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San Pietro Infine (Caserta, southern Italy) is an archaeological area of significant historical interest as it is in the vicinity of the Roman site of Ad Flexum. Based on historical sources, the site would correspond to the junction of a road axis that, during the Roman colonization (3rd century BCE), was crossed by the Via Latina. At the intersection of these two roads, which coexisted for a time, a post station was built, most likely later replaced by an early medieval village near the religious building of S. Pietro, of which only the apse portion is preserved. However, the archaeological evidence is too scarce to allow a reliable historical reconstruction of the site and to direct any excavation work. In this paper, we present the integration of LiDAR and geophysical surveys with the aim of advancing the archaeological interpretation of the San Pietro Infine site over the-state-of-the-art while providing a cutting-edge example in archaeological investigation. In particular, LiDAR data analysis was addressed to recognize and characterize topographic micro-reliefs presumably correlated to buried archaeological structures, while subsurface geophysical prospecting, consisting of magnetic and electromagnetic surveys, was aimed at defining their possible location and extent in depth, due to the expected contrasts in the magnetic and electric properties between the targets (e.g., limestone materials, paving roads) and the host geological setting (mainly marshy deposits). The integrated study allowed us to identify a structure whose characteristics (i.e., location, shape and nature) could well match the hypothesized Ad Flexum junction. In addition, LiDAR micro-reliefs and geophysical anomalies individuate structures that, by location and extent, suggest the presence of a village developed around the religious building of San Pietro.

Fault zones are major sources of hazard for many populated regions around the world. Earthquakes still occur unanticipated, and research has started to observe fault properties with increasing spatial and temporal resolution, having the goal of detecting signs of stress accumulation and strength weakening that may anticipate the rupture. The common practice is monitoring source parameters retrieved from measurements; however, model dependence and strong uncertainty propagation hamper their usage for small and microearthquakes. Here, we decipher the ground motion (i.e., ground shaking) variability associated with microseismicity detected by dense seismic networks at a near-fault observatory in Irpinia, Southern Italy, and obtain an unprecedentedly sharp picture of the fault properties evolution both in time and space. We discuss the link between the ground-motion intensity and the source parameters of the considered microseismicity, showing a coherent spatial distribution of the ground-motion intensity with that of corner frequency, stress drop, and radiation efficiency. Our analysis reveals that the ground-motion intensity presents an annual cycle in agreement with independent geodetic displacement observations from two Global Navigation Satellite System stations in the area. The temporal and spatial analyses also reveal a heterogeneous behavior of adjacent fault segments in a high seismic risk Italian area. Concerning the temporal evolution of fault properties, we highlight that the fault segment where the 1980 Ms 6.9 Irpinia earthquake nucleated shows changes in the event-specific signature of ground-motion signals since 2013, suggesting changes in their frictional properties. This evidence, combined with complementary information on the earthquake frequency–magnitude distribution, reveals differences in fault segment response to tectonic loading, suggesting rupture scenarios of future moderate and large earthquakes for seismic hazard assessment.

SUMMARYSpecific barrier method (SBM) is a method used for ground motion generation from a finite fault surface. It is based on a regular distribution of rupturing circular subevents located on the fault plane and random arrival times of the waves generated by those cracks. This approach does not consider the whole rupture kinematics, that is the rupture propagation from the hypocentre to the subevents, and leaves parts of the fault unbroken (barriers). In this paper, we propose a modified version of the SBM for generation of synthetic ground motions from a fault surface. In this version, we modify the probability density function (PDF) for the arrival time of the waves coming from different parts of the fault in order to better account for the fault kinematics and the distance between fault point and receiver. In this way, we can simulate the middle part of the acceleration spectrum (i.e. between 0.1 and 7 Hz) with more accuracy. Moreover, a new arrangement for locating cracks throughout the fault plane is proposed to add flexibility to the model and enable it to make the part of the spectrum with frequency larger than 7 Hz more like what happens in nature. In such an arrangement, called geometry packing in this paper, the size of circles varies within a chosen specific allowable range, while the circles cover all over the fault plane without any overlaps. To validate the proposed modified SBM technique, the synthetic Fourier spectra are compared with recordings of the 2008 Mw6.9 Iwate–Miyagi (Japan) earthquake. Finally, we present some parametric studies to show how different features of the proposed PDFs affect the results from the SBM approach.

Repeated tomographic inversions in time (the so called 4D tomography) track physical properties and stress changes in the medium hosting fault systems by measuring changes in P and S seismic velocities. These changes may provide insights on fault system dynamics and earthquake triggering mechanisms. We applied 4D tomography to the volume embedding the Irpinia Fault System (IFS, southern Italy) using more than ten years of continuous seismicity monitoring. The IFS is one of the Italian most hazardous fault systems, being able to generate the 1980 Ms 6.9 earthquake, characterized by a multi-segmented rupture. Seismicity was divided into uneven epochs having almost the same spatial resolution of the volume hosting the IFS.The resulting images show time-invariant features, clearly related to crustal lithology, and time-changing (up to 20%) velocity anomalies in the central region. Vp, Vs and Vp/Vs anomalies are referred to the tomographic model obtained using all the data set, and occur at depths ranging between 1 and 5 km, and between 8 and 12 km. These anomalies are temporally well-correlated with groundwater recharge/discharge series and geodetic displacements during the same time intervals. This correlation provides evidence for the existence of pulsating pore pressure changes in a fractured crustal volume at depth of 8-12 km, saturated with a predominant gas phase (likely CO2) and correlated with groundwater recharge processes, We suggest that tomographic measurements of the Vp-to-Vs spatiotemporal changes are a suitable proxy to track the pore pressure evolution at depth in highly sensitive regions of fault systems.

