Dc0.19.X.126 500

DEPARTMET{T ., U{DIA UETEOROLOCICAI,

SCIENTIFIC NOTES VoI. X' l{o. 125

-\

!

of the28thNovember TheMekranEarthquake 1945 -s.i

BY G. G. PENDSE ;

@eeidn qn TihOadct 19/f4

*

' '-\/ .

PBINTED IN INDIA n'OR,TEE MANAGEB GOYERINMEr{TOX'INDIA:POBLICATION! BRANCE DDI,EI DY TEE MANAGE! GOY&RNMEIS-OB INDIA PBESS srMLA, 1948.

':

Piie: Ae.-!10!-qr Tehr

1i

Nuusrp. 125.

(YolumeX.)

55.034(54)

1145. EARTESUAKEOF THE 28thNOVEMBER TEE MEKR.AN DI

C. G. PE}{DSE (Recebed 1946\ on TthOctober ,4bstrac!.-This l{oto contains an account of the great }Iekran Earthquake of the 2Eth Novernber 1915. The seismic history of the area is outlined andlhe availa ble eeisrnometricdata are sunmarised. ',he The magnibude and the energy of the earthquake are calculated and ii, is found that, so far as gre:rt rvith other in comparison this'Larthquake particularlv concerned, is not important nagnitride is earihquakes. Tho important feature of this earthquake is the seismic searvave asscrciatedrvith it' The svailable information regarding tire effects of tlre seawave has been summarised. The isoseismal lines for the e rrthquake, based on field repcrts, are shown in a nap and inferences are drarvn from them. Additionrl information, especieily about the tn'o islets reportcd to have been throrrn up by tho earthquako, is given.

Introrluctisn. The object of this Note, which consists of six sections,is to give a brief account of thc eartlquake of 1945Novcmber 28 which, rvithits epicentreunderseanearthe M^kran Coast, was ettend(d by a disastrorisseismics{a wave. Seclionl givcs a sketch of the earthquake history of the region over which it was felt. Scction 2 gives a summary of ihe available seismometric information. Scction3 gives the seismopotric estimate of the ma,gnitudeand energy of the earthquake. Section 4 contains a map showing the isoseismalliues for the earthquake ancll he concl'.rsiotis drawn from it. Seciion 5 contains an account of the seismic sea wave mentioned. above. In s€ction 6 is given somc additional information regardingthe shock. L. The Beisnoichistory of tho area of the Mekran earthquake.-The earthquako which shook the Mtkran Coast, Baluchistan, Sind and partE of the Punjab in the early hours of the morning of the 28th November 1945was by no mcans a rare event for that portion of the globe. Earthquakes have been known to occur in that ar€a in thc past, and we mention below some important ones. l8l9 1892 1909 193I 1935

June 16 December 20 October 2l August 27 I\Iay 31

Cutch. Cheman, Boluchistan. Balucbistan (Kachhi), trIach, Baluchistan. Quetta.

During the lrst few years there havebeen some earthquakeshaving epicentresnear the Mckran Coast and Karachi. Some of tbem are listed below :Time (G.I[.T.) 1938 Februtr.ry 4 . 00h. 19.0m. l93S September 2 20L.29.0m. 1940 January 7 .. 00h. I '9m. l94l October 29 l3h. l3m. 1 9 4 2J u l v 3 .

Epicentre 25 '5' N., 63.5' D.

Ormara.

02h. 50m.30s. l942July4 . 0 8 h . 4 6 r n .2 0 s . 1943 February 6 02b, 35c. 46e,

. .

lllekran Coast

26'0' N., 63.0'E. 26'6" N., 63.50E. 24.5" N., 65.5e E. N e a r 25o N.. 07' E. 24.2o N., 62'6"E.

I41

,..\

il"JA('/.\\ i'l,tJ,> ,z

.--, ^ L.;

.=i ..',1 '. : ' . . r"' 7- "

-'f--,-.'i a" l , at _ -
.i/

t,.,2

Near Mekran Coast. Bairichistan. Felt at Karachi. SalucListan. N c a r I ' a s nj .

