ALBERT

Description: The stress release (or stress drop) during an earthquake is an important element of seismic hazard forecasting; high stress drop earthquakes radiate more high frequency energy, causing stronger ground shaking. The stress drop also provides information about the energy budget, and the size of fault ruptured, and consequently, earthquake triggering and rupture dynamics. Reliable estimates of stress release are difficult to make, largely because of the ambiguity in removing the distorting propagation effects experienced by waves traveling from earthquake to seismometer from recorded seismograms. Most measurements are made using frequency amplitude spectra. We use two methods to estimate earthquake stress drop for 30 of the larger earthquakes in central Italy (2016–2017) and compare them with the results of previous studies. We find that the variation between absolute values estimated in different studies is much larger than the reported formal inversion errors. The relative values are more reliable, with different studies consistently finding a particular earthquake has relatively high or low stress drop. Direct comparison of the similar-sized, damaging Amatrice and Visso earthquakes reveals that the relative spectral stress drop estimates reflect the relative strength of high-frequency ground motion, but may indicate more complex rupture rather than higher average stress release.

Description: Estimates of spectral stress drop are fundamental to understanding the factors controlling earthquake rupture and high frequency ground motion, but are known to include large, poorly-constrained uncertainties. We use earthquakes from the 2016–2017 sequence in the Italian Appenines (largest event at Norcia, Mw 6.3) to investigate these uncertainties and their causes. The similarly-sized events near Amatrice (Mw 6.0) and Visso (Mw 5.9) enable better constrained relative analysis. We calculate S wave source spectra, corner frequencies, and spectral stress drop for 30 of the larger events. We compare both empirical and modeling approaches to isolate the source spectra and calculate source parameters; we also compare our results with those from published studies. Both random and systematic inter-study variations are larger than the standard errors reported by any individual study. The reported magnitude dependence of stress drop varies between studies, being largest for generalized inversions and smallest for more individual event based approaches. The relative spectral estimates of inter-event stress drop are more consistent; all approaches estimated higher stress drop in the Amatrice earthquake than the similar-sized Visso earthquake. In contrast, finite fault inversions of these two earthquakes found that the Visso earthquake had the larger region of concentrated, higher slip, whereas the Amatrice earthquake had multiple, lower slip, subevents. The Amatrice spectra contain more high frequency energy than those of the Visso earthquake. This comparison suggests that consistent measurement of a higher spectral stress drop indicates greater high-frequency ground motion but may correspond to greater rupture complexity rather than higher stress drop.

Description: Published

Description: e2022JB025022

Description: OST2 Deformazione e Hazard sismico e da maremoto

Description: JCR Journal

Description: The incompleteness of earthquake catalogs is a well-known issue caused by our technical limitation in detecting the small-to very small-magnitude seismicity falling near or below the background seismic noise. The detection of small-magnitude events is fundamental for improving our knowledge of geometry and kinematics of seismogenic sources and the spatio-temporal characteristics of seismicity, thus leading to better models for seismic hazard. Template-matching (TM) is a powerful technique that, based on similarity measure (cross-correlation) of seismic waveforms, allows to detect hidden earthquakes that are similar to known events (called templates). The high computational effort often limits such technique to small areas and for short time frames (less than 1 year). In this work, we present the first application of template-matching at regional scale for the Italian Peninsula, focusing on the Southern Apennines. We use about 3,600 high-quality events as templates, scanning 6-year long continuous recordings (2009–2014), at more than 180 stations of the INGV network. About 20,000 new events are found, showing a comparable quality to the template catalog in terms of hypocentral solution, reaching a decrease of the magnitude of completeness of about one unit. To highlight the improved quality of the TM catalog, we report two main examples regarding the Sannio-Matese area, where TM allowed us to unravel relevant details on the spatio-temporal distribution of the local seismicity.

Description: - PRIN-2017 project MUSE 4D (2017KT2MKE) Overtime tectonic, dynamic and rheologic control on destructive multiple seismic events—Special Italian Faults and Earthquakes: From real 4-D cases to models. - FURTHER project “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” funded by the Strategic Earthquake Department of Istituto Nazionale di Geofisica e Vulcanologia (Italy).