We developed a Bayesian technique to infer the double-couple, focal mechanism parameters (strike, dip and slip angles) of an earthquake source. The method uses 3 independent datasets: P-wave peak amplitude and polarity and S-to-P amplitude ratio wherever it is available.The Bayesian technique works even in absence of one dataset and easily integrates any prior information about the region of study. The parameter space is explored thanks to an octree strategy. The method estimates the Posterior pdf, where the maximum likelihood parameter values (MAP model) both for the principal and auxiliary plane are chosen as the final fault mechanism solution. Furtherly, the uncertainties as the projections of the semi-axis of the 68% confidence ellipsoid centred on the MAP model are provided.The joint use of the three datasets allows to determine a solution even in the case of a limited number of stations that have recorded the event, which is the case for example for small magnitude earthquakes (MWe applied and tested the methodology to a microearthquake sequence (ML 0.4-3.0) occurred in the Irpinia region, South Italy, using an uninformative prior distribution for the parameters. In this area, the background seismicity occurs in a volume delimited by the faults activated during the 1980 Irpinia M 6.9 earthquake. This faults system is complex and composed of northwest–southeast striking normal faults along the Apennines chain. A network of 3-component accelerometers and velocimeters is currently monitoring the area (Irpinia Seismic NETwork).We inferred the focal mechanism of the earthquakes of the sequence. Our results show fault mechanism solutions which are consistent with previous studies, well reflecting the regional stress field. The focus on micro-seismicity can reveal characteristics useful to highlight behaviours of larger scale seismicity.

Seismic sequences are a powerful tool to locally infer geometrical and mechanical properties of faults and fault systems. In this study, we provided detailed location and characterization of events of the 3&ndash, 7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of the main segment that ruptured during the 1980 Irpinia earthquake. Using an autocorrelation technique, we detected more than 340 events within the sequence, with local magnitude ranging between &minus, 0.5 and 3.0. We thus provided double difference locations, source parameter estimation, and focal mechanisms determination for the largest quality events. We found that the sequence ruptured an asperity with a size of about 800 m, along a fault structure having a strike compatible with the one of the main segments of the 1980 Irpinia earthquake, and a dip of 50&ndash, 55&deg, at depth of 10.5&ndash, 12 km and 60&ndash, 65&deg, at shallower depths (7.5&ndash, 9 km). Low stress drop release (average of 0.64 MPa) indicates a fluid-driven initiation mechanism of the sequence. We also evaluated the performance of the earthquake early warning systems running in real-time during the sequence, retrieving a minimum size for the blind zone in the area of about 15 km.

When an earthquake occurs, a key parameter in the emergency’s management is the knowledge of the most stressed areas by the ground motion. The focal mechanism is an essential source parameter for producing realistic shake maps. Although the approaches for estimating earthquake location and magnitude are now consolidated, automatic solutions for the focal mechanism are not always provided by the agencies or available at later times after inversion of waveforms for the determination of moment tensor components. We introduce a new approach for the automatic determination of the earthquake focal mechanism, using the spatial distribution of observed absolute initial P-wave peak amplitudes, corrected for the geometrical attenuation effect, in an evolutionary, Bayesian framework. We applied the proposed methodology to the main earthquakes of the 2016–2017 central Italy seismic sequence finding that our rapid automatic estimates of the focal mechanism are in good agreement with those of the reference solutions.

In September 2016 and again in November 2017, Korea witnessed some of the largest magnitude earthquakes occurred in-land in its recent history. They were located in the South-Eastern part of the pe...

Earthquake Early Warning Systems (EEWS) are potentially effective tools for risk mitigation in active seismic regions. The present study explores the possibility of predicting the macroseismic intensity within EEW timeframes using the squared velocity integral (IV2) measured on the early P wave signals, a proxy for the P wave radiated energy of earthquakes. This study shows that IV2 correlates better than the peak displacement measured on P waves with both the peak ground velocity and the Housner Intensity, with the latter being recognized by engineers as a reliable proxy for damage assessment. Therefore, using the strong motion recordings of the Italian Accelerometric Archive, a novel relationship between the parameter IV2 and the macroseismic intensity (IM) has been derived. The validity of this relationship has been assessed using the strong motion recordings of the Istituto Nazionale di Geofisica e Vulcanologia Strong Motion Data and Osservatorio Sismico delle Strutture databases, as well as, in the case of the MW 6, 29 May 2012 Emilia earthquake (Italy), comparing the predicted intensities with the ones observed after a macroseismic survey. Our results indicate that P wave IV2 can become a key parameter for the design of on-site EEWS, capable of proving real-time predictions of the IM at target sites.

