Pierdominici, Simona

Abstract. The International Continental Scientific Drilling Program (ICDP) STAR (A Strainmeter Array Along the Alto Tiberina Fault System) drilling project aims to study the seismic and aseismic fault slip behavior of the active low-angle Alto Tiberina normal fault (ATF) in the northern Apennines, central Italy, by drilling and instrumenting six shallow boreholes (maximum depth 160 m) with seismometers and strainmeters. During the STAR fieldwork, a geophysical downhole logging campaign was carried out to define the optimal target depth for instrument deployment and formation rock characterization. In particular, the main objectives of this study were to define in situ physical properties of the rocks and the tectonic discontinuity geometry along the boreholes. The downhole logging data provide new findings and knowledge, especially with regards to physical properties such as resistivity and gamma-ray and wave velocity. The collected parameters were compared to the results of literature data collected in similar lithologies, as well as with the results of logging performed in deeper wells drilled for commercial purposes. The physical properties of the Mesozoic–early Tertiary calcareous formations show low gamma-ray values and high compressional (Vp) and shear wave (Vs) velocities (up to 5.3 and 2.9 km s−1, respectively), whereas the overlying clay-rich Late Tertiary formations exhibit high gamma-ray and low resistivity values as well as relatively low Vp and Vs values (up to 3.5 and 2.0 km s−1, respectively). The results obtained from the analysis of the orientations of the tectonic structures, measured along the six boreholes, show good agreement with the orientations of the present-day extensional stress field, which is NE–SW-oriented. Our study allowed us to bridge the gap between the physical properties obtained from literature data and those obtained from the deep well measurements, representing a possible case history for future projects. These new outcomes represent an almost unexplored window of data and will contribute to the advancement of knowledge of the physical properties of the rocks at shallow depths, which are typically overlooked.

Fault slip is a complex natural phenomenon involving multiple spatiotemporal scales from seconds to days to weeks. To understand the physical and chemical processes responsible for the full fault slip spectrum, a multidisciplinary approach is highly recommended. The Near Fault Observatories (NFOs) aim at providing highprecision and spatiotemporally dense multidisciplinary near-fault data, enabling the generation of new original observations and innovative scientific products. The Alto Tiberina Near Fault Observatory is a permanent monitoring infrastructure established around the Alto Tiberina fault (ATF), a 60 km long low-angle normal fault (mean dip 20°), located along a sector of the Northern Apennines (central Italy) undergoing an extension at a rate of about 3 mm yr −1. The presence of repeating earthquakes on the ATF and a steep gradient in crustal velocities measured across the ATF by GNSS stations suggest large and deep (5-12 km) portions of the ATF undergoing aseismic creep. Both laboratory and theoretical studies indicate that any given patch of a fault can creep, nucleate slow earthquakes, and host large earthquakes, as also documented in nature for certain ruptures (e.g., Iquique in 2014, Tōhoku in 2011, and Parkfield in 2004). Nonetheless, how a fault patch switches from one mode of slip to another, as well as the interaction between creep, slow slip, and regular earthquakes, is still poorly documented by near-field observation. With the strainmeter array along the Alto Tiberina fault system (STAR) project, we build a series of six geophysical observatory sites consisting of 80-160 m deep vertical boreholes instrumented with strainmeters and seismometers as well as meteorological and GNSS antennas and additional seismometers at the surface. By covering the portions of the ATF that exhibits repeated earthquakes at shallow depth (above 4 km) with these new observatory sites, we aim to collect unique open-access data to answer fundamental questions about the relationship between creep, slow slip, dynamic earthquake rupture, and tectonic faulting.

