Newly identified active faults in the Pollino seismic gap, southern Italy, and their seismotectonic significance

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Seismicity supports the theory of incipient rifting in the western Ionian sea, central Mediterranean

The present work focuses on earthquake locations and seismogenic stress in the eastern offshore of Sicily, a sector of the central Mediterranean region where geophysical information available is not good enough, yet, for proper geodynamic modeling. I have applied to an updated seismic database of the study area a Bayesian non-linear hypocenter location method already proven to be more effective than linear methods when the recording network geometry is poor, like in the present case. Then, I have selected from literature and official catalogs the local earthquake focal mechanisms computed by waveform inversion, and inverted them for stress tensor orientations. The results confirm the main finding of the previous investigations, i.e. that NW-trending convergence between Africa and Eurasia is a main source of tectonic stress in this area, however they also furnish evidence of additional tectonic factors locally acting together with convergence. In particular, extensional dynamics are detected inside the convergence-related compressional domain: these are characterized by a minimum compressive stress oriented SW-NE (perpendicular to convergence) and can be related to the rifting process (opening SW-NE) detected by previous investigators at the southwestern edge of the Ionian subduction slab. The findings of the present study may also concur to answer several open questions left by previous investigators

Incipient extension along the active convergent margin of Nubia in Sicily, Italy: Cefalu-Etna seismic zone

Recent geodetic data are compatible with NNE– SSW tectonic extension at a rate of ∼5 mm/yr in Sicily, southern Italy, within a broader region of net active compression along the Nubian plate margin (northern Africa). The structures that accommodate such extensional regime and its cause are still unknown. From field structural surveys and seismological analyses, the geometry, kinematics, structural architecture, and seismic potential of an extensional seismic zone linking Cefalù and Mount Etna in central eastern Sicily are defined. The zone includes high‐angle WNW striking normal and right‐lateral strike‐slip faults and subordinate north and NNE striking strike‐slip faults either right or left lateral. The occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage. The ongoing seismic activity possibly reactivates preexisting faults. Instrumentally and historically recorded earthquakes are lower than about 6 in magnitude, and destructive events are historically unknown since at least 1300 A.D. This apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms, which all together suggest a value between 6 and 6.5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area. Lateral extension on preexisting faults and upwelling of melt mantle material beneath Mount Etna are considered viable processes to explain, at least in part, the active extensional tectonics along the Cefalù‐Etna seismic zone. Strike‐slip seismic faulting beneath Mount Etna may be part of a previously proposed diffuse transfer zone affecting northeastern Sicily and including the Tindari Fault

A reappraisal of the 1978 Ferruzzano earthquake (southern Italy) from new estimates of hypocenter location and moment tensor inversion

The March 11th, 1978 Ferruzzano earthquake is the most recent moderate-to-major earthquake occurred in the southern Calabrian region (southern Italy), one among the highest seismic risk areas of the whole Mediterranean. Previous information available from the literature on the 1978 earthquake is quite contrasting and not well framed in the regional seismotectonic scenario. In the present study we selected and digitized analog seismograms coming from stations of the Euro-Mediterranean region to invert for the deviatoric seismic moment tensor through a time-domain algorithm properly implemented to analyze data recorded before the advent of the digital era. Moreover, we estimated a new hypocentral location by using original bulletin data and a non-linear probabilistic earthquake location technique working with 3D velocity models. The quality and stability of the obtained results, both for hypocenter location and moment tensor inversion, were accurately checked by several inversion tests. Our results indicate that the 1978 earthquake (i) occurred westward and at a shallower depth respect to previous hypocenter locations, (ii) is characterized by a ca. N-S trending normal faulting mechanism and (iii) has a moment magnitude of 4.7, thus suggesting an overestimate of previous evaluations. This study furnishes new information on the 1978 Ferruzzano earthquake allowing to better frame it in the regional seismotectonic scenario and also proves that the time-domain waveform inversion algorithm applied to digitized old seismograms is capable to successfully invert also M w < 5 earthquakes. The obtained results pave the way for future analyses of the early instrumental seismicity potentially capable to furnish new constraints to local and regional seismotectonic modeling.Published34-443T. Sorgente sismica4T. Sismicità dell'Italia6T. Studi di pericolosità sismica e da maremotoJCR Journa

