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1. A Seismological Study of the Baluchistan (Quetta) Earthquake of May 31,

1935

K.R. Ramanathan and S.M. Mukherji (1938): Records of the Geological Survey of India,

Vol. 73, Part 4, Page 483-513

2. Preliminary Geological Report on the Baluchistan (Quetta) Earthquake of

May 31st, 1935

W.D. West (1936): Records of the Geological Survey of India, Vol. LXIX, Part 2, Page

203- 240

[Edited Transcription]

1. A Seismological Study of the Baluchistan (Quetta) Earthquake of May 31, 1935

A preliminary account of the earthquake has been published in GSI [Rec.

Geol.Surv.India, LXIX, Pt.2 (1936)] by W.D. West where he concludes “in the case of

the present earthquake there is no doubt about the position and extent of the epicenter,

since severe damage was confined to a long narrow tract, away from which the intensity

of the damage rapidly decreased. This tract extended from Baleli just NW of Quetta

through Dingar and Mastung to Mand-i-Haji and included the Shirinab valley to the west

of the Mastung-Kalat road. It is an area about 68 miles long and 16 miles wide. Within

this area there were clearly places where the intensity was greater than elsewhere, notably

Dingar and Mastung road and possibly Mand-i-Haji. Since it is well known that

earthquakes are more severely felt on alluvium than on solid rock, it is possible that the

length of the epicentral area as compared with its breadth has been enhanced to some

extent by the fact that it is parallel to the valleys of the district”. The surface crack

extended from about 30.3° N, 66.9° E to 29.7° N, 66.7° E. From the seismological

evidence, the best position for the epicenter appears to be 29.6° N, 66.5° E, slightly to

the SE of the above position, but well within the region of maximum intensity. The

origin time calculated is 30d 21h 32m 58.5s (GMT). The depth of focus could be

around 10 Km. The destructive nature of the Quetta earthquake and the fact that the long-

wave phases in the seismograms were exceptionally well-developed show that the depth

of focus of this earthquake was smaller than normal. The energy of the earthquake

calculated from different seismic observatories are; Bombay: energy of the long waves of

the earthquake greater than 3.2 x 1020

ergs; at Kodaikanal, the energy of the long waves

found to be 1.5 x 1021

ergs; from the Gottingen the value is 3.4 x 1020

. No doubt there

are considerable differences in the recorded amplitudes depending on the crustal structure

at the recording station but the above values give an approximate idea of the energy of

the earthquake; it is clear that the energy must have been of the order of 1021

ergs.

The equation connecting the maximum ground amplitude and the magnitude is

M= log a- log A0- 2.5 where M is the magnitude of the earthquake, ‘a’ is the maximum

recorded ground amplitude and A0 is a constant depending on the distance of the station

from the earthquake center, being the maximum amplitude in millimeters in the recorded

trace of a standard torsion seismometer by a shock of magnitude 0. Gutenberg and

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Richter have drawn a curve showing the relation between A0 and ∆ and we extract a table

showing this relation.

Distance in degrees ∆ log A0

1 -3.1

2.5 -4.0

5 -5.0

10 -5.8

20 -6.5

45 -7.0

100 -7.5

150 -8.0

The energy of the earthquake E being proportional to the square of the amplitude, the

relation between energy and magnitude is log E – log E0 =2M, where E0 is the energy of

an earthquake of magnitude 0.

The following table gives the recorded maximum horizontal ground movements at a few

observatories due to the Quetta earthquake and the corresponding calculated values of the

magnitude.

Station ∆

° Maximum horizontal

amplitude (µ)

M

Budapest 40.4 614 7.2

Zagreb 42.3 756 7.4

Hongkong 45.2 c.400 7.1

Barcelona 52.5 580 7.5

Kew 53.1 > 450 > 7.4

S. Fernando 59.9 250 7.1

Melbourne 99.5 157 7.2

Taking 7.3 to be the magnitude of the earthquake, its energy E is given by

Log E= 14.6 + log E0; E0 the energy of a shock of magnitude 0 is given by Gutenberg and

Richter as 107 to 10

8. Taking E0 as 10

7 ergs, E= 4.0 x 10

21 ergs.

Within three days after the main shock, nearly 20 shocks were felt in the vicinity of

Quetta. Of these, the one which occurred on June 2nd

at 9h16m33s GMT was the most

severe.

