ALBERT

Description: The aim of this paper is to evaluate empirical attenuation relationships in order to validate peak values and pseudo-velocity spectra to calibrate shaking scenarios for the Molise area, which was struck by two earthquakes of Mw ¼ 5.7 (INGV-Harvard European- Mediterranean Regional Centroid-Moment tensor project) on October 31st and November 1st, 2002. Before the earthquake occurrence this region was classified as not hazardous, according to the former Italian seismic code. After the main-shocks, felt in many towns of the Molise and Puglia regions, a strong motion and a seismic temporary network were installed in the epicentral area and surrounding regions. This allowed the collection of a large data set, useful to characterize this area. The joint velocity-acceleration data set has been used to derive ground motion models for peak ground acceleration, peak ground velocity, and pseudo-velocity response spectra for both maximum horizontal and vertical components of the motion. The results obtained for the Molise area have been compared with the attenuation pattern of the Umbria-Marche region (central Italy) and the Italian territory. Remarkable differences have been observed leading to a discussion of the possible regional dependence of ground motion.

Description: Published

Description: 198–211

Description: 4T. Sismicità dell'Italia

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

Description: JCR Journal

Description: reserved

Description: A detailed analysis of the intensity attenuation in the Etna and other Italian volcanic districts, was performed using the most recent and complete intensity datasets. Attenuation laws were derived through empirical models fitting ΔI (the difference between epicentral I0 and site Ix intensities) average values versus hypocentral site distances by the least-square method. The huge amount of data available for the Etna area allowed us to elaborate bi-linear and logarithmic attenuation models, also taking source effects into account. Furthermore, the coefficients of the Grandori formulation have been re-calculated to verify the ones previously defined for seismic hazard purposes. Among the tested relationships, the logarithmic one is simple and fairly stable, so it was also adopted for the other volcanic Italian areas. The analysis showed different attenuation trends: on the one hand, Etna and Ischia show the highest decay of intensity (ΔI=4) in the first 20 km; on the contrary, the Aeolian Islands and Albani Hills present a slight intensity attenuation (ΔI=2) at 20 km from the hypocentre; finally, Vesuvius seems to have an intermediate behaviour between the two groups. The proposed regionalization gives a significantly better image of near-field damage in volcanic regions and is easily applicable to probabilistic seismic hazard analyses.

Description: JCR Journal

Description: open

Description: The plain of Gubbio is located in a northwest-southeast oriented, 4-km wide, 20-km long intermountain basin in the northern Apennines, central Italy. The moderate-magnitude earthquakes of the 1997 Umbria-Marche seismic sequence, occurred 40 km southeast of Gubbio, generated displacements as large as 6 cm within the basin. The large amplitude phase, not observed outside of the basin, was followed by low-frequency wave trains lasting up to 1 minute. In order to investigate the mechanism of possible local amplification effects, different kind of geophysical and geological investigation of the basin started within the framework of the Italian DPC-INGV projects. In particular, the GFZ and the INGV deployed two linear seismic arrays. The first one was composed of ten seismological stations with 1-s receivers. It operated from June until December 2005. The array was oriented north-south, approximately: all the stations but two were installed on the sedimentary deposits. The remaining two stations (the northernmost and the southernmost) were installed on rock outcrops at the edges of the basin. The second array, composed by 10 stations with 5-s receivers, was deployed along the main axis of the basin, and is recording since November 2005. For 45 days, the two arrays worked simultaneously. A selected dataset of 250 earthquakes has been analyzed. H/V spectral ratio results show that systematic low-frequency (0.3-0.4 Hz) amplification affects the stations in the middle of the basin. The resonance frequency peaks are consistent with the thickness and the average S-wave velocity of soft sediments derived from microtremor measurements in the basin. The conventional spectral ratio results show a more complex broad-band (0.3-10 Hz) amplification. The analysis of selected records by means of a sonogram approach highlights the arrival of strong late phases increasing the signal duration at the stations located in the middle of the basin.

Description: Unpublished

Description: Geneva, Switzerland

Description: open

Description: A new experiment called SERAPIS (SEismic Reflection/Refraction Acquisition Project for Imaging complex volcanic Structures) has been planned and carried out, based on off-shore seismic energization and data acquisition on land and on sea-bottom. The experiment was performed in September, 2001 during which the vessel NADIR of IFREMER (equipped with 12, 16-liters airgun) produced more than 5000 air gun shots recorded at a sea-bottom seismograph array of 72 OBS and 62 stations installed on-land. Active seismic refraction DSS (Deep Seismic Soundings) acquired during the surveys conducted in 1980 and 1985 were recovered jointly with seismic data acquired in the Campi Flegrei area in the framework of the MareVes97 (an experiment devoted to the definition of the structure of the Somma-Vesuvio complex) offshore survey. The data set acquired during the SERAPIS experiment has been successfully used to infer 3D images of the volcanic structures of Campi Flegrei and Neapolitan bay. Active seismic waveforms and related P-picks (more than 90000 data) from the SERAPIS experiment are also available in the project data server.

Description: Published

Description: 79-87

Description: open

Description: About three-hundred microearthquakes, preceeding and accompanying the 2002-2003 Mt. Etna flank eruption, were considered in this study. On the high-quality velocity seismograms, measurements of the first half cycle of the wave, the so-called rise time τ, were carried out. By using the rise time method, these data were inverted to infer an estimate of the intrinsic quality factor Qp of P waves and of the source rise time τ0 of the events, which represents an estimate of the duration of the rupture process. Two kind of inversions were carried out. In the first inversion τ0 was derived from the magnitude duration of the events, assuming a constant stress drop and Qp was inferred from the inversion of reduced rise times τ−τ0. In the second inversion both τ0 and Qp were inferred from the inversion of rise times. To determine the model parameters that realize the compromise between model simplicity and quality of the fit, the corrected Akaike information criterion was used. After this analysis we obtained Qp=57±42. The correlation among the inferred τ0 and Qp, which is caused by some events which concomitantly have high τ0 (〉30 ms) and high Qp (〉100) indicates that the technique used is able to model rise time versus travel time trend only for source dimensions less than about 80 m.

Description: JCR Journal

Description: open

Description: Earthquake early warning systems (EEWS), based on real-time prediction of ground motion or structural response measures, may play a role in re- ducing vulnerability and/or exposure of buildings and lifelines. Indeed, seismologists have recently developed efficient methods for real-time es- timation of an event’s magnitude and location based on limited informa- tion of the P-waves. Therefore, when an event occurs, estimates of magni- tude and source-to-site distance are available, and the prediction of the structural demand at the site may be performed by Probabilistic Seismic Hazard Analysis (PSHA) and then by Probabilistic Seismic Demand Analysis (PSDA) depending upon EEWS measures. Such an approach contains a higher level of information with respect to traditional seismic risk analysis and may be used for real-time risk management. However, this kind of prediction is performed in very uncertain conditions which may affect the effectiveness of the system and therefore have to be taken into due account. In the present study the performance of the EWWS under development in the Campania region (southern Italy) is assessed by simu- lation. The earthquake localization is formulated in a Voronoi cells ap- proach, while a Bayesian method is used for magnitude estimation. Simu- lation has an empirical basis but requires no recorded signals. Our results, in terms of hazard analysis and false/missed alarm probabilities, lead us to conclude that the PSHA depending upon the EEWS significantly improves seismic risk prediction at the site and is close to what could be produced if magnitude and distance were deterministically known.

Description: Published

Description: 211-232

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: reserved

Description: Predictive relationships for the ground motion in the Marmara region (northwestern Turkey) are parametrized after regressing three-component waveforms from regional earthquakes, in the frequency range: 0.4–15.0 Hz, and in the distance range: 10–200 km. The data set consists of 2400 three-component recordings from 462 earthquakes, recorded at 53 stations. Moment magnitudes, Mw, range between 2.5 and 7.2. The largest event for which we have waveforms available (Mw 7.2) occurred in Duzce on 1999 November 12. The aftershocks of that earthquake, together with the aftershocks of the 1999 August 17 Izmit event (Mw = 7.4), are included in the dataset. Regressions are performed, independently, on Fourier velocity spectra and on peak ground velocities, for a large number of sampling frequencies. A simple model is used to relate the logarithm of the measured ground motion to excitation, site, and propagation terms. Results obtained for peak velocities are used to define a piecewise continuous geometrical spreading function, g(r), a frequency-dependent Q(f ), and a distance-dependent duration function. The latter is used, through random vibration theory (RVT), in order to predict time-domain characteristics (i.e. peak values) of the ground motion. The complete model obtained for the peak ground motion was used to match the results of the regressions on the Fourier amplitudes. Fourier velocity spectra for the combined horizontal motion are best fit by a hinged quadrilinear geometrical spreading function for observations in the 10–200 km hypocentral distance ranges as a function of frequency: f 〈 1.0 Hz, r−1.2 for r ≤ 30 km; r−0.7 for 30 〈 r ≤ 60 km; r−1.4 for 60〈r ≤100 km; r−0.1 for r 〉100, f ≥1.0 Hz, r−1.0 for r ≤30 km; r−0.6 for 30〈r ≤ 60 km; r−0.9 for 60〈r ≤100 km; r−0.1 for r 〉100 km. The frequency-dependent crustal shearwave quality factor Q (f ) coefficient Q( f )=180 f 0.45. The T (5–75 per cent) duration window provides good agreement between observed and predicted peak values. By modelling the behaviour of the small earthquakes at high frequency, we also quantified a regional parameter κ = 0.055 s. Spectral models with one single-corner frequency (Brune), and with two-corner frequencies (Atkinson and Silva) fit the observed high-frequency excitation levels equallywell, whereas the model by Atkinson and Silva fits the low-frequency observations slightly better than Brune’s. RVT is used to predict the absolute levels of ground shaking, following Boore’s implementation of the stochastic ground motion model (Boore’s SMSIM codes). Our regional empirical predictive relationships are compared to the ones adopted in several regions of the world, from California to Western United States.

