Deformation and Fault Propagation at the Lateral Termination of a Subduction Zone: The Alfeo Fault System in the Calabrian Arc, Southern Italy

The Calabrian Arc subduction, southern Italy, is a critical structural element in the geodynamic evolution of the central Mediterranean basin. It is a narrow, northwest-dipping slab bordered to the southwest by the Alfeo Fault System (AFS) and to the northeast by a gradual transition to a collision. We used a dense set of two-dimensional high-penetration (up to 12 s) multichannel seismic reflection profiles to build a three-dimensional model that spans the AFS for over 180 km of its length. We find that the AFS is made up of four deep-seated major blind segments that cut through the lower plate, offset the subduction interface, and only partially propagate upward across the accretionary wedge in the upper plate. These faults evolve with a scissor-like mechanism (mode III of rupture propagation). The shallow part of the accretionary wedge is affected by secondary deformation features well aligned with the AFS at depth but also mechanically decoupled from it. Despite the decoupling, the syn-tectonic Pliocene-Holocene deposits that fill in the accommodation space generated by the AFS activity at depth, constrain the age of inception of the AFS and allows us to estimate its throw and propagation rates. The maximum throw value is 6,000 m in the NW sector and decreases to the SE. Considering the age of faulting, the fault throw rate decreases accordingly from 2.31 mm/yr to 1 mm/yr. The propagation rate decreases from 62 mm/yr to 15 mm/yr during the Pliocene-Pleistocene, suggesting that also the Calabrian subduction process should have slowed down accordingly. The detailed spatial and temporal reconstruction of this type of faults can reveal necessary information about the evolution of subduction systems

Importance of earthquake rupture geometry on tsunami modelling: the Calabrian Arc subduction interface (Italy) case study

SUMMARY The behaviour of tsunami waves at any location depends on the local morphology of the coasts, the encountered bathymetric features, and the characteristics of the source. However, the importance of accurately modelling the geometric properties of the causative fault for simulations of seismically induced tsunamis is rarely addressed. In this work, we analyse the effects of using two different geometric models of the subduction interface of the Calabrian Arc (southern Italy, Ionian Sea) onto the simulated tsunamis: a detailed 3-D subduction interface obtained from the interpretation of a dense network of seismic reflection profiles, and a planar interface that roughly approximates the 3-D one. These models can be thought of as representing two end-members of the level of knowledge of fault geometry. We define three hypothetical earthquake ruptures of different magnitudes (Mw 7.5, 8.0, 8.5) on each geometry. The resulting tsunami impact is evaluated at the 50-m isobath in front of coastlines of the central and eastern Mediterranean. Our results show that the source geometry imprint is evident on the tsunami waveforms, as recorded at various distances and positions relative to the source. The absolute differences in maximum and minimum wave amplitudes locally exceed one metre, and the relative differences remain systematically above 20 per cent with peaks over 40 per cent. We also observe that tsunami energy directivity and focusing due to bathymetric waveguides take different paths depending on which fault is used. Although the differences increase with increasing earthquake magnitude, there is no simple rule to anticipate the different effects produced by these end-member models of the earthquake source. Our findings suggest that oversimplified source models may hinder our fundamental understanding of the tsunami impact and great care should be adopted when making simplistic assumptions regarding the appropriateness of the planar fault approximation in tsunami studies. We also remark that the geological and geophysical 3-D fault characterization remains a crucial and unavoidable step in tsunami hazard analyses

Database of Individual Seismogenic Sources (DISS), Version 3.2.1: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas

Istituto Nazionale di Geofisica e VulcanologiaPublished2T. Deformazione crostale attiva3T. Sorgente sismica4T. Sismicità dell'Italia5T. Sismologia, geofisica e geologia per l'ingegneria sismica6T. Studi di pericolosità sismica e da maremoto4IT. Banche dat

RETRACE-3D PROJECT, a multidisciplinary approach for the construction of a 3D crustal model: first results and seismotectonic implications

The RETRACE-3D (centRal italy EarThquakes integRAted Crustal modEl) Project has been launched with the ambitious goal to build, as first result, a new, robust, 3D geological model of broad consensus of the area struck by the 2016-2018 Central Italy seismic sequencePublishedBologna3T. Sorgente sismica4T. Sismicità dell'Itali