We investigate the elastic properties of the crust in the Gargano promontory, located in the northern part of the Apulia region (Southeastern Italy). Starting on April, 2013, a local-scale seismic network, composed of 12 short-period (1 Hz) seismic stations, was deployed on the Gargano promontory. Starting on October, 2013, the network was integrated with the recordings of nine seismic stations managed by the Italian Institute of Geophysics and Volcanology (INGV). The network recorded more than 1200 seismic events in about 15 months of data acquisition, with more than 700 small magnitude events localized in the Gargano promontory and surrounding areas. A Wadati-modified method allowed us to infer VP/VS = 1.73 for the area. A subset of about 400 events having a relatively smaller azimuthal gap (

Online Material: Figures showing local magnitude versus duration; table of station correction coefficients. The earthquake magnitude estimate is a routine task in all seismological observatories. Several magnitude scales are available, based on amplitude measurement of different seismic phases, and/or on total signal duration. Among them, the duration magnitude ( M D) is adopted in many regional networks because it provides a rapid and reliable estimate of the earthquake size through a fairly simple procedure based on the measure of the duration of recorded seismograms. Bisztricany (1958) first demonstrated the existence of a relationship between magnitude and duration, and several authors (e.g., Sole’vev, 1965; Tsumura, 1967; Bakun, 1984; Vidal and Munguia, 2005; Hara, 2007; among many others) later discussed the use of duration of the recorded seismograms as a measure of the event size. Furthermore, in a recent paper, Lomax and Michelini (2009) proposed a duration magnitude procedure for the rapid determination of the moment magnitude, based on the P ‐wave recordings at teleseismic distances, which can be applied for tsunami early warning. In its more general formulation the duration magnitude depends on the ground‐shaking duration, on the hypocentral distance, and accounts for a station correction coefficient. According to Real and Teng (1973) and Hermann (1975), the duration magnitude is defined as ![Graphic][1] (1)in which τ is the signal duration, R is the hypocentral distance, Sc stands for the station correction, and a , b , and c are coefficients to be determined through a regression analysis. The present work has a double goal. First, we present an automatic procedure, which has been specifically developed to measure the earthquake duration, based on the estimate of the signal‐to‐noise ratio (SNR) along the seismic records. We then calibrate a duration magnitude scale for the area monitored by the … [1]: /embed/inline-graphic-1.gif

We present an approach to infer the slip and rupture velocity distributions on the fault plane from the non-linear inversion of the apparent source time functions, obtained from the empirical Green???s function deconvolution method. The main advantage of this technique is that it allows overcoming, in the forward modelling, the limitations related to the computation of the Green???s function, as the choice of a correct and reliable earth propagation model. We perform a parameter resolution and uncertainty study, which is based on the analysis of the misfit function in the neighbourhood of the best-fitting model. In this paper, we present the results obtained by applying the technique to synthetic and real records from an Mw 4 event which occurred during the 2009 L???Aquila (central Italy) aftershock sequence. Results show a heterogeneous slip distribution, characterized by two main high slip patches located NW of the hypocentre and an average slip of 3.7 cm, corresponding to a seismic model of about 0.82 × 10^15 Nm.

We present the results of a feasibility study of an earthquake early warning system (EEWS) for the Campania region (southern Italy) using schools as specific targets. The study considered the seismogenic zones as sources of potential earthquakes for the area, the Italian accelerometric network as the recording network for seismic event occurrence, and the performances of the software platform PRESTo Plus for data analysis and processing. We analyze the distribution of lead-times for all possible threatening seismic sources for each municipality in the region under study by extracting the lead-time value corresponding to the 5th, 10th and 25th percentiles of the distributions. We discuss the results for the 5th percentile in order to analyze the worst-case scenario: in the case of a single site, the lead-time is expected to be larger than this value in the 95 % of the cases. Since the population distribution in Campania is uneven and most of the people live nearby the coast, whilst the most destructive earthquakes occur along the Apennine chain, we can conclude that an efficient EEWS can allow most of the schools in the area to undertake some mitigating actions. The testing of the EEWS was carried out in the high school ITIS ‘E. Majorana’, located at Somma Vesuviana, about 80 km from the seismogenic Irpinia region. For this purpose, the Sentinel, an actuator made up of low-cost hardware (i.e., Arduino®), was developed in close cooperation with students and teachers of the school to receive alert messages from the PRESTo Plus platform and warn the school users in case of a seismic event. The EEWS and the Sentinel were successfully tested during some blind drills performed during normal school activities.

The occurrence of the M w 6.0 South Napa California earthquake, on 24 August 2014 at 03:20 a.m. local time, triggered discussion in the seismological community about the level of damage associated with such a moderate‐magnitude event and about the geometry and orientation of the causative fault. In addition, coulomb static stress change mapping does not seem to be able to fully explain near‐source aftershock distribution. Here, we find clear evidence of a north‐northwest source directivity from the analysis of the spatial distribution of peak ground motion. The area of the highest values of the estimated peak dynamic strain field, computed accounting for fault extent and source directivity, agrees with the near‐source aftershock distribution. This might suggest that, in addition to coulomb static stress change, dynamic strain also contributed to the triggering of near‐source Napa earthquake aftershocks. The approach used here might be useful to identify areas likely prone to aftershock occurrence.

