Description: This is the editoral of a special issue that is focused on the multidisciplinary approach to cultural heritage preservation, with special care to the impact of earthquakes and their associated effects. For that, we have collected a number of representative studies involving the different research fields, each addressing the problem through a specialized methodological perspective. The final goal is to set up a common ground for interaction, highlighting the need for scientific collaboration and coordinated inter- vention. Below, we briefly summarize the main contri- butions to this special issue, which have been rationally sorted to highlight the diversity in the backgrounds of the different authors and in their methodological approaches, but at the same time to emphasize similar aspects of the addressed problematics and common objectives.

Description: The spectacular Lusi mud eruption started in northeast Java, Indonesia, the 29th of May 2006 following a M6.3 strike slip seismic event. After the earthquake several mud pools aligned along a NE-SW direction appeared in the Sidoarjo district. The most prominent eruption site was named Lusi. Lusi is located ∼10 km to the NE of the northernmost cone of the Arjuno-Welirang volcanic complex with which it is connected by the Watukosek Fault System. In this study, we applied the HVSR method, which is a common tool used for site effect investigations as well as to infer buried structures and reconstruct sub-surface geology. The method is based on the ratio of the horizontal to vertical components of ground motion and it generally exhibits a peak corresponding to the fundamental frequency of the site. Spectral ratio results highlight a fundamental frequency band between 0.4 and 1.0 Hz in the Lusi neighborhood. We interpret these peaks as related to the velocity lithological contrast at depth between alluvial deposits and bluish grey clay. Our analysis also highlights the presence of a “depocenter”, characterized by fundamental frequency up to 0.3 Hz, which is interpreted as the subsidence caused by withdrawal of mud and fluids from depth (as also shown by the comparison of the HVSR results with gravimetry data). Moreover, in the area of the Lusi vent a broad-band frequency range is related to the Lusi conduit. In this paper, we show that detailed microtremor surveys could be used as a preliminary and fast approach to locate mud conduits with sufficient precision.

Description: Mud volcanoes are characterized by emissions of fluids and fragmented sedimentary rocks that may create large structures with different morphologies. The development of these structures occurs due to the presence in the subsurface of a) clay-bearing strata that can be buoyant in the surrounding units and b) over-pressured fluids that facilitate the formation of diapirs through sedimentary rocks, as well as structural and/or lithologic discontinuities. Mud volcanoes have been observed and studied in different localities on the planet. In this framework, we tested ambient vibration methods, which are common tools used for site effect investigations aiming to assess the thickness of the sediments and the body wave velocities. The approach commonly used for this type of studies is based on the ratio of the horizontal to vertical components of ground motion (HVSR) and on passive array techniques. The HVSR generally enable to recognize peaks that point out to the fundamental frequency of the site, which usually fit quite well the theoretical resonance curves. The combination of HVSR and shear wave velocity, coming from passive array techniques, enables to collect valuable information about the subsurface structures. Here we present new data collected at mud volcano and sedimentary hosted hydrothermal system sites in order to investigate the depths of the main discontinuities and of the hypothesized hydrocarbon reservoirs. Our results indicate that the ambient vibrations study approach, represents a swift and simplified methods that provides quick information on the subsoil structure of the investigated areas. This methodology allowed us to delineate a preliminary sketch useful to plan more specific and detailed investigations settled to outline a comprehensive model of the explored targets.

Description: This paper describes the model implementation and presents results of a probabilistic seismic hazard assess- ment (PSHA) for the Mt. Etna volcanic region in Sicily, Italy, considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in standard PSHA, which are broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic data, etc.; presented in Part 1, by Azzaro et al., 2017) and through the development and software implementation of original tools for the computa- tion, such as a new ground-motion prediction equation and magnitude–scaling relationship specifically derived for this volcanic area, and the capability to account for the surfi- cial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been car- ried out after updating the most recent releases of two widely used PSHA software packages (CRISIS, as in Ordaz et al., 2013; the OpenQuake engine, as in Pagani et al., 2014). Re- sults are computed for short- to mid-term exposure times (10% probability of exceedance in 5 and 30 years, Poisson and time dependent) and spectral amplitudes of engineer- ing interest. A preliminary exploration of the impact of site- specific response is also presented for the densely inhabited Etna’s eastern flank, and the change in expected ground mo- tion is finally commented on. These results do not account for M 〉 6 regional seismogenic sources which control the hazard at long return periods. However, by focusing on the impact of M 〈 6 local volcano-tectonic earthquakes, which dominate the hazard at the short- to mid-term exposure times considered in this study, we present a different viewpoint that, in our opinion, is relevant for retrofitting the existing buildings and for driving impending interventions of risk re- duction.