Description: Published

Description: 635-651

Description: JCR Journal

Description: reserved

Description: Taking advantage of a large displacement-release experiment on a twostory reinforced concrete building located in Bagnoli (Naples, Italy), we performed free-field measurements using 3D seismometers, accelerometers, and a 100-m-long vertical array. The ground motion was noticeable: near the building, the acceleration exceeded 5% g. At each measurement point, it was possible to recognize two source terms, due to the tested building and to the reaction structure. The two sources generated different wave trains. High-frequency accelerations propagated as Rayleigh waves, whereas 1–2 Hz waves carrying most of the displacement propagated only as body waves. The experiment lends further support to the hypothesis that buildings are able to modify substantially the free-field ground motion in their proximity: the peak ground acceleration we observed is the 20% of the ground acceleration required to produce a displacement on the building equal to the one imposed during the release test. We recognize, however, the difficulty of a realistic modeling of wave propagation in the topmost layer of a densely urbanized area.

Description: Published

Description: 2457–2464

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

Description: JCR Journal

Description: open

Description: The uplift crisis of the 1982-1984 in the Campi Flegrei area underlined the importance of seismic surveillance for this volcanic caldera. One of the key elements for an effective seismic network is to make use of a reliable velocity model for earthquake location. In the present work we will discuss criteria for the construction and validation of a new 3D P-wave velocity model for earthquake location in the Campi Flegrei area built from the integration of two high-resolution 3D tomographic images of the region. The model is used for locating a group of earthquakes from the uplift event of the 1982-1984.

Description: Published

Description: 38-49

Description: 1V. Storia eruttiva

Description: open

Description: The Campi Flegrei (CF) caldera experiences dramatic ground deformations unsurpassed anywhere in the world. The source responsible for this phenomenon is still debated. With the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes, a multidisciplinary approach dealing with 3-D delay-time tomography and rock physics characterization has been followed. Selected seismic data were modeled by using a tomographic method based on an accurate finite-difference travel-time computation which simultaneously inverts P-wave and S-wave first-arrival times for both velocity model parameters and hypocenter locations. The retrieved P-wave and S-wave velocity images as well as the deduced Vp/Vs images were interpreted by using experimental measurements of rock physical properties on CF samples, to take into account steam/water phase transition mechanisms affecting P-wave and S-wave velocities. Also, modelling of petrophysical properties for site-relevant rocks constrains the role of overpressured fluids on velocity. A flat and low Vp/Vs anomaly lies at 4 km depth under the city of Pozzuoli. Earthquakes are located at the top of this anomaly. This anomaly implies the presence of fractured over-pressured gas-bearing formations and excludes the presence of melted rocks. At shallow depth, a high Vp/Vs anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase. Finally, maps of the Vp*Vs product show a high Vp*Vs horse-shoe shaped anomaly located at 2 km depth. It is consistent with gravity data and well data and might constitute the on-land remainder of the caldera rim, detected below sea level by tomography using active source seismic data. For a more exhaustive description of the utilized methodologies, of synthetic tests for spatial resolution and uncertainty assessment and, the interpretation of results, the reader may refer to the paper Vanorio et al. (2005).

Description: open

Description: This paper introduces the three-dimensional Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), which treats atmospheric dynamics, radiation, and chemistry interactively for the height range from the earth’s surface to the thermosphere (approximately 250 km). It is based on the latest version of the ECHAM atmospheric general circulation model of the Max Planck Institute for Meteorology in Hamburg, Germany, which is extended to include important radiative and dynamical processes of the upper atmosphere and is coupled to a chemistry module containing 48 compounds. The model is applied to study the effects of natural and anthropogenic climate forcing on the atmosphere, represented, on the one hand, by the 11-yr solar cycle and, on the other hand, by a doubling of the present-day concentration of carbon dioxide. The numerical experiments are analyzed with the focus on the effects on temperature and chemical composition in the mesopause region. Results include a temperature response to the solar cycle by 2 to 10 K in the mesopause region with the largest values occurring slightly above the summer mesopause. Ozone in the secondary maximum increases by up to 20% for solar maximum conditions. Changes in winds are in general small. In the case of a doubling of carbon dioxide the simulation indicates a cooling of the atmosphere everywhere above the tropopause but by the smallest values around the mesopause. It is shown that the temperature response up to the mesopause is strongly influenced by changes in dynamics. During Northern Hemisphere summer, dynamical processes alone would lead to an almost global warming of up to 3 K in the uppermost mesosphere.

Description: Published

Description: 3903-3931

Description: reserved

Description: We analyze the dispersion characteristics of ambient noise vibrations. For this purpose, two-dimensional (2D) seismic array data were acquired in four different sites in the Colfiorito plain, an alluvial intramountain basin that exhibits strong site effects. Assuming seismic noise being mainly composed of surface waves, we derive one-dimensional (1D) shallow shear-velocity profiles through the inversion of dispersion curves measured by frequency–wavenumber (f-k) methods. The inverted shear-wave velocity profiles are consistent with a priori information for those sites that can be approximated by 1D simple models. In these cases, the use of passive records of seismic vibrations can be a valuable tool for determining the shallow velocity profile if a detailed depiction of velocity structure is not required. The theoretical dispersion curves for Rayleigh and Love waves were compared with the measured dispersion curves for vertical and horizontal components, respectively. This allows us to discuss qualitatively the composition of ambient vibrations (outlining a large proportion of Love waves in the noise wave field) and the effects of higher modes. We also use the single-station method for investigating the origin of the horizontal-to-vertical (H/V) peak in the plain of Colfiorito in terms of ellipticity of the fundamental Rayleigh mode.

Description: Published

Description: 1915-1933

Description: reserved

Description: The city of Palermo (southern Italy) was severely damaged in the past by moderate-magnitude earthquakes located tens of kilometres offshore. The historical monumental heritage and the high density of population motivated large efforts for the seismic risk assessment. We present the geological and seismological studies performed in downtown Palermo as a study case to show how the complexity of an urban environment can be approached with multidisciplinary investigations. Downtown Palermo is characterized by sea deposits in the coastal zone and the alluvial deposits of two rivers (Papireto and Kemonia) of about 150 m width, which were buried and filled during the XVII century. The difficulty of surface geological surveys was compensated through an analysis of aerial photos and more than 2000 borehole data organized in the City-GIS of the Department of Geology and Geodesy of the University of Palermo. A previous study on the well-documented historical damage indicated the major role played by the two river valleys and the sea deposits in controlling the damage distribution, above the assumption of a fairly homogeneous vulnerability of the existing buildings in downtown. To test the feasibility of using ambient noise for recognizing the presence of alluvial deposits in a densely urbanized environment, a large microtremor measurement campaign was performed in Palermo across several profiles. The frequency peaks inferred from the horizontal-to-vertical spectral ratio were compared with numerical simulations to assess the seismic velocity profile and the soil stratigraphy. Moreover, noise data were analyzed through a statistical approach to establish a possible correlation between damage, resonance frequency and amplitude, and geology. After the moderate earthquake of September 6, 2002 (Mw=5.9, 50 km far away), the analysis of the aftershock sequence provided a well documented estimate of the variation of ground motion within the city in the case of linear soil response. Using these aftershocks we computed also synthetic accelerograms of the main shock through Empirical Green’s Functions that provided ground accelerations as large as 50 gals, consistently with the documented EMS-98 intensity. Synthetic accelerograms showed a large variability of horizontal ground motion within the city (a factor of 3 – 4) that confirms the role of local geology in causing an increase of the seismic hazard on sea and alluvial deposits. Finally, we discuss the comparison between the acceleration response spectra calculated for different soil categories and the design elastic spectra provided by EC8.