Summary: The times of arrival of the P waves from the Quetta Earthquake at different

observatories throughout the world have been analysed and the position of the epicenter

has been determined to be 29.6° N, 66.5° E, and the epicentral time to be 30d 21h 32m

58.5s (GMT). Among the prominent features of the seismograms were the gradual

increase of amplitude interrupted by larger and larger impulses and the large amplitudes

of the long waves compared with those of the preliminary, suggesting block movement

and a shallow depth of focus. An analysis of the S-P residuals using Jeffreys and Bullen’s

normal tables showed that its mean value was about +3 sec. suggesting a depth of focus

definitely less than normal depth (10km) and possibly also complex process at origin.

The energy of the earthquake is estimated to be about 1021

ergs.

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2. Preliminary Geological Report on the Baluchistan (Quetta) Earthquake of May 31st,

1935

This is a preliminary report written before all the information has come to hand. For this

reason the map which forms Plate 23 does not show the isoseismal lines in full. The

earthquake which devastated Quetta and surrounding country on May 31st, 1935, has,

from the point of view of the number of lives lost, to be accounted the most disastrous

earthquake which has visited India within historic times. The tragic irony of the disaster

lay in the fact that, although it occurred in the least populated district of India, yet it

happened to strike that area at its most populated point, thus causing great damage both to

life and property. Although the intensity within the epicentral tract was so great, the

shock was felt over a comparatively small area, probably not much more than 100,000 sq

miles. This may be compared with the figure of 370,000 for the Mach earthquake of

1931, with figures of 1,900,000 for the North Bihar earthquake of 1934, and with the

figure of 1,625,000 for the Kangra earthquake of 1905.

Intensity

Since the main damage to buildings during an earthquake is caused by the horizontal

component of the motion, it is desirable to know the intensity of this force, so that

buildings may be designed to withstand it. This force is generally taken to be proportional

to the rate of acceleration of the wave particle, which is measured in feet or millimeter

per second. Since it is rare for there to be within the area most severely affected an

instrument capable of making the measurements, Intensity scales are most commonly

used like, Rossi-Forel and Mercalli scales, not on any precise measurement of the forces

acting, but on the general way in which the earthquake affects human beings and damage

buildings. For the present earthquake although assigning an intensity of 10 on the R-F

scale to the epicentral tract, I am of the opinion that the shock only just reached that

degree of intensity, and that there may well have been places within the tract which did

not receive a shock greater than 9. The line of greatest intensity is probably closely

marked out by the remarkably straight line of fissuring in the alluvium, which extends for

nearly 70 miles along the center of the tract.

Beyond the outer broken line (plate 23) the shock was not generally perceived. The area

enclosed by this line is approximately 105,000 sq miles, which, considering the intensity

of the shock at the epicenter is unexpectedly small. The Mach earthquake of 1931 was

much less severe at the epicenter, yet it was felt over an area of 370,000 sq miles. In

places where the intensity of the shock must have been as high as 4 on the R-F scale it

was not felt by people who were asleep. Had the shock occurred during the day, it might

easily have been felt over as large an area as that in which the Mach earthquake was felt.

The two earthquakes are alike in the manner in which they extend up the Indus valley.

From this it may be concluded either that alluvium transmits a shock with greater force

than solid rock, or that the alluvium accentuates the motion of the shock when it reaches

it from the solid rock below. Whichever of these two hypotheses is correct, the fact

remains that places situated on alluvium are always more severely affected during an

earthquake than those situated on solid rock.

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Ground Motion

Motion of ground during an earthquake varies in different earthquakes, and even from

place to place in the same earthquake depending to some extent upon the nature of the

ground. In considering the nature of the motion, a distinction has to be made between two

types. In the first place there are the ‘long’ waves by which the earthquake impulse is

transmitted over the surface of the earth. In the second place there are subsidiary surface

waves which are apparently induced in soft ground by the passage of the ‘long’ waves.

