sign in sign up
<<
Home , 1908 Messina earthquake, Taormina

Marine Geology in the Region of the Straits, and a Puzzling Tale of Faults, and

A. Argnani Institute of Marine Sciences, CNR, Bologna, [email protected]

Abstract The Straits of Messina is one of the most tectonically active areas of the Mediter- ranean, and has been the site of the destructive 1908 Messina . In spite of the hazard potential of this marine area, studies based on modern geophysical data are still lacking. A marine multichannel seismic survey was purposely carried out with the aim to outline the fault pattern in the area of the Messina 1908 earth- quake, and to better understand its significance within the tectonic frame of the re- gion. Within the Messina Straits, faults have been imaged on the Calabrian side, with a 30 km long NW-trending fault, located at the SW tip of , that is affecting the sea floor, whereas we did not image any extensional fault plane attributable to the Fault, on the Sicilian side of the straits. The geodynamic implication is that extension in south-eastern , on the Ionian side of the Hyblean Plateau, and extension in southern Calabria and Messina Straits belong to two different tec- tonic systems and, therefore, cannot be mechanically linked. Finally, the damages produced by the1908 ground shaking were aggravated by the effects of a remarkable , with up to 11 m of run-up height, that followed the earthquake. The origin of the tsunami associated with the 1908 earthquake is not yet fully understood, but geological and geophysical evidences substantially undermine a recent proposal that the 1908 tsunami originated by a large landslide offshore Giardini .

1 Introduction and Geo- rine terraces. The flight of emergent ma- logical Setting rine terraces along the coast of Sicily, from Taormina to Briga, were uplifted since 125 ka with rates of 1.07 mm·yr−1 [5]. The oc- The Messina Straits and its surroundings currence of a large and active extensional are one of the most tectonically active areas fault named Taormina Fault, running off- of the Mediterranean, as indicated by sev- shore, has been inferred on the basis of eral lines of geological and geophysical ev- coastal geomorphology (Figure1[6]). Ac- idence. Relatively large earthquakes struck cording to some investigators (e.g., [7]), the area in historical times (Figure1), al- the systems of faults of southern Calabria though the recurrence time for 1908-type and south-eastern Sicily, on the Ionian side events (Mw=7.1) seems to be about 1500 of the Hyblean Plateau (e.g., [8]), both yr [4]. The Sicilian and Calabrian side of associated to large and destructive earth- the straits are characterised by uplifted ma- quakes, can be linked through the Taormina Marine Geology

Figure 1: Map of the Messina Straits with location of relevant historical earthquakes (after [1]; [2]). Dashed boxes represent poorly constrained events.

Fault. However, along the belt correspond- about 1.0-1.3 mm·yr−1 in the last 300-400 ing to the inferred Taormina Fault a lack ka. GPS velocities [11], indicate a NW-SE- of seismicity is indicated by historical data directed extension at a rate between 1.7 to and recent instrumental records [9] (Figure 3 mm·yr−1 between the Sicilian and Cal- 1). The assumption that the hypothesized abrian sides of the Messina Straits. In par- Taormina Fault is part of a single rift sys- ticular, GPS-derived interseismic strain ap- tem, connecting Calabria to south-eastern pears to fit aseismic slip along a 30°, SE- Sicily, implies that it represents one of the dipping normal fault, locked above about 8 most hazardous seismic gaps in Italy, a po- km (Serpelloni, p.c. 2009). Onshore struc- tential site for large future earthquakes. A tural studies (e.g., [3]) have shown the oc- flight of uplifted marine terraces character- currence of a fault system that runs along izes also the Calabrian coast of the Messina the Sicilian coast, but the faults that have Straits. Twelve to fourteen orders of ter- been most active during the Pleistocene are races have been identified, with the high- those located on the Calabrian side of the est terraces, dated Middle Pleistocene, hav- Messina Straits [3]; these faults belongs to ing an elevation of about 1350 m above sea two main sets trending NW-SE and NE- level [10], with an stimated uplift rate of SW and are not obviously related to the N-

846 Marine research at CNR

Figure 2: Map showing the traces of fault planes proposed for the Messina 1908 earth- quake, with the authors annotated.

