Central Italy Seismic Sequence Research Articles

Iconic crumbling of the clock tower in Amatrice after 2016 central Italy seismic sequence: advanced numerical insight

The present paper investigates from an advanced numerical point of view the progressive damage of the Amatrice (Rieti, Italy) civic clock tower, after a long sequence of strong earthquakes that struck central Italy in 2016. Two advanced numerical models are here utilised to have an insight into the modalities of progressive damage and the behaviour of the structure under strong non-linear dynamic excitations, namely a Non-Smooth Contact Dynamics (NSCD) and a FE Concrete Damage Plasticity (CDP) models. In both cases, a full 3D detailed discretization is adopted. From the numerical results, both the role played by the actual geometries and the insufficient resistance of the constituent materials are envisaged, showing a good match with actual crack patterns observed after the seismic sequence.

The Central Italy Seismic Sequence (2016): Spatial Patterns and Dynamic Fingerprints

The paper investigates spatio–temporal aspects of the seismic sequence that started in Central Italy (Amatrice, Lazio region) in August 2016, causing hundreds of fatalities and producing major damage to settlements. On one hand, scaling properties of the landscape topography are identified and related to geomorphological processes, supporting the identification of preferential spatial directions in tectonic activity and confirming the role of the past tectonic periods and ongoing processes with respect to the driving of the geomorphological evolution of the area. On the other hand, relations between the spatio–temporal evolution of the sequence and the seismogenic fault systems are studied. The dynamic fingerprints of seismicity are established with the help of events thread analysis (ETA), which characterizes anisotropy in spatio–temporal earthquake patterns. ETA confirms the fact that the direction of the seismogenic normal fault-oriented (N)NW–(S)SE is characterized by persistent seismic activity. More importantly, it also highlights the role of the pre-existing compressive structures, Neogenic thrust and transpressive regional fronts, with a trend-oriented (N)NE–(S)SW, in the stress transfer. Both the fractal features of the topographic surface and the dynamic fingerprint of the recent seismic sequence point to the hypothesis of an active interaction between the Quaternary fault systems and the pre-existing compressional structures.

Seismic actions on structures in the near-source region of the 2016 central Italy sequence

The central Italy seismic sequence began in the latter half of 2016 and continued well into 2017, causing severe damage in the villages close to the source and causing hundreds of casualties. It is a sequence especially interesting to study, from the perspective of seismic actions experienced by structures, because it saw nine M ≥ 5.0 earthquakes within a period of 5 months, rupturing parts of the complex central Apennine mountain range fault system. Consequently, some of the main earthquake engineering issues that arose are the multiple locations where the code-mandated seismic actions were exceeded in more than one of the main events of the sequence and the number of pre- and low-code existing buildings that suffered heavy damage or collapse due to the intensity of individual earthquakes and the cumulative effect of repeated damaging shocks. The present article picks up on these topics and uses probabilistic seismic hazard, as well as the multitude of strong ground motion recordings available from the sequence, to provide a discussion on certain issues, that are all related to the topical subject of seismic actions. These issues are: (1) the unsurprising exceedance of code spectra in the epicentral areas of strong earthquakes; (2) the particular spectral shape and damaging potential of near-source, pulse-like, ground motions, possibly related to rupture directivity; and (3) structural non-linear behaviour in the wake of a sequence that produces repeated strong shaking without the necessary respite for repair and retrofit operations.

Rupture Directivity of the Strongest 2016–2017 Central Italy Earthquakes

AbstractThe along‐strike rupture directivity of 16 of the strongest earthquakes (4.4 ≤ Mw ≤ 6.5) within the 2016–2017 central Italy seismic sequence is estimated by investigating high‐frequency S wave amplitude variations versus source azimuths with an empirical Green's function deconvolution approach. The results confirm that an along‐strike rupture directivity is a persistent feature of normal‐faulting earthquakes in the Apennines. The preferred rupture directions of the 2016–2017 earthquakes and of similar‐magnitude events from the 1997 Umbria‐Marche and 2009 L'Aquila‐Campotosto seismic sequences show a significant spatial consistency. Different sectors of the Apennines show an alternating trend of preferential along‐strike rupture propagation directions with significant spatial and temporal stabilities independent of the magnitude. These results, if confirmed by further data, could lead to more refined hazard assessments of the investigated region.