The ‘long’ waves travel at about two miles a second, and have a period of about one to

one and a half seconds. It is therefore clear that such wave motion, in which the crests of

the waves are over 2 miles apart and their amplitude perhaps not more than a few inches,

would not be visible. At the same time there is a large body of evidence suggesting that

waves in the ground are definitely seen at the time of an earthquake, though it is possible

that the amplitude of these waves has been much exaggerated. These visible waves are

probably seen in soft ground and they may be subsidiary waves set up in the alluvium by

the main ‘long’ waves as they pass through the solid rock below. In the case of the Quetta

earthquake, since the shock occurred in the night, evidence regarding the nature of the

ground motion is rather confusing. It so happened however that night operations were

being conducted about 4 miles north of Quetta, and thus definite evidence regarding the

nature of movement is forthcoming.

At least five to ten seconds before the main shock started, a small tremor was felt which

was sufficiently strong to be recognized as an earthquake. In Quetta itself a sentry on

duty on top of the Ammunition depot noticed a shake which he considered to have

occurred at least half a minute before the main movement. Those who did not lie down at

once were either flung down or were just able to stagger about. The ground heaved as in a

rough sea, or in a way a small boat behaves in the wake of a larger steamer. The direction

of the waves was mainly from south to north, but occasionally from east to west. The

motion subsided gradually, fading away towards NW, accompanied by the sound of

falling rocks. In Quetta most people described the shock as a rapid horizontal shake in N-

S direction. The Yate Memorial clock tower, situated near the Quetta Club was 60 feet

high and of hexagonal cross-section, and was thus free to fall in most directions; it fell

almost due north. Generally, long buildings which were aligned in an E-W direction were

overturned sideways, whereas those aligned N-S generally remained standing with only

their end walls collapsed. Even this generalization did not hold good in all parts of

Quetta, and that movement varied from place to place. In the cemetery several marble

crosses snapped right through at the level at which they were inset into their plinths; four

monuments were found to have rotated, two clockwise to the extent of 13° and 18°, and

two anti-clockwise to the extent of 11° and 43°.

Rock Falls

When dawn came after the earthquake, it was at once noticed that the mountain sides

around Quetta were in many cases scarred by falling of immense quantities of rock.

These rock falls (mostly limestones) were most in evidence in the hills by the Brewery,

and along the whole length of the Chiltan range. On the afternoon of Sunday June 2nd

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when a severe aftershock occurred, a great number of pockets of dust were seen to arise

from the sides of Chiltan, as though it had been bombarded with shells. This dust, after

coalescing and rising some 1,500 feet above the mountain, was carried horizontally by a

current of air, the whole phenomenon remaining visible for an hour or more after the

shock. Rock falls were occurring on Chiltan as late as June 10th

and were again in

evidence at the time of the severe aftershock of July 15.

Fissuring of the Alluvium

A feature of the earthquake which aroused much interest locally was a line of fissuring in

the ground extending on and off for about 65 miles, from the south side of Chiltan to near

Kalat. Over the greater part of this distance it took the form of a crack or network of

branching cracks in the soil. These were from an inch up to eight inches wide at the top,

but closed in quickly below. Just west of Mastung, the ground on the west side of the

fissure had subsided abruptly about two and a half feet, though a little further south the

subsidence was on the east side. In some places, instead of a subsidence or a gaping

crack, the ground had been heaved up, the elevated portion being a foot or more high and

several paces wide, indicating compression of the soil. To account for these varying

phenomena, it seems likely that motion of the ground during the earthquake was one of

alternate compression and tension. Where the line of fissuring crossed the railway track

that runs from Spezand to Nushki, at about two miles west of Mastung Road station, the

track had been up-rooted and the rails crumpled along the line of the fissure. The average

direction of the fissuring by Mastung was about N15° E, so that it coincided both as

regards direction as well as position with the long axis of the epicentral zone. Particular

care was taken to find out if it affected the solid rock beneath the alluvium or was

confined entirely to the latter. Everywhere it was found that where hills intervened along

the line, the fissuring died out, though rock falls were rather numerous and evidently took

place of the fissuring along the same line. This was well seen to the NW of Mastung

Road, on the southern flanks of Chiltan. It was thus quite clear that the fissuring was a

purely surface phenomenon, affecting only the alluvium, and not penetrating the solid

rock beneath. At the same time it does seem to have coincided with the line of maximum

disturbance, though it continued a long way to the south beyond the epicentral zone.