Description: Published

Description: 1999–2015

Description: 5T. Modelli di pericolosità sismica e da maremoto

Description: JCR Journal

Description: Amplitudes and frequency content of the seismic ground motion generated by an earthquake and recorded at a specific location depends on the characteristics of the source, the path from the source to the site and the local geologic conditions. The local site seismic response is produced by multiple physical phenomena (i.e., reflection, diffraction, focusing, resonance effects, non-linear soil behavior) that can amplify or decrease amplitudes of seismic waves near to the surface causing high variability in the observed ground motions. In particular, vertical discontinuities and abrupt changes in the velocity profile, or lateral heterogeneities such as faults and/or stratigraphic contacts can have a strong impact. A correct and quantitative assessment of site effects is required for both the interpretation of observed waveforms and the reliable prediction of resultant ground motions (e.g., computation of specific earthquake scenarios). In addition, the extent and distribution of building damage due to moderate and large earthquakes in densely populated areas are a result of the combined effect of local site response and the dynamic properties of man-made structures. The quantification of ground motion amplification are therefore of primary interest for seismologists and engineers in order to reduce associated risks. Recent advances in engineering seismology research resulted in improvements in the study of seismic site response both from the theoretical and experimental points of view. For example, new numerical modelling techniques have become available, which account for non-linear soil behavior. Growing seismic networks allow for the more advanced site response estimates compared to the past as well (e.g. the development of more reliable ground motion prediction equations). This thematic issue focuses on local seismic site effects and represents a collection of research papers and case studies on the effect of subsurface structure on ground motion from new observations, numerical modelling, as well as geophysical imaging. This volume also includes contributions related to the Earth system response to earthquake processes. In the first paper of this volume, Germoso et al. (2017) analyse the effects of fractional derivatives in visco-elastic dynamics for site response analysis. They prove that the use of fractional derivatives for representing the viscous terms offers a larger flexibility in the resulting models (compared to standard methods), and allow them to better quantify the degree of dissipation as well as the magnitude of deformation and phase angle. Poggi et al. (2017) present three different soil amplification models for 5% damped pseudo-spectral acceleration response spectra using recordings of 88 selected stations of the Japanese KiKNet strong-motion network. While they do not provide a ranking of the applied methods, they evaluate the strengths and weaknesses of the each tested technique. Michel et al. (2017) present a site amplification study for the city of Basel (Switzerland), by combining data achieved using geophysical site characterization and site response modelling. They obtain amplification maps of the response spectrum at different periods for earthquake engineering and maps for implementation in ShakeMap. Pischiutta et al. (2017) perform geophysical investigations in the northwestern sector of the island of Malta to reconstruct velocity-depth models by using active and passive methods. They observe ground motion amplification at rock sites, highlighting the importance of performing velocity measurements even for such sites. In fact, using only a lithological criterion and following the EuroCode EC8, rock sites would be associated to class “A” where no amplification is expected. Hayashi and Craig (2017) measure S-wave velocity profiles at eleven sites in the Eastern San Francisco Bay area using surface wave methods. A S-wave velocity cross section which runs perpendicular to the Hayward fault is derived and the theoretical site amplification is calculated using a viscoelastic finite-difference method. Their results show that ground motion is amplified on the west side of the Hayward fault as an effect of the lateral variations of the S-wave velocity. Panzera et al. (2017) investigate the characteristics of the local seismic response in Lampedusa (Italy), a carbonate shelf belonging to the foreland domain at the northern edge of the African plate. Ninety-two ambient noise recordings were collected and processed through spectral ratio techniques. Their results point out the importance of seismic site effects by the presence of both morphologic and tectonic structures. Moisidi (2017) examine the potential soil-building resonance at selected buildings in a complex geological setting of the small scale Paleohora Basin (southwest Crete). This study highlights the necessity of incorporating the determination of potential coupling effects between site and buildings into urban planning for risk mitigation studies. Di Naccio et al. (2017) present an interdisciplinary approach to investigate the seismic response of the San Gregorio (L'Aquila, Italy), a rock site severely damaged by L'Aquila 2009 earthquake. Based on geological-structural, geophysical and seismic analyses, their results highlight the role of rock mass fracturing on seismic amplification, that generates lateral variations in seismic velocity. Bonilla et al. (2017) apply seismic interferometry to compute the in-situ shear wave velocity to evaluate the seismic response of sediments. They conclude that their approach is a robust method to extract shear wave velocity profiles and evaluate non-linear soil response. A seismic characterization of the flat Contents lists available at ScienceDirect Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce Physics and Chemistry of the Earth 98 (2017) 1e2 http://dx.doi.org/10.1016/j.pce.2017.04.005 1474-7065/© 2017 Published by Elsevier Ltd. top area of Monteluco (Italy) carbonate mountain using a multidisciplinary approach was performed by Durante et al. (2017). They hypothesize that local seismic amplification is related to topography and to an intensely fractured shallow-seated formation with relatively low shear wave velocity. Pazzi et al. (2017) investigated the Castagnola (La Spezia, Italy) and Roccalbegna (Grosseto, Italy) landslides through ambient vibrations. They estimated horizontal to vertical spectral ratio on a dense grid of points and obtained useful information on the main impedance contrast depths for large areas. The interpolation of the obtained fundamental frequencies enables the detection and reconstruction of the landslides' slip surfaces. The thematic issue is closed by the papers of Bogdanov et al. (2017) and Pierotti et al. (2017) that present the physical and chemical anomalies in the local environment before and after an earthquake.