Dynamic Triggering of Mud Volcano Eruptions During the 2016–2017 Central Italy Seismic Sequence

AbstractOn 24 August 2016 a seismic event (Mw6.0) was the first of the long Central Italy sequence (ongoing at the end of 2017) of medium‐to‐high magnitude earthquakes, with nineMw≥5 up to October 2017, and with about 74.000 seismic events registered after 1 year. The largest was theMw6.5 30 October 2016 event near Norcia. After the major seismic events, 17 mud volcanoes erupted around Monteleone di Fermo village (Marche region). Mud volcano eruptions generally occurred a few hours to a few days after the main earthquakes, suggesting a seismic triggering. We analyzed the peak ground velocities and dynamic stresses during the three largest earthquakes. We also evaluated the static stress changes in order to assess the potential influence of normal stress changes on the feeder system of the activated mud volcanoes. We find a correlation with dynamic stresses, whereas static stress changes are negligible or negative (with values reaching −0.44 bar, clamping feeder dykes). We conclude that seismic shaking (up to ~3.9 bar during Norcia earthquake) is the dominant driver for these eruptions. Finally, we evaluated the response ratio as a function of the dynamic stress. It increases exponentially with peak dynamic stress varying from <10% for peak dynamic stress >0.3 bar to >50% for peak dynamic stress >2 bar, indicating a link between earthquake shaking and mud volcano activity.

Fault Segmentation as Constraint to the Occurrence of the Main Shocks of the 2016 Central Italy Seismic Sequence

AbstractWe perform the finite‐extent fault inversion of the three main events of the 2016 Central Italy seismic sequence using near‐source strong motion records. We demonstrate that both earthquake nucleation and rupture propagation were controlled by segmentation of the (N)NW‐(S)SE trending Quaternary normal faults. The first shock of the sequence (24 August,Mw6.0) ruptured at the relay zone between the Laga Mts (LF) and the Cordone del Vettore (CVF) normal faults. The second shock (26 October,Mw5.9) nucleated at a minor relay zone within the Mt. Vettore‐Mt. Bove fault (VBF), while the third and largest one (30 October,Mw6.5) initiated at the relay zone between the VBF and CVF, triggering the multiple rupture of the VBF, CVF, and probably LF. We show that this latter relay zone corresponds to the deeper, high‐angle, fault zone of the Sibillini Mts cross structure, a thrust‐ramp inherited from the Miocene‐Pliocene contractional phase of the Apennines. This structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largestMw6.5 event that crossed the barrier itself. We suggest that the “young” CVF have started to cut through the barrier acting as a soft‐linkage between the two long‐lived LF and VBF. The evidence that coseismic cumulative slip shows a maximum at the CVF, provided by both slip inversion and original surface rupture data, suggests that the CVF is growing faster than the adjacent faults.

Using multi-band InSAR data for detecting local deformation phenomena induced by the 2016–2017 Central Italy seismic sequence

In this work we exploit X- and C-band InSAR data for detecting local deformation phenomena induced by the 2016–2017 Central Italy seismic sequence. Our goal is to highlight the usefulness of multi-band InSAR analysis for Hazard assessing and Rapid Mapping purposes when in-situ investigations are difficult or dangerous to be performed. Indeed, local seismic-induced effects (such as landslides, avalanches, subsidence, etc.) could severely impact the environment and the population in the surrounding of areas hit by earthquakes. We focused on four areas, named Monte Vettore, Podalla, Bolognola and Cicconi, where InSAR outcomes revealed how the main seismic events of the sequence activated several landslides and secondary faults interested by deformation of ~2–3cm along the satellite Line-of-Sight (LoS). The use of multi-band InSAR data allows the observation of multi-scale deformation phenomena with both different spatial resolution and coverage, highlighting the limits and constraints of different SAR sensors. Moreover, it ensures the crosschecking of displacement patterns retrieved through different InSAR products, especially when no ground truth or in situ ancillary data are available for validation purposes. As a result, the retrieved InSAR information can support the Scientific Community and the Institutions in the management of crisis emergencies.

