Geophys. J . R.astr. SOC.(1966) 10, 347-368.
Mediterranean-Alpine Earthquake Mechanisms
and their Seismotectonic Implications*
Linu Constantinescu, L. Ruprechtova and D. Enescu
(Received 1964 December 17)
Summary
A number of seventy-five fault-plane solutions given by the present
authors for earthquakes having occurred during the last 50 years in
Europe, Asia Minor and Northern Africa and twenty-six solutions
due to other authors are studied from the point of view of the geometry,
kinematics and dynamics of the faulting process.
The main results, entered in Table 1 and plotted on Figs. 12-14,
lead to the conclusion that the forces having determined the geomorphology and the tectonics of the different areas of the MediterraneanAlpine belt have been of the same nature as those continuing to be
active at present at the seismic foci of the corresponding areas. Comparing the present results with previous ones, based on a smaller
number of earthquakes, (Tables 2 and 3) shows a better agreement of the
European pattern of earthquake mechanisms with the world pattern for
all earthquakes. Some differences seem, however, to continue to be
present between the two patterns in the case of shallower earthquakes.
1. Introduction
On examining the geographic distribution of the epicentres corresponding to
the earthquake foci for which fault-plane solutions have been obtained so far, one
linds out that Europe is one of the world’s regions which has been least studied from
this point of view. Striking as this may appear-given the scope of the European
seismological research-the number of focal mechanism studies is comparatively
small for Europe’s earthquakes. For example, in the statistical analysis carried out
in 1959 by Scheidegger (l),for what he considered then as recent fault-plane
solutions, his region No. lL-comprising nearly all of Europe as well as Asia Minor
and the North of Africa-is entered with seventeen earthquakes as against the total
of 265 taken in for the whole world. Bearing in mind the high seismicity of the
Mediterranean region and the important problems related to the Alpine orogeny,
one cannot explain this rather strange situation by an alleged lack of interest of the
problem.
The situation has of course changed since 1959 and, though sporadically, the
number of fault-plane solutions for European earthquakes has notably increased.
*Presented at the Meeting of the European Seismological Commission held m Budapest, 1964
September.
1
347
Liviu Constantinescu, L. Ruprechtova and D. Enescu
348
Nevertheless a lack is still felt in this field as to a comprehensive and systematic
study having a regional character so that it may be given a tectonical significance.
It is in order to make a contribution to filling this lack that the present authors
have undertaken the investigation having led to the results which are to be presented
in this paper. Moreover, they had still another reason-not less important-for
doing it: the hope of arriving at a general picture of the seismotectonics of the
Mediterranean-Alpine belt liable to constitute an appropriate coherent framework
for integrating the seismotectonical information they previously obtained in connection with fault-plane research concerning the Carpathian-Arc -Bend province.
2. Observational data and fault-plane solutions
The earthquakes for which fault-plane solutions are given in this paper represent
larger earthquakes ( M 2 5) having occurred in Europe, Asia Minor and N. Africa
during the last 50 years (1911-62). Their choice has also been determined by the
condition that a sufficient number of observational data should be available for
obtaining solutions as reliable as possible.
The epicentres of the earthquakes having been considered are situated within
the area defined by
1O"W < i< 36"E
and
30"N < cp < 50"N,
entirely contained within the region No. 1 of Scheidegger (1).
For obvious reasons, most of the earthquakes which have been studied here
belong to the Mediterranean region and to the Carpathian -Arc-Bend province
(Vrancea region).
Out of the 101 earthquakes, the fault-plane solutions of which are given in
Table 1 and discussed in this paper, seventy-five earthquakes have been studied
previously by two ( 2 4 ) or
either now by the present authors-reference '0'-or
one (5, 6) of them or then by one of them in cooperation with another investigator
(7,9).The solutions of the remaining twenty-six earthquakes taken into consideration
here represent the results of the research of other authors (10-20).
Two of the seventy-live earthquakes we studied (Nos. 98 and 99 of Table 1)
have also been investigated by Di Filippo & Peronaci (21). Because their preliminary
solutions are obviously incorrect-as not fulfilling the condition of orthogonality
between the two nodal planes--we have not used these solutions but those determined by us, on the basis of a larger number of observational data and, of course,
by taking care of the mentioned orthogonality condition.
The observational data used for determining the fault-plane solutions in the
case of the seventy-five earthquakes we have investigated are those concerning the
first arrivals in the P-waves. Some of these data have been obtained directly from
original seismograms or photostat copies thereof while others have been derived
from seismic bulletins. In most cases the number of data for one earthquake has
been greater than 20 and the spatial distribution of the stations having provided
them has been satisfactorily appropriate for leading to solutions which may be
considered as reliable. In some cases the authenticity of the results seems to be
stressed by the similarity of the solutions arrived at for earthquakes having the
same focus.
Mediterranean-Alpine earthquake mechanisms and their seismotectonic implications
FIG.1.
N
s
FIG.2.
349
3 50
Liviu Constantinescu, L. Ruprechtovi end D. Enescu
N
S
FIG. 3.
N
MediterranewAlpine earthquake mechanisms and their seismotectonic implicatioos
s
FIG.5.
S
FIG.6.
351
352
Liviu Constantinescu, L. Ruprechtova and D. Enescn
s
FIG.7.
N
S
FIG.8.
Mediterranean--Alpineearthquake mechanisms and their seismotectonic implications
N
s
FIG.9.
N
S
FIG.10.
353
354
Uviu Constantinmcu, L. Ruprechtova awl D. Ewscu
N
/ \
\
\
\
S
FIG.11.
The technique applied for obtaining the fault-plane solutions was that already
used in our previous research (2, 4): plotting in the Wulff projection the points
representing the stations with the corresponding sign of the recorded first impulse
in the P-wave and tracing the nodal planes a and b so as to take care of the sign
distribution, under simultaneous fulfilment of the condition of mutual orthogonality
between the nodal planes.
In order to illustrate the quality of the results, some of the solutions we obtainedchosen so as to be representative for the main areas of the region under consideration-are given as plots in the Wulff projection in Figs. 1-11. These figures
render respectively the fault-plane solutions of the earthquakes Nos. 42, 48, 99, 82,
97, 39, 6, 87, 76, 44 and 49 (in order of increasing longitudes of the epicentres and
numbering of Table 1, in which the earthquakes are entered chronologically).
As the observational data have been quantitatively and qualitatively very
satisfactory and their processing was conducted carefully, there seems to be no
reason for suspecting the reliability of the results, within the framework of the
limitations connected to the simplifying assumptions on which the focal mechanism
research is based.