Description: Unpublished

Description: Lisbon, Portugal

Description: open

Description: The Colfiorito basin is located at the boundary between Umbria and Marche districts in Central Italy. The area was struck by several strong earthquakes in the past, and during the September 1997 to April 1998 seismic sequence, the macroseismic intensity was as large as IX (MCS scale) in the region. Ambient noise measurements are carried out over fifty points in the basin; H/V spectral ratios as well as spectral ratios using a reference rock site are calculated. Polarization analyses are also performed in narrow frequency bands where spectral amplitude peaks are observed to dominate, to discriminate preferential directions of propagation in the noise wave field which could be related to source or path effects, other than site effects. In the spectral ratios, the frequencies of the most pronounced peaks generally agree with the resonance frequencies computed for the measurement sites on the basis of 1-D velocity models, at least where no strong lateral variations of the sediment thickness are present.

Description: Unpublished

Description: Nice, France

Description: open

Description: 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 has 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

Description: Published

Description: 279-288

Description: reserved

Description: We estimated the attenuation laws of high-frequency seismic waves in the shallow crust (depth 5 km) and earthquake source parameters by using a selected data set of 320 shallow events (2.6 MD 4.2), recorded at Mt. Etna volcano during the last two flank eruptions occurring in 2001 and 2002–2003. The quality factor (Q) was estimated from spectra of P and S waves for 24 stations of the local permanent network by applying a spectral ratio technique. The results show variations in both QP and QS as a function of frequency, according to the power law Q Q0 f n, with n ranging between 0.3 and 1.3 for P waves and between 0.2 and 0.9 for S waves. As typical of volcanic environments, strong azimuthal variations of QP were also found, suggesting the presence of local strong lateral heterogeneities and/or of fluid-filled cracked volumes. After correction for attenuation, we estimated the source parameters (seismic moment, source radius, and stress drop) of a subset of 66 shallow events, under the assumption of a circular dislocation. The estimated seismic moments M0 range from 1013 to 1015 N m. The source radii (r) are confined between 100 and 1000 m and stress drop (Dr) ranges between 0.2 MPa and about 4 MPa. Combining the source parameters obtained in this study with those calculated by Patane` et al. (1997) for an old data set of smaller microearthquakes (109 M0 1014 N m) recorded in the same area, we re-evaluated the scaling relationship between seismic moment (M0) and corner frequency ( fc) for the earthquakes with M0 ranging between 1013 and 1015 N m. We confirm that microearthquakes at Mt. Etna seem not to obey a M0 fc 3 scaling relationship, as generally observed for moderate to large earthquakes, as the slope of the scale dependence about 4.3 or higher. Assuming that this dependence is real, within the uncertainty in the results, a departure from the self-similarity exists for the volcanotectonic earthquakes at Mt. Etna.

Description: Published

Description: reserved

Description: The Colfiorito Basin is a small intramountain depression in the southern section of the Northern Apennine chain that is filled with Quaternary alluvial deposits. The presence of soft alluvial deposits has significantly influenced the level of local damage that was caused by two major earthquakes (ML 5.6 and 5.8) belonging to the swarm that started in September 1997. To verify the effects of the basin structure on the predominant frequency of seismic motion, ambient noise measurements were carried out in the Colfiorito Basin during two experiments in May and July of 2002. The horizontal-to-vertical spectral ratios (HVSRs) were calculated for data collected at four profiles in the basin. Array techniques were applied to determine the wave types that composed the noise, to estimate their apparent velocity and azimuth of propagation, and to calculate a velocity-dispersion curve from which a velocity-depth structure was derived. The data analysis shows a high amplification in the HVSR at low frequency. This feature is common to most of the sites, including the reference site, and it is interpreted as being due to weather disturbances. The peak frequencies of the spectral ratio calculated at the sites located in the center of the basin coincide with the theoretically estimated resonance frequencies. The arrayaveraged HVSR calculated for the array located in the middle of the plain has a pronounced peak at 0.9 Hz. This corresponds to the peak of the amplification function calculated on the basis of the velocity model deduced from the dispersion analysis. The HVSR method is instead unsuitable for the prediction of the resonance frequencies of sediments in the sites where strong lateral variations of basement topography are present. We measured apparent velocities in the range of 0.3–0.8 km/sec by applying f-k methods to array recordings. These values are compatible with the predominance of surface waves in the noise, as also confirmed by polarization analysis. Both Rayleigh and Love waves are present in the background seismic noise. The results obtained by applying the spatial autocorrelation method to the vertical component of the ground motion recorded at a 240-m-wide circular array deployed in the middle of the basin revealed the presence of Rayleigh waves, and f-k methods combined with polarization techniques revealed the presence of polarized Love waves. The wave-field analysis indicates two main propagation directions: the first is around N100 E in the frequency band of 1.0–2.0 Hz; this radiation can be interpreted as being generated at the east-southeast step borders of the basin. The second main direction is around N300 E in the frequency band of 2.0–3.0 Hz; its source may be a 180-m-deep depression located at the southwest corner of the basin.

Description: Published

Description: 490–505

Description: reserved

Description: Mt Etna lies on the footwall of a large normal fault system, which cuts the eastern coast of Sicily and crosses the volcano eastern flank. These faults are responsible for both large magnitude historical earthquakes and smaller damaging seismic events, closer to the volcano. We investigate here the two-way mechanical coupling between such normal faults and Mt Etna through elastic stress transfer. The comparison between eruptive sequences and historical seismicity reveals that the large earthquakes which struck the eastern Sicily occurred after long periods of activity along the Mt Etna rift zone. The larger the erupted lava volumes, the stronger the earthquake. The smaller earthquakes located on the eastern flank of the volcano occur during periods of rift zone eruptions.We point out that the seismicity rates are well correlated with the rate of erupted lava. By modelling elastic stress changes caused by earthquakes and eruptions in a 3-D elastic half-space, we investigate their interaction. Earthquake dislocations create a vertical stress gradient along fissures oriented perpendicular to the minimum compressive stress and compress shallow reservoirs beneath the volcano. This may perturb the magmatic overpressures in the Etna plumbing system and influence the transport and storage of the magma as well as the style of the eruptions. Conversely, the large rift zone eruptions increase up to several tenths MPa the Coulomb stress along the eastern Sicily normal fault system and may promote earthquakes. We show that the seismic activity of the normal faults that cut the eastern flank of the volcano is likely to be controlled by Coulomb stress perturbations caused by the voiding of shallow reservoirs during flank eruptions.

Description: Published

Description: 697-718

Description: reserved

Description: We evaluate the goodness of fit of attenuation relations commonly used for the Italian national territory (Sabetta and Pugliese, 1996) by using the maximum likelihood approaches of Spudich et al. (1999) and Scherbaum et al. (2004). According to the classification scheme proposed by Scherbaum et al. (2004), the Sabetta and Pugliese (1996) relationships show consistent discrepancies between the predicted and the observed peak ground acceleration (PGA) at rock sites in the Umbria- Marche region, central Italy; however, at soft sites the agreement between observations and prediction is satisfactory. The bias of the residuals, computed with the Sabetta and Pugliese (1996) models for PGA, peak ground velocity, (PGV) and pseudovelocity response spectrum (PSV) (for Ml 4–6 and epicentral distances up to 100 km) is negative. This means that on the average, the predictions overestimate the observations, but the overestimation decreases with increasing magnitude. Then, we present regional predictive relations (UMA05) for maximum horizontal PGA, PGV, and 5%-damped PSV, derived from the strong-motion data recorded in the Umbria-Marche area and classified as to four site categories. The UMA05 attenuation relationships for rock sites are log10 (PGA) 2.487 0.534Ml 1.280 log10 (R2 3.942)0.5 0.268 log10 (PGV) 1.803 0.687Ml 1.150 log10 (R2 2.742)0.5 0.300 and log10 (PGA) 2.500 0.544Ml 1.284 log10 Rh 0.292 log10 (PGV) 1.752 0.685Ml 1.167 log10 Rh 0.297, where PGA is measured in fraction of g and PGV in centimeters per second, Ml is the local magnitude in the range 4–6, R is the epicentral distance in the range 1–100 km, and Rh is the hypocentral distance in kilometers. We used the random effect model (Brillinger and Priesler, 1985; Abrahamson and Youngs, 1992; Joyner and Boore, 1993; Joyner and Boore, 1994) to estimate the component of variance related to the earthquake-to-earthquake, station-to-station, and record-to-record variability, and to quantify the benefit of introducing a site classification in the attenuation model to reduce the variance. The introduction of the site classification in the attenuation model allows a reduction of the station-to-station component of variability (from 0.19 to 0.14 for PGA, and from 0.21 to 0.18 for PGV). We also found that the recordto- record component represents the largest contribution to the model uncertainty.