A methodology for a comprehensive probabilistic tsunami hazard analysis (PTHA) is presented for the major sources of tsunamis (seismic events, landslides, and volcanic activity) and preliminarily applied in the Gulf of Naples (Italy). The methodology uses both a modular procedure to evaluate the tsunami hazard and a Bayesian analysis to include the historical information of the past tsunami events. In the Source module the submarine earthquakes and the submarine mass failures are initially identified in a gridded domain and defined by a set of parameters, producing the sea floor deformations and the corresponding initial tsunami waves. Differently volcanic tsunamis generate sea surface waves caused by pyroclastic density currents from Somma‐Vesuvius. In the Propagation module the tsunami waves are simulated and propagated in the deep sea by a numerical model that solves the shallow water equations. In the Impact module the tsunami wave heights are estimated at the coast using the Green's amplification law. The selected tsunami intensity is the wave height. In the Bayesian module the probabilistic tsunami analysis computes the long‐term comprehensive Bayesian PTHA. In the prior analysis the probabilities from the scenarios in which the tsunami parameter overcomes the selected threshold levels are combined with the spatial, temporal and frequency‐size probabilities of occurrence of the tsunamigenic sources. The prior probability density functions are integrated with the likelihood derived from the historical information based on past tsunami data. The posterior probability density functions are evaluated to produce the hazard curves in selected sites of the Gulf of Naples.

In this paper we explore the feasibility of formulating the hazard assessment procedure to include the information of past earthquakes into the probabilistic seismic hazard analysis, together with the use of an ensemble modeling technique. This strategy allows, on the one hand, to enlarge the information used in the evaluation of the hazard, from alternative models for the earthquake generation process to past shaking and, on the other hand, to explicitly account for the uncertainties. The Bayesian scheme we propose is applied to evaluate the seismic hazard of Naples. The framework in which we have embedded the tools is flexible to include all types of uncertainties. Here we focus on a sensitive study of the earthquake occurrence by implementing models that span from random to cluster‐type temporal behavior and models that include quasiperiodic occurrence of earthquakes on faults. We implement five different spatiotemporal models to parameterize the occurrence of earthquakes potentially dangerous for Naples. Subsequently, we combine these hazard curves with ShakeMaps of past earthquakes that have been felt in Naples since 1200 A.D. The results are posterior ensemble hazard curves for three exposure times, e.g., 5, 10, and 50 years, in a dense grid that covers the municipality of Naples, considering rocky soil and including the site amplification. Our results show the importance to include the data from past shaking since the difference between the prior and the posterior is about 8–15% for the different exposure times.

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

We propose a methodological approach for a comprehensive and total probabilistic tsunami hazard assessment (TotPTHA), in which many different possible source types concur to the definition of the total tsunami hazard at given target sites. In a multi-hazard and multi-risk perspective, the approach allows us to consider all possible tsunamigenic sources (seismic events, slides, volcanic eruptions, asteroids, etc.). In this respect, we also formally introduce and discuss the treatment of interaction/cascade effects in the TotPTHA analysis and we demonstrate how the triggering events may induce significant temporary variations in short-term analysis of the tsunami hazard. In two target sites (the city of Naples and the island of Ischia in Italy) we prove the feasibility of the TotPTHA methodology in the multi-source case considering near submarine seismic sources and submarine mass failures in the study area. The TotPTHA indicated that the tsunami hazard increases significantly by considering both the potential submarine mass failures and the submarine seismic events. Finally, the importance of the source interactions is evaluated by applying a triggering seismic event that causes relevant changes in the short-term TotPTHA.