3. Analysis and interpretation of the results
The elements defining the nodal planes are entered in Table 1 together with
supplementary data concerning the focal mechanism as deduced within the framework of the dislocation theory. The information synthesized in Table 1 is a threefold
1
13 1949.vii.23
15' 03'
14 1950.vi.m
OI'l8'47'
I 5 1951.i.M
23b07'
16 1951.iv.8
21' 38'
17 195l.viii.8
20.56-
04'48"58'
11 1945.xii.9
06b06-45'
I2 1948.v.29
15'48'22'
2 1934.iii.29
20.Mm51'
3 1935.vii.13
W03-46'
4 1938.iv.13
02'45'50'
5 1940.vi.24
09'57'24'
6 1940.x.22
06' 36-57.
7 1940.xi.10
01'39'07'
8 1941.iii.16
16'35- 13'
9 1945.iii.12
20.52"30'
10 1945.ix.7
21'25"
I 1911.xi.16
2
No.
6
8
9
I1
Trend
59' S22'E
90" N68'E N22'W
56" N30'E
56- N25'E
N22'W N68"E
N43'E N47"W
6 3 0 N40"E N50'W
NIO'W N80'E
42'6N; 13".5E
40' N40"W S5O'W
N40"E SSO'E
N17"W S73'W
36'.7N; 35'68
55'
65' N 2O"W S70"W
N65'W N25"E
60' N 3 V W S W W
39' N25"W S65'W
N84"E N 6'W
5.50 N42'W N48"E
7
S65"E
56' N25'E
5.75 N40'E
N5O"W
56" N25"E S 6 Y E
6.25 N W E N5o"W
S65'E
S60'E
36" N63"W
55" N27"E S63"E
7 4 0 N42"E N48'W
5.50
35' N65"W
S65"E
56* N25'E
6.50 N W E N50'W
55* N W E
5 5 * N5O"W
35" N 70"E
52' N65"E
55" N60"E
35' N65"W
35' N65'W
35" N65"W
35' N60'W
36" N63"W
N27'E S63'E
55'
5.50 N42"E N48'W
62" N74"W
65' N16"E S74'E
35' N22"W
59' N16"W
10' S63"W
10
Dip
N59'WS3IsW
S22'E
59" N68'E
5.25 N40'E N50"W
84' N27'W N63'E
7
Plane b
Dip
direction
63' N74"E S16'E
N22"E N68'W
5
Dip
Strike
direction
6.25 N33'W N57"E
4
Plane o
Mag- Strike
Dip
nitude direc- direction
tion
45'9N; 26"3E
h = 170h
32'4N; 33"4E
48'.3N; 9'.1 E
h =40h
45'.8N; 26O.58
h = l50km
45'.7N; 26O.78
h = 150km
39".3N; 15".2E
h = 290lan
45'9N; 26O.68
h = ll5lan
45".8N; 26'4E
h = 122km
45'.8N; 26".7E
h = 133 h
38"3N; 12'E
h = 85 h
45'.7N; 26O.88
h=I5Oh
43'.3N; 26'3E
h=100km
45'.3N; 26"4E
h = I 0 0 lan
45'9N; 26'.7E
h =l50h
38'6N; 26O.38
3
Earthquake
Date
Hypocentrr
Possible positions of the fault planes
axis
14
35"
35"
5 5 O
38"
35-
55'
66" S8O"W
45O N73'E
65' S25'W
77' S48'W
41' S 6'E
82' S50'E
82' S50'E
82" S50"E
55"
55'
82' S47"E
31" S68'W
50'
35"
25'
51'
30"
34'
34"
34"
34'
0"
35'
34"
82' S50'E
84' S48'E
35"
84" S48"E
55'
31"
54"
55'
54"
32" N31'E
28'
25"
31"
73" S50'E
55*
59"
N22'W
0"
70'
S28'E
NIO'E
SIYE
S62'W
S60"E
N57"W
SI8'E
N57'W
16" NSO'W
34'
22'
N55'W
50"
S I2'W
9"
40'
6'
6'
6"
N31'W
44"
S28"W
N58'W
N57"W
N58'W
NIYW
N40"W
N70"W
S57'E
19
Trend
S71'E
S17"E
S18'E
S 17'E
S18'E
N57'W
S 18'E
70'
55'
S64-W
N77'W
8"
2'
17'
W
N42'E
80"
5'
75"
lo"
75'
6 ' S W E
46" N25"E
lo"
75"
10'
10"
20"
74'
75'
74'
3'
70'
S8O"E
38'
22
2'
S69'W
Shock
type
dt
dt
dt
sp
dt
dp
st
dp
st
d-
dp
dp
dp
dt
sp
st
st
23
a
[3, 4,
1121
[3,4]
[3,4]
[3, 41
[3,4]
[ I I . 181
[3,4. 61
13.4, 61
[3, 4, 61
Ill, 191
st
st
st
(121
[I21
(121
dp 13.41
st
sp
dt
sp
dt
s
sp
sp
sp
st
fl
25
[lo, 181
Referen=
dp f3.41
dt
dt
24
b
Plunge Plane Plane
N23'E
75'NSS'W
20'
10"
10"
10'
38'
10'
42'
N74"W
21
20
50"
Trend
Axis of dilatational
stresses
Plunge
pressional
stresses
Axis of a m -
6'S18'E
78"
N67'W
N36"E
78"
35'
N36'E
N36'E
78"
78'
78'N39'E
7'
6"
N37'E
75'
7'
N36"E
51'
N37'E
S24"E
28"
14"
78'
S5I'W
65'
50'
75"
S65-E
33"
N2I"E
42"
6"
9'
18
17
16
15
27"
82' S68"E
13
Plunge
Null
direction
x axis
Slip
Plunge angle Trend
y axis
36' S57"W
31"
80"
12
Slip
Plunge angle Trend
Z
Possible positions of the
motion vector
Table 1
W
w
1f
t
w
f
L
.
c
l
6
0
k
B
w8
B
2
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
42"N; 33"E
3
1952.vi.3
4 5 " 4 N ; 27"E
0 9 531952.xii.17 34".7N; 24O.78
23b06"
1952.xii.26 40"N; I5".5E
23b55m56' h = 2W25O
1953.iiu.18 W . 1 N ; 27"-3E
19b06m
1953.viii.9 3 8 " 3 N ; 2I"E
07b41" 05'
1953.viii.12 38".5N; 21"E
06h08" 03'
1953.viii.12 38"-5N; 21"E
09b23m55'
1953.viii.12 38".5N; 21"E
1Zb05"22'
1953.viii.12 38"-5N; 2I"E
13.39" 23'
1953.viii.12 38"-5N; 21"E
14h08" 38'
1953.viii.12 3 8 " 3 N ; 21"E
I 6h08" 32'
1954.viii.13 38"-5N; 21"E
03' 22" 06'
1954.iii.29 37"N: 3"-3W
06' 17-05'
h = 630 I;m
1954.iv.30 39"5N; 22"-ZE
13'02"36'
1954.ix.9 36"-3N ; I " 3 E
Olh04'37"
1954.x.l 45O.5 N ; 27".1 E
13'30"
h =S o h
1954.xi.23 38'6N: 14"SE
1 3 h ~ " W ' h = 2Mkm
18 1951.viii.13
I
No.