Assessment of a monumental masonry bell-tower after 2016 Central Italy seismic sequence by long-term SHM

The response of the San Pietro monumental bell-tower located in Perugia, Italy, to the 2016 Central Italy seismic sequence is investigated, taking advantage of the availability of field data recorded by a vibration-based SHM system installed in December 2014 to detect earthquake-induced damages. The tower is located about 85 km in the NW direction from the epicenter of the first major shock of the sequence, the Accumoli Mw6.0 earthquake of August 24th, resulting in a small local PGA of about 30 cm/s2, whereby near-field PGA was measured as 915.97 cm/s2 (E–W component) and 445.59 cm/s2 (N–S component). Similar PGA values also characterized the two other major shocks of the sequence (Ussita Mw5.9 and Norcia Mw6.5 earthquakes of October 26th and 30th, respectively). Despite the relatively low intensity of such earthquakes in Perugia, the analysis of long-term monitoring data clearly highlights that small permanent changes in the structural behavior of the bell-tower have occurred after the earthquakes, with decreases in all identified natural frequencies. Such natural frequency decays are fully consistent with what predicted by non-linear finite element simulations and, in particular, with the development of microcracks at the base of the columns of the belfry. Microcracks in these regions, and in the rest of tower, are however hardly distinguishable from pre-existing ones and from the physiological cracking of a masonry structure, what validates the effectiveness of the SHM system in detecting earthquake-induced damage at a stage where this is not yet detectable by visual inspections.

The Central Italy Seismic Sequence between August and December 2016: Analysis of Strong‐Motion Observations

ABSTRACT Since August 2016, central Italy has been struck by one of the most important seismic sequences ever recorded in the country. In this study, a strong‐motion data set, consisting of nearly 10,000 waveforms, has been analyzed to gather insights about the main features of ground motion, in terms of regional variability, shaking intensity, and near‐source effects. In particular, the shake maps from the three main events in the sequence have been calculated to evaluate the distribution of shaking at a regional scale, and a residual analysis has been performed, aimed at interpreting the strong‐motion parameters as functions of source distance, azimuth, and local site conditions. Particular attention has been dedicated to near‐source effects (i.e., hanging wall/footwall, forward‐directivity, or fling‐step effects). Finally, ground‐motion intensities in the near‐source area have been discussed with respect to the values used for structural design. In general, the areas of maximum shaking appear to reflect, primarily, rupture complexity on the finite faults. Large ground‐motion variability is observed along the Apennine direction (northwest–southeast) that can be attributed to source‐directivity effects, especially evident in the case of small‐magnitude aftershocks. Amplifications are observed in correspondence to intramountain basins, fluvial valleys, and the loose deposits along the Adriatic coast. Near‐source ground motions exhibit hanging‐wall effects, forward‐directivity pulses, and permanent displacement.

Time–Space Evolution of Seismic Strain Release in the Area Shocked by the August 24–October 30 Central Italy Seismic Sequence

In this study, we analyze the space–time evolution of the seismic strain release in the area shocked by the still ongoing Italian Central Apennines seismic crisis started on August 24, 2016 and culminated with the October 30 main shock of Mw 6.5. Specifically, we examine the variation in time and space of the seismic strain release rate with the aim of identifying the presence of peculiar seismicity patterns, such as seismic gaps, according to the seismic cycle theory. To this end, seismic strain rates are checked for consistency with strain rates from GPS measurements to possibly adjust them for missing events due to limited seismic catalog extension or incompleteness at large magnitudes. Our results has revealed that the seismic crisis followed a long-term quiescence of about 310 years, characterized by the absence of M6.5+ earthquakes, and marked by an almost steady release of seismic deformation. Such temporal gap started after the occurrence of two nearby strong events in 1703 (Valnerina and L’Aquila earthquakes with magnitudes of 6.9 and 6.7, respectively) and terminated with the beginning of the current Central Apennines seismic crisis.

The 2016 Central Italy Seismic Sequence: A First Look at the Mainshocks, Aftershocks, and Source Models

