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On 24 August 2016, a Mw 6.0 earthquake started a damaging seismic sequence in central Italy. The historical center of Amatrice village reached the XI degree (MCS scale) but the high vulnerability alone could not explain the heavy damage. Unfortunately, at the time of the earthquake only AMT station, 200 m away from the downtown, recorded the mainshock, whereas tens of temporary stations were installed afterwards. We propose a method to simulate the ground motion affecting Amatrice, using the FFT amplitude recorded at AMT, which has been modified by the standard spectral ratio (SSR) computed at 14 seismic stations in downtown. We tested the procedure by comparing simulations and recordings of two later mainshocks (Mw 5.9 and Mw 6.5), underlining advantages and limits of the technique. The strong motion variability of simulations was related to the proximity of the seismic source, accounted for by the ground motion at AMT, and to the peculiar site effects, described by the transfer function at the sites. The largest amplification characterized the stations close to the NE hill edge and produced simulated values of intensity measures clearly above one standard deviation of the GMM expected for Italy, up to 1.6 g for PGA.

The Amatrice earthquake of August 24th, 2016 (Mw 6.0) struck an area that in the national reference seismic hazard model (MPS04) is characterized by expected horizontal peak ground acceleration (PGA) with 10% probability of exceedance in 50 years higher than 0.25 g. After the occurrence of moderate-to-large magnitude earthquakes with a strong impact on the population, such as the L’Aquila 2009 and Emilia 2012 ones (Mw 6.1 and 5.9, respectively), possible underestimations of the seismic hazard by MPS04 were investigated, in order to analyze and evaluate the possible need for its update. One of the most common misunderstanding is to compare recorded PGA only with PGA with 10% probability of exceedance in 50 years. Moreover, by definition, probabilistic models cannot be validated (or rejected) on the basis of a single event. However, comparisons of forecasted shakings with observed data are useful for understating the consistency of the model. It is then worth highlighting the importance of these comparisons. In fact, MPS04 is the basis for the current Italian building code to provide the effective design procedures and, thus, any modification to the seismic hazard would also affect the building code.In this paper, comparisons between recorded ground motion during the Amatrice earthquake and seismic hazard estimates are performed, showing that the observed accelerations are consistent with the values expected by the MPS04 model.

The 2016 August 24 Amatrice earthquake occurred at 03:36 local time in Central Apennines Italy with an epicentre at 43.36°E, 38.76°N, Istituto Nazionale di Geofisica e Vulcanologia (INGV), few kilometers north of the city of Amatrice. The earthquake ruptured a North-West (NW)–South-East (SE) oriented normal fault dipping toward the South-West (SW) (Scognamiglio et al., 2016). High values of peak ground acceleration (~0.45 g) were observed close to Amatrice (3 stations being few kilometer distances from the fault). The present study presents an overview of the main features of the seismic ground shaking during the Amatrice earthquake. We analyze the ground motion characteristics of the main shock in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and spectral accelerations (SA, 5 per cent of critical damping). In order to understand the characteristics of the ground motions induced by Amatrice earthquake, we also study the source-related effects relative to the fault rupture directivity.

We present some preliminary results on the mapping of coseismically-induced ground ruptures following the Aug. 24, 2016, Central Italy earthquake (Mw 6.0). The seismogenic source, as highlighted by InSAR and seismological data, ruptured across two adjacent structures: the Vettore and Laga faults. We collected field data on ground breaks along the whole deformed area and two different scenarios of on-fault coseismic displacement arise from these observations. To the north, along the Vettore fault, surface faulting can be mapped quite continuously along a well-defined fault strand while such features are almost absent to the south, along the Laga fault, where flysch-like marly units are present. A major lithological control, affects the surface expression of faulting, resulting in a complex deformation pattern.

A macroseismic investigation of the August 24, 2016, Mw=6.0 Central Italy earthquake, was carried out through an online web survey. Data were collected through a macroseismic questionnaire available at the website www.haisentitoilterremoto.it, managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). Over 12000 questionnaires were compiled soon after the seismic occurrence, coming from over 2600 municipalities. A statistical analysis was applied to the data collected in order to investigate the spatial distribution of intensity of the earthquake. The macroseismic intensity field (I) was described by identifying three main components: an isotropic component (II), a regional anisotropic component (IA) and a local random variations parameter (). The anisotropic component highlighted specific and well-defined geographical areas of amplification and attenuation. In general, the area between the Adriatic coast and Apennines Chain was characterized by an amplification of intensity, while the West side of the Apennines showed attenuation, in agreement with the domains found by other works focused on the analysis of instrumental data. Moreover, the regional macroseismic field showed similarities with instrumental PGA data. The results of our analysis confirm the reliability of web questionnaire data.

