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We retrieve 3-D attenuation images of the crustal volume embedding the fault system associated with the destructive Ms 6.9, 1980 Irpinia earthquake by tomographic inversion of t* measurements. A high QP anomaly is found to be correlated with the 1980 fault geometry, while the QS model shows regional-scale variations related to the NE edge of the uplifted pre-Tertiary limestone. An upscaling strategy is used to infer rock properties such as porosity, consolidation, type of fluid mixing, and relative saturation percentage at 8–10 km fault depth. We constrain the porosity and consolidation in the ranges 4–5% and 5–9, respectively, with the possible fluid mixes being both brine-CO2 and CH4-CO2. The consolidation parameter range indicates high pore pressures at the same depths. These results support the evidence for a fracture system, highly saturated in gases and a seismicity triggering mechanism at the fault zone, which is strongly controlled by fluid-induced pore pressure changes.

We propose a P wave based procedure for the rapid estimation of the radiated seismic energy, and a novel relationship for obtaining an energy-based local magnitude (MLe) measure of the earthquake size. We apply the new procedure to the seismic sequence that struck Central Italy in 2016. Scaling relationships involving seismic moment and radiated energy are discussed for the Mw 6.0 Amatrice, Mw 5.9 Ussita, and Mw 6.5 Norcia earthquakes, including 35 ML > 4 aftershocks. The Mw 6.0 Amatrice earthquake shows the highest apparent stress, and the observed differences among the three main events highlight the dynamic heterogeneity with which large earthquakes can occur in Central Italy. Differences between estimates of MLe and Mw allows identification of events which are characterized by a higher proportion of energy being transferred to seismic waves, providing important real-time indications of earthquakes shaking potential.

Earthquake early warning studies are shifting real-time seismology in earthquake science. They provide methods to rapidly assess earthquakes to predict damaging ground shaking. Preventing false alarms from these systems is key. Here we developed a simple, robust algorithm, Authorizing GRound shaking for Earthquake Early warning Systems (AGREEs), to reduce falsely issued alarms. This is a network threshold-based algorithm, which differs from existing approaches based on apparent velocity of P and S waves. AGREEs is designed to function as an external module to support existing earthquake early warning systems (EEWSs) and filters out the false events, by evaluating actual shaking near the epicenter. Our retrospective analyses of the 2009 L'Aquila and 2012 Emilia earthquakes show that AGREEs could help an EEWS by confirming the epicentral intensity. Furthermore, AGREEs is able to effectively identify three false events due to a storm, a teleseismic earthquake, and broken sensors in Irpinia Seismic Network, Italy.

[1] The south of the Iberian Peninsula is a region in which large, damaging earthquakes occur separated by long time intervals. An example was the great 1755 Lisbon earthquake (intensity Imax = X) which occurred SW of San Vicente Cape (SW Iberian Peninsula). Due to this risk of damaging earthquakes, the implementation of Earthquake Early Warning System (EEWS) technologies is of considerable interest. With the aim of investigating the feasibility of an EEWS in this region of the Iberian Peninsula, empirical scaling relationships have been derived between the early warning parameters and the earthquake size and/or its potential damaging effects for this region. An appropriate and suitable strategy is proposed for an EEWS in the SW Iberian Peninsula, which takes into account the limitations of the existing seismological networks.

We have analysed the seismicity that occurred at Campi Flegrei caldera (Italy) in the period 1982-1984, during an unrest episode. Earthquake locations describe a system of inward dipping ring faults. Focal mechanisms of such events show a normal dip component, which is not in agreement with the differential uplift of the inner caldera, as defined by static ground deformations. We have performed a simulation of the stress field generated by overpressure in a magma chamber in presence of lateral discontinuities, using a boundary element method. Lateral discontinuities simulate the ring fault system marking the border of the inner caldera collapse. Results allow us to hypothesize that reverse fault slip on the ring fault is mainly aseismic, and such aseismic movement is able to focus normal fault shear stress along the lateral discontinuities. Aseismic slip on the ring fault in response to static deformation is also supported by the low seismic moment released (M-0 congruent to 10(15) Nm), about two orders of magnitude lower than expected from the shear slip on the discontinuities needed to accomplish the total static surface deformation (1.8 m). Such results have been compared with observations at Rabaul caldera, during a similar unrest episode. In this area, the seismic moment release is in good agreement with shear slip produced on a system of outward dipping ring faults, and seismicity is much more focused on the fault structures. Such a different behaviour can be interpreted, in the framework of our model, as due to the different sign of the stress normal to the ring faults, for inward and outward dip. The comparison between the two areas shed new light about the dynamics of earthquakes in calderas, in terms of the role played by ring fault systems.