We present a nonlinear technique for the purpose of estimating the distribution of the final slip and the rupture velocity on the fault plane from the inversion of strong‐motion records. In this work, the ground‐motion simulation is obtained by evaluating the representation integral in the frequency domain, through a finite‐element approach, based on a Delaunay’s triangulation of the fault plane. The slip distribution is parameterized by a linear combination of 2D overlapping Gaussian functions. This choice allows us to relate the maximum frequency in the data to the smallest resolvable wavelength on the fault plane, insuring a smooth representation for the slip function. We investigate the capability of such a representation to describe complex slip maps, and we relate the width of the Gaussian function and the overlapping to the minimum wavelength of the slip function. The inverse problem is solved by a two‐step procedure aimed at separating the computation of the rupture velocity from the evaluation of the slip distribution. While a global exploration is maintained for the rupture velocity, for each explored value of this quantity, the slip solution is computed as the best solution approaching the observations in the sense of the L2 norm. The nonlinear step is performed through the neighborhood algorithm (NA), while the linear one uses the nonnegative least‐squares (NNLS) method. The technique has been applied to retrieve the rupture history of the 2008 Iwate–Miyagi, Japan, earthquake. The slip distribution is characterized by a large slip patch extending from the hypocenter to the southern shallow part of the fault plane, with a maximum amplitude of 6 m. In addition, a relatively smaller asperity is located in the north shallow part of the fault. We found that the rupture lasted about 12 s with an average rupture velocity of about 2.0 km/s. Online Material: Figures showing synthetic inversion test results.

We investigate the possibility of inferring the dominant horizontal‐rupture direction for moderate earthquakes from the inversion of peak ground‐motion parameters. To this aim, we adopt a technique that was devised and applied to large earthquakes for retrieving both the dominant rupture direction and the surface fault projection to be used with a proper distance metric to refine the ShakeMap computation. In the present paper, the procedure was applied to three moderate earthquakes that occurred in 2012 in Northern Italy three days apart: the M 4.2 Pre‐Alpi Venete earthquake on 24 January, the M 4.9 Reggio Emilia earthquake on 25 January, and the M 5.4 Parma earthquake on 27 January. For two of the three analyzed events, the technique identifies a dominant horizontal‐rupture direction, which is consistent with the strike directions inferred from the focal mechanisms. For the M 5.4 event, which is a deep (about 61 km) thrust‐faulting mechanism earthquake, the inferred dominant rupture direction allows identification of the northeast‐dipping plane as the fault plane in accordance with the aftershocks distribution.

Rapid evaluation of strong ground‐shaking maps after moderate‐to‐large earthquakes is crucial to recognizing those areas where the largest damage and losses are expected. These maps play a fundamental role for emergency management. This is particularly important for areas having high seismic risk potential and covered by dense seismic networks. In near‐real‐time applications, ground‐shaking maps are produced by integrating recorded data and estimates obtained by using ground‐motion predictive equations, which assume point‐source models. However, particularly for large earthquakes, improvements in the predictions of the peak ground motion can be obtained when fault extension and orientation are available. In fact, detailed source information allows one to use a more robust source‐to‐site distance metric compared with hypocentral distance. In this paper, a technique for estimating both fault extent (in terms of its surface projection) and dominant rupture direction is presented. This technique can be used in near‐real‐time ground‐motion map calculation codes with the aim of improving ground‐motion estimates with respect to a point‐source model. The model parameters are estimated by maximizing a probability density function based on the residuals between observed and predicted peak‐ground‐motion quantities, the latter obtained by using predictive equations. The model space to be investigated is defined through a Bayesian approach, and it is explored by a grid‐searching technique. The effectiveness of the proposed technique is demonstrated by offline numerical tests using data from three earthquakes occurring in different seismotectonic environments. The selected earthquakes are the 17 August 1999 M w 7.5 Kocaeli (Turkey) earthquake, the 6 April 2009 M w 6.3 L’Aquila (Italy) earthquake, and the 17 January 1994 M w 6.7 Northridge (California) earthquake. The obtained results show that the proposed technique allows for fast and first order estimates of the fault extent and dominant rupture direction, which could be used to improve ground‐shaking map calculations.

In this paper, we adopt three ground-motion simulation techniques (the stochastic finite-fault simulation code from Motazedian and Atkinson, 2005; the hybrid deterministic-stochastic approach with approximated Green's functions from Pacor et al., 2005; and the broadband hybrid integral-composite technique with full-wavefield Green's functions from Gallovic and Brokesova, 2007), with the aim of investigating the different performances in near-fault strong-motion modeling andpredictionfrompastandfutureevents.Thetestcaseisthe1980M6.9Irpiniaearth- quake, the strongest event recorded in Italy in the last 30 years. First, we simulate the recorded strong-motion data and validate the model parameters by computing spectral accelerationandpeakamplituderesidualdistributions.Thevalidatedmodelisthenused to investigate the influence of site effects and to compute synthetic ground motions around the fault. Afterward, we simulate the expected ground motions from scenario events on the Irpinia fault, varying the hypocenters, the rupture velocities, and the slip distributions. We compare the median ground motions and related standard deviations from all scenario events with empirical ground-motion prediction equations (GMPEs). The synthetic median values are included in the median 1 standard deviation of the considered GMPEs. Synthetic peak ground accelerations show median values smaller and with a faster decay with distance than the empirical ones. The synthetics total stan- dard deviation is of the same order or smaller than the empirical one, and it shows considerable differences from one simulation technique to another. We decomposed the total standard deviation into its between-scenario and within-scenario components. The larger contribution to the total sigma comes from the latter, while the former is found to be smaller and in good agreement with empirical interevent variability. Online Material: Comparison of observed and simulated waveforms and spectra.

