu, Onhne and Kawa had their fair share of aftershocks

following the great earthquake of May 5th

, the most active center of seismic disturbances

since then has lain somewhere in the vicinity of Pado (18° 02′ N: 96° 36′ E). This place

lies 48 miles north of Pegu and some four miles east of the steep flank of the Pegu Yoma

as it arises from the plain. Pado probably fell within isoseist line No VI of the Pegu

earthquake, but the latter was sufficient to develop those strains in the line of weakness

that lies to the west of Pado and caused small earthquakes since. The aftershocks reported

from Penwegon, Kyauktaga and Nyaunglebin probably had a similar origin. The shock

which took place about 5-30 p.m. on September 16th

and cracked the brick walls of the

police station in Pado, was experienced at least as far south as Pegu, to the east in

Myitkyo on the Sittang river and to the southeast in Yitkangale of Thanatpin township,

14 miles in that direction from Pegu itself. On 3rd

and 4th

December the activity was

transferred some 30 miles further north again, along the same line of weakness to the Pyu

region and caused disaster there, but earth movements have been renewed in the Pado

neighbourhood since then.

General Conditions and their bearing on the cause of the Earthquake

With the exception of a low ridge of lateritised Upper Tertiary rocks at Pegu, the whole

of the epicentral tract forms part of a wide alluvial plain bounded on the east and south by

the estuary of the Sittang river and the Gulf of Martaban and on the west by the Rangoon

and Pegu rivers. It consists of low deltaic lands built up by tidal accretions from the Gulf

of Martaban and the Sittang estuary. South of the Pegu-Sittang Canal the total area of this

plain is roughly 1800 sq miles, while 340 sq miles of cultivable lands in it are subject to

flooding (surveyed by A.J. Clark completed in 1926). This figure does not include the

new lands on the east and south now in the process of formation and at present covered

with tidal forest. The epicentral tract covers 364 sq miles in a long pear-shaped enclosure

through the middle of this plain. Within this plain there are six separate areas which

owing to their relatively low levels are liable to severe and periodical flooding. Plate 11

shows the disposition of the flooded areas with reference to the two innermost isoseismal

lines, from which it will be seen that with the exception of the greater part of the Yitangyi

and the adjoining Kokko area in the northeast, they are all practically enclosed within

these isoseismals. The mouth of Sittang river has been moving eastwards. The river has

eroded large tracts of paddy land in Thaton district on its eastern bank which have helped

to build up accretions to the Pegu plain extending over 20 miles east of Onhne, as can be

seen from the diagrams on Plate 12 incorporating the shore lines of 1893 and 1926.

The raised beaches of the Arakan coast high above present tide limits, point to an

elevation of the land in recent times. The older alluvial clay of the Irrawaddy delta is

11

believed to be of estuarine or marine origin gradually elevated to its present position from

sea level. Recent investigations in connection with the water supply of Rangoon have led

to the belief that the peculiar physiographical character of streams flowing from the

termination of the Pegu Yomas are probably due to uplift of the land. The minor

earthquakes which disturbed the city in September and December 1927 and again in

January 1929, could be due to forces of uplift causing movement along lines of weakness

below the deltaic alluvium. In the elevation of the Tawa lock and the surrounding country

during the Pegu earthquake there is positive proof of a slight elevation change.

The Pegu earthquake, quite apart from its usual and normal series of small aftershocks,

cannot be dissociated from others which belong to the series of which it is a member. On

8th August 1929, a very severe but local shock occurred which seems to have had its

epicenter a few miles west of Swa in the Toungoo district. Here a private meter- gauge

railway was severly damaged. In places the track was twisted and bent, fishplates and

bolts were snapped, bridges and culverts collapsed, the sides of cuttings fell in, loaded

trucks turned over and coolie lines were shaken to pieces. This earthquake was reported

from Yamethin, Pyinmana, Yenangyaung and Tharrawaddy. For some time after the

Pegu earthquake the main center of seismic activity moved into the neighbourhood of

Pado [18°02′ N and 96°36′ E], 48 miles north of Pegu and close to the steep eastern flank

of the Pegu Yoma. Here 13 separate earthquakes, mainly of slight intensity, were

recorded in the six months from July to December 1930. A smarter shock on September

16th

cracked the walls of the police station in Pado and was felt over an area extending at

least 60 miles to the southeast.