Description: Published

Description: 984-1002

Description: JCR Journal

Description: reserved

Description: During three moderate-magnitude earthquakes occurred in September–October 1997 in the central Apennines, Italy, accelerations larger than 0.5 g were recorded in the town of Nocera Umbra, 10 to 15 km N-NW of the epicenters. The accelerograph is sited in a fault zone, close to a N30 E tectonic contact. Six temporary seismological stations installed across the fault recorded 82 aftershocks occurred in two seismogenic zones: the Colfiorito-Sellano area, S-SE of the array, and the Gualdo Tadino area, to the north. The array data reveal large variations in terms of both peak ground motions and spectral amplitudes. Within the fault zone, amplifications show a strong dependence on the source azimuth. At the accelerograph site, the effects are particularly large for events from S-SE: peak ground motions are a factor of 14 larger than those of a reference site and conventional spectral ratios attain amplitudes as large as 50 at 7 Hz along the N30 E direction of motion, parallel to the strike of the fault. Nineteen strong motion accelerograms were then used to compare ground motion properties between weak and strong events up to M0 = 1.2 1025 dyn cm. A particle motion analysis shows that the directional effect is also present in the strongest motions, even though the amplification of peak ground motion decreases when M0 increases. Results from stochastic simulations indicate that such a behavior is not due to nonlinearity: applying the empirical weak motion transfer functions in a purely linear model the observed peak ground motions of the largest events are fit satisfactorily.

Description: Published

Description: 2156

Description: JCR Journal

Description: reserved

Description: During the two mainshocks of September 26, 1997 in the Umbria-Marche border a strong-motion accelerograph recorded peak ground accelerations as large as 0.6 g, approximately, in the town of Nocera Umbra, at distances of 10 to 15 km from the epicentres. This value is significantly larger than expected on the basis of the usual regressions with magnitude and distance. A broad-band amplification up to a factor of 10 was consistently estimated in previous papers, using both weak and strong motion data recorded at the accelerograph site during local moderate earthquakes. To study the cause of this amplification we deployed six seismologic stations across the tectonic contact between the Ceno-Mesozoic limestone and the Mesozoic marly sandstone where the accelerograph is installed. Seismograms of 21 shallow aftershocks in the magnitude range from 2.2 to 4.0 and a subcrustal Mw = 5.3 event are analysed. Regardless of epicentre location, waveforms show a large complexity in an approximately 200 m wide band adjacent to the tectonic contact. This is interpreted as the effect of trapped waves in the highly fractured, lower velocity materials within the fault zone.

Description: Published

Description: 543-554

Description: JCR Journal

Description: reserved

Description: In order to empirically obtain the scaling relationships for the high-frequency ground motion in the Western Alps (NW Italy), regressions are carried out on more than 7500 seismograms from 957 regional earthquakes. The waveforms were selected from the database of 6 three-component stations of the RSNI (Regional Seismic network of Northwestern Italy). The events,MW ranging between 1.2 and 4.8, were recorded within a hypocentral distance of 200 km during the time period: 1996–2001. The peak ground velocities are measured in selected narrow-frequency bands, between 0.5 and 14 Hz. Results are presented in terms of a regional attenuation function for the vertical ground motion, a set of vertical excitation terms at the reference station STV2 (hard-rock), and a set of site terms (vertical and horizontal), all relative to the vertical component of station STV2. The regional propagation of the ground motion is modeled after quantifying the expected duration of the seismic motion as a function of frequency and hypocentral distance. A simple functional form is used to take into account both the geometrical and the anelastic attenuation: a multi-variable grid search yielded a quality factor Q( f ) = 310 f 0.20, together with a quadri-linear geometrical spreading at low frequency. A simpler, bilinear geometrical spreading seems to be more appropriate at higher frequencies (f 〉 1.0 Hz). Excitation terms are matched by using a Brune spectral model with variable, magnitude-dependent stress drop: at Mw 4.8, we used σ = 50MPa. A regional distanceindependent attenuation parameter is obtained (κ0 = 0.012 s) by modelling the average spectral decay at high frequency of small earthquakes. In order to predict the absolute levels of ground shaking in the region, the excitation/attenuation model is used through the Random Vibration Theory (RVT) with a stochastic point-source model. The expected peak-ground accelerations (PGA) are compared with the ones derived by Ambraseys et al. (1996) for the Mediterranean region and by Sabetta and Pugliese (1996) for the Italian territory.

Description: Published

Description: 315-333

Description: JCR Journal

Description: reserved

Description: The West side of lake of Garda, in Northern Italy, was struck by a ML=5.2 earthquake on November 24, 2004. The felt area is rather large (from Venice to Milan) and the damaged area consists of 66 municipalities, with a number of homeless of about 2200 and estimated direct damages of 215 millions of euros. Most of the damaged structures are old masonry buildings and churches, while there were almost no damage to reinforced concrete structures. The observed distribution of macroseismic intensity shows a strong azimuthal dependence, with high intensity level in a 10x10 km2 area located SW to the epicentre and rather large dispersion of values (ranging from V to VII-VIII) in the first 10 km epicentral distance. Taking into account the vulnerability level of the damaged structures and the features of the geological formations, we tried to explain the observed damage distribution in terms of finite fault properties of the source, despite the moderate magnitude of the event. Thus we hypothesised a fault geometry from seismotectonic considerations and we simulated the event by a high frequency simulation technique (Deterministic Stochastic Method, DSM). The synthetic ground motion parameters were converted into intensity values by empirical relationships and local geological conditions were considered to explain some discrepancies between simulated and observed intensities. It was possible to adequately reproduce both the observed distribution of macroseismic intensity and the ground motion recorded by an accelerometric station located at about 13 km epicentral distance.

Description: Unpublished

Description: Geneva, Switzerland

Description: open

Description: The investigation of local amplification phenomena by seismic signal analysis is a fundamental step in carefully defining the seismic response of an area. In this study we investigate the use of teleseismic recordings in assessing seismic wave amplification in the Pellice Valley (North-western Alps, Italy). Assuming that teleseismic P-waves are sensitive to the deep structure of a basin, we deal with the computation of horizontal to vertical spectral ratios and with the estimate of teleseismic P-wave arrival time delays and P-wave amplifications with respect to a reference site. The reliability of the H/V results obtained by considering teleseismic signals is confirmed by the agreement with the results coming from both H/V of noise and H/V of S-wave of local events methods. Strong correlation between the P-wave arrival time delays and the relative P-wave amplifications with respect to thickness of the low velocity layers and the geometry of the bedrock is found.

Description: Unpublished

Description: open

Description: Published

Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce

Description: open

Description: After the 2002 Molise earthquake, a wide survey of the damage and the seismic vulnerability of the churches was carried out, using specific forms extensively tested and recently acknowledged at a national scale (G.U. 07/03/2006). This approach has allowed one to compare the observed and the expected medium damage, calculated through vulnerability curves correlated to the specific form used. This comparison has enabled to evaluate inhomogeneous values in some cases, pointing out how the surveyed damage could not be put down just to a structural lack of the building. Studying the sites morphology for the churches located on the ridges, it was observed a damage level always greater than expected. To study the influence of the local amplification phenomena due to the topography, it has been analyzed some churches damaged by the Appennino Abruzzese (1984) and Molise (2002) earthquakes. These churches are located on the ridges top, with slope in-clination alfa≥15°, height H≥30m and characterized by homogeneous lithological subsoil, almost to consider it having an elastic behavior under dynamical stress. Taking into account this hazard increase inside a vulnerability analyses (based on a macroseismic or a mechanical approach), it has been proposed a double approach, validated through local seismic response (RSL) modeling of the ground (estimation of amplification factors and of elastic response spectra) and through the seismic response of the macroelements, damaged by the reference earth-quake (linear and not-linear kinematic analysis). Through the vulnerability analysis based of the macroseismic approach, the influence of the site morphology on the building behavior has been preliminary defined by a vulnerability modifier (deltaVml), that represents an additional parameter to reach the equivalent value between the surveyed and the expected damage. The study of the amplification effects has been performed using the BEM numerical analysis; the results are represented by the amplification factors (Fa), defined as the ratio between the spectral intensity of output and input, considering the range period of 0.1s-0.5s, and the corresponding elas-tic response spectra: they confirm the results of the macroseismic approach. Considering the mechanical approach, two churches have been examined in detail (S Pietro in Vincoli at Castellino del Biferno and S. Michele Arcangelo at Campolieto): the kinematic analyses have been performed applied the calculated amplified and not-amplified response spectra (considering the earthquake 2002) and the design response spectrum. The analyses show that the results obtained applying the calculated amplified response spectrum are better correlated to the surveyed damage of the churches than the results obtained applying the not-amplified response spectrum.

Description: Published

Description: Pisa, Italia

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: The damage and vulnerability survey of the monumental buildings, damaged by the 2002 earthquake in the Molise Region, has allowed singling out of a correlation between the observed damage of the churches and their morphological site conditions. The vulnerability model connected to the survey methodology provides an evaluation of the expected mean damage. Comparison with the observed damage determined the introduction of a local morphological behaviour modifier, able to take into account the vulnerability increase due to the site effects. In order to validate the previous results, a numerical 2-D analysis of the seismic local response has been performed. In particular, a numerical code, working with boundary elements, has been applied to the analyzed situations. The results, in terms of pseudo-acceleration response spectra and amplification factors, allow one to compare the numerical and the observed analyses. This comparison shows good agreement and allows one to find some correlations between the geometric characteristics of the sites, the values of the amplification coefficients and the damage mechanism activated.