In this paper we report the results of several investigations aimed at evaluating ground motion scenarios for the September 26th, 1997 Colfiorito earthquake (Mw 6.0, 09:40 UTC). We model the observed variability of ground motions through synthetic scenarios which simulate an earthquake rupture propagating at constant rupture velocity (2.7 km/s) and the inferred directivity. We discuss the variability of kinematic source parameters, such as the nucleation position and the rupture velocity, and how it influences the predicted ground motions and it does not account for the total standard deviation of the empirical predictive model valid for the region. Finally, we used the results from the scenario studies for the Colfiorito earthquake to integrate the probabilistic and deterministic approaches for seismic hazard assessment.

Ground‐motion prediction equations (GMPEs) play a crucial role for estimating the seismic hazard in any region using either a deterministic or a probabilistic approach. Indeed, they represent a reliable and fast tool to predict strong ground motion, given source and propagation parameters. In this article, we estimated GMPEs for the South Korea peninsula. GMPEs were computed for peak ground displacement, peak ground velocity, peak ground acceleration, and spectral accelerations (damping at 5%) at 13 different periods from 0.055 to 5 s. We analyzed data from 222 earthquakes recorded at 132 three‐component stations of the South Korea Seismic Network, from 2007 to 2012, with local magnitude ranging between 2.0 and 4.9 and epicentral distances varying from 1.4 to ∼600 km. A nonlinear mixed effects technique is used to infer the GMPE coefficients. This technique includes both fixed and random effects and accounts for both inter‐ and intraevent dependencies in the data. Station‐specific corrective coefficients were estimated by a statistical approach and were included in the final ground‐motion prediction model. Finally, predictions for peak ground acceleration and spectral acceleration are compared with observations recorded for an M L 5.1 earthquake that occurred in 2014, the data for which were not included in the modeling. Online Material: Figures showing final ground‐motion prediction equation models versus observations, and intra‐ and interevent residuals.

We present an analysis of the reliability of focal mechanisms obtained through moment tensor inversion at the Irpinia Seismic Network, southern Italy. Our analysis is based on the methods proposed by Zahradnik and Custodio (2012) and Sokos and Zahradnik (2013). We present two different studies: (1) we compute maps of theoretical focal mechanism resolution for the Irpinia region and (2) we study the reliability of the solutions obtained from waveform inversion of five regional earthquakes. Theoretically, we find that when data error is the dominant source of error, focal mechanism resolution is better close to the spots of higher station density rather than at the center of the network. Using real data, we were able to successfully study four of the five regional events, in spite of the large source–station distances (up to ∼280 km) and significant azimuthal gaps (>319°). We used variance reduction, double‐couple percentage, signal‐to‐noise ratio, condition number, and focal mechanism variability index to assess the quality of the solutions. Our quality assessment is validated by comparison with independent focal mechanism solutions.

We present an approach to Earthquake Early Warning for Southern Italy that integrates regional and on-site systems. The regional approach is based on the PRobabilistic and Evolutionary early warning SysTem (PRESTo) software platform. PRESTo processes 3-components acceleration data streams and provides a peak ground-motion prediction at target sites based on earthquake location and magnitude computed from P-wave analysis at few stations in the source vicinity. On the other hand, the on-site system is based on the real-time measurement of peak displacement and dominant period, on a 3 s P-wave time-window. These values are compared to thresholds, set for a minimum magnitude 6 and instrumental intensity VII, derived from empirical regression analyses on strong-motion data. Here we present an overview of the system and describe the algorithms implemented in the PRESTo platform.We also show some case-studies and propose a robust methodology to evaluate the performance of this Early Warning System.

Earthquake Early Warning Systems (EEWS) are real-time, seismic monitoring infrastructures that are able to provide a rapid notification of the potential damaging effects of an impending earthquake. This objective is achieved through the fast telemetry and processing of data from dense instrument arrays deployed in the source region of the event of concern (regional EEWS) or surrounding/at the target infrastructure (front-detection or site-specific EEWS). A regional EEWS is based on a dense sensor network covering a portion or the entire area that is threatened by earthquakes. The relevant source parameters (event location and magnitude) are estimated from the early portion of recorded signals (initial P-waves) and are used to predict, with a quantified confidence, a ground-motion intensity measure at a distant site where a target structure of interest is located. Site-specific (or on-site) EEWS consist of a single sensor or an array of sensors deployed in the proximity of the target structure that is to be alerted and whose measurements of amplitude and predominant period on the initial P-wave motion are used to predict the ensuing peak ground motion (mainly related to the arrival of Sand surface waves) at the same site. Frontdetection EEWS is essentially a variant of the on-site approach, where a barrier-shaped, accelerometric network is deployed between the source region and the target site to be protected. The alert is issued when two or more nodes of the array record a ground acceleration amplitude larger than a default threshold value. For typical regional distances, the peak acceleration at the barrier nodes is expected to be associated with the S-wave train, so that the distance between the network and the target is set to maximize the lead time (i.e., the time available for warning before the arrival of strong ground shaking at the target sites), which is, in this case, the travel time of S-waves from the barrier to the target site. EEWS have experienced a very rapid improvement and a wide diffusion in many active seismic regions of the world in the last three decades (Fig. 1). They are operating in Japan, Taiwan, Mexico, and California. Many other systems are under development and testing in other regions of the world such as in Italy, Turkey, Romania, and China. Most of these existing EEWS essentially operate in the two different configurations described above, i.e., regional and on-site, depending on the source-tosite distance and on the geometry of the considered network with respect to the source area. The “front-detection” EEWS such as the barrier-type, Seismic Alert System (Espinosa-Aranda

Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterized by low signal-to-noise ratio, automated location methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this paper, we propose a picking free earthquake location method based on the use of the short-term-average/long-term-average (STA/LTA) traces at different stations as observed data. For the P phases, we use the STA/LTA traces of the vertical energy function, whereas for the S phases, we use the STA/LTA traces of a second characteristic function, which is obtained using the principal component analysis technique. In order to locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a 3-D grid, we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event. A pilot application was performed in the Campania-Lucania region (southern Italy) using a seismic network (Irpinia Seismic Network) with an aperture of about 150 km. We located 196 crustal earthquakes (depth < 20 km) with magnitude range 1.1 < ML < 2.7. A subset of these locations were compared with accurate manual locations refined by using a double-difference technique. Our results indicate a good agreement with manual locations. Moreover, our method is noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals.