Earthquake
Date
Hypocenw
6O S58'E
12" SZB'E
10
17"
6"
12"
70" S 5 P W
73" N 8 5 " E
84" S34"W
78" N 59"E
52'
60' N53"W
59' S75"E
17'
38"
57'
17"
73" N 55"E
N 7"E
33" S 15" W
73" N42"W
70" N 32" W N 58" E
83" N V W N 8 6 " E
32" N3S"W S55"W
50" N 8 3 " W S 7"W
N32"W
N58'E
N 8 3 " E N 7"W
76' N 75" W N 15"E
20" N 4 8 " E S 4 2 " E
4-50 N 3 7 " E S53"E
N 1 5 " E N75"W
52'
20"
70" S 8 6 " W
71" N 6"W NS4"E
N 8 4 " E N 6"W
N50"E N W W
0"
900 s 5 v w
72" N 2 4 " W S 6 6 " W
N69"E N2I"W
6.7
0"
90" S84"W
84" N W E N90'W
N 8 8 " W N 2"E
N 8 4 " E N 6"W
I I " S2I"E
10"
80" N 6 6 " E
72" N S I " W S39"W
N46"E N W W
7.0
16" S 2"W
15"
75" S W E
71" N 3 1 " W S59"W
N62"E N28"W
S40'E
33" S 6"E
20" S 7"E
0" S32"E
0" S 6 " E
26" S 4 4 " E
24"
66" N 39"E
69" N 5 6 " W N 3 4 " E
N32"E N58"W
19" S I"E
21" N33"W
76" N 5"W S85"W
54" E
so* N 360 w N
45- S17'E
45
45" N W E
81" N 2 6 " W S64'W
S77'E
N88"E
S42"E
S68'E
S53"E
68"
50"
73"
70"
71"
N62"W
S48"E
62"
N23"W
70"
N45"E
S45"W
27"
80"
10"
S32"E
51"
N85"W
28"
14"
N 73"E
2"
SI5'E
27'
55-
s76"w
40"
S34"W
52"
N89"E
27"
N43'W
62"
58"
dt
dt
26"
SP
dt
24"
63"
24"
St
9"
N51"W
18"
S36"W
70"
N67"E
8"
7"
d-
13"
S15"W
13"
S78"E
70"
N32"W
20"
20"
1
[14, 181
s
d13"
S41"W
13"
N 6"W
19"
[14, 181 0
st
dt
4"
S23"W
18"
L
dt
[14, 181
3r
6"
st
13. 4. 51
[13, 181
N45"E
15'
dt
7"
SP
SP
25
m
dt
St
10"
dl
dt
b
24
References
vl
w
17"
S W E
30"
SIS'W
19"
N52"W
N67'W
N76"E
20"
19"
N42"E
22'
3"
6"
s
21"
9-w
36"
S52"E
18"
6"
S80'W
dt
5"
S87"E
19"
SP
dp
70'
S58"W
8"
24"
dp
17"
S25"W
4"
23
a
Plunge Plane Plane
type
Shock
22
21
Trend
20
Plunge
Axis of dilataiional
stresses
18"
6"
20"
20"
19"
SIWE
68"
N42"W
21"
21"
S48"E
68"
N 55"W
15"
N78"W
14"
18'
S 8'W
44" N16"E
70"
S68'E
66"
S8I"W
N85'E
10"
NlWW
17"
73"
N35"E
N 18"E
19
18
17
N W W
Trend
Axis of cornpressional
stresses
Plunge
Trend
Null
direction
x axis
11"
10"
9"
II"
10'
17" S50"W
16"
68"
52"
II"
16
60" S47"E
15
10"
14
Slip
Plunge angle
16' SZWE
13
Trend
74" S43"E
-
34"
14"
12
Slip
Plunge angle
Possible positions of the
motion vector
z axis
y axis
N89"E N I"W
7, 50 N 5 7 " E S33"E
N 7 3 " E N17"W
N J 7 " E NJ3'W
80'
6. 50 N W W N 5 0 " E
II
56" N84"W
10
38" N 6"E S84"E
9
Trend
5 , 10 N43"E N47"W
8
7
Dip
76" S73"W
6
Dip
Plane b
Dip
direclion
80" N 1 7 " W N 7 3 " E
5
Strike
direction
N 7 0 " E N20"W
4
Plane a
Dip
Mag- Strike
direcnitude direction
tion
Possible positions of the fault planes
Table 1-continued
36 1954.~1~23 38"N: 21"E
16b27"17'
37 1955.i.3 39O.1 N: 21".8E
Olb07"04'
38 I955.iv.13 3 7 " 4 N ; 2 P 4 E
20h 45" 45'
39 1955.iv.19 39"4 N ; 23'E
16b47" 19'
40 1955.iv.21 39-4 N ; 23"E
07b 18" 17'
41 1955.v.l 45O.5 N: 26O.3 E
2Ib22"52'
h = lsOkm
42 1955.vi.5 36O.5 N : I' 5 E
14h56" 13'
43 1955.~11.16 3 7 " 9 N : 27".1 E
Olh07" 12'
44 1955.ix.12 32'.9N: 29".8E
06b09" 29'
45 1955.xi.12 25O.2 N : 34O.5 E
0Sh 32" 15'
46 1956.i.6
W f N ; 26"E
I Zh IS" 42'
47 1956.i.12 47".4N; 19".IE
0 9 46" 08'
48 1956.ii.l
39'.2N: 15".8E
h = 215 km
15b IO"49'
49 1956.ii.10 30" 4 N : 30" 4 E
20"31*37'
50 1956.iv.18 &".IN; 27".4E
12' 52"
5 1 1956.v.lS
38"N: 20".8E
h = 33 km
22' 56-56,
52 1956.vi.N) 43" f N ; 29" E
Olb5P26'
53 1956.vii.9 36"9N: 26"OE
03b11"38'
54 1956.vii.10 37":
26"E
03b01" 25'
55 1956.vii.30 35'3 N ; 25" + E
09b14" 57'
56 1956.viii.15 43".1 N : I5".9E
I 2b 02" 54'
57 1956.xi.2 39'3 N : 23" E
16'04"33'
58 1957.ii.19 36".5N; 2 1 ' t E
07b43n56'
59 1957.ii.23
36"4N; 9"E
0 4 b 40" 59'
14" N 6 8 " W
N89'W
S16"E
S81'E
S35"W
S86"W
21"
24'
80"
38'
12'
22'
20'
16'
41'
80'
25'
40"
18'
30"
19"
19"
19"
21"
11"
48"
4"
10"
19"
24'
40"
34'
12"
20"
20"
IS"
30'
70"
20'
13'
18-2
30"
18"
17"
17'
20"
10'
45"
4"
44" S I I ' W
30" S 4'W
s 16" w
84" S48"W
29" N 82"E
6" S S P E
22" S55"E
22" N72"E
I I " N48"W
49" S76"E
60" S 8 7 " E
35' S25"E
15" N 6 8 " E
N48"W
II'
0" N35'E
20" S47"E
S39"E
22"
23'
20" S45"E
22' N52"E
31" S 8"E
20" S72"E
20" S85"E
43"
27'
20'
49 "
24"
6"
21"
20"
10"
42"
17"
33"
70"
10"
0"
19'
22"
19"
20"
3015"
20"
47" S89"E
63" N 8 5 " E
70' S84"E
41" N63"E
66" S 7"W
84" S41"W
69" N26"E
70" N27"W
80" S39"E
48O N 14"W
73" N54"W
57" N 4 9 " E
20" N56"W