Seismological analyses in the Calabrian Arc Region (South Italy) : investigating the northern edge of the Ionian slab

A joint evaluation of seismotomography models, hypocenter distribution and focal mechanism solutions has been performed in the northern Calabria region, where the lateral edge of the Ionian slab may be located. The recent history of the Ionian subdcution process marked by gravity induced south-eastward retreating of the lithospheric slab and progressive detachment of its deepest portions has led to a present configuration characterized by an in-depth continuous slab only beneath the central sector of the Calabria Arc. Recent investigations have indicated the southern edge of the Ionian slab in northeastern Sicily and relative offshore and have also highlighted that the signatures of the northern slab edge are less clear with respect to the southern one. Our investigation aims to better define this poorly recognized region of northern slab edge by means of a seismological study focused on the wide area proposed for its location (corresponding to the northern Calabria area and running from central Calabria to southern Apennines). By using a recently developed shallow-to-intermediate 3D velocity model we located the earthquakes occurred in this region between 1997 and 2012. We also selected the available high-quality focal mechanisms and integrated them with original solutions obtained by applying the Cut and Paste waveform inversion method to the events of the last decade. The joint evaluation of seismic velocity structure, hypocenter locations and focal mechanism solutions allows us to better define the lithospheric units configuration and to properly relate it with the seismic activity so furnishing also new insights onto the kinematics at the northern edge of the Ionian slab.peer-reviewe

Investigating the Pollino mts. seismic sequence south Italy) by high-resolution analysis

We present an high-quality analysis of the space-time evolution of the seismic activity occurred between 2010 and 2013 in the Pollino Mts. region, in the junction area between the Calabrian Arc and the southern Apennines domains (south Italy).PublishedIstambul2T. Tettonica attivaope

Integration of geological and geophysical data for re-evaluation of local seismic hazard and geological structure: the case study of Rometta, Sicily (Italy)

The village of Rometta, northern-eastern Sicily (Southern Italy), experienced severe damage during the most energetic earthquakes that occurred in eastern Sicily and southern Calabria in the last centuries. Geological maps indicate that Rometta primarily lies on a stiff plate of Upper Pliocene – Lower Pleistocene calcarenites and only to minor extent on Middle Pleistocene overlying clays. Rometta represents an interesting case study for site response investigation because of the apparent mismatch between the currently available geological knowledge and the level of damage caused by historical seismic events. The local seismic response has been investigated through a grid of 64 single-station measurements of ambient seismic noise by the Horizontal to Vertical Noise Spectral Ratio technique (H/V). Also, phase velocity dispersion curves from seismic array through the Extended Spatial Auto-Correlation method were analyzed. The H/V curves obtained show a ubiquitous frequency peak between 0.5 Hz and 0.9 Hz due to the deep interface between the metamorphic substrate and sedimentary sequence, and a secondary peak in the 2.5–15 Hz interval in most of the measurement points that may be related to a larger extent of the clay outcrops with respect to what is already known from geological investigations. Joint inversion of dispersion and H/V curves was also performed in order to obtain the velocity profile. Results acquired through the combined use of geophysical methods furnished useful information for seismic hazard evaluation where surface geology is not clearly visible because of urbanization and vegetation cover, thus suggesting that a wide extent of clays may reasonably be the cause of past earthquake damage distribution.

Investigating the Pollino mts. seismic sequence south Italy) by high-resolution analysis

We present an high-quality analysis of the space-time evolution of the seismic activity occurred between 2010 and 2013 in the Pollino Mts. region, in the junction area between the Calabrian Arc and the southern Apennines domains (south Italy)