142

O. G. PENDSE

An increasein the seismicactivity in this regionis noficoablein recentyea?s, eince,accordingto the InternationalSeisrnological Summary,thareateonly abouthalf a dozenearthquakeswith epicentresin this area,for the period1913-34. This relative increasecannotand shouldnot, however,be usedto makea forecastof the earthquakeactivity in the regionin the comingyears. 2. A summary of the available seismomehictlats.-The earthquake of the 28th throughoutihe world, November 1945was, as recorded. by the seismographs oneof greatintensity. It is notpossibleto locatethedifferentphasesoftheearthquakein the availableInilian scismograms ; in the caseof plotographicrecordsof the traceswere invisiblefor sometime after the first imMilne-Shawseismographs, pulse; in the caseof mechanicallyregisteringseismogrnphs, the motionsweresolarge and rapid that the onsetscould not be marked with certaini:yand accuracy.The epicentreand the origin time of the earihquakehavebeend.eterminedfrom the times of the onsetsof thc P-nhascat the different etations. The data ere summarisedbeIow:Time of commoncoment

Station

(G.I\t.T.)

Bombav

iF*:= Sit Zii:33#:l3J:

New Delhi Calcutta Uyalrrfna (Deccan) Kodaikanal

27d. 2lh. 59m. 64s. iP; iPp : 27d. 2lh. 59m. 56s, : 27d. 22h. 02m.00s. iP6 iPx : 27d. 22h.00m. 3le.

::

iPE

:

27d. 22h.01n.

v

mu-@a' , ? o : 0 . 8 s e c s .D, - 0 . 8 . To ,4 givesthe amplitude(in millimetres)of the tracerecordedat the stationby a stand(a seismometer ard torsionseism.ometer havins the constantsprescribedabove)corre_sponding t 9A' . M (themagnitudeof the earthquake)wastheil calculatedby means of the formula M - log A--7og A", wherelog ,4oclependsonlyon [ (theepicentralciistance of the recordingstation). A comprehensive discussion ofthequestionofthemagnitudeandenergyof eerthquakes is givenin s"ction V of B. Gutenbergand C. tr'. Richter's paper(' On Seisnric \Vaves(Third Paper)", GerlandsBeitriigezur Geophvsik,vol. 47, pp. ?8-131, 1936;anclthevalu oe flogA"correspondingtoanausignedvalueofIcanbercacoff froru Fig, 6 on p. I20 of the-paper. w h e r e7 : 2 8 0 0 , u : ' 1

rrhere t authors Thr Stc Bombav New Dblb

IIer E

Thu the energ their esti are appr D l93i 1932 r934 1934 1934 1934

l9s.

Origintime : 27d.21h. 56m.40s.G.M.T. Epicentre: 24'2oN.,62'6oE. The epicentreis und.erseanearthe l\fckran Coastand is about 76 milesawayfrom Pasni. 8. Ihe nag[itutle enal energy of the earthquake.-X'rom the availablo the Milne-Shawnorth-southcomponentseismogralnsof Bombay and seismograms, New Dclhi wereuseful. The following method for calculatingthe magnitude of the earthquakewas used for the data of eachstation. A' (the maximum amplitude of the record.edtrace in millimetres)and ? (the corweremeasuredfrom the seisrespondingperiodof the groundmov,ment in seconds) nrogram. a (the true ground displecenentin microns correspondingto zt') was computed(usingthe appropriatedynamicmagnificationfactor). Then the values of o and ? were substituted in the equation

r-

Af the ene

tr'or1

asregards material1 1905 l9l 2 r9l2 1922 1923 1933 1934, 1935:

It is sr past,the Il tude is cor associatcd fn con this earthq \Pave.

4. Ihe tant from .l Khan and tr to the earth tr'rom t

(1)r than alon

(2) T the north.

-_

it I

t I tI

143

TtE TTEKRAN E-IRTdQU-{KE ori TEE 28rir NoveMi}en1945.

t I

eent yeafS, ,abouthaH This relaf the earthrf the 28th ; ihe world, rfthc earthc recorcls of bhe first im' vere so large ;curacy. The lm the timos rmarised be'

i

After calculating.ll,/for botht.l:esta;rions takingthe averageoi the two values arLcl the eneigyof the earthquakewas calculaiedby mcans'ofthe foi'irula E - B^ lgztt wherethe value of .Bo has been empiricailv taken to be 108 ergsby the above authors. The resultsof the calculationsare given in the followingtable :Station.

A'T

Bombay New nehi

mm.

8ec.