80" S38"W
90" N 5 5 " W
71" N37"E
68' N 4 3 " E
71" N 3 9 " E
70' N W W
60" N 7 W E
75' N 4"E
70" N 4"E
N84"W
71" N 5OWS85-W
50" N27'W S63"W
56' N 8 3 " W N 7'E
78" N 4 9 " W N 4 I 0 E
70" N64'W S26"W
70" N 6 3 " E S27"E
N 8 6 " W N 4"E
N74"W N16"E
N42"W N 4 8 " E
N 4 2 " E S48"E
5.25
7.0
6.75 N 3 5 " E N55"W
N18"WS72"W
5.9
5.25 N 8 " W S 8 2 " W
N 3 8 " E N52"W
6.0
6.0
55
20" N36"E
N 3"E N87"W
N 6 5 " E N25"W
N22"WS68"W
N 4 2 " E S48"E
N55"W S35"W
N 4 3 " E N47'W
6.0
5.6
4.50
5.0
5.4
7.25
S54"E
S 14"E
N34"E S56"E
73" N 5 I o W S 3 9 " W
70" N 4 4 " E S 4 6 ' E
80" N14'W S76"W
45" N 8 6 " W S 4"W
86" N 8 6 " W S 4"W
5.75 N45"E N45"W
5.50 N38"WSSZ"W
N 8 2 " E N 8"W
5.75 N I 8 " E N 7 2 " W
5.25 N Y E N 8 5 " W
5.0
73" N 4 7 " W S43"W
N53"WS37'W
N55"W
5.50 N 5 I " E N39"W
72'
60" N35'E
72" N52" W N 3 8 " E
77'
70" N 4 I m W S 4 9 " W
60" N76'E
5.75 N I4"E N 76"W
75" N S l ' W N 3 9 " E
66' N 6'E
80" N 1"E N89"W
S28'E
S43"E
22'
6"
s
dt
dt
dt
20'
2'
3'
2"
N87"E
S87"E
N30"E
N45"E
N42"W
63'
60"
56"
42"
69"
S86'W
s
S 17"W
S82'W
N82"W
2"W
12"
42"
14"
I'
N52"E
S26"E
S5I"E
N 3"E
N 5"W
S86"E
60"
25'
N 6'W
26'
N87"E
63'
N 3'F
N 15'W
20"
N78"E
60"
27"
N 5'W
20"
S83"W
16"
SP
dt
dt
6"
69'
N 53'E
30'
SP
SP
55"
S85'W
16'
N II'E
19"
dt
9"
S73"E
49"
SP
dt
250
N36"W
10"
28"
SP
53"
N41"W
34"
28
SP
19"
S85"W
3"
N 4"W
71"
N52"E
dt
2'
N68"W
29"
N22"E
60"
15"
SP
28"
N 78"E
2"
N 14"W
59"
dp
10"
S 5-E
4"
N84"E
76"
St
7"
N43"E
41"
S W E
47"
SP
83"
N 56"E
6"
38"
S88'W
SP
34"
S 5'E
S3S"E
58"
S62"E
S33'W
SP
38"
dt
dp
37'
5"
31"
N42"E
6"
SP
47"
2"
N42'E
54'
N49"E
15"
S56"W
N43"E
S43"E
51'
45"
S23"E
37"
62"
S38"W
S83"E
s20"w
S75'W
N22'W
N53"W
N36"W
N31'W
N54"W
S55'W
25'
21"
32" N 6"W
31"
59" S85"E
5.25 N 7 9 " W N I I " E
5.0
S8O'W
50"
46"
29" S64"E
19"
71" N 5OE
N85'W S 5"W
69" N 5 " E N85"W
44'
N84"E S 6"E
5.75 N 2 6 " E N64"W
2
10" S48'E
14" S54'E
16" N22'E
5'
10'
13'
16'
N 7"E
80' S44"W
17' N32"E
74' N73"E
57' N2O"W
70' N83"W S 7'W
80' N46"W N44'E
70' N58"W S32'W
77' N17"E S73'E
64" N70'E S20"E
N82"W
N42"E N48'W
N 54" W
5.75 N 68'W S22'W
N 2'W S88"W
86" N27'W S63"W
5.60 N W E N24'W
5.25 N 22" W S68" W
37"N; 28'38
45'43N; 27'6E
70" N45"E S45'E
N38'W S52"W
85'
6.25 N55"E N35"W
37"N; 28'3E
48"
32'
58' N63"E
42" N45'W
31'
20'
10"
19"
N 52" E
59'
lo' N26"W
N64"E S26"E
81'
N24"W S66'W
11"N; 8'E
80" N52'E
60' N 38" W S 52'W
N33"W
5.50 N57'E
37'.7 N ; 22'E
71" N40'E
64' N50"W S40'W
N41"W
5 . 5 0 N49'E
4.15 N 36'E
36'3 N : 27" E
h = IOl%15OL;m
36.5 N ; 21.4 E
h = 60-100h
50'.8N; 10'.2E
40'tN; 23"tE
5.0
5 . 5 0 N 8'E
33'
52"
60" S47'E
34'
56' N W W
38" N 6"E S84'E
N43"E N47"W
3 Y t N ; 27'tE
41"N; 20" i E
45"4N; 26'98
85'
IS'
4" N I2'W
4'
86' S17"W
75' N 13"W N17"E
SI2"E
N78'E
7.3
40',7N; 31".2E
25" N42'W
S42"E
6.75 N48'E
36'5N; 28",9E
25"
N45"W
6.75 N45'E
36O.3 N ; 29O.1 E
S45"E
55- N68'E
32' S24"E
31" S35'E
21" N66'E
12" S33'E
22" S41'E
36" N88'E
5" S82'E
20'
44" N l7'W
65' S41"W
83" N 10"W S 8O'W
S 17'E
5.50 N13'E
39"3 N ; 22'43E
20'
4"
5"
9"
30'
26'
26'
13"
20"
10"
20'
2'
15"
7'
30'
88' N43"W N47"E
60' N 2"E N88'W
SI0"E
6.70 N80'E
39'4 N ; 22".8E
20'
81' N13"W S17'W
6.50 N12"E S18"E
9'
15
70' N37"E
14
75' N53"W S37'W
13
44'
I2
46' N 80"E
11
21' N I 0 " W
10
33'
4'
5"
9'
31"
28'
32'
13'
21'
10'
20'
68'
14"
3'
16'
11"
32'
11"
16
S 7"E
S74'W
N16'E
N30"E
36'
N 5'E
N70'W
S64'E
N85'W
52'
S76'E
N22'E
S85"E
N88"E
N3VE
N25"W
SII'E
S 3"E
N50"E
S68'E
N33"E
N82"W
N 6'W
NZ1"E
N 52'W
N20'E
21
Trend
type
Shock
16'
23"
23"
20"
28"
34"
43
20'
6"
14'
17'
8"
8"
18"
3'
35"
9"
34"
22
SP
24
b
Plunge Plane Plane
Axis of dilatational
stresses
19"
19"
9"
13"
5'
S 1"W
S 13'W
3"
4'
23'
I'
10'
70'
N57'W
S63"W
N11"E
S87"W
S36"E
S58"W
N58"W
58'
59"
61'
S Z'E
S65'W
58"
56'
45"
68'
65'
150
70'
17'
75'
14'
17'
3"W
s
64'
24"
N 88'E
63'
23'
34'
21'
20
Plunge
S51'E
NWE
S53"E
19
Trend
pressional
stresses
Axis of com-
44'
53'
47-
18
N56'W
N83"W
S3O'W
S32"E
N88'W
N 3"W
S88'W
N 18"E
S28'E
N52"E
S77"W
SWW
S27"W
S61"W
17
Plunge
Null
direction
x axis
Slip
Plunge angle Trend
73' S88"E
9
slip
Plunge angle Trend
axis
42' N 18"W
8
7
Trend
y
17'
6
Dip
z axis
41'
5
Dip