Considerable fissuring of the alluvium was also to be seen to the northwest of Quetta. At

one place near the 11th

milestone along the Regi road, a number of fissures crossed the

road over a distance of about 230 yards. They were also prominently developed by the

Baleli village, and in many places along and parallel to the banks of the Quetta Lora,

causing considerable damage to the bridge on the Brewery road and to several bridges

near Baleli.

Mud Vents and Volcanoes

NW of Quetta there occurred a number of small mud vents which had been formed by

water spouting out of the ground and bringing up the fine silt which forms so much of the

‘pat’ of the Quetta valley. Since the earthquake occurred during the night it is not

possible to say if the water came out with any force. At dawn cold water was seen to be

welling out slowly. These vents varied from a foot up to 12 feet in diameter but were

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never mote than from six inches to a foot high. Some 12 miles south of Kalat on the main

road to Surab, about three miles east of the road near the village of Thok, large quantities

of liquid mud were observed issuing from the top of a low mound at the time of the

earthquake. This continued until about noon the next day, when it gradually died down

after an eruption lasting for nine hours. When I visited the place on June 20th

it was

evident that the mound was an old mud volcano which had burst into eruption again,

though none of the local inhabitants could recall any similar event in the past. The new

flows had spread out beyond the limits of the old, the distance between the tips of the

flows on opposite sides of the vent being just over three hundred yards. The term ‘mud

volcano’ is a misnomer since they are not thought to be connected with true volcanic

activity.

Geological Structure and Baluchistan Earthquakes

The mountains of Baluchistan are formed of comparatively simple folds, the axes of

which are parallel to the alignment of the mountains. In general the anticlines form ridges

and the synclines the valleys. In general the folds should be aligned in a NE-SW

direction. This however is not the case and instead the mountains are looped up to the

northwest between Jacodabad and Quetta. Thus the geology around Quetta is more

complicated than it is in other part of Baluchistan and the rocks have yielded here not

only by folding but also by fracture. It is therefore around this re-entrant angle that one

would expect most earthquakes to originate. On the map forming Plate 24, there are

shown the epicenters of earthquakes which have occurred in Baluchistan in the last 83

years and strong enough to damage buildings. Against the position of each epicenter is

given a serial number. These indicate the order in which the earthquakes have occurred

beginning with the Kahan earthquake of 1852. The manner in which these earthquakes

are grouped around the re-entrant is very striking. Earthquakes have also occurred

elsewhere, but their intensity has been slight, and what may be termed the danger zone of

this part of the earthquake belt of India appears to lie within a radius of about 150 miles

of Mastung.

Chaman is situated some seven miles to the west of a well marked fault, which has been

the epicenter of several earthquakes in the past. The fault is seen as a well marked

depression in the ground, which meets the main road close to the 70/2 furlong stone, near

where the shorter alternative route from the hills joins the main road, and less than half a

mile east of Old Chaman. The depression can clearly be seen running in a straight line to

the S15°W, cutting right across the surface topography. Its position is also marked out by

a long line of springs. It evidently continues for many miles to the south, ascending the

slopes of the Khwaja Amran range, and continuing on across hill and valley to near

Nushki. Col. Sir A.H. McMahon, who examined this fissure when he was demarcating

the Baluch-Afgan boundary in 1896, wrote in the Geographical Journal ‘We found that

the old greybeards of the tribes residing in the neighbourhood all know of its existence.

They told us that during their lifetime, on some three occasions after severe earthquake

shocks, deep fissures had appeared along this line, and they had had similar accounts

handed down to them by their fathers. At the time of the well known earthquake of 1892,

very clear evidence was provided of movement along this fault. According to Vredenburg

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[Baluchistan District Gazetteer, V, p.18, 1907], there is geological evidence suggesting

that the country west of this fault has subsided altogether more than a thousand feet. This

amount of movement must, of course, have taken place over a very long period of time,

but it is evident from the facts concerning the 1892 earthquake that the movement has not

yet ceased. During a short visit to Chaman, I questioned a number of the older inhabitants

with a view to finding out if there had been any serious earthquake since the one in 1892.

Several of them spoke of a fairly severe shock which occurred about thirty years ago.

This also caused movement and fissuring along the same fault line; and although it did

not damage the railway line, it cracked a number of buildings in Chaman. Since then,

there had been about a dozen little shocks of slight intensity.