NEAMTHM18

European-Union Civil Protection Mechanism, DG-ECHO, Agreement Number: ECHO/SUB/2015/718568/PREV26Published6T. Studi di pericolosità sismica e da maremoto1SR TERREMOTI - Sorveglianza Sismica e Allerta Tsunami2SR TERREMOTI - Gestione delle emergenze sismiche e da maremoto4IT. Banche dat

The making of the NEAM Tsunami Hazard Model 2018 (NEAMTHM18)

The NEAM Tsunami Hazard Model 2018 (NEAMTHM18) is a probabilistic hazard model for tsunamis generated by earthquakes. It covers the coastlines of the North-eastern Atlantic, the Mediterranean, and connected seas (NEAM). NEAMTHM18 was designed as a three-phase project. The first two phases were dedicated to the model development and hazard calculations, following a formalized decision-making process based on a multiple-expert protocol. The third phase was dedicated to documentation and dissemination. The hazard assessment workflow was structured in Steps and Levels. There are four Steps: Step-1) probabilistic earthquake model; Step-2) tsunami generation and modeling in deep water; Step-3) shoaling and inundation; Step-4) hazard aggregation and uncertainty quantification. Each Step includes a different number of Levels. Level-0 always describes the input data; the other Levels describe the intermediate results needed to proceed from one Step to another. Alternative datasets and models were considered in the implementation. The epistemic hazard uncertainty was quantified through an ensemble modeling technique accounting for alternative models' weights and yielding a distribution of hazard curves represented by the mean and various percentiles. Hazard curves were calculated at 2,343 Points of Interest (POI) distributed at an average spacing of ∼20 km. Precalculated probability maps for five maximum inundation heights (MIH) and hazard intensity maps for five average return periods (ARP) were produced from hazard curves. In the entire NEAM Region, MIHs of several meters are rare but not impossible. Considering a 2% probability of exceedance in 50 years (ARP≈2,475 years), the POIs with MIH >5 m are fewer than 1% and are all in the Mediterranean on Libya, Egypt, Cyprus, and Greece coasts. In the North-East Atlantic, POIs with MIH >3 m are on the coasts of Mauritania and Gulf of Cadiz. Overall, 30% of the POIs have MIH >1 m. NEAMTHM18 results and documentation are available through the TSUMAPS-NEAM project website (http://www.tsumaps-neam.eu/), featuring an interactive web mapper. Although the NEAMTHM18 cannot substitute in-depth analyses at local scales, it represents the first action to start local and more detailed hazard and risk assessments and contributes to designing evacuation maps for tsunami early warning

The Making of the NEAM Tsunami Hazard Model 2018 (NEAMTHM18)

ABSTRACT: The NEAM Tsunami Hazard Model 2018 (NEAMTHM18) is a probabilistic hazard model for tsunamis generated by earthquakes. It covers the coastlines of the North-eastern Atlantic, the Mediterranean, and connected seas (NEAM). NEAMTHM18 was designed as a three-phase project. The first two phases were dedicated to the model development and hazard calculations, following a formalized decision-making process based on a multiple-expert protocol. The third phase was dedicated to documentation and dissemination. The hazard assessment workflow was structured in Steps and Levels. There are four Steps: Step-1) probabilistic earthquake model; Step-2) tsunami generation and modeling in deep water; Step-3) shoaling and inundation; Step-4) hazard aggregation and uncertainty quantification. Each Step includes a different number of Levels. Level-0 always describes the input data; the other Levels describe the intermediate results needed to proceed from one Step to another. Alternative datasets and models were considered in the implementation. The epistemic hazard uncertainty was quantified through an ensemble modeling technique accounting for alternative models' weights and yielding a distribution of hazard curves represented by the mean and various percentiles. Hazard curves were calculated at 2,343 Points of Interest (POI) distributed at an average spacing of ∼20 km. Precalculated probability maps for five maximum inundation heights (MIH) and hazard intensity maps for five average return periods (ARP) were produced from hazard curves. In the entire NEAM Region, MIHs of several meters are rare but not impossible. Considering a 2% probability of exceedance in 50 years (ARP≈2,475 years), the POIs with MIH >5 m are fewer than 1% and are all in the Mediterranean on Libya, Egypt, Cyprus, and Greece coasts. In the North-East Atlantic, POIs with MIH >3 m are on the coasts of Mauritania and Gulf of Cadiz. Overall, 30% of the POIs have MIH >1 m. NEAMTHM18 results and documentation are available through the TSUMAPS-NEAM project website (http://www.tsumaps-neam.eu/), featuring an interactive web mapper. Although the NEAMTHM18 cannot substitute in-depth analyses at local scales, it represents the first action to start local and more detailed hazard and risk assessments and contributes to designing evacuation maps for tsunami early warning

Gravity modelling of central Apennines deep structures along CROP11 seismic profile.