Plane b
Dip
dim
tion
Possible positions of the
motion vector
49' N77"E
4
Strike
direction
39-4 N ; 22'4 E
3
Earthquake
Date
Hypoantre
60 1957.iii.8
IZb14" 14'
61 1957.iii.8
12.21"l4'
62 1957.iii.8
23.35" 11'
63 l957.iv.24
19L10" 16'
64 1957.iv.25
02b25" 36'
65 1957.v.26
0 6 b 33" 30'
66 1951.xii.23
23b38"
67 1958.iv.3
02'23"40'
68 1958.iv.3
07b 18-37.
69 1958.v.27
ISb27"42'
70 1958.vi.30
08L42"41'
71 1958.vii.8
O Y Or 26'
72 1958.vii.17
05137-06'
13 1958.xi.l5
0 P 42" 42'
14 1959.i.29
23'24" 30'
15 1959.iv.25
0Oh26"4l'
76 1959.iv.25
0Ib05"42'
77 1959.v.31
12'15"
1
No.
Plane a
Mag- Strike
Dip
nitude direc- direction
tion
Possible positions of the fault planes
Table 1-continued
[Ol
25
Referenas
v,
00
w
54'01'
5.50 N24"E N66'W
5.75 N I I " E S79'E
36" N; 4O.1 E
42";
21'E
30-5 N ; 9O.6 W
N27"E S63'E
0'
90' S27"W
63' N 7'W
65" N 63" W N 27" E
S 7"E
5.5
32'
S52'W
S36'W
59" N54"W N36'E
N42'E S48"E
80'
61" N 1 - E
10'
29'
32'
58" S47"W
58'
10'
S32"W
80'
52' N89'W S I"W
77" N38"W N52'E
59' N43"W N41'E
86' N 58'W N 32" E
N66"W
6.75 N24'E
N43"E N47'W
S23"E
5.75 N67'E
60
S5l'E
5.50 N33'E
12' N48"W
38' S66"E
33' S47"E
38' N23'W
10' N57'W
8" S52"E
83' N36'E
70' N54'WS36"W
N38"E N52"W
7"
88" N 1"W
64" N89"E S I'E
N 1"E N89"W
5.75
31'
38"
13'
31"
4'
20"
26"
44"
80" S W W
3" S89'E
450
45' N73'E
46" N 17'W S 13'W
5.50 N 30" W N 60'E
32"
31"
N60'E
20"
S86"E
11'
23'
28'
S88"E
25'
0'
N63"W
21"
33'
S 66"E
45"
9' N79"W
55"
72" S47"W
2'
9'
SIO'W
81'
20"
59' N 80" W N 10' E
58" N48"E S42'E
lO"N83'E
70' N 4 P W
7"
83' S S"W
57" N 8 5 " W N Y E
27'
50'
40" N 3"W
N 8 7 " E S 3"E
69'
43'
47" N72"E
45' N 18'W S72'W
6.30 N 4"E N 86'W
N30"W S60'W
5.50 N 2"E N88'W
5.75
5.25 N43'W N47"E
41'
75' S83"W
43"
47' S7S"E
N75'W
56'
43" N I S ' E
62' N42"W
58" S78"E
5.40 N 7'W N83"E
S42"E
10'
36'
51'
28'
34' N48'E
6.20 N I2"E N78'W
39'.3N; 15".3E
h = 25&290 lan
44"6N; 27",IE
h = l00hn
46'0 N ; 2 6 Y E
h = l50km
35";
22'48
73' S88'E
12' N W W
15" S68'E
W
20"
27'
36'
17' N 2"W
N 2'E N88"W
80'
5.25 N88"E S 2"E
N46'E
S82"E
8' S68"E
5'
34' S77'E
39' S72"E
17'
I I"
79" S38'W
54' N 52-W N 38" E
SWE
37'.8N; 20".5E
h = l00km
38";
20V E
9'
N12"E
85'
81'
N83"W S 7'W
39' N78"W SI2'W
5.25 N22"E N68"W
19"fE
41";
70'
6'
N 8"E N82"W
84" N16"E
5.50 N22"E N68"W
19'fE
41";
30'
46' N 14" W S 16'W
60
60' N 2-W
S 2"E
63" N88'E
31'
5-
N77'W
5.00 NI3'E
45"6N; 26'3E
h = 140km
41"N; 19"fE
59' N 6"W
S 6"E
54" N84'E
N 7'E
N72'W
5 . 5 0 N 18'E
3 Y t N ; 24'tE
92 1960.iv.10 37'SN; 27'6E
22' 0 5 m 25'
93 1960.~26 40-6N ; 20O.6 E
05.10" 1 I'
94 1960.x.13 45".8N; 26'68
02'21"
h = I50km
95 1960.N.S 39'4N; 20'3E
20' 20" 54'
h = 49 hn
96 1960.xii.5
36";
6'3W
21'21'52'
h = 50lan
91 1962.vii.6 38"N; 2O'jE
09' 16' 19'
98 1962.viii.21 41'.2N; 15'.1E
18b09"01* h = 40km
99 1962.viii.21 41".2N; 15".1E
18'19"28'
h =40b
100 1962.viii.28 3T.7 N ; 23'E
h = 120 lan
10' 59m55'
101 1962.ix.10 33".6N; 27".5E
h = 33 km
09' 36'28'
Ilb
78 1959.vi.10
04' 16" 03'
79 1959.vi.26
13'46'34'
80 1959.viii.17
01'33' 14'
81 1959.x.5
2oL 34'06'
82 1959.x.7
08'30'41'
83 1959.N.I5
17'08'41'
84 1959.xii.l
12'38"49'
85 1960.i.3
2oL 19' 34'
86 1960.i.4
12h51'55*
87 1960.i.26
20'27'05'
88 I96O.ii.l
11" 59' 39'
89 1960.ii.21
08' 13" 32'
90 1960.ii.29
23'41" 14'
91 1960.iii.12
31"
44'
14"
36'
5'
20'
26'
80'
32'
33'
22'
25'
33'
S7WE
S65'W
N22'E
S79"E
N 55'E
N7WW
S87'W
N25'W
N67'W
S20'W
S34'W
S63'E
N85"E
S40'W
N30'W
72"
34'
N 4'E
56"
38'
56'
42'
80'
68'
64"
6"
58"
50"
55'
65'
56"
33"
lz"
12"
17"
S38'W
70"
75"
71"
S62"W
52"
10'
S65"E
N86"W
52"
36"
44'
N80"W
44'
38"
70'
S88"W
20'
48"
37'
S5O"W
S56"W
32'
43'
S80'W
S29'E
N83'W
28"
6'
14'
450
10'
S78"W
N78'W
9"
20'
N42'E
S 6"E
2"
16'
8'
N67"E
N49'E
S80'E
34'
17"
S 71'W
N44'E
27'
52"
2'
3'
66"
N 3'W
N54"E
S 2'E
SI3"W
SIPE
N81"E
S42"E
S 10"E
S33"E
N 5"E
N47"W
N14"W
N33'W
N38"W
S25"E
14'
51'
31'
I'
3"
20'
16"
84"
28'
37'
4'
17"
17"
16'
78'
78'
s
3"W
15'
19"
17'
41"
25'
17'
43"
5"
S54"E
N W E
N 2'E
33"
4"
N48'E
26"
S48"W
N73'E
N60O'E
N84'W
N 2'W
S43'E
S82'W
S18'E
S17"E
N50'E
N55'E
S37'E
35'
10'
S36"E
NS3"E
4"
50'
N40"W
N48"E
360
Liviu Comtantinescu, L. Ruprechtova and D. Enescu