Naples is one of the most vulnerable cities in the world because it is threatened by several natural and man-made hazards: earthquakes, volcanic eruptions, tsunamis, landslides, hydrogeological disasters, and morphologic alterations due to human interference. In addition, the risk is increased by the high density of population (Naples and the surrounding area are among the most populated in Italy), and by the type and condition of buildings and monuments. In light of this, it is crucial to assess the ground shaking suffered by the city. To create a ShakeMap atlas for the region and to reconstruct the seismic history of the city from historical to recent times, we gather information from the most reliable and complete databases of macroseismic intensity records dating back to the eleventh century. The events felt in Naples cover a time span ranging from 1293 to 1999. The first event (Mw 5.8) was an earthquake in 1293, located in the southern Apennines, at a distance of 100 km from Naples. The most recent event was an earthquake of moderate magnitude in 1999, located beneath Vesuvius (Fig. 1). In the previous release of the macroseismic databases, two additional events associated with the volcanic activity of Vesuvius in 62 and 79 A.D. were included. They are not included in the new release of the databases because they occurred before 1000 A.D., and likewise they have been not included in this atlas because they are too ancient to be incorporated into any time and magnitude window of completeness. For instrumental events (e.g., after 1980), we merge these macroseismic records with strong-motion data. Basically, we integrate information from five Italian databases and catalogs. This gives us the opportunity to explore several sources of information, expanding the completeness of our data set in both time and magnitude. A total of 84 earthquakes have been analyzed. For each event, we compute the shakemap set (Wald et al., 1999; Michelini et al., 2008; Worden et al., 2010) using an ad hoc implementation developed for this application, with (1) specificground-motion prediction equations (GMPEs) accounting for the different attenuation properties in volcanic areas compared with the tectonic ones, and (2) detailed local microzonation to include the site effects. These shakemaps are provided in terms of Mercalli–Cancani–Sieberg intensity (MCS hereinafter) and peak ground acceleration (PGA). For PGA, the maps are provided in terms of median values and 16th and 84th percentiles, to quantify the epistemic uncertainties associated with the ground-motion measurements. In our prospective, the ShakeMap atlas has a dual application. On one hand, it is an important instrument in seismic risk management because it quantifies the level of shaking suffered by a city during its history, and it could be implemented to the quantification of the number of people exposed to certain degrees of shaking (Allen et al., 2009). Intensity data provide the evaluation of the damage caused by earthquakes; the damage is closely connected with the ground shaking, building type, and vulnerability, and it is not possible to separate these contributions. On the other hand, the atlas can be used as starting point for Bayesian estimation of seismic hazard. This technique allows for the merging of the more standard approach adopted, for example, in the compilation of the national hazard map of Italy used in this Bayesian framework as prior mode, with the site-type approach to the purpose of likelihood function (Selva and Sandri, 2013). The site-type technique is based on ground shaking data recorded in a given area; because the majority of earthquakes occurred when no seismometers were available, site data are mainly from macroseismic evaluation, that is, the felt effect is reconstructed from historical documents. The first two sections of the paper describe the databases and catalogs used, and the specific shakemap configuration applied. In the final section, we analyse the completeness of the atlas in terms of time for different magnitude/intensity thresholds, adopting and comparing two different strategies, one based mainly on historical analysis and the other on statistical evaluation.

Deliverables D9-28/a2-c2 of S1 Project

We present high-resolution Vp models of the Middle Aterno basin obtained by multi-scale non-linear controlled-source tomography. Seismic data have been collected along four dense wide-aperture profiles, that run SW-NE for a total length of ~ 6 km in the hangingwall of the Paganica - S. Demetrio Fault, source of the 6th April 2009 (Mw 6.3) L'Aquila normal-faulting earthquake. Seismic tomography expands the knowledge of the basin with high spatial resolution and depth penetration (> 300 m), illuminating the Meso-Cenozoic substratum that corresponds to high-Vp regions (Vp > 3500-4000 m/s). Low Vp (1500-2000 m/s) lacustrine sediments (Early Pleistocene in age) are imaged only in the SW sector of the basin, where they are up to 200 m thick and lie below coarse fluvial and alluvial fan deposits. The overall infill consists of Early to Late Pleistocene alluvial fan and fluvial sediments between the Paganica Fault and the Bazzano ridge, with Vp reaching 3000 m/s for the oldest conglomeratic bodies. The substratum has an articulated topography. The main depocenter, ~ 350 m deep, is in the SW sector of the basin south of the Bazzano ridge. Remarkably, this depocenter and the overlying thick lacustrine body match the area of maximum coseismic subsidence observed after the 2009 earthquake. In the Paganica area, Vp images unravel large steps in the substratum related to two unreported SW-dipping buried strands, synthetic to the Paganica Fault, with ~ 250 m associated total vertical throw. This finding has important implications on the long-term history of the Paganica – S. Demetrio Fault system, whose total vertical displacement has been previously underestimated. An additional ~ 250 m vertical offset along this complex Quaternary extensional structure should therefore be considered.