Description: Published

Description: Thessaloniki, Greece

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: 4.2. Scenari e mappe di pericolosità sismica e danno

Description: open

Description: On April 5, 2003, one of the largest eruptions in the last decades was observed at Stromboli volcano, Italy. The eruption occurred in a period of increased volcanic activity, following a first explosion in December 2002, which interrupted the typical moderate “Strombolian” behaviour. We present an exhaustive analysis of the available broadband seismic data and relate them to the observed eruption phases. Prominent features of the seismic signals include an ultra long period signal starting a few tens of seconds prior to the explosive eruption as well as a strong energetic signal a few seconds after the onset of the eruption. Both signals are not exactly synchronized with the other geophysical observations. We present a detailed study of those signals using spectral and particle motion techniques. We estimate eruption parameters and seismic source characteristics by different inversion approaches. Results clearly indicate that the paroxysmal eruption was triggered by a shallow slow thrust-faulting dislocation event with a moment magnitude of Mw=3.0 and possibly associated with a crack that formed previously by dike extrusion. At least one blow-out phase during the paroxysmal explosion could be identified from seismic signals with an equivalent moment magnitude of Mw=3.7 and is represented by a vertical linear vector dipole and two weaker horizontal linear dipoles in opposite direction, plus a vertical force.

Description: Published

Description: 164-178

Description: 3.1. Fisica dei terremoti

Description: JCR Journal

Description: reserved

Description: INGV Osservatorio Vesuviano

Description: Published

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: 3.1. Fisica dei terremoti

Description: 3.6. Fisica del vulcanismo

Description: open

Description: We perform a regional study in order to provide the seismic hazard community of Israel with new predictive relationships for the earthquake-induced ground motion in Israel. This work is essential for the development of a new generation of hazard maps, for the planning of the development of the Israel’s region, and the design of earthquake resistant structures and facilities. The main goals of our work is to provide a quantitative description of the expected ground motion within the Israel region, as a function of the hypocentral distance and frequency of motion. For this purpose we use the regression technique that was proposed by Yazd (1993), Herrmann (1999), Raoof et al., (1999) and Malagnini et al.,(2002). The undoubted advantage of this method is the possibility to use for analysis the data of frequent, small earthquakes that are typical for this region. In our analyses we use 4786 waveforms recorded by 30 stations of the Israel Seismic Network from 2000 to 2005. We restricted our analysis to events recorded at 10 or more stations, resulting in 330 appropriate earthquakes, with a magnitude range between 1.8 and 5.2. We derive the empirical excitation, site, and regional attenuation terms by regressing the peak amplitudes of narrowband-filtered seismograms around the shear-waves arrivals, and the rms Fourier spectral amplitudes taken around the specific sampling frequency. A theoretical modeling effort is performed by using Random Vibration Theory (RVT) on the parameters derived from the observations. For prediction we use the quality parameter Q(f)=270f^0.7 , whereas the geometrical spreading g(r) used in the model was parameterized as a bilinear, piecewise function: r^-0.95 for r〈60 km , and r^-0.5 for r〉60 km . The modeling of the excitation terms is based on the Brune’s source spectrum.

Description: Submitted

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: Time-series acquired during last years by surface monitoring parameters are compared, and the results are discussed, following a theoretical approach. Surface parameters are fluid temperature, soil temperatures and seismic activity at La Fossa of Vulcano. Discussed periods are 1998 and from 2004 to 2007, when time relationship between changes of the heat flow from the ground and seismic activity, resulted worth noting. Earthquakes originating in the area of Vulcano are associated with both fracturing and degassing mechanisms. The formers are related to the activity of tectonic structures; while the latter are connected to fluid dynamics within the interior of the volcanic apparatus. In November 1998 seismic activity at La Fossa sharply increased: Five events were registered, with seismic signals of typical faulting earthquakes, triggered by mechanism of shear fracturing and focal depths ranging 1-4 km. Fumaroles temperatures, recorded by continuous monitoring system of INGV - Palermo, showed a growing trend since October to November 1998, highlighting a big increase of heat transfer during the period, and also the soil temperature, out of the fumaroles field showed a marked increase. Fumaroles temperatures heralded the increase of heat and energy flow during a pre-seismic period of about 1 month. The transient variation of surface release reflect an excited state of the system and may have many different causes, not directly related to the magma. Indeed, stress drops generated by small fracturing earthquakes, introduce a significant perturbation in the system resulting in a relevant production of mass and energy flow. Until these flows counteract every stress gradient, they support stationary state of the system. The observed time relationships only allow a qualitative discussion about cause and effects, but doesn’t allow any quantitative evaluation. Pressure transients generate anomalies (flows of matter, differential in heat flows, chemical reaction rates) whose time frame is specific, depending on many possible processes and path-ways. Fluid phases, along fumarolic conduits, reach the surface faster than the co-genetic earthquake, as the earthquake is embedded in a strain transient that broadly exceeds the time-space frame of the seismic transient (Lomnitz, 1994). On the other hand, in a volcano-tectonic context, different energy flows can either be a cause, either an effect of perturbation, depending on depth of their primary source. Thus, in some instances the strain transient related to local earthquakes produces anomalous chemical flows, while, in other instances the local seismic activity may be produced by chemical flows from the magmatic source. Following a period of lower energy release, other 3 anomalous periods were observed from November 2004, either in the seismic release and in the surface heat flow, even out from fumaroles. So far, the monitored sites resulted very sensitive to minor perturbations of the system. The comparative analysis of different time-series supplies information related to perturbations of the state variables, useful to verify conceptual framework and to better define “classical” and “new” monitoring techniques for volcanic, as well as seismic surveillance.

Description: This research work has been carried out with the help of the National Institute of Geophysics and Volcanology and with the contribution of the Department for the Civil Defence

Description: Published

Description: Vien, Austria

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: We describe the characteristics of crustal wave propagation in eastern Sicily by using the background seismicity of the area. We follow the approach described by Malagnini, Hermann, and Di Bona (2000) and Malagnini et al. (2002). Our data set consists of 106 earthquakes recorded by nine three-component digital seismic stations between 1994 and 2001. We used only crustal events (depths shallower than 25 km), with local magnitudes ranging from 1.0 to 4.3, and hypocentral distances from 10 to 130 km. Peak ground velocities from 1311 narrow bandpass-filtered waveforms are measured in the frequency range 1.0–16.0 Hz, and regressed to define crustal propagation, excitation, and site characteristics, with respect to a reference station. A subsequent modeling effort is carried out, through the use of random vibration theory (RVT), for obtaining a quantitative evaluation of the apparent geometrical spreading g(r), and of the crustal quality factor Q( f ). An attenuation parameter, j0, is also evaluated relative to a reference rock site. The attenuation and source parameters estimated in this study are used through the RVT in order to predict the peak horizontal ground acceleration (PGA), and the 5% damping pseudoacceleration spectra (PSA).

Description: This study was supported by the Ministero dell’Universita’ e della Ricerca Scientifica, Dipartimento per la Programmazione, il Coordinamento e gli Affari Economici, Servizio per lo Sviluppo e il Potenziamento delle Attivita’ di Ricerca (SSPAR), under contract FIRB, Prot. RBAU013NRZ.

Description: Published

Description: 568-578

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: In the text

Description: Published

Description: Roma

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: This paper deals with the problem of seismicity at Mt. Vesuvius with a view to providing an estimation of the maximum expected earthquake. Integrated analysis of both historical and current seismicity as well as the geological conditions of Vesuvius and the surrounding areas show that seismogenetic structures may fall within the crater axis and at the boundaries of the volcanic complex. While activation of the whole seismogenetic volume detected by seismicity in the past 30 years would indicate a total seismic moment of Mo = 7.1E+ 15 Nm for a magnitude M = 4.5, knowledge of the area's geological structure suggests faulting surfaces of about 32 km2 with an associated magnitude of M = 5.4. The areas of maximum expected damage differ according to the orientation of the hypothesized structure. Analysis of geological and geophysical data and the damage associated to the AD 62 earthquake shows that the prevailing directions in the faulting planes are NE–SW in the eastern sector of the volcanic complex, and roughly WNW–ESE in the southern part of the volcano along the coast. Comparison of instrumental seismicity and historical data reveals two significantly different energy levels: a lower earthquake level with Mmax = 4.5, corresponding to current seismicity and that which accompanied volcanic activity in the eruptive period from 1631–1944; an upper level with Mmax = 5.4, represented by the AD 62 earthquake. The two levels correspond to two stress states and different seismogenetic structures.