one, containing geometrical as well as kinematical and dynamical parameters
characterizing the faulting process within the focus.
Each earthquake is defined in the table by a number and by its date of occurrence,
hypocentre and magnitude (columns 1-4). The possible positions of the fault planes
result from the values of the angles indicating the strike direction, dip direction and
dip for the nodal planes a (columns 5-7) and b (columns 8-10). The motion vector
is characterized by the values of the angles defining its trend, plunge and slip for its
two possible orientations: along the z axis (columns 11-13) or along the y axis
(columns 14-16). The trend and the plunge are then given for the null direction
oriented along the x axis (columns 17-18), the axis of compressional stresses
(columns 19-20) and that of dilatational stresses (columns 21-22). The shock type
is defined separately for the nodal plane a being fault plane (column 23) or for the
plane b playing this role (column 24) by indicating its compressional (p) or dilatational ( t ) character as well as the kind of relative displacement of the two blocks of
the fault, either clockwise = dextral (d) or anticlockwise = sinistral (s). Finally the
source of the information is indicated (column 25) by numbers corresponding to
references at the end of the paper (reference ‘0’ designates the present paper, showing
that the corresponding solution has now been established by the present authors.)
The information contained in Table 1 admits of some comments concerning the
analysis and interpretation of its main items.
4. Geometry of the faulting
The first category of data provided by the focal mechanism research is that defining the possible positions of the fault planes, represented by the nodal planes a and b.
The results obtained in this respect for the earthquakes discussed in this paper and
synthesized in the columns 5-10 of Table 1 were plotted on Fig 12, on which the
main trends of the Mediterranean-Alpine orogenetic system are also represented,
according to Kober (22).
For most of the earthquakes one has represented cartographically the strike of
the two planes a and b. The removal of the ambiguity in the fault-plane solution
has been effected-and consequently the chosen solution alone has been plottedonly for the twenty earthquakes of the Vrancea region, for the earthquake the epicentre of which is situated in the vicinity of the Bulgarian shore of the Black Sea
and for seven other earthquakes: four of them with the epicentres in N. Turkey,
one with the epicentre in Greece and the other two with the epicentres near the S.W.
shores of Turkey (Fig. 12).
The way in which the ambiguity has been removed was shown by Constantinescu
& Enescu (3,4)and by Enescu (6) for the Vrancea earthquakes and for that having
its epicentre near the Bulgarian shore.
As to the remaining seven earthquakes, for four of them (Nos. 22, 32,44 and 53)
the ambiguity was removed by Aki (20)by means of surface waves data, while for
the other three (Nos. 18,49 and 65), having the epicentres in the zone of the Anatolian
fault, the possibility of determining the actual fault plane has been given by the
geological information concerning this great fault (23).The criteria adopted for
removing the ambiguity in this latter case are the following ones:
1. Situation of the epicentres in the area affected by the fault.
2. Coincidence of the direction of one of the nodal planes with the direction of
the observed fault.
Mediterranean-Alpine earthquake mechanisms and their seismotectonic implications
36 1
362
LMIIcollrrtmtkscu, L. Rupredttova nad D. Eoesm
3. Agreement between the relative displacement of the blocks (dextral or clockwise displacement) in the case of that nodal plane of the focal mechanism solution
which is parallel with the plane of the real fault and in the case of the latter. It is
beyond any doubt that the mechanism solution indicates that the earthquake is due
to the displacement of the blocks of a previously existing fault, the Anatolian fault.