Description: Published

Description: e2023GC011160

Description: OST5 Verso un nuovo Monitoraggio

Description: JCR Journal

Description: Abstract Tomographic images of the lithosphere are the first step to constrain the evolution of mountain belts and their interaction. By inverting new high-quality P- and S-wave arrivals that sample the entire lithosphere, we determined Vp and Vp/Vs models with reliable resolution in the critical depth range (40–80 km) where plates of the central Mediterranean area interact. This data set yields homogeneous representation of the 3D structure over a critical area at a regional scale. Here, we show that the Alps derive from a laterally continuous underthrusting of the European plate and that the Adria lithosphere was delaminated after the collision. Tomograms resolve the lateral changes of the continental versus oceanic subduction along the Alpine belt and identify original evidence of fluids beneath the orogens able to facilitate the current deformation. Plain Language Summary A high resolution imaging of the lithosphere/asthenosphere system is crucial to understand tectonic processes of orogens and subductions. The Alpine chain is an exemplary case of complexity, with its lateral heterogeneity and changes. The largest seismic array ever developed in the Alpine chain (Alparray Seismic Network) has enabled the creation of a high-quality seismic data set contributing to new images of the entire central Mediterranean area. The novelty of this work lies in the enhanced resolution of velocity anomalies in a critical depth range (35–80 km) and with optimal homogeneity at the regional scale. The new 3D Vp and Vp/Vs models allow us to get insights into many open questions about the structure and evolution of the circum-Mediterranean orogens.

Description: Published

Description: e2023JB026411

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: JCR Journal

Description: We have provided the first estimate of scat- tering and intrinsic attenuation for the Gargano Prom- ontory (Southern Italy) analyzing 190 local earthquakes with M L ranging from 1.0 to 2.8. To separate the intrin- sic Q i and scattering Q s quality factors with the Wen- nerberg approach (1993), we have measured the direct S waves and coda quality factors ( Q 𝛽 , Q c ) in the same volume of crust. Q 𝛽 parameter is derived with the coda normalization method (Aki 1980) and Q c factor is derived with the coda envelope decay method (Sato 1977). We selected the coda envelope by performing an automatic picking procedure from T start = 1.5T S up to 30 s after origin time (lapse time T L ). All the obtained quality factors clearly increase with frequency. The Q c values correspond to those recently obtained for the area. The estimated Q i are comparable to the Q c at all frequencies and range between 100 and 1000. The Q s parameter shows higher values than Q i , except for 8 Hz, where the two estimates are closer. This implies a pre- dominance of intrinsic attenuation over the scattering attenuation. Furthermore, the similarity between Q i and Q c allows us to interpret the high Q c anomaly previ- ously found in the northern Gargano Promontory up to a depth of 24 km, as a volume of crust characterized by very low seismic dumping produced by conversion of seismic energy into heat. Moreover, most of the earth- quake foci fall in high Q i areas, indicating lower level of anelastic dumping and a brittle behavior of rocks.

Description: Published

Description: 827-846

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: JCR Journal

Description: Abstract We present the first rupture models of the two mainshocks of the 2012 northern Italy sequence, determined by jointly inverting seismic and geodetic data. We aim at providing new insights into the mainshocks for which contrasting seismotectonic interpretations are proposed in literature. Sources' geometric parameters were constrained by seismic reflection profiles, 3-D relocations and focal mechanisms of mainshocks/aftershocks. Site-specific velocity profiles were used to model accelerograms affected by strong propagation effects related to the Po basin. Our source models differ significantly from previous ones relying on either seismic or geodetic data. Their comparison against geological sections and aftershock distribution provides new insights about the ruptured thrust faults. The May 20th Mw6.1 mainshock activated the Middle Ferrara thrust-ramp dipping ∼45° SSW-wards, breaking a main eastern slip patch 4–15 km deep in Mesozoic carbonates (maximum slip 0.7–0.8 m) and Paleozoic-Triassic basement rocks, and a small western patch in the basement. The May 29th Mw6.0 mainshock featured two separated asperities along the Mirandola thrustramp dipping ∼42° S-wards: an eastern asperity 4–15 km deep in Mesozoic carbonates and basement rocks (maximum slip 0.7 m) and a deeper western one (7–16 km depth) mainly in the basement (slip peak 0.8 m). On-fault aftershocks were concentrated within the basement and Mesozoic carbonates, devoiding highslip zones. Slip and aftershock distribution was controlled by the rheological transition between Mesozoic carbonates and Cenozoic sediments. Unlike previous thin-skinned tectonic interpretations, our results point to a complex rupture process along moderately dipping (40°–45°) thrust-ramps deeply rooted into the Paleozoic crystalline basement. Plain Language Summary The two M6 mainshocks of the 2012 Italy sequence are the strongest earthquakes ever observed in the Po Plain, a strategic region for the Italian economy. The mainshocks ruptured blind thrust-faults, however their source models and seismotectonic interpretation are still debated because the thrust-system architecture is controversial. Contrasting thick-skinned and thin-skinned tectonic models are proposed. In thick-skinned interpretations, shortening is accommodated by thrust-ramps rooted into the crystalline basement that represent main seismogenic structures, whereas in thin-skinned interpretations, shortening and seismicity are controlled by listric faults splaying out from dècollement levels in the sedimentary crust. A comprehensive analysis of the mainshocks' source represents an opportunity to provide new insights into the seismogenesis in northern Italy and on a broader scale into seismotectonics of thrust-and-fold belts. We get a complete picture of the mainshocks kinematics by jointly inverting, for the first time, seismic and geodetic data, and unravel rupture heterogeneities not resolved by previous studies. By integrating source models with aftershock locations and geological models, we propose a comprehensive seismotectonic interpretation of the sequence. We conclusively identify the ruptured faults that correspond to thrust-ramps rooted into the crystalline basement and evidence the key role played by lithological changes in the rupture process.