95 100

l8 28

a It 960 2220

Hence E

LogA A tnm. 5.3 0.72 6.1 0.71 Itlean value of if

rogAo 4 n.0 -5.9 13.9 -6.0 :6.65

M 6'6 6.7

6'!l X l0' X erqs x l0r3.t ergs l 0 2 I ' s ergs.

=108

-l0r E

Thus the estimateof the magnitudeofthe earthquakeis about 6.7 and that for the.energyof the order of l02r e-rgs. From Gutenbirgend Richter's tables giving their estimatesof selectedshocks, w-efind the followingeirthquakeswhosemagniludei are approximately6.7, i.e.,the magnitudeof the Mrktan darthquake. Dato

le32ruly 12 E. The ePi' rom Pasni. :he availablo iBombaYand uake wasuseal anil f (tl',ecorI fromthe seising to zi') was nen the values

e1#""?Hlt1,:,"i"

1932 December 7 .. 1934 January 28 l934May4 . 1934 July 28 1934 November 30

Mexico Mexico Alaska Alaska Mexico

tr'or-purposes of comparisonof the earthqua,ke with others unclerconsicleration asregardsmagnit_udo, { hefollowingIist of a fevselcctedearthquakes is givenfrornthe materialprovidedby Gutenber!and Richter. Date 1905 April 4 l9l2 May 23 l 9 l 2 A u g u s tI 1 9 2 2N o v e m b e lrl 1923SeptemberI 1933March 2 1934Januarv 15 1935 ryro rvray Mav iru May 3d

, .. ., .. .

., ..

Dpicentre in Kangra, India . Burma.

Magnitude 7t 8

Turkcy Chilo. Japan .

8'4 I'l

Baluchistan(euetta)

8.3 8.2 7.7

I! is 1e_e1, therefore,tbat in comparisonwith promincn largeeartbquakesof the

past, f,ne pas!, the lvlekr8.n earl,bquake was Mekra.n earthquake w.s not n-ot particularly particular^ly important i so far as its magnitude is cedcerned. Itslmporta.nce and-intrrest are due to the seismic suu, *irr"

,tion by a stancl' ibed above)corrulateilby means Jingstation). A ryoI earthquakes ilber " On Seis4?. pp. ?3-131, n caiitu read off

associatcdwith it. fn contrastwith the Quettaearthquake,which caus'd gpeatdestructionlocally, this earthquake,by itself, did little damag"i th. damagerris due to the seismicsea wave. 4. rhe area afiectealby the eartlquake.- The places in rnclia most clisftoq t_heepicentrewherethe carihquakewas exieriencedwere Dera Ismail $,nt Khan and lHontgomer-y.The distributionof the intensiiy of t be groundmotion due to the earthquakeis shownin the accompanying map showingthi isoseismallines. x'rom the ellipticalisoseismal lines,we can draw the followingconclusions:(t) The intensityof the shockfalls off much lessrapidly alongthe major axis than along the minor a,xis. (2) The main directionof the distribution of the shockis almostparallel tc the north-eastthrough the epicentre.

t++

G.

PE}IDSE

(3) The are_as in squaremrlesfor the different intensitiescanbe approxinately indicatedas follows* :Intensity

(R,ossi-Forel Soale)