As the remaining seventy-three earthquakes are concerned, there is at present no
gbjective basis available for removing the ambiguity affecting the fault-plane solutions and for some of these earthquakes one might attempt such a removal only by
having recourse to reasonable hypotheses. Such hypotheses may be formulated on
the basis of some criteria as:
1. Coincidence between the orientations of one of the nodal planes for successive
earthquakes with foci having practically the same coordinates.
2. Parallelism between such nodal planes and the orientations of the fractures
observed within the corresponding epicentral region.
3. Systematic agreement between the orientation of one of the nodal planes and
major features of the Mediterranean-Alpine orogenetic system.
On this hypothetic basis one might suggest the following issues for removing the
fault-plane ambiguity :
1. In the case of the Agadir earthquake (No. 90), the actual fault plane may be
taken as modal plane a, as supported by wide information given by RothC (24) and
as chosen also by Petrescu & Purcaru (25) who have arrived at practically the same
fault-plane solution as that of Schaffner (19) adopted in\our paper.
2. For the earthquakes with the foci in N. Africa (Nos. 33, 42, 59 and 89), the
fault-planes would be represented by the nodal planes b, having a general strike
direction from W to E, in agreement with the main geologic geomorphologic and
geotectonic information available (26).
3. The earthquakes originating in the region of the Tyrrhenian Sea (Nos. 4, 8,
21, 35, 48 and 85) and those with their foci in Italy (Nos. 17, 98 and 99) might have
as the actual fault plane the nodal plane b. Supporting evidence is given in this respect
by geological considerations (27) as well as by comparing data concerning the seismicity of the corresponding region with geological and tectonic information (21,28).
4. The general orientation along directions nearly N-S of the nodal plane a in the
case of the earthquakes with foci in the Dinarides region (Nos. 67, 80,81,91,93 and
(95) suggests that this plane might be the actual fault plane.
5. Some information of seismological as well as geological and tectonical nature
(20,23,29) seems to give support to the conclusion that for the earthquakes originating in Greece and in its immediate vicinity the fault plane might be represented by
those nodal planes the strike of which is directed generally NW-SE.
In conclusion, by adding to the more firm information-resulting from an objective removal cf the ambiguity-the supplementary information provided by the
above hypothetical considerations, one might express the principal result of the
investigation concerning the geometry of the faulting process by stating that, for
most earthquakes of the area under investigation, the faulting occurs along directions parallel to the main trend of the Alpine chain.
5. Kinematics of faulting
Examining the columns 11-16 of Table 1 concerning the possible positions of
the motion vector shows the predominance of the strike-slip motion for the shallow
(h < 60km) as well as for the deeper earthquakes. A useful discussion may be
Mediterranean-Alpine earthquake mechanisms and their seismotectonic implications
363
Table 2
Area
Europe
World
N
101
17
265
All earthquakes
s
d
i
77.2 22.8
0
88.2 11.8
0
68.8
28.9
sld
3.4
7.5
2.4
2.3
N
75
16
179
Shallow earthquakes
s
d
i
sld
91.0
9.0
0
10.4
90.6
9.4
0
9.7
75.7
22.9
1.4
3.3
Ref.
(0)
(1)
made of the nature of faulting by comparing the results of our research with those
obtained previously by Scheidegger (1) on the basis of a smaller number of European
earthquakes. The main elements of this comparison are entered in Table 2, in the
columns of which are indicated separately for ‘all earthquakes’ studied and for the
shallow ones of them the total number taken into consideration ( N ) and, in per cent,
the contribution to this number of those with predominantly strike-slip (s),dip-slip
( d ) or indeterminate ( i ) motion as well as the ratio s/d. It is to be noted that while
maintaining the predominance of the strike-slip earthquakes over the dip-slip ones
for ‘all’ as well as for the shallow earthquakes, our results show a reduction of the
ratio s/d in the first case and an increase thereof in the second one, in respect to
Scheidegger’s results. The trend shown by our analysis, based on a larger number
of earthquakes, is in the direction of a better agreement with the world pattern for
‘all’ earthquakes but manifests a more pronounced departure from this pattern for
the shallow earthquakes. The explanation is to be sought in the presence among
the earthquakes of our analysis, of the Vrancea and Tyrrhenian ‘deep’ earthquakes
with a predominant dip-slip motion, the former with predominantly reverse faulting,
the latter due mostly to normal faulting.
As to the shock type, the data of columns 23 and 24 indicate in general the quasiequality of the numbers of earthquakes of the compressional and dilatational type.
Table 3
Area
Europe
World
N
101
17
265
All earthquakes
p
t
i
47.5 47.5
5.0
52.9
35.8
17.6
40.8
29.4
23.4
t/p
1.0
3.0
0.9
N
75
16
179
Shallow earthquakes
p
t
i
5.3
50.7 44.0
56.2
35.8
12.5
40.8
31.2
233
tlp
1.2
4.5
0.9
Ref
(0)
(1)
This result was established by Scheidegger (1) for the whole world but not for
Europe. Table 3, representing for the comparison between our results and those of
Scheidegger concerning the shock type the equivalent of what was Table 2 for the
nature of faulting, contains similarly for ‘all earthquakes’ and for the shallow ones
the number of earthquakes ( N ) and, in per cent, what is represented in this number
by the compressional earthquakes (t), by the dilatational ones ( p ) and by those
remained indeterminate ( i ) ; the ratio t / p is also given. One sees that in Scheidegger’s
results the European pattern of shock type is quite different from the world pattern
while in our results the European pattern shows a clear trend to approach the world
pattern. The small number of deeper earthquakes entering in our analysis makes it
impossible to decide whether there is a clear difference between the ratio t / p for
the shallow and deeper earthquakes, as found by Ritsema (30).
2
364
Liviu Constantinescu, L. Ruprechtova and D. Enescu
k
'n.*
Mediterranean-Alpine earthquake mechanisms and their seismotectonic implications
365
Given the diagnostic qualities for tectonic analysis of the ‘null direction’-previously designated as ‘null vector’-we have plotted its horizontal component in
Fig. 13 together with the same schematic representation of the Alpine chain as in
Fig. 12, in order to find out the connection between its orientation and those of the
main tectonic features. As far as the Vrancea and Tyrrhenian earthquakes are
concerned-both categories having their foci in regions of marked bending of the
mountainous chains and of large isostatic anomalies (31)--one may speak of a
clear parallelism between the null direction and the main trends of the orogenetic
system as shown by its folding. It is only for few earthquakes originating in these
two regions that a tendency towards iransversality with rcspcct to the Alpine chain
is observed.
