Vertical movements along the northwestern side 
of Messina straits, in the 1967-1970 period 

V . A C H I L L I * * - F . B R O C C I O * - F . MULARGIA * 

Received on April 8th, 1982 

A B S T R A C T 

T h e r e s u l t s of a comparison of the spirit levelling data made by I.G.M. in 1967 
a n d in 1970, a r e p r e s e n t e d . An analysis of these d a t a shows that the altitude 
v a r i a t i o n s of b e n c h m a r k s in the considered triennial period seem to originate from 
t h e c o l l e c t i v e r o t a t i o n of an inclined plane, which intersects the geoid surface with 
a n a z i m u t h of 43° to the N o r t h . 

T h i s is in a c c o r d a n c e with the orientation of the fault pattern given by local 
g e o l o g y . 

T h e fact t h a t the existing bench marks were sited along the coastline, and the 
l a c k of a c o m p a r i s o n with d a t a relative to motion on more compact geological 
s t r u c t u r e s , lead necessarily to provisional conclusions. 

R I A S S U N T O 

V e n g o n o r i p o r t a t i i risultati ottenuti da un confronto di livellazioni effettuate 
d a l l ì . G . M . dal 1967 al 1970. Un'analisi di questi dati mostra che le variazioni di 
a l t e z z a dei c a p o s a l d i , nel triennio preso in esame, s e m b r a n o essere originate da una 
r o t a z i o n e collettiva di un piano inclinato che interseca la superficie del geoide con 
u n a z i m u t di 43° N. Ciò è in accordo con l'orientamento del modello di faglia dato 
d a l l a geologia locale. Il fatto che i caposaldi esistenti siano situati lungo una linea 
c o s t i e r a e la m a n c a n z a di un confronto con i dati relativi al moto su s t r u t t u r e 
g e o l o g i c h e più c o m p a t t e , p o r t a necessariamente a conclusioni provvisorie. 

* I s t i t u t o Geofisico e Geodetico, Università di Messina, Italy. 
** I s t i t u t o Nazionale di Geofisica, Roma, Italy. 



9 6 V. ACHILLI - F. BROCCIO - F. MULARGIA 

I N T R O D U C T I O N 

T h e S t r a i t s of Messina is one of the most i m p o r t a n t areas, 
f r o m t h e geological point of view, of the whole Mediterranean. 
D i s a s t r o u s e a r t h q u a k e s repeatedly occurred in this zone (Baratta, 
1901), r e a c h i n g a m a x i m u m on the 28th December 1908, with a 
m a g n i t u d e 7.2 e a r t h q u a k e which completely destroyed the cities of 
M e s s i n a a n d Reggio Calabria a n d caused over 120,000 victims. 

C o n s i d e r i n g just one of the relatively recent periods of strong 
s e i s m i c activity, i.e., the period beginning in 1783, which consisted 
of s e v e r a l e v e n t s reaching a m a g n i t u d e M > 7.0, we can infer an 
a l o n g a t e d elliptical mesoseismic area, with m a j o r axis in the 
N E - S W d i r e c t i o n (Baratta, 1901). This a r e a extended its bound-
a r i e s f r o m Nicotera to the lower p a r t of Aspromonte, while some 
of t h e following great shocks seem to have origin in the area of 
M e s s i n a S t r a i t s . 

B e c a u s e of the complex seismicity of the area, it is very 
d i f f i c u l t to estabilish precisely which are the seismogenetic 
s t r u c t u r e s , especially since for most of the events i n s t r u m e n t a l 
r e c o r d s a r e not available. 

For t h e greatest e a r t h q u a k e in this area, the 28,h December 
1908 one, s o m e i n s t r u m e n t a l records are available. 

M a n y r e s e a r c h e r s studied this e a r t h q u a k e (Schick, 1977), 
s t a r t i n g f r o m the d e t e r m i n a t i o n of focal p a r a m e t e r s a n d concluded 
t h a t it is r e l a t e d to the Sicilian and Calabrian tectonics structures, 
s h o w i n g a c l e a r correlation with a fault that s t a r t i n g from Comiso 
a n d p a s s i n g t h r o u g h E t n a and Messina, reaches S. Eufemia (see 
fig. 1). 