We use recordings at a single station of a shallow crustal S-to-S reflected phase generated by microearthquakes (ML, 2.5–3.5) in the Northern Apennines (Italy) to analyze source, path attenuation and site effects. A site resonance phenomenon in a narrow frequency band (6–8 Hz) has been clearly detected in the shear wave acceleration spectra, consistent with similar observations from records of microseismic noise. The non-linear inversion of acceleration spectra (which have been corrected for an average site response) yields estimates of apparent corner frequencies that are approximately constant with moment, with a mean value of 2 Hz. A significant increase with seismic moment of the spectral decay parameter at high frequencies is also observed. The anomalous moment dependence of these spectral parameters is found to be related to the existence of a cut-off high frequency limit, close to the smallest event corner frequency, which could be originated by combined site and travel path effects rather than source characteristics in the frequency range of observations (0.5–15 Hz). Independent geological, well soundings and seismic data for this site in the Apennines, suggest that the spectral shape on short-period records is mainly controlled by the damping and resonance effects of a surficial layer of alluvium Quaternary sediments (100–200 m thick) characterized by low values of shear velocity and attenuation parameter.

The Mw 9.0, 2011 Tohoku-Oki earthquake has reopened the discussion among the scientific community about the effectiveness of earthquake early warning for large events. A well-known problem with real-time procedures is the parameter saturation, which may lead to magnitude underestimation for large earthquakes. Here we measure the initial peak ground displacement and the predominant period by progressively expanding the time window and distance range, to provide consistent magnitude estimates (M = 8.4) and a rapid prediction of the potential damage area. This information would have been available 35 s after the first P-wave detection and could have been refined in the successive 20 s using data from more distant stations. We show the suitability of the existing regression relationships between early warning parameters and magnitude, provided that an appropriate P-wave time window is used for parameter estimation. We interpret the magnitude under-estimation as a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process.

[1] We present an evolutionary approach for magnitude estimation for earthquake early warning based on real‐time inversion of displacement spectra. The Spectrum Inversion (SI) method estimates magnitude and its uncertainty by inferring the shape of the entire displacement spectral curve based on the part of the spectra constrained by available data. The method consists of two components: 1) estimating seismic moment by finding the low frequency plateau W0, the corner frequency fc and attenuation factor (Q) that best fit the observed displacement spectra assuming a Brune w 2 model, and 2) estimating magnitude and its uncertainty based on the estimate of seismic moment. A novel characteristic of this method is that is does not rely on empirically derived relationships, but rather involves direct estimation of quantities related to the moment magnitude. SI magnitude and uncertainty estimates are updated each second following the initial P detection. We tested the SI approach on broadband and strong motion waveforms data from 158 Southern California events, and 25 Japanese events for a combined magnitude range of 3 ≤ M ≤ 7. Based on the performance evaluated on this dataset, the SI approach can potentially provide stable estimates of magnitude within 10 seconds from the initial earthquake detection. Citation: Caprio,M.,M.Lancieri,G.B.Cua,A.Zollo, and S. Wiemer (2011), An evolutionary approach to real‐time moment magnitude estimation via inversion of displacement spectra, Geophys. Res. Lett., 38, L02301, doi:10.1029/ 2010GL045403.

[1] From inspection of a large set of Japanese events, we investigate the scaling of the early radiated energy, inferred from the squared velocity integral (IV2) with the final magnitude of the event. We found that the energy can only discriminate whether the event has a magnitude larger or smaller than 5.8, and in the latter case it can allow for real-time magnitude estimation. However, by normalizing IV2 for the rupture area, the initial slip scales with the magnitude between 4 < M < 7 following the expected scaling laws. We show that the ratio between the squared peak displacement and IV2 is a proxy for the slip following the same scaling but it can be directly derived from the data, without any assumption on the rupture area. The scaling relationship between initial slip and magnitude can be used for early warning applications, when integrated in a probabilistic, evolutionary approach.

[1] Campi Flegrei is an active, resurgent caldera that is located a few kilometres west of the city of Naples, a densely populated urban settlement in southern Italy. Identifying, locating at depth and better defining the geometry of the magma feeding system of the caldera is highly relevant for assessing and monitoring its volcanic hazard. Based on a high resolution seismic reflection data set, we investigated the deep structure of the volcano. Here we show that seismic wave amplitude variations with distance from the radiating source provide clear evidence for large amplitude seismic reflections from the top of an extended supercritical fluid-bearing rock formation at about 3,000 m and of an about 7,500 m deep, 1,000 m thick, low velocity layer, which is associated with a mid-crust, partial melting zone beneath the caldera. The modeling of magma properties based on measured seismic velocities indicates a relatively high melt percentage (in the range 80–90%). These new data suggest that a large magmatic sill is present well within the basement formations, which is possibly linked to the surface through a system of deep fractures bordering the caldera. The lateral extension and similar depth of the melt zone observed beneath the nearby Mt.Vesuvius support the hypothesis of a single continuous magma reservoir feeding both of these volcanoes.

