Isoseismal map of the Vrancea earthquake of March 4, 1977

187

Tectonophysics, 53 (1979)187-193 0 Elsevier Scientific

Publishing

Company,

Amsterdam

-Printed

in The Netherlands

ISCSSIS:LALI;APOF THE VRANCEA EARl&L'AKE OF MARCI;4, 1977

C.

1 2

RADUl , V. KiRWfK2 , C. POLONICl , D. ?RO&ZKOVh

r2

and 2. SCRENKOV~2

Centre of the Earth's Physics and Seismology, Bucharest - Eag&ele

(Romania)

Geophysical Institute, Czechoslovak Academy of Sciences, 141 31 Praha 4 SpoIilov (Czechoslovakia)

ARSTRACT

Radu, C., Karnik, V., Polonic, G., Prochazkova, D. and Schenkovb, Z., 1979. Isoseismal map of the Vrancee earthquake of War-ohjr 1977. Teatonophpsicn, 5';:lR7-195* The isoseismal map of the intermediate Vrancea earthquake of Xarch 4, 1977 was compiled using the contributions from many European countries within the shaken area. Characteristic features of the macroseismic field are discussed. Xean radii of isoseismals and intensity attenuation are determined.

1:JTRODUCTlON

The Romanian earth?uake of Xarch 4, 1977 was one of the strongest events in the seismic history of the country (Atanasiu, 1962). It belongs to the well xnown category of subcrustal intermediate earthquakes of the Vrancea region. This peculiar focal zone

involves only a very restricted area (2000 - 9000 km')

at t!lelargest bend of the Carpathian mountains. The parameters of the shock were determined by Romanian seismologists as follows: R = 1gh21m56' G.M.T.,

Y = 45.C!'N, A=

26.S0E, Io = VIII (KSK-64), 1: p 7.2, m = 6,9.

Various parameters, properties and effects of the shock were immediately studied by!many national and international teams and some preliminary were

results

already reported (Radu et al., 1977; Ambraseys, 1978; Despeyroux, lY783;

&ndrescu,

1970; &za,

197P; Peterschmitt, 1977). In this paper we are pre-

sent.ingthe results of a compilation of the isoseismal map. The macroseismic field of the earthquake of Xarch 4, 1977 has a shape similar to earlier large shocks of the same magnitude class. The outer boundary goes as far as Northern

Finland acd Central Greece in the direction of the

l&rgeat axis of the elliptical field. In the East the western edge of the Cau-

188 casus was hit, in the West weak effects were observed in some localities of the German Democratic Republic. Newspapers published also some information on macroseismic effects in Egypt and in Lebanon, however, it was not yet confirmed by seismologists. Several preliminary maps were compiled by some seismologists (e.g. S. V. Medvedev and Ii.V.Shebalin)for a rapid information immediately after the earthquake. These maps reflect only general features and are based partly on newspaper reports. Because of the unique character of the Vrancea focus and of the importance of macroseismic data for seismic zoning of countries shaken by the earthquake a detailed macroseismic survey YI'BS made in all countries. The data lere collected by the Centre of the Earth's Physics and Seismology in Ruchnrest and by the Geophysical Institute in Prague. The principles of cooperation among the countries participating in the present K.A.P.G. project "atlas of Iso6eis7al.Zaps for Central and Eastern Surope" (Atlas, 19'78)were followed also in this case (c.A.P.3. - Commission of Academies of Sciences of Socialist Countries for Planetary Geophysical Research). The seismologists from the following countries contriouted with the corresponding portions of the isoseismal ;nap: Albania - K. Collaku and E, Sulstarova: Seismic bulletin, Ssis:aologicalCentre, Academy of Sciences of People Socialist Relxblic of Albania, Tirana. Austria - J. Drimmel: Isoseismal map (scale 1 : 1 million), Seismological station, :;ien. Bulgaria - Z. Grigorova and R. Glavcheva: Isoseismal map (scale 1 : 833 COO), Geophysical Institute, Bulgarian Academy of Sciences, Sofia. Czechos1ovaki.a- I. SrouEek: Isoseional map (scale 1 : 1 million), Geophysical Institute, Slovak Academy of Sciences, Sratislava. Finland - I'.Teikari: Personal communictition,Institute of Seismology, University of heljinki, Iielsinki. G.D.K. - G. Grunthal: Isoseissal map (scale 1 : 1 million), Central Institute of Earth's Physics, Academy of Sciences of G.D.R., ?otsdam. Greece - J. Drakopoulos: Isoseisnal r:ap (scale 1 : 1 million), Xational Obaervatory of Athens, Seismological Institute, Athens. Toland - 3. Cuterch and Ii.Lewandovrska-?.Y,arziniak: isoseismal map (scale 1 : 1 nillion) , Institute of Geophysics, Polish Academy of Sciences, Garszawa. Romania - C. Radu, G. Polonic and I. Apopei: Isoseis.nalmap (scale 1 : 1 mil, lion), Centre of Earth s 2hysics and Seismology, Bucharest. Hungary - 5. Csomor: Iaoseisxtalmap (scale 1 : 1 million), Geophysical Institute, I:unt;arian hcade:,i,y of Sciences, Budapest. U.S.S.R. - V. Drumea, A. .2.Roman, T, P. Xos~alenko, I. V. Ananin, I.I. A.