A long sequence of earthquakes causing few casualties and considerable damage in a wide zone struck Central Italy starting on September 26, 1997. Theearthquakes are characterized by normal faulting mechanism, with a NE-SW(anti-Apenninic direction) tension axis. In this paper we analyze the accelerometric recordings collected by the accelerograph stations belonging to the National Accelerograph Network. About 10 stations were triggered by the mainshocks of the sequence. In particular, a small size foreshock and the two mainshocks that occurred on September,26 (00:33(GMT) MW = 5.7 and 09:40 MW = 6.0) have been recorded by two digital 3-C accelerometers located at near source distances (within 30 km from the faults). These records are relevant to investigate the detail of therupture kinematics, due to the close epicentral distance and azimuthallocation relative to the fault orientation and geometry. Using a trial and error approach we modeled the source mechanism through the fit of the arrival times, the apparent source time duration, the main polarization features and the entire waveforms of the recorded signals, in order to get some insight on the rupture evolution, the location of the fracture origin point and the fault geometry. Based on this fault kinematic model, inferences on fault slip distribution are obtained by modeling the S acceleration waveform, comparing the ray theory synthetics with 1–5 Hz band filtered ground velocity records.The final model shows that the seismic ruptures occurred along two adjacent,sub-parallel, low angle dipping normal faults. Ruptures bothnucleated from the fault bottom and propagated up-dip, showing differentrupture velocity and length. The presence of a transfer zone (barrier)can be suggested by the mainshocks rupture evolution. This transfer zonehas probably controlled the amplitude increase of local stressreleased by the first rupture at its NW edge which triggered about 9 hourslater the second rupture. The inferred model was used to compute the predictedground acceleration in the near source range, using a hybridstatistical-deterministic approach.A similar trial and error method has been also applied to the October 14, 199715:23 earthquake (MW = 5.6). The inferred kinematic model indicates a rupture nucleating from the faultbottom and propagating up-dip, toward the SE direction. Thus the three mainshocks ruptured distinct fault segments, adjacent and slightly offsetfrom one to another.

A hybrid statistical-deterministic approach has been applied to estimate strong ground motion parameters (PGA, spectral ordinates) in South-Eastern Sicily for a M = 7 earthquake. A number of 100 different rupture processes have been simulated along a composite fault system representing two segments of the Ibleo-Maltese fault scarp. Map at regional scale of mean PGA in the 0.5–20 Hz frequency band shows highest values (0.4–0.5 g) nearby and North of Catania, due to a dominant directivity effect. The COV parameter, which expresses the variability of PGA values as a function of source complexity, is higher in the region nearby and South of the town of Augusta, where, depending on the rupture history, rather large PGA values can be observed (>0.4 g). PGA attenuation curves suggest that an azimuthal variation could be related to the source extent and directivity. The response and pseudo acceleration spectra are computed for different sites in the town of Catania including an approximate 1D site response. Ground motion amplification effects at high frequency (5–20 Hz) are produced by thin shallow layer of soft clay, loose pyroclastites and fill. We observe small amplification effects, in the frequency ranges 2–3 Hz and 5–10 Hz, in sites where recent alluvia reach a thickness of some tens of meters. Otherwise, sites located on outcrops of massive lavas show moderate attenuation.

A mixed statistical-deterministic model of earthquake rupture is developed for evaluating the strong ground motion in the near source range (receiver distance comparable to the fault length). The source parametrization is based on the k-square model and the propagation is computed by asymptotic Green's functions. The method is applied to the case of 1976, Friuli earthquake (M = 6.5) in northern Italy which occurred on a low-dip thrusting fault. Acceleration records at 29 stations are computed for 100 simulations of rupture histories. The mean value map of peak ground accelerations shows clearly a maximum to the south due to the inner geometry and directivity of the source. The variation of the estimated PGA versus the epicentral distance is strongly dependent on azimuth and is not decreasing monotonically. The comparison of these curves with those predicted by empirical acceleration–distance relationships shows discrepancies in the near source distance range. This study shows the importance of considering the complexity of the source rupture process for strong motion estimate in the near source range.