Description: Published

Description: e2022JB026278

Description: OST3 Vicino alla faglia

Description: JCR Journal

Description: Foreshocks are spatially clustered seismic events preceding large earthquakes. Since the dawn of seismology, their occurrence has been identified as a possible mechanism leading to further crustal destabilization, hence, to major failures. However, several cases occurred without any previous anomalous seismic activity, so that the hypothesis of foreshocks as reliable seismic precursors fails to pass statistical tests. Here, we perform an all‐round statistical comparative analysis of seismicity in Southern California to assess whether any differences can be identified between swarms and foreshocks. Our results suggest that extremely variable seismic patterns can forerun mainshocks, even though they tend to be preceded by clusters with more numerous events spread over larger areas than swarms and with a wider range of magnitudes. We provide a physical explanation of such dissimilarity and conclude, despite it, that foreshocks can hardly be reliable short‐ term precursors of large earthquakes in California.

Description: Published

Description: e2023JB027337

Description: OST4 Descrizione in tempo reale del terremoto, del maremoto, loro predicibilità e impatto

Description: JCR Journal

Description: A catalogue of precisely located micro-seismicity is fundamental for investigating seismicity and rock physical properties in active tectonic and volcanic regions and for the definition of a ‘baseline’ seismicity, required for a safe future exploitation of georesource areas. In this study, we produce the first manually revised catalogue of micro-seismicity for Co. Donegal region (Ireland), an area of about 50K M2 of on-going deformation, aimed at localizing natural micro-seismic events occurred between 2012 and 2015. We develop a stochastic method based on a Markov chain Monte Carlo (McMC) sampling approach to compute earthquake hypocentral location parameters. Our results indicates that micro-seismicity is present with magnitudes lower than 2 (the highest magnitude is 2.8).The recorded seismicity is almost clustered along previously mapped NE-SW trending, steeply dipping faults and confined within the upper crust (focal depth less than 10 km). We also recorded anthropogenic seismicity mostly related to quarries' activity in the study area.

Description: Published

Description: 62-76

Description: OST1 Alla ricerca dei Motori Geodinamici

Description: JCR Journal

Description: This study focuses on two weak points of the present procedure to carry out microzoning study in near-field areas: (1) the Ground Motion Prediction Equations (GMPEs), commonly used in the reference seismic hazard (RSH) assessment; (2) the ambient noise measurements to define the natural frequency of the near surface soils and the bedrock depth. The limitations of these approaches will be discussed throughout the paper based on the worldwide and Italian experiences performed after the 2009 L’Aquila earthquake and then confirmed by the most recent 2012 Emilia Romagna earthquake and the 2016–17 Central Italy seismic sequence. The critical issues faced are (A) the high variability of peak ground acceleration (PGA) values within the first 20–30 km far from the source which are not robustly interpolated by the GMPEs,(B) at the level 1 microzoning activity, the soil seismic response under strong motion shaking is characterized by microtremors’ horizontal to vertical spectral ratios (HVSR) according to Nakamura’s method. This latter technique is commonly applied not being fully compliant with the rules fixed by European scientists in 2004, after a 3-year project named Site EffectS assessment using AMbient Excitations (SESAME). Hereinafter, some “best practices” from recent Italian and International experiences of seismic hazard estimation and microzonation studies are reported in order to put forward two proposals: (a) to formulate site-specific GMPEs in near-field areas in terms of PGA and (b) to record microtremor measurements following accurately the SESAME advice in order to get robust and repeatable HVSR values and to limit their use to those geological contests that are actually horizontally layered.