S trend of the faults inferred to be respon- human life in Italy’s history of seismicity, sible for (Figure with over 80,000 people dieing in the cities 2). Most authors agree that the extensional of Messina and and the faults bounding the Reggio Calabria basin surrounding area. Besides buildings col- have been active through Late Pliocene lapse and fires, the damages produced by and Early Pleistocene. However, subse- ground shaking were aggravated by the ef- quent fault activity is debated, and some fects of a remarkable tsunami, with up to authors suggest that the faults were not ac- 11 m of run-up height, that followed the tive since Middle Pleistocene (e.g., [10]). earthquake [12]. Despite such catastrophic The large 1908 Messina earthquake (Mw = effects the location of the causative fault is 7.1 [2]), for which extensional focal mech- not fully assessed (e.g., [13]). Inverse mod- anisms were obtained, occurred within this elling of seismograms and geodetic lev- tectonic frame. The December 28, 1908 elling, and geological studies have pro- Messina Earthquake has been ranked as duced a variety of results in terms of posi- one of the most destructive events of the tion, direction, length and dip of the fault, last centuries, and costed the highest toll in with the most recent solutions proposing

847 Marine Geology

Figure 3: Map with traces of multichannel seismic profiles in the study area. The trace of the supposed Taormina Fault is in red. Onshore faults after Ghisetti [3]. Seismic profiles shown in Figures 4-6 are in thick green lines. long, E-dipping faults trending about N-S a matter of debate [15], and contribution (e.g., [14,2], and references therein Fig- from a so far unidentified submarine slide ure2). At present, the most accepted seis- is called upon. In spite of the hazard poten- mogenic source for the 1908 earthquake tial of this marine region, geophysical sur- is a 40 km-long, blind fault dipping 30° veys purposely devised to investigate the to the ESE which is thought to accounts neotectonic features are lacking, with the for the topography of the Messina Straits notable exception of the early work of Selli (DISS, http://diss.rm.ingv.it). This fault [16] which, however, did not employ mod- plane, which trends NNE-SSW, has a min- ern geophysical techniques. In order to imum depth of 3 km, and would crop out bridge this gap a multichannel seismic sur- along the coast of Sicily (Figure2). As vey, aimed at defining the structural pat- for the seismogenic fault, the source of the tern of the Messina Straits, was carried out tsunami related to the earthquake is still within the frame of INGV-DPC seismolog-

848 Marine research at CNR

Figure 4: Seismic profile TAO 09 across the central part of the supposed Taormina fault. Arrows mark the South Calabrian fault. See Figure3 for location. ical projects (Figure3[13]). rine strata along the offshore slope (Fig- ure4), but such deformation cannot be re- lated to footwall uplift of a normal fault. 2 Discussion The geodynamic implication is that exten- sion in south-eastern Sicily, on the Ionian Three key aspects related to the tectonics side of the Hyblean Plateau, and extension of the Messina Straits will be briefly dis- in southern Calabria and Messina Straits, cussed below, based on the results obtained belong to two different tectonic systems from multichannel seismic data. A more and cannot be mechanically linked. The detailed presentation of the data and in- seismological implication is that the lack terpretation procedures is given elsewhere of earthquakes is not indicating the occur- [13], with references therein), together rence of a seismicity gap. with the correlation of seismic units with onshore outcrops and short offshore wells 2.2 The faults of the Messina that allows to date the seismic units. Straits and the 1908 Earth- quake 2.1 The elusive Taormina Fault Within the northern part of the Messina The hypothesized occurrence of a large ex- Straits, the imaged faults are located on the tensional fault parallel to the coastline and Calabrian side and dip to the west. These located offshore, between Taormina and faults appear connected to the fault sys- Briga (Taormina Fault) can be rejected by tem reported onshore near Reggio Calabria seismic data [13]. That stretch of coast- (Figure3[3]). A fault trending NW-SE line is actively deforming, as suggested by has been mapped between the towns of uplifted marine terraces and tilting of ma- Reggio Calabria and Messina. The fault