The Emilia seismic sequence (Northern Italy) started on May 2012 and caused 17 casualties, severe damage to dwellings and forced the closure of several factories. The total number of events recorded in one month was about 2100, with local magnitude ranging between 1.0 and 5.9. We investigate potential mechanisms (static and dynamic triggering) that may describe the evolution of the sequence. We consider rupture directivity in the dynamic strain field and observe that, for each main earthquake, its aftershocks and the subsequent large event occurred in an area characterized by higher dynamic strains and corresponding to the dominant rupture direction. We find that static stress redistribution alone is not capable of explaining the locations of subsequent events. We conclude that dynamic triggering played a significant role in driving the sequence. This triggering was also associated with a variation in permeability and a pore pressure increase in an area characterized by a massive presence of fluids., Scientific Reports, 3, ISSN:2045-2322

ShakeMap package uses empirical Ground Motion Prediction Equations (GMPEs) to estimate the ground motion where recorded data are not available. Recorded and estimated values are then interpolated in order to produce a shaking map associated with the seismic event of interest. The ShakeMap approach better works in regions with dense stations coverage, where the observed ground motions adequately constrain the interpolation. On the other hand, in poorly instrumented regions, the ground motion estimate mainly relies on the GMPEs that account only for average characteristics of source and wave propagation processes. In this study we investigated the improvement of ShakeMap in the near-fault area accounting for source effects, at different level of approximation, and including synthetic estimates at sites where recordings are not available. We focus on the 2008, Mw 7.0, Iwate-Miyagi Nairiku (Japan) earthquake as a case study because of the large amount of recorded data. As first step, we calculated the shakemaps to be used as reference using all station recordings and simple source information such as the earthquake magnitude and fault geometry. We then removed several subsets of stations from the original data-set and computed the shakemaps (i) using the estimations of the ground motion obtained by GMPE and (ii) replacing them with the peak values from synthetic time-histories. Simulated seismograms are computed by a hybrid deterministic-stochastic method for extended fault, using rupture fault models with different degree of approximation of source properties. In fact, within few hours, a preliminary rupture model can be obtained from the inversion of teleseismic data, and after 24 hours a kinematic source inversion of strong-motion records can be available. We evaluate the deviations from the reference map and the sensitivity to the number of sites where recordings are not available. Our results show that shakemaps are more and more reliable as the coverage of stations is uniformly distributed in the near-source area. Moreover, the shakemaps obtained by the use of combination of slip inversion model and strong-motion simulations are more reliable than those obtained by the use of GMPEs. The accuracy of source model does not significantly affect the results, making the proposed methodology applicable to regions with sparse station coverage. As an example, we apply it to a poorly instrumented earthquake of similar magnitude, the 1980, Ms 6.9, Irpinia (Southern Italy) earthquake. When the peak motions inferred from synthetic seismograms are included in the database, the fit with respect to the observed Mercalli–Cancani–Sieberg intensities improves.

International audience; The 6 April 2009 Mw 6.3 L'Aquila earthquake, central Italy, has been recorded by the Irpinia Seismic Network (ISNet) about 250 km southeast of the epicenter. Up to 19 three-component accelerometer stations could be used to infer the main source parameters with different seismological methods. We obtained an approximate location of the event from arrival times and array-based back-azimuth measurements and estimated the local magnitude (6.1) from an attenuation relation for southern Italy. Assuming an omega-square spectral model, we inverted S-wave displacement spectra for moment magnitude (6.3), corner frequency (0.33 Hz), stress drop (2.5 MPa), and apparent stress (1.6 MPa). Waveform modeling using a point source and an extended-source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast. The relatively high corner frequency and an overestimated moment magnitude of 6.4 from moment tensor inversions are attributed to the rupture directivity effect. To image the rupture geometry, we implemented a beamforming technique that back-projects the recorded direct P-wave amplitudes into the earthquake source region. A northwest-southeast striking rupture of 17 km length is imaged, propagating with an average velocity up to 3 km/s. This value is significantly higher than our estimate of 2.2 km/s from S-wave spectra. Our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate-sized earthquakes located outside the network.

The Irpinia Seismic Network (ISNet) is deployed in Southern Apennines along the active fault system responsible for the 1980, November 23, M s 6.9 Campania–Lucania earthquake. It is set up by 28 stations and covers an area of about 100 × 70 km2. Each site is equipped with a 1-g full-scale accelerometer and a short-period velocimeter. Due to its design characteristics, i.e., the wide dynamic range and the high density of stations, the ISNet network is mainly devoted to estimating in real-time the earthquake location and magnitude from low- to high- magnitude events, and to providing ground-motion parameters values so to get some insights about the ground shaking expected. Moreover, the availability of high-quality of data allows studying the source processes related to the seismogenetic structures in the area. The network layout, the data communication system and protocols and the main instrumental features are described in the paper. The data analysis is managed by Earthworm software package that also provides the earthquake location while custom software has been developed for real-time computation of the source parameters and shaking maps. Technical details about these procedures are given in the article. The data collected at the ISNet stations are available upon request.

This study investigates the engineering applicability of two conceptually different finite-fault simulation techniques. We focus our attention on two important aspects: first to quantify the capability of the methods to reproduce the observed ground-motion parameters (peaks and integral quantities); second to quantify the dependence of the strong-motion parameters on the variability in the large-scale kinematic definition of the source (i.e., position of the nucleation point, value of the rupture velocity, and distribution of the final slip on the fault). We applied an approximated simulation technique, the deterministic-stochastic method and a broadband technique, the hybrid-integral-composite method, to model the 1984 M w 5.7 Gubbio, central Italy, earthquake, at five accelerometric stations. We first optimize the position of the nucleation point and the value of the rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 Hz. We found that the best model is given by a rupture propagating at about 2.65 km/sec from a hypocenter located approximately at the center of the fault. In the second part of the article we calculate more than 2400 scenarios varying the kinematic source parameters. At the five sites we compute the residuals distributions for the various strong-motion parameters and show that their standard deviations depend on the source parameterization adopted by the two techniques. Furthermore, we show that Arias Intensity (AI) and significant duration are characterized by the largest and smallest standard deviation, respectively. Housner Intensity is better modeled and less affected by uncertainties in the source kinematic parameters than AI. The fact that the uncertainties in the kinematic model affects the variability of different ground-motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events.