Description: Published

Description: 1-2

Description: 4T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: Pyroclastic cones are a typical feature on volcanoes characterized by flank activity. Their distribution and orientation are important markers to obtain information on the maximum horizontal compressional stress acting on a volcano. A geophysical survey was performed on the pyroclastic cone of Mt. Vetore (Mt. Etna volcano, Southern Italy) to obtain information on its internal structural setting and to support the standard morphometric analysis. Results highlighted evident frequency peaks at 1.0 Hz inside the cone, which are attenuated away from it. The random decrement method was applied to this peak to compute damping and then to exclude links with anthropogenic sources. Moreover, time-frequency polarization analysis revealed that ambient vibrations are strongly polarized in a narrow frequency band, centered at a frequency of 1.0 Hz, with a preferred oscillation azimuth of 70–90° N. Array measurement of ambient vibrations was also used to obtain a shear wave velocity profile and then to retrieve the main interfaces with high seismic impedance. Results suggest a cone structure having a feeder dike consisting of fractured rocks with thickness of about 50 m surrounded by pyroclastic material lying on a high-velocity substrate. Finally, a 3D model of Mt. Vetore cone was built employing the finite element method to reproduce an experimental modal frequency of the cone itself. The numerical results successfully reproduced the experimental ones collected by the geophysical survey.

Description: Published

Description: id 74

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: The Victoria Lines Fault (island of Malta) is a 〉15 km-long and N260°-striking segmented normal fault-system, which is probably inactive since the late Pliocene. In the westernmost part, the Fomm Ir-Rih segment displays comparable geologic throw and escarpment height (~150–170 m), moreover its hangingwall hosts thin patches of Middle Pleistocene clastic continental deposits (red beds), which are poorly preserved elsewhere. We acquired two seismic transects, by collecting ambient vibration recordings, processed by using horizontal-to-vertical spectral ratios, complemented by one high-resolution 2-D refraction tomography survey crossing this fault where it is locally covered by red beds and recent colluvial deposits. We found a resonance peak at ~1.0 Hz in the hangingwall block, whereas clear peaks in the range ~5.0–10.0 Hz appear when approaching the subsurface fault, and we relate them to the fractured bedrock within the fault zone. The best-fit tomographic model shows a relatively high-Vp shallow body (Vp 2200–2400 m/s) that we relate to the weathered top of the Miocene Upper Coralline Limestone Fm., bounded on both sides by low-Vp regions (〈1400 m/s). The latter are the smeared images of steep fault zones. Tomography further reveals a thick (~15–20 m) low-Vp (〈1000 m/s) zone, which could be a syn-tectonic wedge of colluvial deposits developed in the downthrown block. Surface waves analysis indicates lateral changes of the average shallow shear wave velocity, with Vs ~130 m/s within the inferred fault zone, and Vs 〉230 m/s above the weathered top-bedrock. Our results depict a clear seismic signature of the Victoria Lines Fault, characterized by low seismic velocity and high amplification of ground motion. We hypothesize that, during the Middle Pleistocene, faulting may have affected the basal part of the red beds, so that this part of the investigated complex fault-system may be considered inactive since ~0.6 Myr ago.

Description: Published

Description: 220-233

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Mud volcanoes are rapidly-evolving geological phenomena characterized by the surface expulsion of sediments and fluids from over-pressurized underlying reservoirs. We investigate the Nirano Mud Volcano, Northern Italy, with seismic methods to better understand the dynamic evolution of the system and shed light on its subsurface structure. Our study allowed to detect and characterize three different types of high-frequency drumbeat signals that are present in the most active part of the mud volcano plumbing system. With a back-projection method based on the cross-correlation envelope of signals recorded at different station pairs, we can determine the source location of the drumbeats. These coincide with the location of V/H (vertical-to-horizontal) amplitude peaks obtained from an ambient vibration profile and resistivity anomalies identified in a previous study. We observe that the drumbeats are P-wave dominated signals, with characteristics similar to those found in magmatic settings, i.e. LPs (long-period signals). We suggest that such tremors originate from the migration of mud and gas inside the mud volcanic conduits. The source location, waveform and frequency content of the drumbeats evolve over time. We found that drumbeat occurrence is directly linked with morphological changes at surface.

Description: Published

Description: 107619

Description: 7A. Geofisica per il monitoraggio ambientale

Description: JCR Journal