T h e focal m e c h a n i s m was found to be a n o r m a l fault with 
d i p p i n g of 70° a n d a z i m u t h aligned on a NE-SW direction. A 
m a p p i n g of the e a r t h q u a k e s recorded in the last two decades with 
e p i c e n t e r in this a r e a (see fig. 1), shows a clear correlation with 
t h e m a i n tectonic a l i g n m e n t s (Bottari, 1971), while the focal 
m e c h a n i s m s of these events show a typical s t r u c t u r e with n o r m a l 
a n d vertical f a u l t i n g . 

2 . G E O L O G I C A L PATTERN OF T H E M E S S I N A S T R A I T S A R E A 

T h e geological l i t e r a t u r e concerning Sicily and Calabria has, 



15° 10' 20' 30' 40' 50' 16° 

Fig. 1 - T h e e p i c e n t e r s of the seismic events instrumentally located 
in the Messina S t r a i t s area in the last 20 years (3). 

o n a v a r i e t y of ways, supported an overthrust model which has 
t a k e n t h e p l a c e (Bottari et al., 1975) of an earlier model based on 
t o t a l a u t o c h t o n y given by Cortese (1882, 1895); he was the first to 
r e c o g n i z e t h e Messina S t r a i t s fault and to set its origin in the 
l o w e r to u p p e r Pliocene. 

T r e v i s a n (1954) in a study of Quaternary tectonic movements, 
a r g u e s t h a t these are the continuation of previous movements, and 
d i v i d e s Sicily into four separate units, two of which are the 
P e l o r i t a n i m o u n t a i n s a n d the Ragusa plateau, and the other two 



9 8 V. ACHILLI - F. BROCCIO - F. MULARGIA 

a r e s e p a r a t e d by a NE-SW strike faults system in agreement with 
s e i s m i c activity d a t a . Vecchia (1956) considers the fault system in 
t h e S t r a i t s as active, and, given the continuity of positive isostatic 
a n o m a l o u s zones, both in the Peloritani a n d Calabrian areas, 
f a v o u r s t h e idea of vertical movements along a large fault-system. 

G l a n g e a u d (1952a, 1952b) formulates a geodynamic model of 
t h e M e d i t e r r a n e a n area, by supporting the hypothesis of the 
e x i s t e n c e in the Mesozoic of two continental blocks, one African 
a n d t h e o t h e r E u r o p e a n , divided by Sial-free-zone. 

In t h i s tectonic scheme, Sicily and Calabria are clockwise 
t u r n e d a n d s h i f t e d to the South, because they are p a r t of the edge 
of t h e African c o n t i n e n t a l block. 

O g n i b e n (1960, 1966, 1971, 1973) taking u p Limanowski's 
i d e a s (Limanowski, 1913), develops an Alpine type structural 
m o d e l f o r the centre-southern Apennines a n d for Sicily. On the 
b a s i s of t h e g r a v i m e t r i c m a p s and the positions of the axes of 
i s o s t a t i c u p l i f t , he emphasizes the p r o b a b l e Pleistocenic n a t u r e of 
t h e g r e a t t r a n s c u r r e n t fault of the Gela — Messina — S. Eufemia 
f a u l t i n g zone, with anticlockwise t r a n s c u r r e n t movement. 

In the last years, the overthrust models have been given 
f u r t h e r s u p p o r t by global Tectonics. Following the a p p r o a c h of the 
t w o c o n t i n e n t a l blocks of Europe a n d Africa (including Sicily), a 
s u b c o n d u c t i o n of the oceanic crust began a n d continued u p to the 
m i d Miocene, when the collision of the two blocks w a s ac-
c o m p a n i e d by the f o r m a t i o n of the Peloritani m o u n t a i n s (Barberi 
et a l „ 1973; Bottari a n d Lo Giudice, 1975b; Caputo et al., 1970; 
F i n e t t i a n d Morelli, 1972; Ritsema, 1971). 