[1] Based on the analysis of Mediterranean, near-source, strong motion records Zollo et al. [2006] (hereinafter referred to as ZLN) showed that peak displacement amplitudes of initial Pand S-wave seismic signals scales with the earthquake size in the moment magnitude range 4 6.1. [9] In Figure 1 we report data distribution vs. magnitude and hypocentral distance. Note that the distance distribution of analyzed events for Japan (Figure 1) is clearly different from that for the Mediterranean (MED) earthquakes given by ZLN. Whereas most of MED records occur at an HD 40 km. [10] At odds with RWH, we did not apply any cut-off at M = 5.5 on hypocentral distance for small and moderate events; indeed this may introduce a bias on the estimation of attenuation law parameters retrieved from both small and large earthquakes records. We follow the ZLN procedure involving among others sensitivity correction, P and S phase identification, double integration, filtering in a frequency band (0.075, 3 Hz). Peaks are read on the modulus of displacement expressed in meters. Starting from the Pwave and S-wave picked arrivals, we measure peaks within a 2 second window. For the P arrival, we also test the method with 4 second windows. [11] The distance attenuation effect is corrected for by assuming a simple log-linear model [Wu and Zhao, 2006; ZLN]; the amplitudes are normalized to a reference distance of 10 Km (i.e., the same as for ZLN in the Mediterranean study, to facilitate comparison). Though RWH show data normalized at a distance of 20 km (ZLN, Figures 2a and 2b), the use of a different normalization distance does not change the slope of the log(peak) vs Magnitude relationships and thus does not alter the graphical interpretation. [12] In Figure 2 we show the relation between the logarithm of distance normalized, peak displacement for P and S waves in different time windows vs final magnitude of the events (following ZLN, statistical significance was GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L20303, doi:10.1029/2007GL030560, 2007 Click Here for Full Article

[1] We show that the low-pass filtered, peak amplitudes of initial P- and S-wave seismic signals recorded in the vicinity of an occurring earthquake source correlates with the earthquake magnitude and may be used for real-time estimation of the event size in seismic early warning applications. The earthquake size can be therefore estimated using only a couple of seconds of signal from the P- or S-wave onsets, i.e. while the rupture itself is still propagating and rupture dimension is far from complete. We argue that dynamic stress release and/or slip duration on the fault in the very early stage of seismic fracture, scales both with the observed peak amplitude and with the elastic energy available for fracture propagation. The probability that a fracture grows to a larger size should scale with the energy initially available. Citation: Zollo, A., M. Lancieri, and S. Nielsen (2006), Earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records, Geophys. Res. Lett., 33, L23312, doi:10.1029/ 2006GL027795.

[1] With the aim of exploring the deep structure of the Larderello-Travale (LT) geothermal field, a high resolution 3-D tomographic inversion of microearthquake traveltimes has been performed. Results show that the deep part of the Larderello-Travale field is characterized by the presence of a structure having a velocity range of 6.0–6.5 km/s and a convex shape deepening towards the northeastern and the southeastern sides of the field. Earthquakes are mostly concentrated on the top of the high velocity structure and below the ‘K horizon’ implying a transition of rheological properties at depth. The reported dependence on time of ts-tp observed at one station located above an earthquake cluster suggests that the variation in pore fluid pressure might be responsible for the transition of rheological properties along the contact. In such an area, changes in pore fluid pressure might be related to time-dependent hydraulic mechanisms that are very effective in crustal rocks at elevated temperatures. INDEX TERMS: 7215 Seismology: Earthquake parameters; 7280 Seismology: Volcano seismology; 8045 Structural Geology: Role of fluids; 8180 Tectonophysics: Tomography; 8424 Volcanology: Hydrothermal systems. Citation: Vanorio, T., R. De Matteis, A. Zollo, F. Batini, A. Fiordelisi, and B. Ciulli (2004), The deep structure of the Larderello-Travale geothermal field from 3D microearthquake traveltime tomography, Geophys. Res. Lett., 31, L07613

[1] A high-resolution multi-fold wide-angle seismic survey carried out across the Irpinia fault, Southern Italy, yields new information about the shallow structure of this normal fault that was reactivated in 1980. The fault zone is imaged to a depth of about 60 m by using a non-linear tomographic technique that is specially designed to image strongly heterogeneous media. Results confirm the location of the fault, as previously inferred by a trench excavated in soft soils, and clearly delineates a 30–35 m step in the bedrock. This single step is indicative of a narrow fault zone, which corresponds upward to warped soils exposed in the trench, thus demonstrating that the near-surface warping is directly related to a brittle faulting in the bedrock. Assuming that the vertical slip rate yielded by paleoseismic data (0.25–0.35 mm/yr) has been constant since the fault's inception, the latter should date back to about 100–140 kys ago. Such a young age may explain why the Irpinia fault is not associated with evident, large-scale geomorphic indicators of its activity.