Description: Published

Description: id 11

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Set of data and metadata that characterize a site hosting a seismic station

Description: In this paper we describe an advanced database for the site characterization of seismic stations, named “CRISP—Caratterizzazione della RIsposta sismica dei Siti Permanenti della rete sismica” (http:// crisp. ingv. it, quoted with https:// doi. org/ 10. 13127/ crisp), designed for the Italian National Seismic Network (Rete Sismica Nazionale, RSN, operated by Istituto Nazionale di Geofisica e Vulcanologia). For each site, CRISP collects easily accessible station information, such as position, type(s) of instrumentation, instrument housing, thematic map(s) and descriptive attributes (e.g., geological characteristics, etc.), seismic analysis of recordings, and available geophysical investigations (shear-wave velocity [VS] profile, non-linear decay curve). The archive also provides key proxy indicators derived from the available data, such as the time-averaged shear-wave velocity of the upper 30 m from the surface ( VS30) and site and topographic classes according to the different seismic codes. Standardized procedures have been applied as motivated by the need for a homogenous set of information for all the stations. According to European Plate Observing System infrastructural objectives for the standardization of seismological data, CRISP is integrated into pre-existing INGV instrument infrastructures, shares content with the Italian Accelerometric Archive, and complies map information about the stations, as well as local geology, through web services managed by Istituto Superiore per la Protezione e la Ricerca Ambientale. The design of the CRISP archive allows the database to be continually updated and expanded whenever new data are available from the scientific community, such as the ones related to new seismic stations, map information, geophysical surveys, and seismological analyses.

Description: Published

Description: 2415 - 2439

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Lifelines, such as pipelines, roads, and tunnels, are critical infrastructure and when crossing active tectonic faults, a reliable estimation of the fault displacement in case of an earthquake is required. The first and simplest approach is to use empirical fault scaling relations to compute the design fault displacement, but this may result in an unknown level of safety. Thus, the probabilistic fault displacement hazard analysis (PFDHA) is the appropriate tool to assess the fault displacement hazard within a performance-based framework. Based upon an established PFDHA model, we present a simplified approach for engineering applications focusing on the lifeline–fault crossing along with appropriate simplifications and assumptions to extend its applicability to numerous faults. The aim is to provide a structure-independent approach of PFDHA that can be used when a site-specific study is not required, not possible (e.g., absence of recent sediments for dating past events), or too cumbersome, e.g., for lifeline route selection. Additionally, an in-depth investigation is presented on the key parameters, such as maximum earthquake magnitude, fault length, recurrence rate of all earthquakes above a minimum magnitude, and lifeline-fault crossing site, and how they affect the hazard level. This approach will be the basis for deriving hazard-consistent expressions to approximate fault displacement for use within the Eurocodes. The latter is intended to serve as a compromise between hazard-agnostic fault scaling relations and a comprehensive PFDHA, which requires detailed calculations and site-specific seismological data.

Description: Open access funding provided by HEAL-Link Greece. The current work has been undertaken as part of the Horizon 2020 Seismology and Earthquake Engineering Research Infrastructure Alliance in Europe (SERA, Grant Agreement No. 730900). The first and the third author have received partial funding from the European Union’s Horizon 2020 research and innovation programme “METIS-Seismic Risk Assessment for Nuclear Safety” under Grant Agreement No. 945121. Also, the financial support provided by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Faculty Members & Researchers”, Project "TwinCity—Climate-Aware Risk and Resilience Assessment of Urban Areas under Multiple Environmental Stressors via Multi-Tiered Digital City Twinning ", (Number: 2515) is gratefully acknowledged.

Description: Published

Description: 4821–4849

Description: 2T. Deformazione crostale attiva

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: JCR Journal