T h e s u b c o n d u c t i o n u n d e r the Calabrian arc seems to be 
c o n t i n u i n g still. The impact of the two continental blocks occurred 
in d i f f e r e n t phases, progressing in an anticlockwise direction from 
West t o E a s t . In the lower Miocene, E a s t e r n Sicily w a s the limit 
b e t w e e n t h e zone of collision of the continental blocks and the 
z o n e of s u b c o n d u c t i o n of the oceanic crust u n d e r the Calabrian 
a r c . Sicily, therefore, w a s involved in a local distensive tectonics 
p e r p e n d i c u l a r to the direction of movements of the oceanic crust. 

T h e origin of the Messina Abyssal Plain a n d the Messina Cone, 
w h i c h b e g i n s in the south of the Straits, is therefore based on this 



VERTICAL MOVEMENTS ALONG, ECC. 9 9 

d i s t e n s i v e tectonics, opening up in an anticlockwise direction 
( B o t t a r i et al., 1975). 

I n t e r e s t i n g results are also available from geohpysical studies. 
F r o m t h e o c e a n o g r a p h i c seismic reflection explorations (Finetti 
a n d Morelli, 1972), it seems that the African continental shelf 
c o n t i n u e s b e y o n d the Messina S t r a i t s and the Ionian Sea up to the 
s o u t h e r n edge of the Calabrian arc, and includes the Ragusa 
m a s s i f . 

F r o m these explorations it is also clear that the African 
c o n t i n e n t a l shelf, due to a system of subvertical direct faults along 
t h e e a s t e r n edge of Sicily, is still subsiding u n d e r the Ionian Sea. 

T h e first result of geodimetric measurements carried out 
b e t w e e n t h e t w o shores of the Messina Straits (Caputo et al., 1974) 
gives p a r t i a l s u p p o r t to the idea of a n o r t h w a r d drift of Sicily and 
a n a n t i c l o c k w i s e r o t a t i o n of the Calabrian arc. 

3 . G R O U N D DEFORMATION MEASUREMENTS. 

In o r d e r to detect vertical movements, we can utilize the 
v a r i a t i o n in a l t i t u d e of fixed bench-marks, i.e. the variation of the 
h e i g h t of fixed points on the ground with respect to the geoid 
s u r f a c e . 

Levelling, which consists of measuring differences in level 
b e t w e e n t w o or m o r e fixed points, is well suited to investigate 
s l o w a n d c o n t i n u o u s E a r t h crustal movements. In particular spirit 
l e v e l l i n g w h i c h is the most accurate levelling technique appears 
b e s t s u i t e d to this purpose. 

In t h e 1908, the " I s t i t u t o Geográfico Militare" (I.G.M.), has 
b e e n in c h a r g e of a precision geometric levelling in the region 
m o r e violently shaken by 1908 earthquake. The results of this 
s u r v e y (Loperfido, 1909), are particularly interesting because the 
p r e v i o u s levelling survey had been completed just a few days 
b e f o r e t h e d i s a s t r o u s event. Unfortunately the latter levelling 
c o u l d n o t b e referred to the mean sea level because the earthquake 
d a m a g e d t h e tide gauges. 

It w a s therefore referred to a reference plane which was 
a s s u m e d as fixed. 



1 0 0 V. ACHILLI - F. BROCCIO - F. MULARGIA 

T h e r e s u l t s of these levelling surveys were corrected in order 
to set t h e gravity level surface ortometric. Dynamic corrections 
w e r e also m a d e according the Clairaut's hypothesis, in order to 
t a k e i n t o a c c o u n t the defective parallelism of the level surface. 

T h e r e s u l t s showed a m a x i m u m a l t i t u d e variation of about 71 
c m n e a r the h a r b o u r office; variations of the same order of 
m a g n i t u d e w e r e found along the coastline. With regards to these 
m a x i m u m a l t i t u d e variations, we must take into account superfi-
c i a l l a n d s l i d e s which took place and were observed along the 
M e s s i n a coastline (Loperfido, 1909). After these, no f u r t h e r survey 
w a s m a d e , until 1967-70 when I.G.M. carried out two high 
p r e c i s i o n levelling surveys on two different lines but having some 
c o m m o n p a t h in the Messina S t r a i t s area (Istituto Geografico 
M i l i t a r e , 1972). As it will be a p p a r e n t in the following, the results 
of t h i s survey are highly interesting. 