The Colfiorito Mw 6.0 (September 26, 1997, 09:40 UTC) and the Sellano Mw 5.6 (October 14, 1997) normal-faulting earthquakes are the two strongest events of the 1997–1998 Umbria–Marche seismic sequence (central Italy). They provided accelerograms recorded at epicentral distances within nearly two fault lengths. Previous studies on these events revealed clear evidence of unilateral rupture propagation and directivity effects on the source time functions. We developed an approximate procedure to correct the observed peak ground motion for the site effects, and we found a systematic increase of peak ground acceleration (PGA) and peak ground velocity (PGV) at sites located in the direction of the rupture propagation respect to the stations located to the backward. In particular we showed that, for the Colfiorito earthquake, the average PGV at the north-west sites is 2.8 times larger than the PGV at south-east sites (2.1 for PGA); an opposite behaviour is found during the Sellano earthquake, with an amplification factor of about 1.9 for PGV (1.5 for PGA) recorded at south-east sites respect to the north-west stations. We explained these behaviours in terms of directivity effect, by comparing recorded ground accelerations with synthetics simulated by a deterministic–stochastic technique. This method computes high-frequency ground motions (f > 0.5 Hz) from extended faults, generalizing the point-source stochastic method to capture the essence of near-source effects. The synthetic PGAs decrease with distance in agreement with the ground-motion empirical predictive model available for the area and describe the azimuthal variation of recorded data in terms of source effects.

In the framework of an ongoing project financed by the Campania Region, a prototype system for seismic early and post-event warning is being developed and tested, based on a dense, wide dynamic seismic network (ISNet) and under installation in the Apennine belt region.

Probabilistic seismic hazard analysis (psha) is classically performed through the Cornell approach by using a uniform earthquake distribution over the source area and a given magnitude range. This study aims at extending the psha approach to the case of a characteristic earthquake scenario associated with an active fault. The approach integrates psha with a high-frequency deterministic technique for the prediction of peak and spectral ground motion parameters in a characteristic earthquake. The method is based on the site-dependent evaluation of the probability of exceedance for the chosen strong-motion parameter. The latter is obtained from the statistical analysis of the synthetic waveform database produced for a large number of possible rupture histories occurring on the characteristic earthquake fault. The method has been applied to a hazard evaluation in the Umbria region, where the threat is represented by a fault having the same geometry and mechanism as the 26 September 1997, Colfiorito earthquake (central Italy; moment magnitude, M w 6).

We describe a technique to infer the kinematic parameters of the earth- quake rupture process by the nonlinear inversion of near-source high-frequency seis- mic records. The model assumes that each point on the fault plane slips, when the rupture front passes, with a variable slip amplitude. For a given rupture model syn- thetic seismograms are computed by using the ray theory and a plane-layered velocity structure. The rupture velocity and the final slip are specified at a set of control points on the fault plane and the values at any point on the fault are then obtained by a bicubic interpolation. The final slip and rupture velocity at the fault-grid nodes are determined by searching for the minimum of a misfit function by using the Genetic Algorithm. The number of control points is progressively increased to move from a high- to low-wavelength description of final slip and rupture velocity on the fault plane. The optimal model parameter set is chosen according to the minimum of the corrected Akaike Information Criterion parameter. The uncertainty on the source parameters has been estimated through the analysis of cross-correlation of the misfit function in the neighborhood of the final, best-fit, rupture model. The method is applied to near-source, strong motion records of the 1989 Loma Prieta earthquake. We find that the most earthquake slip occurred in two regions located northwest and southeast of the hypocenter, consistent with previous models obtained using other data and techniques. Moreover, we find that the rupture propagated faster toward the southeast than in the northwest direction. The total duration of the rupture is found to be approximately 9 sec.

We applied a hybrid stochastic-deterministic method to simulate the strong ground motion characteristics associated with the September 26, 1997 Umbria-Marche main shocks. One hundred different rupture processes on previously inferred fault planes were simulated. The maps of computed PGA (mean values from 100 simulations) show a SE alignment for the 00:33 event and a NW alignment for the 09:40 event, in accordance with the macroseismic data. Moreover, we found a good agreement between the predicted 1ó interval for the PGA values and the data recorded at several accelerometric stations. As a further test, we computed the response spectra at the station Cerreto di Spoleto and found a satisfactory agreement with the synthetic results.

We examine here a number of parameters that define the source of the earthquake that occurred on 23rd July 1930 in Southern Italy (in the Irpinia region). Starting from the source models proposed in different studies, we have simulated the acceleration field for each hypothesized model, and compared it with the macroseismic data. We then used the hybrid stochastic-deterministic technique proposed by Zollo et al. (1997) for the simulation of the ground motion associated with the rupture of an extended fault. The accelerations simulated for several sites were associated with the intensities using the empirical relationship proposed by Trifunac and Brady (1975), before being compared with the available data from the macroseismic catalogue. A good reproduction of the macroseismic field is provided by a normal fault striking in Apenninic direction (approximately NW-SE) and dipping 55° toward the SW.