POpOV,

11. Postavutenko, G. N. gugayevskiy, C. 2. Xostyuk, 2. 5. Troniahin, T.S.Xar-

PiV9P*SKarmazin, V.S. ::nyazeba,A. Y. Sklyar, E. ?. Lotko: Isoseisxal cap (scale

189 1 : of

5 :r,illion), Sciences

Yugoslavia 2.

seis.:.fAs

on the

scale

in

signs

in

several

Figure

plotted

area

VIII

of

were

the

involvi.ng The

R,ere

ii;

the

a steep

VII

to

‘“he

vely

pattern

upper

peripherial

refully

of

permit

B. Xontic:

Institutes

to

map is

of

IsoSerbia,

The map for on the

were

of

the

based

on observations the

large

data

isoseisnals

the

reduced

print

in Romania

number

from

and in

12000 the

processed.

of

then

of

four

al.

tie

observed

to

localities,

e.g.

one

first

very

to

the

which

N1 (two

hic;hest

fault

plane

the

VIT Iasi,

macro-

region

zones

of

?O km)

shielding The large

the

X,

isoseismals

-

curve.

within

by the

and

I = VII

a closed

ridge.

solution

previous

The final

Vrancea

degrees

to

the

Bucharest, of

difficult.

Carpathian diatnncea

the

the

forms

of

intensities

in

the

mag he c.s.used

large

of

?uring the

scatter-e:?

one

towards

in

lack

determination

covering

main

the

in-

3 and N, reflects

determined

the for

the

, 1973). cannot

observed

only It

of

be

so guaranteed

population.

Intensity

by people

must

isoseismals

isoseismals.

was observed

earthquake

the

is

corresponding

phenomenon

bellow

of

number

field

geo,graphically

intensity

majority

involved

which

the

is

this

were

et

macroseismic

and made the

The deformation

the

by a large

‘3 e 3lurI‘ace.; mean re.dii

Tssi.c:

V.

and !M. Jankovic’:

: 1 million.

drawing

I = VIII,

I = VII

buildings.

where

the

after of

isoseismals

the

effects

floors

territory,

supic’

1

instance for

effects

corresponding

(XGller

seak

not

separated

crust

VIII

lowland.

of

that

basi.n,

ter,*i”,ies

3ervations

for

of

largely

decrease

thickened

earthiuake

Academy

and reproduced

The whole

intensities

zones

of

the

radiation

scale

locaZ.ties

confusing

Sucharest,

i soseisxal

the

at

two

Transylveniar

in

does

,

1200

fact

aas

Df”%>(.t o‘ ” L.,

:L.-iP

Physics,

!v;onte Negro.

: 4 million

and used

l

hietovlc,

Seismological

on the 1

sbservation.

immediately

reveals

one

scale

highest

observed

epicentre

7IiI.

: 1 million,

feature

The

and Craiova

seis:.iic

V.

pre_oared

from

:&es.

evaluation

D. Cvijanovic:

localities

conspicuous

earth;

Zimnicea

Xarth’s

OdSERVATIONS

The most central

, 2.

and Hercegovina,

evaluated

observations

XCROSZISKIC

to

of

of

. .’ NedelJkovlc

The reduction

each

thousands

1J.S.S.R.

to

1.

were

1

on the

for

questionnaires

of

were

was drawn the

of

, 3.

EIosnia

contrijutions area

iari;e

scale

Croatia,

Institute

Acanin,

!Aoscow.

’ I!. 3ad%ievsr;i,

Aaccdonia.,

whole

I.V.

U.S.S.E., “. .’ Vukaa~nov:c

- X.

zulatovi.c,

Lost

Editor: of

III

be noted and

seismologists

by individual They

are

in

quiet that

(see

given

in

the

list

Table

those

survey extend, of

were

based

corresponds

conditions

IV largely

isoseismals

as III

or

on obto

relati-

living

on the

in

U.S.S.R.

was made very

co-authors). used

I together

for nith

the

calculating ellipticity

ca-.

A

191 ratios ( 6

= b/a ) and isoseisrialradii measured from the epicentre in diffe-

rent azimuths.