This paper deals with a preliminary spatial and temporal analysis of the b-value variability, observed in the ar-ea where the August 2016 Amatrice earthquake (M_L 6.0) occurred. With comparison of the pre-and post-periods of the mainshock, an investigation of anomalous zone of b-values was performed aiming to find possi-ble links with barriers and/or asperities in the crustal volume where seismic sequence was developed. Prelimi-nary results show an area with high b-value (b=1.6) where the mainshock originated. Conversely, two low b-value (b=0.8) volumes are located at the border of the seismogenic structure. The location of these two areas is consistent with a preliminary fault slip inversion, suggesting the presence of two highly stressed patches of co-seismic deformation located NW and SE of the mainshock, with a high potentiality to rupture causing a possible moderate or larger event: the first one in the North (Norcia), the second one in South, next to the area of Amatrice and Campotosto.

On 24 August 2016, at 1.36:32 GMT, a MW 6.0 earthquake with epicenter located below the village of Accumoli, struck a wide area among the boundaries of Lazio, Abruzzo, Umbria and Marche regions (Central Italy): the main event caused the collapse of several buildings and about 300 fatalities, mainly in the towns of Amatrice, Arquata del Tronto and Accumoli. The main event was recorded by about 350 sensors, belonging to Italian Accelerometric Network (Rete Accelerometrica Nazionale, RAN), operated by the Department of Civil Protection (DPC), to the Italian Seismic Network (Rete Sismica Nazionale, RSN), managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and to other local networks. All the corrected data are available at the Engineering Strong Motion Database (esm.mi.ingv.it). This paper reports the preliminary results of the analysis of the strong-motion recordings.

The recent Amatrice strong event (Mw6.0) occurred on August 24, 2016 in Central Apennines (Italy) in a seismic gap zone, motivated us to study and provide better understanding of the seismic hazard assessment in the macro area defined as “Central Italy”. The area affected by the sequence is placed between the Mw6.0 1997 Colfiorito sequence to the north (Umbria-Marche region) the Campotosto area hit by the 2009 L’Aquila sequence Mw6.3 (Abruzzo region) to the south. The Amatrice earthquake occurred while there was an ongoing effort to update the 2004 seismic hazard map (MPS04) for the Italian territory, requested in 2015 by the Italian Civil Protection Agency to the Center for Seismic Hazard (CPS) of the Istituto Nazionale di Geofisica e Vulcanologia INGV. Therefore, in this study we brought to our attention new earthquake source data and recently developed ground-motion prediction equations (GMPEs). Our aim was to validate whether the seismic hazard assessment in this area has changed with respect to 2004, year in which the MPS04 map was released. In order to understand the impact of the recent earthquakes on the seismic hazard assessment in central Italy we compared the annual seismic rates calculated using a smoothed seismicity approach over two different periods; the Parametric Catalog of the Historical Italian earthquakes (CPTI15) from 1871 to 2003 and the historical and instrumental catalogs from 1871 up to 31 August 2016. Results are presented also in terms of peak ground acceleration (PGA), using the recent ground-motion prediction equations (GMPEs) at Amatrice, interested by the 2016 sequence.

We used continuous Global Positioning System (GPS) measurements to infer the fault geometry and the amount of coseismic slip associated to the August 24, 2016 Mw 6 Amatrice earthquake. We realized a three dimensional coseismic displacement field by combining different geodetic solutions generated by three independent analyses of the raw GPS observations. The coseismic deformation field described in this work aims at representing a consensus solution that minimizes the systematic biases potentially present in the individual geodetic solutions. Because of the limited number of stations available we modeled the measured coseismic displacements using a uniform slip model, deriving the geometry and kinematics of the causative fault, finding good agreement between our geodetically derived fault plane and other seismological and geological observations.

We reconstruct the tectonic framework of the 24 August 2016, Amatrice earthquake. At least three main faults, including an older thrust fault (Sibillini Thrust), played an active role in the sequence. The mainshock nucleated and propagated along an extensional fault located in the footwall of the Sibillini Thrust, but due to the preliminary nature of the data the role of this thrust is still unclear. We illustrate two competing solutions: 1) the coseismic rupture started along an extensional fault and then partially used the thrust plane in extensional motion; 2) the thrust fault acted as an upper barrier to the propagation of the mainshock rupture, but was partially reactivated during the aftershock sequence. In both cases our tectonic reconstruction suggests an active role of the thrust fault, providing yet another example of how structures inherited from older tectonic phases may control the mainshock ruptures and the long-term evolution of younger seismogenic faults.

The August 24, 2016 Amatrice earthquake (Ml 6.0) struck a region of the central Apennines (Italy) where several active faults were known since decades, most of which are considered the surface expression of seismogenic sources potentially able to rupture during earthquakes with M of up to 6.5-7. The current debate on which structure/s activated during the mainshock and the possibility that conterminous faults may activate in a near future urged us gathering all the data on surface geological evidence of fault activity we collected over the past 15-20 years in the area. We then map the main tectonic structures of the 2016 earthquake epicentral and mesoseismal region. Our aim is to provide hints on their seismogenic potential, as possible contribution to the national Database of Individual Seismogenic Source (DISS) and to the Database of the active and capable fault ITaly HAzard from CApable faults (ITHACA).