The 2016 central Italy seismic sequence consists so far of a series of moderate‐to‐large earthquakes activating within a few months along a 60‐km‐long and Apenninic‐trending normal‐fault system. Regrettably, the high vulnerability of the local infrastructure and the shallowness of the largest events (depth around 8 km) resulted in 299 casualties and more than 20,000 homeless, with great difficulties in the disaster management. The sequence evolved around its largest event ( M w 6.5, 30 October) that occurred right in the middle of a fault system already activated two months before with a first M w 6.0 mainshock (on 24 August) located to the south near the town of Amatrice. Then, another M w 5.9 mainshock occurred just four days before the largest mainshock (26 October) at the northernmost extent of the sequence, near the town of Visso. We analyze the space–time evolution of the first four months of seismic activity through the relocation of ∼26,000 earthquakes and the kinematic source models of the three mainshocks. All the main events nucleated at the base of a southwest‐dipping normal‐fault system segmented by the presence of crosscutting compressional structures. The presence of these inherited faults, separating diverse geological domains, appears to modulate evolution of the sequence interfering with coseismic slip distribution and fault segments interaction. Several secondary antithetic and synthetic faults are located at a shallow depth (<4 km), both in the hanging wall and footwall. The whole normal fault system, confined within the first 8 km of the upper crust, is bounded below by a shallow east‐dipping and 2–3‐km‐thick layer in which small events plus a series of large extensional aftershocks (≈ M w 4) occur, possibly decoupling the upper and lower crusts.

The development of a cloud-GIS platform for the management and sharing of geographic data during the central Italy seismic sequence

&lt;p&gt;&lt;em&gt;For several years, the &lt;/em&gt;&lt;em&gt;Istituto Nazionale di Geofisica e Vulcanologia&lt;/em&gt;&lt;em&gt; (INGV, National Institute of Geophysics and Volcanology) uses ArcGIS Online (&lt;/em&gt;&lt;a href="http://www.arcgis.com/"&gt;&lt;em&gt;www.arcgis.com&lt;/em&gt;&lt;/a&gt;&lt;em&gt;), to share information about the real-time seismicity in Italy with other geographical data, geological and seismological, through the development of different WebGIS applications with various customized functionalities. During the earthquake emergency in Central Italy in August 2016, WebGIS applications have been widely used. They derive from a common platform developed a few months earlier by the LABGIS of INGV-Irpinia.&lt;/em&gt; &lt;em&gt;This platform has enabled the management and updating of the seismic data of the sequence in real time and their integration with the leading INGV databases seismological and seismotectonic and those of other Institutes.&lt;/em&gt; &lt;em&gt;Moreover, these applications have permission to manage and share information and even data from the activities of the INGV Emergency Groups , such as the location and characteristics of seismic and accelerometric temporary stations installed by the teams of SISMIKO and EMERSITO and the geological observations from the EMERGEO Group.&lt;/em&gt;&lt;/p&gt;

Some reasoning on the improvement of the ETAS modeling at the occurrence of the 2016 Central Italy seismic sequence

&lt;p&gt;This study presents an application of the ETAS model to the first 20 days of the 2016 Central Italy sequence. Despite of the provisional nature of data, the model is able to describe the occurrence rate, but for the first hours after the mainshock occurrence. A sensitivity analysis of the model to two uncertainty sources, the model parameters and the occurrence history, shows that the second has a main role in controlling the performance of the ETAS model, more than the uncertainty on parameters.&lt;br /&gt;Previous results, together with the clear inability of ETAS to forecast the occurrence of a sequence before its starting time, give important suggestions about possible improvements. Here, a very preliminary attempt in this sense is presented.&lt;/p&gt;

Preliminary remarks on the earthquake focal mechanism forecasts applied in the Amatrice sequence (central Italy)

&lt;p&gt;We place the Amatrice (central Italy) seismic sequence and the related epicentral area in a contest of Probabilistic Seismic Hazard Analysis (PSHA). We apply a procedure to compute the probability to observe in the future a normal, reverse or strike-slip event and the average distribution of the P, T and N axes. This is a fundamental step to reduce the uncertainty connected to the Ground Motion Prediction Equation models, part of PSHA. For this purpose we use a significant focal mechanism catalogue and the latest present-day stress field data release for Italy to produce forecasted information that we compare with the equivalent data observed during the sequence.&lt;/p&gt;

SISMIKO: emergency network deployment and data sharing for the 2016 central Italy seismic sequence