Area (Thousand square miles) 11.5

2l-5 OJ

oc

88 440

(Inmakingtheabove

esr,inates of the areas the following assumption has been

The portions of the isoseismallines in the resion under sea are such that the complete isoseismalsare symmetrical about the iorth-west direction tLroueh the poinl 24'3"N.,63o8., which is approximately at the centre of the system of iioseismals.) 5. The sea wave associatetl with the earthquake.-Level changes of as much as 50 feet have beenrecordedin connectionwith fault movements caus]insearthquakes. Sea waves are produced whenever such changes, or extensive landslides, occur in thc sea bed. Owing to thcir association, in m.,st cases,with earthquakes, these waves are called seismicsea waves or " Tunamis " and, popularly thoug-herroneously, Tidal Waves. Not all land earthquakes are accompaniedby surface fault moverrents. Similarly, n_ot-ellsubm.arineshocks are accompaniedby changesin the level of the sea bed and the resuli'ing seismic se& waves. Actually, it is found that the number of submarine earthquakes, which causc destructive sea .wavesis very small. The earthquake in question was attended by a seismic sea wave which affected the whole of ihe Arabian sea-board. Karwar, aLout 1,t00 miles away from the epicentre, was the most distant place of which the'tidal'w.ave was relor{ ed to h#e produced tangible effects. At Karwar, the wave floodedthe creeks ind inlets, and boats anchorid in the hcrbour were cut off from their nr.oorings,though no ilamago was done. The availabLeinformation regarding the wave is summarised below. furelcranCoesr.-Pasni,-an important trading centre along the Mrkran Coasb and disiani about 75 m :lesfrom th,: epicentre, wa i overwhelmealy tne wave, there beirg serious loss of life and properiy. At about 4 A.l\i. a wave was nobicedbut it did noi come inland. At about ?-15 A.M. another wave swept over the town ancl caused.widespread havoc. The hcight of this wave has been estimatedrvariousiy from 40 fi. to 60 ft. Serious loss of life and property was also caused ut or*uru (about 130 r"lilesawayfromthe epiceni,re)and in several coastal viliages. Large quanlities of f sh were washed inland ou the coast. Ihrachi'.-Karachi, vhich is at a distance of about 2?6 miles fromthe epicentre, experiencedwaves affecting the harbour at 5-30 A.Iu., ? A.M., ?-b0 A.lI. and g. Ib A.Ii. The last one was the largest and.its heisht was estimated to be 4* ft. above normal. Fortunately, ihe time--s at which the"waves occurredwere djffirent from the times of high tide at Karachi on th.atday, namely, 06h. BTm.and tgh. 4bm. I.s.T. The last wave, which wgs $e largest,is reported to have produced a sirong ebbing curreub of between 4 and 5 kaots, rpparently during its recessron. The *un. damage in the Karachi barbour and lossof life ancl property along the Karachi"uo..d coast. *The figurosin rO"t".r O.r*r* . tha suoc€rivo isoseismals.

Bo' 8-r5A.l the timt 6. portedir I80 mile about30 and a hal ing the chartsan in the ap 15 minutr ship has immediat by a huge Sersmlose

Sld7DeofOD_d0

oF rEE 28rn Novpuarn 1945. ?EE MEKRANEARTEQUaKE

roximatelY quare miles) 21.5 DO

n has been ch that the tlrough the n of isoseisrnges of as luiing earthe landslides, aarthquakes, though erro-

awave at Bombay.-Bombay, ?50 miles away from th_eepic-entre,experienced, 8-I5 A.M.,iis heightbeing6] ft. Therewassomelossof life. X'ortuaately,howevet, the tines of high ticlefor ihe day were06h.5Bm.and 20h.12m.I.S.T. 8. Adtlittonal inlonnation rcgading the earthquake.-Jt has been reabout ported in the ?ressthat two rocky oval isletswerethrown up by the earFhquake t8O miler west-south-westof Karachi. The islets are aboub3 miles apart, onerising about 30 feet abovethe water and the other about 100feet ; the former is about one and a half squaremilesandthe latter about a squaremile. Whenthe ofrcercomyrrsnding the In&an naval ship Hinilustan first saw the new islets, he examinedhis charts and then sent out the following Signal: " Two uncharted.isletshave appeared in the approximateposition of 25 degreesand 7 minutes north, ancl 64 degreesand Ib minutes east". A correspondentofthe AssociatedPressof India who was on thc ship has reported that, according to the information gathered from the villagers, immediately after the earthquakea loud rumbling noisewasheardand was followed by a hugesheetof flameand columnsof smokeantl that thesowoSefollowecl by the seismiose& w&ve.

rents. Simi'eI of the sea re number of lI. ,hich affected from the ePioil ed to have nd inlet's, and th no d.amago ed below. Mr kran Coast re wave, theto noiicetl but it the town and' ateckvariouslY sed at Ormara illages. Large nthc ePicentre' A.M. and 8 15 be 4* ft. above , diff6rent from

th. 45m.I.S'T' a sirong ebbing 'he wave causeo : Karachi coast' portions betwecu

r46

Ob-500-I0{.r8-CtrBPS DUTDOof

fiinm;^,,f.,."p$:: i 4-. rnrKarPur r 5o Ee ia!a ta

ib--.r ara c nl

l s o s e i s m a l s o l tt h e e a r l h q u a k e-

of 1945Nov.27 d. 2l h. 57 m. Capprox)6.M.T. G, P.

Z. p, POOil),

t947.