ALBERT

Description: Since 1997 we maintain and systematically update the European–Mediterranean Regional Centroid Moment Tensor (RCMT) catalog, which contains seismic-moment tensors for earthquakes with moderate magnitude (4.5 〈 M 〈 5.5) in the Mediterranean and European regions. We present 354 new solutions for the period 2005–2008. The Catalog now spans 12 years and contains more than 1000 definitive RCMT solutions. In addition to definitive solutions, we maintain and update a dataset of recent ‘quick’ solutions that are computed soon after an earthquake occurs using the more limited set of data available in quasi-real time. We investigate the reliability of the moment tensor results in the RCMT catalog. Comparison with Global CMT results, which is possible for the larger events (M 〈 5.0) in the RCMT catalog, shows that for 75% of the events, the Kagan angle measure of the similarity of two moment tensors is smaller than 20°, reflecting good agreement of the results. We describe improvements and enhancements in the dissemination of the RCMT results through our web site.

Description: In May 2012, a seismic sequence struck the Emilia region (northern Italy). The mainshock, of Ml 5.9, occurred on May 20, 2012, at 02:03 UTC. This was preceded by a smaller Ml 4.1 foreshock some hours before (23:13 UTC on May 19, 2012) and followed by more than 2,500 earthquakes in the magnitude range from Ml 0.7 to 5.2. In addition, on May 29, 2012, three further strong earthquakes occurred, all with magnitude Ml ≥5.2: a Ml 5.8 earthquake in the morning (07:00 UTC), followed by two events within just 5 min of each other, one at 10:55 UTC (Ml 5.3) and the second at 11:00 UTC (Ml 5.2). For all of the Ml ≥4.0 earthquakes in Italy and for all of the Ml ≥4.5 in the Mediterranean area, an automatic procedure for the computation of a regional centroid moment tensor (RCMT) is triggered by an email alert. Within 1 h of the event, a manually revised quick RCMT (QRCMT) can be published on the website if the solution is considered stable. In particular, for the Emilia seismic sequence, 13 QRCMTs were determined and for three of them, those with M 〉5.5, the automatically computed QRCMTs fitted the criteria for publication without manual revision. Using this seismic sequence as a test, we can then identify the magnitude threshold for automatic publication of our QRCMTs.

Description: We present an update, for years 2003 and 2004, of the European– Mediterranean Regional Centroid Moment Tensor (RCMT) catalog that we maintain since 1997. This update adds 177 new solutions to the database, relating to moderate-magnitude () earthquakes. About 30% of our new solutions also appear in the global CMT catalog: comparison of the two independent determinations generally shows very good agreement. Within the time span covered, the most noticeable seismic sequences occurred in Northern Africa (Boumerdes, Algerian coast in 2003 and Al Hoceima, Morocco in 2004) and in Southern Greece and Dodecanese region (August 2003 and 2004). The complete RCMT catalog for the European and Mediterranean region now covers 8 years, and contains about 600 solutions.

Description: The INGV-Harvard European-Mediterranean Regional Centroid Moment Tensor (RCMT) Catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude (4.5≤M≤5.5) in the Mediterranean region. The database represents an extension to smaller magnitudes of the Harvard global CMT catalog, based on analysis of seismograms recorded at regional distance, and modeling of intermediate period surface waves. The catalog includes about 600 events, 200 of which in the Italian region. This study extends the catalog back in time, for the Italian region, as long as made possible by available digital data – i.e. since 1977 – with the same analysis and inversion method used for current seismicity. As a result, we present here 65 new moment tensors, for years between 1977 and 1997. These solutions represent 45% of the total number of events analyzed, the existing seismograms being often too scarce to allow a stable solution. The new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented, e.g., the Po Plain, the Central to Southern Apennines and the Adriatic Sea. The complete dataset, including previously determined RCMTs and CMTs, represents the seismic deformation in the Italian area during the last 25 years.

Description: On 2009 April 6, the Central Apennines were hit by an Mw = 6.3 earthquake. The region had been shaken since 2008 October by seismic activity that culminated in two foreshocks with Mw 〉 4, 1 week and a few hours before the main shock. We computed seismic moment tensors for 26 events with Mw between 3.9 and 6.3, using the Regional Centroid Moment Tensor (RCMT) scheme. Most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively. The focal mechanisms are all extensional, with a variable and sometimes significant strike-slip component. This geometry agrees with the NE–SW extensional deformation of the Apennines, known from previous seismic and geodetic observations. Events group into three clusters. Those located in the southern area have larger centroid depths and a wider distribution of T-axis directions. These differences suggest that towards south a different fault system was activated with respect to the SW-dipping normal faults beneath L'Aquila and more to the north.