849 Marine Geology

Figure 5: Seismic profile TAO 08 within the Messina Straits. A listric fault (arrows) is flattening at shallow depth. Location in Figure5. plane dips to the west and displays a listric within the narrower part of the Messina shape, with growth strata in the lower part Straits might support the interpretation of of the half graben sedimentary fill, that a seismogenic fault located to the south of can be dated as Late Pliocene-Early Pleis- this area or, alternatively, of a blind fault lo- tocene (Figure5). Towards the coast of cated within the northern Messina Straits. Calabria the fault is sealed by a sedimen- Hints suggesting that the occurrence of a tary wedge, which can be dated as Mid- blind fault, possibly east-dipping as indi- dle Pleistocene-Holocene. The profiles ap- cated by seismological studies, are not ob- proaching SW Calabria show a 30 km- vious on seismic profiles in the northern long west-dipping fault that is affecting part of the straits. Moreover, given the the sea floor with a NW-SE trend, which large magnitude of the 1908 event, it can- represents the longest lineament observed not be ruled out that more than one fault within the Messina Straits (Figure6). The were activated at the same time, as al- W-dipping southern Calabrian fault has ready proposed (Figure2). In this event, a low-angle plane when depth-migrated the long fault observed offshore southern therefore, assuming that the epicentre is lo- Calabria could be activated together with cated above the deeper, seismogenic por- a blind east-dipping fault located further tion of the fault plane, it does not satisfy to the north, possibly contributing to the the 1908 macroseismic intensity observed tsunami related to the 1908 earthquake the along the Calabrian coast. However, this tsunami waves observed all along the east fault might be responsibile for the March coast of Sicily, in fact, are hardly compat- 28, 1780 and May 22, 1932 earthquakes ible with a blind fault located within the (Figure7), two events for which a seis- northern part of the Messina Straits [15]. mogenic fault is difficult to be identified [1]. The lack of evident extensional faults

850 Marine research at CNR

Figure 6: Seismic profile TAO 17. Arrows mark the South Calabrian fault. See Figure3 for location.

2.3 The 1908 Messina Earth- phobathymetry and seismic profiles clearly quake and its related show that the morphology of the area is the Tsunami product of long-lasting erosion without any trace of a 100 yr-old large-scale landslide. Because of the uncertainty in the location of the causative fault, the modelling of the associated tsunami is not satisfactory 3 Conclusions [15], and the possibility to have a contri- bution from a submarine slide has been ex- The data collected during the Taormina- plored [19, 20, 21]. A. Billi et al. [22] 2006 survey open some interesting ques- have recently proposed that the tsunami tions concerning the position, direction and that stroke the coast of the Messina Strait extent of active faults within the Messina in December 1908 originated from a very Straits, where it is difficult to find a sin- large submarine landslide (20 km3) located gle fault that is long enough to account offshore Giardini-Naxos. However, geo- for the Mw 7.1, 1908 Messina earthquake. physical data and work on tsunami mod- Moreover, the trend of the observed faults, elling cast doubt on the proposed hypoth- though consistent with faults onshore Cal- esis that a large submarine landslide that abria, is different from the trend of many was caused by the 1908 earthquake is lo- of the faults proposed on the basis of in- cated offshore Giardini-Naxos [23]. The version of seismological and geodetic data morphological expression of a 100-yr old (Figure2). Seismic data show that there is landslide, of its headscarp and its deposit, no N-S fault cutting the sedimentary suc- should be little affected by subsequent ero- cessions south of the epicenter of Schick, sion and reworking. High-resolution mor- 1977 (Figure7). In fact, the only long

