COMMENTS

The source included in the Database is low angle-E-dipping normal fault, which is 
mainly derived by the work of Valensise (1988) and Valensise and Pantosti
(1992). 

The main point that is still debated concerns the geometry of the seismogenic 
fault responsible for the 28 December 1908 earthquake, and consequently the 
structural setting of the Messina Straits. There are two main contrasting 
hypotheses derived using different approaches.

Based on seismologic, geodetic and geomorphic evidence, some workers (among 
which are De Natale and Pingue [1987], Capuano et al. [1988], Valensise [1988], 
Boschi et al. [1989], and the compilers of this Database), suggest the existence 
of a low-angle, E-dipping normal fault, characterised by a cumulative vertical 
deformation field that would mimic the shape of an asymmetric trough; this 
hypothesis is seen by Valensise and Pantosti [1992] to suit the overall long-
term deformation recorded by the geology and geomorphology of the Straits. 

A second group of investigators (among which are Bottari et al. [1986], Bottari 
et al. [1992], Tortorici et al. [1995]) uses a standard structural approach 
along with geomorphic observations to propose the existence of a graben 
structure composed of three main fault systems (trending NE-SW, NW-SE and E-W). 
According to this scheme, the master, earthquake-generating element would be a 
high-angle, NE-trending, W-dipping fault reaching the surface on the Calabrian 
side east of Reggio Calabria.

It should be remarked that, despite the great deal of field work performed by 
several contemporary investigators, no coseismic fault scarps were reported 
after the occurrence of the 1908 earthquake, in agreement with the hypothesis of 
blind faulting. This circumstance might indeed suggest offshore faulting, but 
this option would be in contrast with several other lines of evidence and has 
never been seriously advocated by any of the investigators of the recent 
tectonics of the Straits. It should also be pointed out that the overall 
reliability of the coseismic elevation changes measured by Loperfido [1909] has 
never been questioned and that these observations positively do not support 
significant (i.e., seismogenic) shallow faulting on the Calabrian side of the 
Straits.

The pattern of deformation shown by selected Mid- to Late-Pleistocene 
geomorphic and geologic features indicates that the long-term evolution of 
the Messina Straits can be explained by the repetition of 1908-type 
earthquakes on a low-angle, E-dipping normal fault. The predicted long-term 
strain pattern of such a low-angle normal fault describes a slightly 
asymmetrical syncline, having the western limb steeper, in agreement with 
the topography and distribution of recent deposits on the two sides of the 
Straits. Although open to improvements and refinements, this model is 
strongly supported (1) by the most recent paleoshorelines, which all exhibit 
a seaward concavity consistent with the progressive generation of a roughly 
N-S fault-related syncline; (2) by the elevation fluctuations of the 125 ka 
marine terrace, which appear to be related with the distance from the axis of 
the syncline; (3) by the distribution of recent deposits (the Middle-Late 
Pleistocene Messina Gravels) that appear to mimic the subsidence pattern 
associated with 1908-type earthquakes; and (4) by the local drainage 
pattern, which exhibits attraction of and rotation of streams of all 
hierarchical levels towards the areas of largest fault-related subsidence.


OPEN QUESTIONS

1) Is the causative fault of the 1908 earthquake truly shallow-dipping (<35 
degrees), or is this an artefact due to uncertainties in the coseismic elevation 
changes or in their elaboration?

2) What are the relationships between this source and faulting in the Gioia 
Tauro Plain? Does the northern end of the source really terminate against a 
transverse structure, as suggested by historical seismological and geomorphic 
evidence?

3) How does the fault terminate at its southern end? And how is it related with 
the lineaments of the Tindari-Giardini (or Tindari-Letojanni) transverse system?

4) How does the faulting trend delineated by all Calabrian faults continue south 
of the 1908 rupture? Does it stop, rotate westward toward mainland Sicily, 
or continue southwestward along coast of northern Sicily? 