TA3i.3I

Iutcnuity Surface /km"/

E

VIII (1.26)103

VII (1.18)105

VI (2.98)105

V (5.72)X5

IV (2.00)106

III (3.03)lO'

0.56

0.61

0.59

0.49

0.65

X ic E

200

304

440

1368

1700

s 2 6 .I;

316

372

512

688

800

S 57 T

352

476

580

720

888

:: 57 ';:

168

292

464

860

1180

0.38

Radii in different azimuths /km/

40

172

212

528

1012

S 33 E

160

304

440

488

612

me:2nraJ.ii/km/

206

320

441

775

1032

?J3 3 ::

1'igher intensities observed within the zones of lower intensity can be explaiino?,ml.inly by the amplifying:effects of local soil layers and of their thicknczs a?.ichdetermine also the predominant periods. X;ller et al. (Ytiller et al., 1978) explain the anomalous extension of largest intensities to SW by the movs .ent in the focus in this direction. Bowever, this assumption does not expioin the extension of isoseis;;ial IV and III towards Ii%.The comparison of

of isoseismols of the Vrancea earthquake of Xsrch 4, 1277. yditors Fit. 1. :ilap of this map are: C. Radu, V. Karnik, G. Polonic, 1).Prochbzkov4 and 7,.Scr,enkovb.Co-authors are: K.Collaku, E. Sulstarova (Albania), J. Drimmel (Austria), E. Grigorova, R. Glavcheva (Bulgaria), I. BrouEek (Czechoslovakia), P. Teikari (Finland), G. Criinthal(C.D,R.), J. Drakopoulss (Greece), D. Csomor (Hungary), B.Guterch, Ii.Lewandowska-Yarcinia!c(Poland), C. Radu, G. Polonic, I. Apopei (Romania), V. Drumea, A .A. Roman, T. P. Mos:\alanko,I. V, Ananin, I. I. Popov, A. H. Postovutenko, G. N. Bugayevskiy, 0. P. Kostyuk, R. S. Pronishin, T. P. Karpiv, P.S. Karmasin, V. S. Snyazeba, A. !i:. Cklyar, E. P. Hotko (U.S.S.R.), Y. Vu&eginovic: S. Nedeljkovic: !i.Petovic: V. Tesic: d. Sontic: B. Yulatovic: D. Kadz?ievski,D. Cvijanovic; X. Jankovic: V. Supic'(Yugoslavia).

192 areas shaken by three last Vrancea earthquakes of 1802, 194C a d 1977 shows

9

the largest value for the last shock ( l/3 of Europe was shaken ), however, the organisation of collection of macroseismic data can influence the extension of the zone of intensity III, i.e. the boundary of the shaken area. The mean radii of isoseismals (Tab. I) were used for an orientational calculation of the focal depth. The lcvesligethy formula yields the following results: h = 108 km, d/ = 0.0017, the formula of Blake: h = 112 km, supposing k = 4.5 and using all isoseismals. Both formulae with the above ;lentionedcoefficients represent empirical relations for an average attenuation of intensity with distance from the Vrancea focus in case of an extreme event. Details of intensity distribution are under study, first results of a comparative study for Bucharest have been already published (Mcndrescu, 19'78).It is hoped that the present isoseismal map can contribute to the complex study of the last destructive

and to further investigation of the peculiar Vrancea focus.

skock

The editors of the isoseismal map C. Radu, V. Ibrnik, G. Polonic, D. ProI. ChazKovd and Z. Schenkovd express their sincere appreciation to all contributors. The compilation of the map covering several countries cannot be implemented without a good spirit of international collaboration.

H3FEXENCES

Ambraseys, R.N., 1978. The earthquake of 4 March 1977 and its principal effects. Le tremblement de terre du 4 mars 1977, Part I, UNESCO, Paris. Atanasiu, I., 1962. Cutremurele de pgment in Romania. Acad. PW,

Bucuresti.

Atlas of Isoseismal Maps for Central and Eastern Europe, 1978. Editors: Prochl.zKovi,D. and Karnik, il..Geoph. Inst., Czechosl. Acad. Sci., Prague, in press. Despeyroux, Y., 1978. Analyse du comportement des constructions. Le tremblement de terre du 4 mars 1977, Partie II, WWSCO,

Paris.

!/i&drescu,il.,1978. The Vrancea earthquake of btarch4, 1977 and the seismic microzonation of Bucharest. Central Institute of Physics, EP -.3, ducharest. &za,

V.I., 1978. The 11arch4, 1977 Vrancea earthquake seismic gap. Central

Institute of Physics, EP - 2, Bucharest. %iiller,3.,

iionier,X.P., St6ck1, il.and Enescu, D., 1978. The Romanian earth-

quake of &larch4, 1977. I. Rupture process inferred from fault-plane solution and multiple-event analysis. J. Geophys., 44:203 Peterschmitt, E., 1977. Diffusions hypocentrales du le mars, 31 mars, 13 april,

193 21 april, 30 juin et 8 aott pour le seisme d e Vrancea du 4 mars 1977. CSEM, Straabourg. Radu, C., Folonic, G. and Apopei, I., 1977. Mzcroseismic field of the Vrancea earthqualteof hlarch4, 1977. Report SCITE,I, Bucharest.