&lt;p&gt;At 01:36 UTC (03:36 local time) on August 24th 2016, an earthquake Mw 6.0 struck an extensive sector of the central Apennines (coordinates: latitude 42.70° N, longitude 13.23° E, 8.0 km depth). The earthquake caused about 300 casualties and severe damage to the historical buildings and economic activity in an area located near the borders of the Umbria, Lazio, Abruzzo and Marche regions. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) located in few minutes the hypocenter near Accumoli, a small town in the province of Rieti. In the hours after the quake, dozens of events were recorded by the National Seismic Network (Rete Sismica Nazionale, RSN) of the INGV, many of which had a ML &amp;gt; 3.0. The density and coverage of the RSN in the epicentral area meant the epicenter and magnitude of the main event and subsequent shocks that followed it in the early hours of the seismic sequence were well constrained. However, in order to better constrain the localizations of the aftershock hypocenters, especially the depths, a denser seismic monitoring network was needed. Just after the mainshock, SISMIKO, the coordinating body of the emergency seismic network at INGV, was activated in order to install a temporary seismic network integrated with the existing permanent network in the epicentral area. From August the 24th to the 30th, SISMIKO deployed eighteen seismic stations, generally six components (equipped with both velocimeter and accelerometer), with thirteen of the seismic station transmitting in real-time to the INGV seismic monitoring room in Rome. The design and geometry of the temporary network was decided in consolation with other groups who were deploying seismic stations in the region, namely EMERSITO (a group studying site-effects), and the emergency Italian strong motion network (RAN) managed by the National Civil Protection Department (DPC). Further 25 BB temporary seismic stations were deployed by colleagues of the British Geological Survey (BGS) and the School of Geosciences, University of Edinburgh in collaboration with INGV. All data acquired from SISMIKO stations, are quickly available at the European Integrated Data Archive (EIDA). The data acquired by the SISMIKO stations were included in the preliminary analysis that was performed by the Bollettino Sismico Italiano (BSI), the Centro Nazionale Terremoti (CNT) staff working in Ancona, and the INGV-MI, described below.&lt;/p&gt;

The Italian Seismic Bulletin: strategies, revised pickings and locations of the central Italy seismic sequence

&lt;p&gt;The central Italy seismic sequence, started with the Mw = 6.0 Amatrice earthquake on August 24th 2016, is the first significant one after the Italian Seismic Bulletin (BSI) changed its analysis strategies in 2015. These new strategies consist on the release of the BSI every four months, the review of the events with ML ≥ 1.5 and the priority on the review of events with ML ≥ 3.5. Furthermore, in the last year we improved the bulletin tools and made possible the analysis of all the stations whose data are stored in the European Integrated Data Archive (EIDA). The new procedures and software utilities allowed, during the first month of 2016 emergency, to integrate, in the Bulletin, the temporary stations installed by the emergency group SISMIKO, both in real–time transmission and in stand-alone recording. In the early days of the sequence many of the BSI analysts were engaged in the monitoring room shifts, nevertheless at the end of August all events occurred in those days with ML ≥ 4 were analyzed; the largest event recovered and localized is a ML = 4.5 event immediately following the main shock. In September 2016, 83 events with ML ≥ 3.5 were analyzed and re-checked, the number of pickings greatly improved. The focal mechanism of the main shock was evaluated using first motion polarities, and compared with the available Time Domain Moment Tensors and Regional Centroid Moment Tensor. The first eight hours of the day on August 24th, the most critical for the INGV surveillance room, were carefully analyzed: the number of located events increased from 133 to 408. The magnitude of completeness, after the analysis of the BSI, has dropped significantly from about 3.5 to 2.7. The mainshock focal mechanism and the relative locations of the first 8 hours’ aftershocks give clues on the initial fault activation. The seismic sequence in November 2016 is still ongoing; it included a mainshock of Mw = 6.5 on October 30th and 3 events of magnitude greater than 5.0 one on August 24th and two on October 26th.&lt;/p&gt;

Assessing soil-structure interaction during the 2016 Central Italy seismic sequence (Italy): preliminary results

&lt;p&gt;&lt;em&gt;We used the moderate-magnitude aftershocks succeeding to the 2016 August 24&lt;sup&gt;th&lt;/sup&gt;, Mw = 6.0, Amatrice (Italy) mainshok to asses, specially during an ongoing seismic sequence, the soil-structure interaction where cultural Heritage is involved. We have chosen as case study the&lt;/em&gt;&lt;em&gt; San Giovanni Battista&lt;/em&gt;&lt;em&gt; church (A.D. 1039) in Acquasanta Terme town, about 20 Km northeast of Amatrice. First of all we studied the soil shaking features in order to characterize the input to the monument. Then, using the recordings in the church, we tried to figure out how the input seismic energy is distributed over the different monument parts. Some preliminary results are shown and discussed.&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;em&gt;&lt;br /&gt;&lt;/em&gt;&lt;/p&gt;