Description: Published

Description: 139-149

Description: 3.6. Fisica del vulcanismo

Description: 3.10. Sismologia storica e archeosismologia

Description: 4.3. TTC - Scenari di pericolosità vulcanica

Description: 5.1. TTC - Banche dati e metodi macrosismici

Description: JCR Journal

Description: reserved

Description: Source inversion for long period (LP) events in volcanic areas is an ongoing research topic. The high interest of volcanologists to understand the physical phenomena which govern these characteristic events is related to the fact that they may be directly generated by uid transfers and some of them could be candidates for volcanic activity parameters, or precursors of volcanic eruptions. The signal class of LP-type events generally includes di erent volcanic transients with dominant frequencies in the range between 0.5 and 5 Hz. Although some source models have been proposed to explain their generation (vibration of uid- lled cavities, etc.), the large variety of LP signal forms and the existence of alternative models to explain some of the observations, make it interesting to develop new inversion schemes. Our main goal is to propose an inversion methodology to determine LP source mechanisms and study these events through an exhaustive source inversion by using synthetic data.

Description: Published

Description: Bremen (Germany)

Description: 3.1. Fisica dei terremoti

Description: open

Description: Abstract: On April 5, 2003, one of the largest eruptions in the last decades was observed at Stromboli volcano, Italy. The eruption occurred in a period of anomalous volcanic activity, after a previous explosion in December 2002 interrupted the typical moderate "Strombolian" behaviour. An exhaustive analysis of the available broadband seismic data is here presented and related to the observed eruption phases. Prominent features of the seismic signals include a very long period signal a few tens of seconds prior to the explosive eruption, as well as a strong energetic signal a few seconds after the onset of the eruption.

Description: Published

Description: San Francisco

Description: 3.1. Fisica dei terremoti

Description: open

Description: For early-warning applications in particular, the reliability and efficiency of rapid scenario generation strongly depend on the availability of reliable strong ground-motion prediction tools. If shake maps are used to represent patterns of potential damage as a consequence of large earthquakes, attenuation relations are used as a tool for predicting peak ground-motion parameters and intensities. One of the limitations in the use of attenuation relations is that these have only rarely been retrieved from data collected in the same tectonic environment in which the prediction has to be performed. As a consequence, strong ground motion can result in underestimations or overestimations with respect to the recorded data. This also holds for Italy, and in particular for the Southern Apennines, due to limitations in the available databases, both in terms of distances and magnitude. Moreover, for “real-time” early-warning applications, it is important to have attenuation models for which the parameters can be easily upgraded when new data are collected, whether this has to be done during the earthquake rupture occurrence or in the post-event, when all the strong motion waveforms are available. Here we present a strong-motion attenuation relation for early-warning applications in the Campania region (Southern Apennines), Italy. The model has a classical analytical formulation, and its coefficients were retrieved from a synthetic strong-motion database created by using a stochastic approach. The input parameters for the simulation technique were obtained through the spectral analysis of waveforms of earthquakes recorded by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) network for a magnitude range Md (1.5,5.0) in the last fifteen years, and they have been extrapolated to cover a larger range. To validate the inferred relation, comparisons with two existing attenuation relations are presented. The results show that the calibration of the attenuation parameters, i.e., geometric spreading, quality factor Q, static stress drop values along with their uncertainties, are the main concern.

Description: Published

Description: 133-152

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: reserved

Description: Using data from two dense array of short period seismometers, we analyse the kinematic properties of volcanic tremor preceding and accompanying the 2004–2005 eruption of Etna Volcano, Italy. Results from slowness analyses indicate the action of at least two distinct sources. The first dominates the pre-eruptive period, and is likely associated with the main plumbing system feeding the Summit and southeast craters. Following the onset of the eruption, secondary directions of wave-arrival encompass the eruptive fissures, located on the lower eastern flank of the southeast crater. Nonetheless, significant energy radiation from this latter source was also occurring prior to the onset of the lava effusion, likely suggesting the presence of a resident magma batch, in agreement with independent petrologic and geochemical data.

Description: Published

Description: 699-705

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: 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. This paper reports the characteristics of the seismic network, focussing on the required technological innovation of the different seismic network components (data-logger, sensors and data communication). To ensure a highly dynamic recording range, each station is equipped with two types of sensors: a strong-motion accelerometer and a velocimeter. Data acquisition at the seismic stations is performed using Osiris-6 model data-loggers made by Agecodagis. Each station is supplied with two (120 W) solar panels and two 130 Ah gel cell batteries, ensuring 72-h autonomy for the seismic and radio communication equipment. The site is also equipped with a GSM/GPRS programmable control/alarm system connected to several environmental sensors (door forcing, solar panel controller, battery, fire, etc) and through which the site status is known in real time. The data are stored locally on the hard-disk and, at the same time, continuously transmitted by the SeedLink protocol to local acquisition/analysis nodes (Local Control Center) via Wireless LAN bridge. At each LCC site runs a linux Earthworm system which stores and manages the acquired data stream. The real-time analysis system will perform event detection and localization based on triggers coming from data-loggers and parametric information coming from the other LCCs. Once an event is detected, the system will performs automatic magnitude and focal mechanism estimations. In the immediate post-event period, the RISSC performs shaking map calculations using parameters from the LCCs and/or data from the event database. The recorded earthquake data are stored into an event database, to be available for distribution and visualization for further off-line analyses. The seismic network will be completed in two stages: • Deployment of 30 seismic stations along the southern Apennine chain (to date almost completed) • Setting up a carrier-class radio communication system for fast and reliable data transmission, and installation of 10 additional seismic stations.

Description: Published

Description: 325 - 341

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: reserved

Description: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano

Description: Unpublished

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: The area of Serravalle, sited in the northern part of the town of Vittorio Veneto (TV), NE Italy, has been the target of a seismic microzonation campaign. 10 seismic stations have been deployed for a 7 months period to record in continuous mode. Three stations were installed on bedrock outcrops and seven on sedimentary sites with variable cover thickness. Spectral analyses have been performed on the collected data-set using the Generalized Inversion Technique (GIT, e.g. Andrews, 1986). In particular, spectral ratios have been calculated for each station relatively to the average of the three reference, bedrock sites. The spectral ratios provide quantitative estimates of the seismic motion amplifications which occur in each of the monitored sites. Two sites show high values of amplification, 5 times larger than signal amplitude at the reference sites, in correspondence of well discernible peak frequencies of 5 Hz. Results for the other stations show smaller amounts of site amplification spreading over a broad range of frequencies. Sites where the highest amplifications were recorded all lie on the left bank of the Meschio River and in areas farther away from its outlet into the plain correlating with the presence of thick layers of Quaternary deposits.

Description: Published

Description: 31-49

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: We investigate the complex propagation of seismic waves beneath the Campi Flegrei caldera, Italy, using multichannel recordings of artificial explosions. The sources consisted of air gun explosions shot in the Gulf of Pozzuoli at offsets ranging between 3 and 7 km. A multichannel recording device was deployed in the Solfatara crater and consisted of ten vertical-component and two three-component short-period seismometers with a maximum aperture of about 150 m. The zero-lag correlation (ZLC) technique was adopted to estimate horizontal slowness and backazimuth of coherent waves crossing the array. For sources located in the northern sector of the Gulf, with maximum offset 5 km, ray parameters and backazimuths are in agreement with those predicted for the 1D velocity model used for routine locations. For sources at offsets larger than approximately 5 km, the ZLC curves depict prominent maxima associated with a secondary phase propagating with a lower velocity than the first-arrival P wave. Using finite-difference synthetic seismograms generated for a 2D realistic velocity model, we explain these late arrivals in terms of a lateral velocity variation located at depths of about 1 km. Such discontinuity would correspond to a positive V (sub p) anomaly imaged by a recent 3D tomographic study, and interpreted as the submerged southern rim of Campi Flegrei caldera collapsed during the explosive eruption of 12 ky B.P. The small spacing among adjacent shot points allowed simultaneous wave-field decomposition at the source and receiver arrays. Using a modified version of the double-beam method, we retrieve the independent variation of horizontal slowness at both the source and receiver regions. For both cases, we found azimuthal deviations as large as 50 degrees with respect to the great circle path. At the source region, these discrepancies may be interpreted in terms of ray bending at the interface of the aforementioned positive anomaly. At the receiver array, the observed anomalies may be attributed to either velocity variations marking the Solfatara crater rim, or to a near-receiver, low-velocity body whose position would coincide with negative gravimetric anomalies and a high V (sub p) /V (sub s) ratio region inferred by independent geophysical and seismological studies.