A series of violent shocks on December 3rd

and 4th

, 1930, the severest of which occurred

about 1-22 AM on 4th, wrecked the masonry buildings in the town of Pyu and caused

about 30 deaths. An examination of the ground has led to the conclusion that the

epicenter of the Pyu quake lies a few miles to the west of that place, where the edge of

the Pegu Yomas rises in a wall- like escarpment to a maximum height of over 1700 feet

above sea level from the alluvial plains of the Sittang. A local railway line crossing this

tract was badly damaged and exhibited twisting of rails and displacement of

embankments similar to those caused by the Swa shock in its area. Loases trucks were

overturned in Pyu station and along the line to the west, cracks in the ground and sand

vents, the wrecking of a timber house and the destruction of flimsy huts, which usually

escape damage, again betokened a high degree of intensity.

A straight line passing through the epicenters of the Swa and Pyu earthquakes and

continued to the south crosses the Pado area and passes approximately through the center

of the most disturbed region of the Pegu quake. It is parallel more or less to the outer

eastern boundary of the Tertiary rocks and to the main trend line of the Pegu Yomas, a

direction of about 10° east of south. It seems to follow closely the foot of the well-

marked ridge containing the peaks Pondaung (1505 ft), Khengdan (1754 ft),

Myayabengkyo (1408 ft) and others on the west of the Sittang plain. This linear

arrangement of the epicenters of so many earthquakes cannot be accidental and it is

necessary to seek for its cause.

12

On the other side of the Sittang valley, the steep edge of the Karen hills and the Shan

plateau rises and it has long been held that the junction between the Tertiary and the

crystalline rocks is marked by a great boundary fault. T.D. La Touche wrote [Geology of

the Northern Shan States, Mem Geol Surv Ind XXXIX, 1913; p. 352]- It is observed that

these rocks were brought to the surface in upper Tertiary times, since on the western side

they are in continuous contact with sandstones of that age. In fact it is evident that the

whole length of the western edge of the Shan plateau is a fault scarp, due to a great fault.

The faulted junction of the Tertiaries with the crystallines further north still in the

Shwebo district has been mapped recently by V.P. Sondhi. In the area with which we are

dealing, however, we do not know where this junction lies below the alluvium, but it is

not without significance that crystalline rocks crop out through it some two miles east of

Sittang near Toungoo, and there is every probability that some somewhere below the

deep alluvium of the Pegu-Sittang plain the faulted junction of the two diverse geological

systems continues. Whether movements of the outer boundary fault or faults are causing

the earthquakes or whether they are the result of the growth of associated smaller faults

within the Tertiary rocks themselves, further to the west, has still to be provided. The

great escarpment of the Shan plateau including the Karen hills is one of the major

structural features of the Burmo-Malayan region. It forms a complete break where the

Tertiary rocks of the Irrawaddy and Sittang valleys finish abruptly and give place to an

entirely different series of strata which stretches across the Shan States and far into the

Chinese Provinces.

It is concluded therefore that the Pegu earthquake and its associates are of geotectonic

origin; that sufficient external evidence is available to suspect their origin in the growth

of a fault or faults which lie in an instable region at the foot of the Shan plateau and either

under the alluvium of the Sittang valley or close to it, in the Tertiary strata which form its

border on the west in Toungoo and northern Pegu; that this instable zone continues south

of Pegu beneath the alluvium of the Pegu-Sittang plain; that the linear arrangement of the

epicenters of the Pegu, Pado, Pyu and Swa earthquakes supplies additional internal

evidence which turns suspicion into practical certainty, and, finally that although the

present series of movements commenced in what may be termed the central portion of

this zone of weakness, their later and more violent extension further south, which resilted

the Pegu earthquake, may have been in some way accelerated by increasing strains

demanding isostatic readjustment, consequent on the rapid growth of the delta into the

Gulf of Martaban.