851 Marine Geology

Figure 7: Summary map with main faults in the study area. For the 1908 Messina earth- quake the followings are indicated: a) the relocation of [17] (ellipse with green star), b) the epicenter of [18] (yellow star), c) the isoseismal X [12], and the breaks in the telegraph cables. The DISS fault plane is indicated in green. fault that is affecting the sea floor is lo- long term) deformation. This interpretation cated at the SW tip of Calabria, trends NW- leaves the possibility to have more than SE and dips to the west with a low an- a fault active at the same time an event gle. Such fault parameters are not com- that has been inferred for the 1908 earth- patible with the 1908 earthquake, as the quake (e.g., Figure2). At present it is dif- hypocentral depth would be located too far ficult to say whether the observed active to the west. However, this fault could have faults are just the surface expression of a contributed to the tsunami wave that came single, deeper and blind seismogenic fault, together with the 1908 earthquake better as suggested by seismological arguments than any faults located within the northern (e.g., DISS), or if they truly represent the part of the Messina Straits. As a work- complex response of an area that suffered ing hypothesis, it seems that a system of a great deal of geological deformation and interconnected faults (e.g.,[3]), partly ex- where more than one fault can be active at ploiting preexisting fault planes, can bet- the same time. The large magnitude of the ter describe the observed geological (i.e., 1908 earthquake makes the first hypothesis

852 Marine research at CNR perhaps more appealing. As far as the 1908 tsunamigenic slide, however, is difficult to tsunami is concerned, an alternative to a constrain from the inversion of poor quality fault that extends to the south of the Straits tsunami runup observations, and no land- consists in introducing a submarine slide slide deposit that can be related to the 1908 that adds to the earthquake in contributing earthquake has been so far identified on to the tsunami. In this regards, the recent swath bathymetry. The 1908 earthquake proposal that the 1908 tsunami was due to has been a complex event. At present, a very large landslide of about 20 km3, the the combined action of a blind fault and deposit of which would be located offshore a submarine slide is thought to be able to Giardini-Naxos [22], is not supported by account for the observed ground shaking evidence [23]. Moreover, modelling of the and tsunami. However, given the struc- 1908 tsunami indicates that a much smaller tural complexity of the area, other solu- slide, less than 2 km3, is enough to pro- tions, where more than one slide, and per- duce the effects observed along the shores haps more than one fault, are active at the [20, 21]. The location of this potentially same time, cannot a priori be disregarded.

References

[1] R. Azzaro, F. Bernardini, R. Camassi, and V. Castelli. The 1780 seismic sequence in NE Sicily (Italy): shifting an underestimated and mislocated earthquake to a seismically low rate zone. Natural Hazards, 42:149–167, 2007. [2] N.A. Pino, A. Piatanesi, G. Valensise, and E. Boschi. The 28 December 1908 Messina Straits Earthquake (Mw 7.1): A Great Earthquake throughout a Century of Seismology. Seismological Research Letters, 80:243–259, 2009.

[3] F. Ghisetti. Fault parameters in the Messina Strait () and relations with the seismogenic source. Tectonophysics, 210:117–133, 1992. [4] G. Valensise and D. Pantosti. A 125 Kyr-long geological record of seismic source repeatability: the Messina Straits (southern Italy) and the 1908 earthquake (Ms 7 1/2). Terra Nova, 4:472–483, 1992.

[5] F. Antonioli, L. Ferranti, K. Lambeck, S. Kershaw, V. Verrubi, and G. Dai Pra. Late Pleistocene to Holocene record of changing uplift rates in southern Calabria and northeastern Sicily (southern Italy, Central ). Tectonophysics, 422:23–40, 2006. [6] S. Catalano and G. De Guidi. Late Quaternary uplift of northeatern Sicily: relation with the active normal faulting deformation. J. Geodynamics, 36:445–467, 2003. [7] C. Monaco and L. . Active faulting in the Calabrian arc and eastern Sicily. J. Geodynamics, 29:407–424, 2000.