Description: Published

Description: 440-456

Description: 3.6. Fisica del vulcanismo

Description: JCR Journal

Description: reserved

Description: In this paper we present a deterministic study to estimate seismic ground motions expected in urban areas located near active faults. The purpose was to generate bedrock synthetic time series to be used as seismic input into site effects evaluation analysis and loss estimates for the urban area and infrastructures of Thessaloniki (Northern Greece). Two simulation techniques (a full wave method to generate low frequency,~〈 1Hz, and a hybrid deterministic-stochastic technique to simulate high-frequency seismograms, ~〉 1 Hz) were used to compute time series associated with four different reference earthquakes having magnitude from 5.9 to 6.5 and located within 30 km of Thessaloniki. The propagation medium and different source parameters were tested through the modeling of the 1978 Thessaloniki earthquake (M 6.5). Moreover two different nucleation points were considered for each fault in order to introduce additional variability in the ground motion estimates. Between the two cases, the quasi-unilateral rupture propagation toward the city produces both higher median PGA and PGV values and higher variability than bilateral ones. Conversely, the low-frequency ground motion (PGD) is slightly influenced by the position of the nucleation point and its variability is related to the final slip distribution on the faults of the reference earthquakes and to the location of the sites with respect to the nodal planes of the radiation pattern. To validate our deterministic shaking scenarios we verified that the synthetic peak ground motions (PGA, PGV) and spectral ordinates are within one standard deviation of several ground-motion prediction equations valid for the region. At specific sites we combined the low- and high-frequency synthetics to obtain broadband time series that cover all the frequency band of engineering interest (0-25 Hz). The use of synthetic seismograms instead of empirical equations in the hazard estimates provides a complete evaluation of the expected ground motions both in frequency and time domains, including predictions at short distances from the fault (0 – 10 km) and at periods larger than 2 – 3 seconds.

Description: In press

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: JCR Journal

Description: open

Description: Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico”

Description: Published

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: A predominantly deterministic viewpoint has been adopted for computing seismic ground motion both for urban areas (SP10) and infrastructures loss modeling (SP11) at three selected areas: the cities of Lisbon (Portugal) and Thessaloniki (Greece), and the metropolis of Istanbul (Turkey). The generation of earthquake ground motion scenarios involves both the particular choice of earthquake sources with associated fault rupture parameters, and the ensuing ground motion field calculated by an appropriate numerical tool, or empirically estimated, at a set of selected points within the urban area of interest. Ground shaking values are predicted for rock conditions and for two distinct frequency bands, i.e. the high frequency range (from 1.0 Hz to 4-5 Hz) in the case of damage evaluation for the vast majority of ordinary building, and the low frequency (≤ 2 Hz) more appropriate for lifeline system damage assessment. The advanced simulation techniques allowed to properly consider the finite fault effects and directivity, which imply extreme expected values, and they are capable of quantifying the spatial variability of the ground motion near the extended fault.

Description: Published

Description: Hotel Villa Carlotta, Belgirate (VB)– Italy

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico”

Description: Published

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: Vengono presentate nuove relazioni empiriche, definite per il territorio italiano, per la stima dell’intensità in un dato sito a partire da informazioni epicentrali o relative a località vicine. Queste relazioni, espresse in forma probabilistica e quindi direttamente utilizzabili per la stima della pericolosità sismica, condividono la stessa formalizzazione e la medesima base informativa. In particolare, sono state seguite tre diverse strategie: le prime due hanno portato alla definizione di una relazione di attenuazione per la stima dell’intensità al sito da dati epicentrali utilizzando una forma parametrica rispettivamente Gaussiana e Binomiale; la terza analisi è stata invece mirata a definire le modalità di “correzione” del valore locale di intensità, dedotto dalle informazioni epicentrali, con dati di risentimenti osservati in località vicine al sito in esame.

Description: Istituto Nazionale di Geofisica e Vulcanologia

Description: Published

Description: 5.1. TTC - Banche dati e metodi macrosismici

Description: open

Description: GIS effetti suolo Gubbio (DVD)

Description: Progetto S3 - Scenari di scuotimento in aree di interesse prioritario e/o strategico

Description: Published

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico”

Description: Published

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: The eruption, in January 2002, of Mount Nyiragongo in eastern Congo, and the humanitarian disaster that followed in its wake, underlined the critical importance of accurate seismology to predict when such events will take place. Thus, a seismic telemeterd network, with centre in Goma Observatory, was built across Virunga area to help the moniotring of Volcano. Mount Nyiragongo is a volcano in the Virunga Mountains associated with the Great Rift Valley. The most prominent feature of the Democratic Republic of Congo's geology is the Western Rift Zone (WRZ), which runs through its eastern border regions and neighbouring countries (e.g. Uganda, Rwanda, Burundi, Tanzania) between 28°E to 32°E and 4°N to 12°S. The WRZ extends over a 1600 km arc, including lakes Albert, Eduard, Kivu and Tanganyika, until it joins the eastern branch. The Western Rift Valley of Africa has experienced severe earthquakes and volcanic eruptions in recent historical times. Earthquakes with magnitude 〉=6 are not frequent, but may cause significant destruction. They occur mostly in DRC and neighbouring countries (e.g. Uganda and Tanzania). In 1991, IAVCEI selected the Nyiragongo volcano as the ‘African decade volcano’ for the International Decade of Natural Disaster Reduction (IDNDR) program. Nyiragongo is located about 20 km north of Lake Kivu and 15 km north of Goma, a city of about 500,000 inhabitants. Goma is twinned to Gisenyi in Rwanda, which has a population of about 100,000. Several small villages are also located on the flank of the volcano. Population growth and poor or non-existent planning has led to relatively uncontrolled use of land for building, and the development of sites vulnerable to earthquake and/or volcanic risk.

Description: EUROPEAN CENTER FOR GEODYNAMICS AND SEISMOLOGY Royal Museum for Central Africa, B National Museum of Nat. History, L

Description: Unpublished

Description: Luxembourg

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: On 6 September 2002 a Mw 5.9 earthquake occurred in the southern Tyrrhenian sea, 40 km off the coast of Palermo (Italy). In the days after the mainshock, eight temporary stations were installed in the city to record aftershocks on different geological formations. Seismograms of about 30 earthquakes with magnitude 〉 2.8 are analyzed. The data analysis confirms the role of near-surface geology in causing locally significant variations of the ground-shaking level as already inferred by Guidoboni et al. (2003) from historical damage scenario studies. The largest spectral variations estimated through aftershock recordings result in a factor of 10 difference between stiff and soft sites, in frequency bands varying from 1 to 3.5 Hz. The geological structure of the study area is reconstructed by using data from more than 2000 boreholes organized in a Geographic Information System specifically dedicated to the assessment of natural hazards in urban areas. Vertically varying velocity models are used for a comparison with the observed data. In general, 1D transfer functions fit the largest amplification frequency but underestimate amplitudes of observations probably because of 2D and 3D complexity. Because the seismic stations were not installed in free field but at ground or underground level inside buildings, a possible influence of the structure was also investigated. Simultaneous ambient noise measurements were performed on the top, at the base, and outside the buildings where stations were installed. For all but one site, this analysis shows that the estimated ground-motion amplifications do not reflect the building vibration modes and therefore, in these cases, soil–structure interaction does not bias the free-field response of the study sites. Finally, speculations on the effect of the local geology in terms of response spectra of the Mw 5.9 mainshock are discussed in the framework of the Eurocode 8 prescriptions.

Description: Published

Description: 2328-2341

Description: reserved

Description: Between 26 and 29 October 2002, the Mt. Etna area was struck by a seismic swarm that counted some hundred events some of them well felt by the population. A first group of epicenters is located in the E-NE part of the volcano, reaching a maximum local magnitude of 4.6 on October 27 at 02:50 UT. A second group, occurring since October 28, is located in the SE flank close to the town of Zafferana Etnea and culminated with the ML 4.4 earthquake of October 29 at 10:02 UT. The seismic swarm was concomitant with the opening of a system of fractures in the eastern part of the volcano and the reactivation of the eruptive fracture system originated by the 2001 eruption. The most damaging event was the ML 4.4 earthquake of October 29, which occurred in a densely urbanized territory and attained intensity VIII on the European Macroseismic Scale (EMS). In spite of its small local magnitude, the shock caused significant damage to many buildings including reinforced concrete ones in an area that extends for about 4 km in a NNW-SSE direction and is centered around the villages of S. Venerina and Guardia. A long system of surface fractures originated along the damaged area. Other similar and even stronger events of the 2002 swarm in the northern zone did not cause diffuse damage since they occurred in a not densely urbanized area; however, they were highly destructive for the few sparse buildings close to the epicenters. The sequence was well recorded by the Broad Band Station of Antillo (Mednet Network), the most energetic events also triggered the Strong Motion Stations of Bronte (BRNT) and Catania (CATA). The latest part of the sequence (Dec. 2003 – Jan. 2004) was recorded by the local micronetwork installed in Santa Venerina (SVN). Two of these stations were also operating in Santa Venerina from Nov. 2003 to Aug. 2004. Moreover, data from a broad band station installed in Catania are available from Mar. 2001 to Dec. 2001.