4 . D I S C U S S I O N AND R E S U L T S . 

T h e a n a l y s i s of the geological situation of the area, together at 
1908 levelling d a t a , shows a clear tendency to a sinking of the 
c o a s t w i t h respect to the Peloritani m o u n t a i n s . The same tendency 
is c l e a r i n g a p p a r e n t in the 1967-1970 d a t a . 

Fig. 2 shows the variations of the considered bench-marks 
d i f f e r e n c e of levels, in the 1967-70 period (table 1). We will see 
t h a t f u r t h e r m o r e these variations can be ascribed to the pivoting 
c o l l e c t i v e m o t i o n of a rigid plane sinking on one side. 

If Y i n d i c a t e s the reference plane respect to which we measure 
t h e v a r i a t i o n s of the a l t i t u d e differences detected in the considered 
t r i e n n i a l p e r i o d , let 8 indicate the inclined plane produced by 
t h e s e v a r i a t i o n s , then elementary trigonometric considerations 
give a n expression that relates the a l t i t u d e variation of a bench-
m a r k as a f u n c t i o n of a and <p, which are respectively the angle 
t h a t OA f o r m s w i t h the nodal line of the planes Y and 8, and the 
p i v o t i n g a n g l e between the planes Y and 8 (see fig. 3). 

In p a r t i c u l a r we have: 

AA' = OA sen a sen ? 



VERTICAL MOVEMENTS ALONG, ECC. 1 0 1 

T A B L E I 

T h e d i f f e r e n c e in level between the 1967 and 1970 surveys. Note that there 
is a d i f f e r e n c e in the absolute reference level between them since the 1967 
d a t a w e r e referred to the mareograph of Catania while the 1970 was 
r e f e r r e d to a t r i g o n o m e t r i c survey vertix of the I.G.M. 

B E N C H - M A R K S SITING 1967 1970 

1 STAZIONE * 5.0941 4.9359 

2 DUOMO * 7.1442 6.9896 

3 MUNICIPIO * 4.8920 4.7367 

4 FIERA * 2.9011 2.7460 

5 V. LIBERTÀ 3.5313 3.3797 

6 PARADISO 3.2126 3.0600 

7 VILLA PRESTOPINO 5.0064 4.8557 

8 PORTICATELLO 6.4898 6.3406 

9 GROTTA 4.3040 4.1547 

10 GUARDIA 6.1851 6.0326 

11 S. AGATA 11.4666 11.3138 

12 LAVALLE 2.0999 1.9468 

13 ROCCA 1.2737 1.1194 

14 GRANATARI 3.0473 2.8914 

15 VILLA DE BERNARDIS 6.3993 6.2456 

16 MURO SOSTEGNO 13.7917 13.6363 

17 TIMPAZZI 14.0933 13.9464 

18 CASABLANCA GEMELLI 16.3348 16.1817 

19 CASABIANCA AGRILLO 13.9021 13.7506 

20 TONO 13.2598 13.1065 

* In t h e m e t r o p o l i t a n a r e a of Messina. 



1 0 2 V. ACHILLI - F. BROCCIO - F. MULARGIA 

2 0 Km 

Fig. 2 - Differences in level from the 1967-70 I.G.M. survey. The 
d i f f e r e n c e s in level a r e referred to bench-mark 1 (Stazione di 

Messina). 

w h e r e AA' r e p r e s e n t s the difference of level variation in the 
c o n s i d e r e d interval of time, when we proceed f r o m " O " to "A" 
b e n c h - m a r k s . 

If (J is t h e a z i m u t h w i t h respect to the North of the line EF, 
w h i c h is given f r o m the intersection of T and 8 planes, letting 

AA' s e n = K, we h a v e - = K sen ( (J - a ) and therefore 
OA' 

AA' 
= K (sen p cos a - cos fj sen a ) [ 1 ] 

OA 

We c an easily solve equation [1] by taking couples of d a t a 
a n d c o n s i d e r i n g the a z i m u t h of the connecting path together with 
t h e i r d i f f e r e n c e in level. 