The first month of the 2016 central Italy seismic sequence: fast determination of time domain moment tensors and finite fault model analysis of the ML 5.4 aftershock

&lt;p&gt;We present the revised Time Domain Moment Tensor (TDMT) catalogue for earthquakes with M_L larger than 3.6 of the first month of the ongoing Amatrice seismic sequence (August 24th - September 25th). Most of the retrieved focal mechanisms show NNW–SSE striking normal faults in agreement with the main NE-SW extensional deformation of Central Apennines. We also report a preliminary finite fault model analysis performed on the larger aftershock of this period of the sequence (M_w 5.4) and discuss the obtained results in the framework of aftershocks distribution.&lt;/p&gt;

Short-term earthquake forecasting experiment before and during the L’Aquila (central Italy) seismic sequence of April 2009

&lt;div class="page" title="Page 1"&gt;&lt;div class="layoutArea"&gt;&lt;div class="column"&gt;&lt;p&gt;In this paper, we compare the forecasting performance of several statistical models, which are used to describe the occurrence process of earthquakes in forecasting the short-term earthquake probabilities during the L’Aquila earthquake sequence in central Italy in 2009. These models include the Proximity to Past Earthquakes (PPE) model and two versions of the Epidemic Type Aftershock Sequence (ETAS) model. We used the information gains corresponding to the Poisson and binomial scores to evaluate the performance of these models. It is shown that both ETAS models work better than the PPE model. However, in comparing the two types of ETAS models, the one with the same fixed exponent coefficient (&lt;span&gt;alpha)&lt;/span&gt; = 2.3 for both the productivity function and the scaling factor in the spatial response function (ETAS I), performs better in forecasting the active aftershock sequence than the model with different exponent coefficients (ETAS II), when the Poisson score is adopted. ETAS II performs better when a lower magnitude threshold of 2.0 and the binomial score are used. The reason is found to be that the catalog does not have an event of similar magnitude to the L’Aquila mainshock (M&lt;sub&gt;w&lt;/sub&gt; 6.3) in the training period (April 16, 2005 to March 15, 2009), and the (&lt;span&gt;alpha)&lt;/span&gt;-value is underestimated, thus the forecast seismicity is underestimated when the productivity function is extrapolated to high magnitudes. We also investigate the effect of the inclusion of small events in forecasting larger events. These results suggest that the training catalog used for estimating the model parameters should include earthquakes of magnitudes similar to the mainshock when forecasting seismicity during an aftershock sequence.&lt;/p&gt;&lt;/div&gt;&lt;/div&gt;&lt;/div&gt;

The 2012 Emilia, Italy, Quasi-Consecutive Triggered Mainshocks: Implications for Seismic Hazard

The 2012 Emilia seismic sequence in central Italy represents an illustrative example of quasi‐consecutive triggering with several mainshocks occurring within a few hours or a few days. The sequence was characterized by seven earthquakes of moment magnitude M w>5, rupturing adjacent fault segments of the buried fold arc of the northern Apennines, for a total length of about 50 km (Scognamiglio et al. , 2012; Fig. 1). The occurrence of so many large earthquakes, in such a short time window, suggests a possible interpretation in terms of mutual, static (Ganas et al. , 2012), or dynamic (Convertito et al. , 2013) triggering. In this article, we discuss the consequences of a consecutive succession of earthquakes, that is, a succession of close earthquakes that occur almost simultaneously. Figure 1. Geographic representation of the area interested by the Emilia sequence. The figure shows the epicenters and magnitudes of the seven major events analyzed in this study (black stars). Gray stars represent the aftershocks of the whole sequence, whereas the black triangles identify the stations used to compute the response spectra. Multiple triggering—with variable time delays—has been observed in several damaging earthquake sequences of the Italian Apennine belt. In the central Apennines, the 2009 L’Aquila M w 6.3 earthquake was followed, the day after, by an M w 5.6 event occurred at the southeast edge of the main fault. This seismic sequence has been the deadliest one in Italy, with almost 300 victims, since 1980. The seismicity of the whole sequence spread over a 40 km long fault system (Chiarabba et al. , 2009). The 2002 Molise seismic sequence is remembered for two major shocks M w 5.8 and 5.7 that occurred within a few hours causing severe damage and destroying a school populated by children (Vallee and Di Luccio, 2005). The 1997–1998 Umbria–Marche seismic sequence was characterized by …