If for the deeper Vrancea 2nd Tyrrhenian earthquakes the horizontal component
of the null direction is generally much greater t!zn its vertical ccmponent, for most
of the shallow earthquakes the situation is reversed. Consequently the smaller
horizontal components of the null direction do not show 3n the whole any regularities in their relations to the major geomorphological dircctions. Nevertheless, for
some groups of shallow earthquakes some regnlarities are to be noted in this
respect, as, for example, in the case of the Dinarides earthquakes (Nos. 67, 80, 81
and 93) for which the horizontal component of the null direction is clearly transverse
with respect to the mountain (and shore) line.
6. Dynamics of faulting
Information concerning the dynamics of faulting is to be obtained-as allowed
by the conceptions of the dislocation theory-by means of the stress pattern at
earthquake foci, while correlating its main peculiarities with characteristic surface
features. In order to get such in~ormation,the horizontal components of the
compressional stresses acting at the foci of the earthquakes discussed in this paper
have been represented cartographically in Fig. 14.
For most of these earthquakes one may recognize in Fig. 14 the trend toward
tiansversality of the compressional stresses with respect to the main orientations of
the Alpine tectonic features as shown by the mountainous chains and their folds (26),
as well as with respect to the shore directions. It is obvious that, in such cases, the
orientations of the plane in which the dilatational and intermediate stresses are
acting are consequently parallel to the mentioned surface features.
One is thus entitled to generalize a conclusion arrived at when studying the
stress pattern at the foci of the Carpathian-Arc-Bend earthquakes ( 2 4 by stating
that for the whole of the Mediterranean-Alpine belt the forces having determined the
geomorphology and the tectonics of its different areas have been of the same nature
as those continuing to be active at present at the seismic foci of the corresponding
areas.
7. Concluding remark
It is not the point to repeat here the results and conclusions of the research
reported in this paper. It seems however that some words on their significance
could be useful. As stated in the Introduction the present authors have endeavoured
to bring their contribution to filling an important lack in the body of knowledge
concerning Europe’s seismological features. They cannot claim to have filled this
lack. What they do claim is to have provided important elements for a future
synthesis of the European earthquake mechanisms, synthesis which remains to be
carried out.
366
LMn Constpntineacll, L. Rnprechtova and D. Enescu
Mediterranean- Alpine earthquake mechanisms and their seismotectonic implications
367
Acknowledgments
The present research has been effected within the framework of a collaboration
between the Academy of the Roumanian P.R. (Centre for Geophysical Research of
Bucharest) and the Czechoslovak Academy of Sciences (Geophysical Institute of
Prague).
The contribution of D. Jianu in carrying out a part of the calculations is acknowledged with thanks.
Centre for Geophysical Research,
Roumanian P.R. Academy,
Bucharest.
Geophysical Institute,
Czechoslovak Academy of Sciences,
Prague.
1964 December.
References
1. Scheidegger, A. E., 1959. Bull. seism. SOC.Am., 49, 337.
2. Constantinescu, L. & Enescu, D., 1962. Rev. GPol. GPogr. Acad. R. P. Roum,
6, 157.
3. Constantinescu L. & Enescu, D., 1963. St. Cerc. Gegf Acad. R. P. Rom., 1, 51.
(In Roumanian.)
Constantinescu, L. & Enescu, D., 1964. J. geophys. Res., 69, 667.
Enescu, D., 1962. Com. Acad. R. P. Rom., 12, 1291. (In Roumanian.)
Enescu, D., 1962. Com. Acad. R. P. Rom., 12, 1279. (In Roumanian.)
Vvedenskaya, A. V. & Ruprechtova, L., 1958. Izv. Akad. Nauk. S S S R (Geophys.
Ser.), 3, 277. (In Russian.)
8. Enescu D. & Ionescu-Andrei, 1963. Probl. GeoJiz. Acad. R. P. Rom., 2, 87. (In
Roumanian.)
9. Enescu, D. & Jianu, D., 1964. St. Cerc. GeoJ Geogr. ser. geofiz. Acad. R. P.
Rom., 2, 27. (In Roumanian.)
10. Hordejuk, T., 1957. Acta geophys. pol., 5, 103. (In Polish.)
11. Di Filippo, D. & Peronaci, F., 1959. Annuli Geofis., 12, 579.
12. Shirokova, E. I. Personal communication.
13. Karapetyan, N. K., 1958. Izv. Akad. Nauk SSSR (Geophys. Ser.), 2, 260. (In
Russian.)
14. Hodgson, J. H. & Cock, J. I., 1956. Publs. Dom. Obs. Ottawa, 18, 149.
15. Hodgson, J. H. & Cock, J. I., 1958. Publs. Dom. Obs. Ottawa, 19, 223.
16. Hodgson, J. H. & Stevens, A., 1958. Publs. Dom. Obs. Ottawa, 19, 281.
17. Ocal, N., 1960. Publs. Dom. Obs. Ottawa, 24, 365.
18. Schaffner, H.-J., 1959. Die Grundlagen und Auswerteverfahren zur seismischen
Bestimmung von Erdbebenmechanismen. Freiberger Forschhft. C63. AkademieVerlag, Berlin.
19. Schaffner, H.-J., 1959. Tabelle kinematischer Erdbebenherdparameter. Veroffentl.
Nr. 115. Inst. Angew. Geophys. Freiberg.
20. Aki, K., 1964. Bull. seism. Soc. Am., 54, 529.
21. Di Filippo, D. & Peronaci, F., 1963. Annuli GeoJis., 16, 625.
22. Kober, L., 1942. Tektonische Geologie. Gebr. Borntraeger, Berlin-Zehlendorf.
23. Richter, F., 1958. Elementary Seismology, pp. 61 1418. Freeman, San Francisco.
24. Rothk, J. P., 1962. Sew. GPol. Maroc, 154, 7.
25. Petrescu, G. & Purcaru, G., 1963. St. Cerc. GeoJ Acud. R. P. Rom., 1, 169.
4.
5.
6.
7.
368
Liviu Constantinescu, L. Ruprechtova, and D. Enescu
26. De Sitter, L. U., 1956. Structural Geology, pp. 344-347 and 395-396. McGrawHill, New York.
27. Grandjacquet, C. & Glengeand, L., 1963. Bull. SOC. gtol. Fr., 4, 760.
28. Di Filippo, D. & Peronaci, F., 1964. Annuli Geofis., 17, 195.
29. Galanopoulos, A. G., 1963. Annuli Geofis., 16, 37.
30. Ritsema, A. R., 1957. Trans. Am. Geophys. Un., 38, 349.
31. de Bruyn, J. W., 1955. Geophys. Prospect, 3, 1.