VERTICAL MOVEMENTS ALONG, ECC. 1 0 3 

F 

Fig. 3 - The pivoting plane geometry. EF is the pivoting axis, 
w h i l e 9 is t h e pivoting angle. 0, A' and A are points on the 
g r o u n d ( b e n c h - m a r k s ) in the 1967 while a. is the a z i m u t h to plane 

strike. 

If t h e solution of (3 , relative to different couples, are similar 
w e will c o n c l u d e t h a t the measured vertical movements possibly 
o c c u r a s a consequence of the collective pivoting of an inclined 
p l a n e , w h i c h intersect the reference plane with an azimuth (3 . 

I n o r d e r to c a u t i o n from local level anomalies, we use the fact 
t h a t s o m e b e n c h - m a r k s are consecutively aligned and therefore by 
a l i n e a r regression we find the best fit line A h = (a, + b{D) a =cost. 
T h e l a t t e r expression allows to calculate the kilometric trends, i.e. 
t h e d i f f e r e n c e in level per kilometer along the considered direc-
t i o n s . 

In o u r analysis we have considered six sets of equations 
o b t a i n i n g six solutions for (3 with average values of [3 = 43° a n d 
a p e r c e n t s t a n d a r d deviation of 10,9%. 

A s i m i l a r analysis performed for the 1907-1909 data shows 
t w o a l i g n m e n t s (Scala — km 5 and Zona Militare — Castanea) 
w h i c h do not show variations in their differences of level. The 
d i f f e r e n c e in a z i m u t h of these two alignments is very small (circa 
10°) a n d t h e fact t h a t differences in level are found going 



1 0 4 V. ACHILLI - F. BROCCIO - F. MULARGIA 

w e s t w a r d suggests t h e m as representative of the pivoting axis 
f o u n d w i t h the above technique. 

This see m s c o n f i r m e d also by the 1967-1970 d a t a relative to 
t h e T i m p a z z i - T o n o . 

If it is a s s u m e d that the 1907-09 equal level points lie 
a p p r o x i m a t e l y on the pivoting axis, then two plate collective 

Fig. 4 - T h e t w o pivoting planes. Both show a sinking rotation of 
t h e i r e n d s . The n u m b e r s indicate the position of the bench-marks 

as indicated in table I. 



VERTICAL M O V E M E N T S ALONG, ECC. 1 0 5 

r o t a t i o n s a r e f o u n d . The first, which has been already described is 
o n t h e east side of the axis and shows a sinking (clockwise) 
r o t a t i o n (see fig. 4); the second one is found on the left of the axis, 
a n d , a l t h o u g h the evidence is based on fewer points, shows as well 
a s i n k i n g (anticlockwise) rotation (see fig. 4). 

C O N C L U S I O N S . 

T h e a n a l y s i s of the results of high precision levelling surveys 
p e r f o r m e d by I.G.M. in 1967 and 1970 shows a trend of crustal 
v e r t i c a l s t r a i n s in agreement with the coseismic movements of the 
1908 Messina e a r t h q u a k e . The movement found consists of two 
p l a n e s , one on the western and the other on the eastern side of a 
p i v o t i n g axis w i t h a z i m u t h strike P = 43° to the the North; both 
t h e p l a n e s show a sinking rotation of their ends. On the other 
h a n d t h e sitting of the existing bench marks is mainly along the 
c o a s t l i n e a n d d a t a on compact geological structures are sparse. 
T h i s led t h e a u t h o r s to start a high precision levelling survey 
( p r e s e n t l y in progress) which, together with a trigonometric — 
t r i l a t e r a t i o n survey, will hopefully help to settle more precisely 
t h e n a t u r e a n d the entity of the movements in the whole Messina 
S t r a i t s a r e a . 

A C K N O W L E D G E M E N T S . 

We t h a n k Prof. E. Boschi and Prof. P. Baldi for helpful advise, 
d i s c u s s i o n a n d c o n t i n u o u s support. 



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