Description: A methodology for a comprehensive probabilistic tsunami hazard analysis is presented for the major sources of tsunamis (seismic events, landslides, and volcanic activity) and preliminarily applied in the Gulf of Naples (Italy). The methodology uses both a modular procedure to evaluate the tsunami hazard and a Bayesian analysis to include the historical information of the past tsunami events. In the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0001 the submarine earthquakes and the submarine mass failures are initially identified in a gridded domain and defined by a set of parameters, producing the sea floor deformations and the corresponding initial tsunami waves. Differently volcanic tsunamis generate sea surface waves caused by pyroclastic density currents from Somma‐Vesuvius. In the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0002 the tsunami waves are simulated and propagated in the deep sea by a numerical model that solves the shallow water equations. In the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0003 the tsunami wave heights are estimated at the coast using the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0004's amplification law. The selected tsunami intensity is the wave height. In the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0005 the probabilistic tsunami analysis computes the long‐term comprehensive Bayesian probabilistic tsunami hazard analysis. In the prior analysis the probabilities from the scenarios in which the tsunami parameter overcomes the selected threshold levels are combined with the spatial, temporal, and frequency‐size probabilities of occurrence of the tsunamigenic sources. The urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0006 probability density functions are integrated with the urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0007 derived from the historical information based on past tsunami data. The urn:x-wiley:jgrc:media:jgrc23818:jgrc23818-math-0008 probability density functions are evaluated to produce the hazard curves in selected sites of the Gulf of Naples.

Description: We describe the main structure and outcomes of the new probabilistic seismic hazard model for Italy, MPS19 [Modello di Pericolosità Sismica, 2019]. Besides to outline the probabilistic framework adopted, the multitude of new data that have been made available after the preparation of the previous MPS04, and the set of earthquake rate and ground motion models used, we give particular emphasis to the main novelties of the modeling and the MPS19 outcomes. Specifically, we (i) introduce a novel approach to estimate and to visualize the epistemic uncertainty over the whole country; (ii) assign weights to each model components (earthquake rate and ground motion models) according to a quantitative testing phase and structured experts’ elicitation sessions; (iii) test (retrospectively) the MPS19 outcomes with the horizontal peak ground acceleration observed in the last decades, and the macroseismic intensities of the last centuries; (iv) introduce a pioneering approach to build MPS19_cluster, which accounts for the effect of earthquakes that have been removed by declustering. Finally, to make the interpretation of MPS19 outcomes easier for a wide range of possible stakeholders, we represent the final result also in terms of probability to exceed 0.15 g in 50 years.

Description: While very large earthquakes are generally confined to subduction zones, the SW Iberian margin –setting of the famous Mw 8.5–8.7, 1755 Lisbon tsunami earthquake- may be an exception to this rule. Evidence for active subduction is not conclusive here, but instead plate convergence in old oceanic lithosphere with large brittle layer thickness can account for the occurrence of great earthquakes along moderate-length faults. We estimate the source parameters of the February 12th 2007, Horseshoe earthquake. Regional moment tensor inversion yields an Mw 6.0, reverse to strike-slip faulting source in the upper mantle. Modelling teleseismic, surface-reflected body waves (pP, pwP, sP) indicates a source depth of 40 km beneath the seafloor. Analysing apparent source time functions allows identifying the preferred fault plane (strike N245°E/ dip 55°/ rake 50°), and estimating rupture area (53 km2) and average slip (0.27 m). Scaling the source characteristics to the size of the 1755 earthquake suggests a fault length of 230–315 km, being compatible with the length of mapped faults in the area.

Description: Active and past subduction systems influence the interpretation and understanding of current tectonics and velocity structures of the upper mantle of the Alps and Apennines. Computational advances over the years made it possible to identify remnant and active slabs up to great depths. 824 stations were used in this study to calculate splitting intensities in an automated process. Compared to SKS measurements, more stable fast polarisation directions were recovered with a pattern paralleling the strike of the mountain belts and a clockwise rotation in the Alps. While strong anisotropy has been recovered over the bulge of the Alps and Apennines chain, weaker anisotropy has been found beneath the Po plain, the eastern sector of the Apennines, in the western sector of Sicily and the external European domain. On the other hand it is still difficult to get reliable depth-dependent anisotropy, therefore we adopted the tomographic method relying on the inversion of splitting intensity (SI). Since it is linearly related to the elastic perturbations of the medium through the 3-D sensitivity kernels, SI can be easily inverted, providing the basis for a better interpretation of shear wave splitting measurements. The anisotropic tomography models obtained so far allowed us to recover the most prominent splitting patterns and see some changes with depth, especially for the strength of anisotropy. Directional changes often seem to be related to the slab domain or dimension (e.g. Central Italy or Sicily).