Gravity method represents an important tool for the definition of the deep structural style of a mountain belt. Moreover, the possibility to use independent geophysical data sets, such as seismic reflection data and gravity data results particularly appropriate for the reconstruction of the deeper portion of the crust.In the present work 2D and 3D gravity data inversion was used to study deep crust. The interpretation of gravity data are based on the deep-sourced gravity anomalies map obtained by means of the stripping procedure starting from the Bouguer anomalies. The reduction density for Bouguer anomaly correction was 2.67 g/cm3. The stripping has been done on the base of accurate 3D lithological model of the surficial Apennine units (BERNABINI et alii, 1996a; BERNABINI et alii, 2002a; 2002b). As the stripped gravity data concerns essentially the deep crust, the modelling presented in this work takes into account only deep-sourced gravity anomalies. The gravity modelling are constrained by DSS data (NICOLICH, 1981; SCARASCIA et al., 1994; BIELLA et al., 1997) and by deep reflection seismic data obtained along the CROP 11 line (BILLI et al., 2001; BIGI et al., 2003), that crosses the Apennine from Marina di Tarquinia (W) to Vasto (E).The regional gravity anomaly trend of Central Italy is interpreted and its role as an independent constraint for the geological interpretation of the CROP 11 seismic line is also discussed. Gravity data used in this work consist in Bouguer anomaly values provided by National Geological Service and obtained by a 3 km sampling of the database of all the Italian gravimetric stations. (*) This work has been carried out within the CROP 11 project (prof. M. Parotto co-ordinator)

Il contributo dell’analisi gravimetrica alla ricostruzione dell’assetto strutturale profondo.

This study, carried out in central-southern Italy, shows that surficial density contrasts markedly affect the regional gravity anomalies trend, conditioning both the reconstruction and the interpretation of this trend. Actually, Bouguer anomalies can be very dependent on density contrast in the upper crust, which can, in turn, greatly condition the Bouguer anomalies spatial distribution. Therefore the Bouguer anomalies distribution cannot be considered a direct expression of the deep structures. Maps of the Moho based on the Bouguer anomaly trend, or on filtered gravity anomalies, are affected by this uncertainty.To deal with this problem we applied a methodology that can be used to sort out the contributions of deep and surficial bodies. Such a methodology, called “stripping”, was applied in the present work. The obtained map of the deep-sourced gravity anomalies from this region provides a useful tool for investigating the deep features of the Apennines, revealing that also the deep structures of the Apennine chain are characterized by low cylindrism

Earthquake-fault dip angle statistics for PSHA analyses

The dip angle is one of the fault parameters that mostly affects seismic hazard analyses because it not only influences the inference of other fault parameters (e.g. down-dip width, earthquake maximum magnitude based on fault scaling laws) but also, and most importantly, controls the fault-to-site distance values of ground motion estimates. We present the results of a global survey of earthquake-fault dip angles (G-DIP) and analyze their empirical distribution for various faulting categories. These new empirical statistics are derived from an extended and homogeneous dataset, thereby improving previous fault dip-angle distributions. Subduction interface sources are considered separately from other thrust faults. In agreement with other studies, important deviations from the classical Anderson’s predictions are found for all faulting categories (Fig. 1). Our results can effectively be used as distribution priors for characterizing the geometry of poorly known seismogenic faults in seismic hazard analyses and earthquake-fault modeling experiments.This work was supported by the INGV projects “Abruzzo” (code: RBAP10ZC8K_003). MMT was supported by the INGV-DPC-CPS Agreement.PublishedLenzburg, Switzerland1T. Deformazione crostale attiva5T. Modelli di pericolosità sismica e da maremot