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

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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.

Present-day kinematics and deformation processes in the southern Tyrrhenian region: new insights on the northern Sicily extensional belt

We performed a new analysis of updated and accurate sets of seismic and GNSS data relative to the southern Tyrrhenian region. Detailed velocity field and crustal strain distribution coming from integration of episodic and continuous measurements at more than 160 geodetic sites (spanning the 1994-2015 period) have been evaluated together with the spatial distribution of recent seismicity and an updated catalogue of waveform inversion fault-plane solutions relative to the period 1976-2014. In agreement with previous investigations, we have found that the kinematics of the study area is quite homogeneous except for the north-eastern corner of Sicily which moves almost coherently with southern Calabria in response to the SE-ward rollback of the Ionian slab. The rest of the study region shows a NNW-trending velocity field in agreement with the direction of the Nubia-Eurasia convergence and it is mainly interested by a major compressive domain. NNW-oriented compression is particularly highlighted by seismic data along the E-W trending seismic belt located in the southern Tyrrhenian Sea. In the framework of such compressive regime, the E-W trending extensional domain of northern Sicily is also clearly depicted both by seismic and geodetic data. The cause of this extensional domain framed inside a mainly compressive one represents an open question in the recent scientific debate. Comparisons between our results and literature information on regional geology and crustal structure led us to investigate whether the extension could occur as local response to the thrusting dynamics of the southern Tyrrhenian belt, favoured by the presence of pre-existing weakness zones. We then propose a first attempt to evaluate such a possible causal relationship by means of Finite Element Method (FEM) and Coulomb Stress Change (CSC) modelling. In particular, we adopted a FEM approach to investigate the deformation pattern produced by thrust faulting of southern Tyrrhenian belt, along a 2D profile crossing both the compressive belt and the extensional one in northern Sicily. We also estimated the CSC due to the thrust faulting on normal receiving faults fairly reproducing pre-existing structures of northern Sicily. Modelling results indicate that the thrust faulting activity along the Southern Tyrrhenian compressive margin could be effective in promoting extensional processes in northern Sicily. We have so shown that the local response to thrust faulting activity may concur, even in combination with other processes, to generate the crustal stretching of northern Sicily.Published418-4331T. Deformazione crostale attivaJCR Journa

Ambient noise measurements for preliminary microzoning studies in the city of Messina, Sicily

On December 28th 1908 the city of Messina was destroyed by one of the most catastrophic Italian earthquakes of the last centuries (Mw=7.1, I = XI) which caused more than 60000 deaths and destruction in many localities of Sicily and Calabria. In this study we present the results of more than 100 seismic ambient noise measurements carried out in the framework of the first massive seismic site response survey performed in the city of Messina. Starting from geological information and historical reports reconstructing the damage scenario of the 1908 event, we have identified several sites particularly interesting for seismic response investigations. This extensive survey allowed us to evaluate the fundamental resonance frequency for each investigated site and to identify the areas prone to site amplification. Measurements have been performed by using 3-component velocimeter, Micromed Tromino, and the collected dataset has been processed by applying the Horizontal-to-Vertical Spectral Ratio technique. For each investigated site we provide the fundamental resonance frequency and a preliminary information on the metamorphic bedrock depth. The massive dataset collected and the results obtained will be useful for the seismic microzonation of the urban territory of Messina.