853 Marine Geology

[8] A. Argnani and C. Bonazzi. The Escarpment fault zone offshore eastern Sicily: Pliocene-Quaternary tectonic evolution based on new multichannel seismic data. Tectonics, 24(TC4009):1–12, 2005. [9] G. Neri, G. Barberi, G. Oliva, B. Orecchio, and D. Presti. A Possible Seismic Gap within a Highly Seismogenic Belt Crossing Calabria and Eastern Sicily. Bull. Seismological Society of America, 96:1321–1331, 2006.

[10] B. Dumas, P. Gueremy, and J. Raffy. Evidence for sea-level oscillations by the “characteristic thickness” of marine deposits from raised terraces of Southern Cal- abria (Italy). Quaternary Sci. review, 244:2120–2136, 2005. [11] E. Serpelloni, G. Vannucci, S. Pondrelli, A. Argnani, G. Casula, M. Anzidei, P. Baldi, and P. Gasperini. Kinematics of the Western Africa-Eurasia plate bound- ary from focal mechanisms and GPS data. Geoph. J. International, 169:1180–1200, 2007. [12] M. Baratta. La catastrofe sismica calabro-messinese. 28 Dicembre 1908. pages 1–426, 1910.

[13] A. Argnani, G. Brancolini, C. Bonazzi, M. Rovere, F. Accaino, F. Zgur, , and E. Lodolo. The results of the Taormina 2006 seismic survey: Possible implications for active tectonics in the Messina Straits. Tectonophysics, 476:159–169, 2009. [14] A. Amoruso, L. Crescentini, and R. Scarpa. Source parameters of the 1908 Messina Straits, Italy, earthquake from geodetic and seismic data. J. Geoph. Res., 107(B4):1–11, 2002. [15] E. Boschi, D. Pantosti, and G. Valensise. Modello di sorgente per il terremoto di Messina del 1908. Atti VIII Convegno GNGTS, pages 246–258, 1989. [16] R. Selli. Geologia e simotettonica dello Stretto di Messina. Atti Accademia Nazionale dei Lincei, 43:119–154, 1978.

[17] A. Michelini, A.J. Lomax, A. Bono, A. Nardi, B. Palombo, A. Rossi, and the INGV SISMOS Group. Relocation of instrumentally recorded, historical earthqukes in the Italian region. Geophysical Research Abstracts, 6(07642), 2004. [18] R. Schick. Eine seismotektonische Bearbeitung des Erdbebens von Messina im Jahre 1908. Geol. Jahrb., 11:3–74, 1977. [19] A. Piatanesi, S. Lorito, , and F. Romano. Il Grande maremoto del 1908: analisi e modellazione. 2008. [20] S. Tinti, A. Armigliato, F. Zaniboni, R. Tonini, G. Pagnoni, S. Gallazzi, A. Manucci, and P. Pontrelli. Quale sorgente per il maremoto del 28 Dicembre 1908 nello Stretto di Messina? Terremoto, frana sottomarina o entrambe? GNGTS, 27° Convegno Nazionale, Extended Abstract, pages 191–192, 2008.

854 Marine research at CNR

[21] M. Favalli, E. Boschi, F. Mazzarini, and M.T. Pareschi. Seismic and landslide source of the 1908 Straits of Messina tsunami (Sicily, Italy). Geoph. Res. Lett, 36(L16304):1–6, 2009. [22] A. Billi, R. Funiciello, L. Minelli, C. Faccenna, G. Neri, B. Orecchio, , and D. Presti. On the cause of the 1908 Messina tsunami, southern Italy. Geophys. Res. Lett., 35(L06301):1–5, 2008.

[23] A. Argnani, F.L. Chiocci, S. Tinti, A. Bosman, M.V. Lodi, G. Pagnoni, F., and Zaniboni. Comment on “On the cause of the 1908 Messina tsunami, southern Italy” by Andrea Billi et al. Geoph. Res. Lett., 36(L13307):1–2, 2009.

855