Description: Unpublished

Description: Quito (Ecuador)

Description: open

Description: Seismic attenuation in the area of Mt. Vesuvius is reappraised by studying more than 400 S-coda envelopes of small local VT earthquakes recorded at Mt. Vesuvius from 1996 to 2002 at the three-component stations of OVO and BKE. The purpose is to obtain a stable separate estimate of intrinsic and scattering quality factors for shear waves. We investigate in the present paper four frequency bands, centered respectively at fc = 3, 6, 12 and 18 Hz with a bandwidth of 0.6fc. Stacked coda envelopes are fit to the multiple scattering model according to the Zeng approximation in the hypothesis of constant velocity half space. Results show that the diffusion regime is a good approximation as the scattering attenuation (proportional toQ−1 S , the inverse scattering-quality factor) is much stronger than the intrinsic dissipation (proportional to Q−1 I ). Q−1 S decreases with frequency while intrinsic attenuation is much less frequency-dependent. We also fit the stacked coda envelopes at BKE to the diffusion equation solved with the boundary condition of a 2 km thick diffusive layer over a homogeneous half space. Results show that the diffusivity, D, estimated in the assumption of reflecting boundary condition is greater than that estimated in the assumption of uniform half space, whereas the diffusivity estimated with the absorbing boundary condition is close to the estimate done in the assumption of half space. OVO station shows results different from those obtained at BKE and at a group of five stations located on Mt. Vesuvius for the frequency bands centered at 12 and 18 Hz. In these two bands, scattering attenuation at OVO is comparable to the intrinsic dissipation, and is much smaller than that measured at the other stations. We interpret this anomaly as due to an effect of strong lateral heterogeneity which modifies the redistribution of the seismic energy into the coda at OVO. A comparison of the results obtained using passive data (the present data set) and the active data obtained in the same area during TOMOVES experiment by Wegler (2004) show that the diffusivity estimated with shot data during TOMOVES is smaller of a factor greater than 4. This discrepancy is interpreted as due to different earth volumes sampled by the coda waves in the two cases.

Description: Published

Description: 202-212

Description: reserved

Description: We present a multifractal analysis of Mount St. Helens seismic activity during 1980–2002. The seismic time distribution is studied in relation to the eruptive activity, mainly marked by the 1980 major explosive eruptions and by the 1980–1986 dome building eruptions. The spectrum of the generalized fractal dimensions, i.e. Dq versus q, extracted from the data, allows us to identify two main earthquake time distribution patterns. The first one exhibits a multifractal clustering correlated to the intense seismic swarms of the dome building activity. The second one is characterized by an almost constant value of Dq ≈ 1, as for a random uniform distribution. The time evolution of Dq (for q = 0.2), calculated on a fixed number of events window and at different depths, shows that the brittle mechanical response of the shallow layers to rapid magma intrusions, during the eruptive periods, is revealed by sharp changes, acting at a short time scale (order of days), and by the lowest values of Dq (≈ 0.3). Conversely, for deeper earthquakes, characterized by intense seismic swarms, Dq do not show obvious changes during the whole analyzed period, suggesting that the earthquakes, related to the deep magma supply system, are characterized by a minor degree of clustering, which is independent of the eruptive activity.

Description: Published

Description: 179-186

Description: reserved

Description: We applied an automatic pattern recognition technique, known as Support Vector Machine (SVM), to classify volcanic tremor data recorded during different states of activity at Etna volcano, Italy. The seismic signal was recorded at a station deployed 6 km southeast of the summit craters from 1 July to 15 August, 2001, a time span encompassing episodes of lava fountains and a 23 day-long effusive activity. Trained by a supervised learning algorithm, the classifier learned to recognize patterns belonging to four classes, i.e., pre-eruptive, lava fountains, eruptive, and posteruptive. Training and test of the classifier were carried out using 425 spectrogram-based feature vectors. Following cross-validation with a random subsampling strategy, SVM correctly classified 94.7 ± 2.4% of the data. The performance was confirmed by a leave-one-out strategy, with 401 matches out of 425 patterns. Misclassifications highlighted intrinsic fuzziness of class memberships of the signals, particularly during transitional phases. Citation: Masotti, M., S. Falsaperla, H. Langer, S. Spampinato, and R. Campanini (2006), Application of Support Vector Machine to the classification of volcanic tremor at Etna, Italy, Geophys. Res. Lett., 33, L20304, doi:10.1029/2006GL027441.

Description: Published

Description: (L20304,)

Description: reserved

Description: In the text

Description: Gruppo Nazionale per la Vulcanologia

Description: Published

Description: Roma

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: The seismicity which affects Mt.Vesuvius is, at present, the only clear indicator of the volcano dynamics. In the last years, two periods of increased seismic activity occurred (August-October 1995 and March-May 1996). This seismicity was detected by the 10 analog stations of the Permanent Seismic Network as well as by up to 7 three-component temporary digital stations. A total number of about 600 events have been recorded, four of which showing magnitude 〉3.0. The maximum magnitude earthquake (M=3.4) was the strongest in the last fifty years and occurred on 25 April 1996. The use of three-component seismometers allowed us to obtain very reliable hypocentral locations. The focal volume of the two seismic crises does not exceed 5-6 km of depth below the crater area. Fault plane solutions of the most energetic events show focal planes oriented NW-SE and NE-SW, in agreement with the regional tectonic features, indicating that at present the seismicity of Mt.Vesuvius develops along pre-existing discontinuities. In addition, the occurrence of a fluiddriven source mechanism suggests a role played by the underground water on the seismic energy release. Shear wave splitting analyses confirmed the presence of an anisotropic volume related to a distribution of cracks andlor fractures parallely aligned to the main faults system of the volcano.

Description: Published

Description: 977-983

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: THE ISTITUTO NAZIONALE DI GEOFISICA E VULCANOLOGIA (INGV) AND THE ITALIAN DEPARTMENT FOR CIVIL DEFENSE (DPC)

Description: Published

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: In the text

Description: Istituto Nazionale di Geofisica e Vulcanologia

Description: Published

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: 3.6. Fisica del vulcanismo

Description: open

Description: Two swarms of microearthquakes (ML ≤ 2.2), occurred on July 2-7 and August 22, 2000 at Campi Flegrei, accompained by a ground uplift episode (4 cm) which interrupted on early March 2000 the descending trend started on 1985. Spectral analysis indicates a direct involvement of magmatic/hydrothermal fluids in the source process of the July swarm, while the August events are typical of shear failure, similar to most of the earthquakes that occurred during the last (1982-1984) bradyseismic crisis. Precise 3-D relative location applied to similar earthquakes allows for the recognition of two parallel alignments trending NE-SW at depths of 1.7 and 3.2 Km. This trend is consistent with the direction of the main focal plane obtained from fault plane solutions and evidences tensile failure in close proximity to the zone of maximum uplift as depicted by geodetic measurements. A fault weakening mechanism triggered by increasing pore pressure is invoked as the cause of these earthquakes.

Description: Published

Description: 2525-2528

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: Questo rapporto vuole descrivere l’attività svolta dal gruppo di lavoro incaricato della gestione e manutenzione della Rete Sismica Permanente (analogica ed a larga banda) dell’Osservatorio Vesuviano-INGV (OV-INGV) da me coordinato nel periodo 2000-2005 per la parte relativa alle stazioni remote ed al sistema di ricezione centralizzato. In esso sono sinteticamente riportate anche le attività svolte negli anni 2000 e 2003 e già oggetto di precedenti rapporti (Castellano, 2001; Castellano, 2004). Il gruppo di lavoro ha subito delle modifiche nel tempo, determinate dall’assunzione di nuovo personale e dal passaggio di ruolo di altri. In definitiva, oltre il sottoscritto, è stato costituito da Marco Capello, Ciro Buonocunto ed Antonio Caputo, a cui va aggiunto, per il periodo iniziale, Mario La Rocca. Comunque, in caso di necessità, tutto il personale afferente all’U.F. “Centro di Monitoraggio” ha dato sempre un eccellente contributo alle operazioni di gestione della Rete Sismica Permanente. L’esigenza di un rendiconto scaturisce dalla convinzione che, dopo circa sei anni di intensa attività, si possa considerare concluso un ciclo e che siano state gettate le basi per procedere ad un ulteriore potenziamento della Rete Sismica Permanente, con un marcato sviluppo tecnologico dei sistemi di rilevamento ed acquisizione, al fine di incrementarne la dinamica ed il potere di risoluzione nell’ambito di un progetto che garantisca la totale affidabilità dell’intero Sistema di Monitoraggio.

Description: Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano

Description: Published

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: open

Description: Distance scaling of earthquake-induced ground motion is studied in the Erzincan region, located in the eastern part of the North Anatolian Fault zone. The data set used in this study consists of 170 aftershocks of the MS ! 6.8 Erzincan earthquake of 13 March 1992, with moment magnitudes between 1.5 and 4.0. In order to empirically obtain the scaling relationships for the high-frequency S-wave motion, regressions are carried out on 352 horizontal-component short-period seismograms, all recorded within a hypocentral distance of 40 km, to empirically obtain the scaling relationships for the high-frequency S-wave motion. Peak ground velocities are measured in selected narrow-frequency bands, in the frequency range of 1.0–16.0 Hz, and are subsequently regressed to define a piecewise linear attenuation function, a set of excitation terms, and a set of site terms. Results are modeled in the framework of random vibration theory, using a bilinear geometrical spreading function, g(r), characterized by a crossover distance at 25 km: g(r)!r"1.1 is used for r ! 25 km, whereas g(r)!r"0.5 is used for larger distances. An extremely low-quality factor, Q(f ) ! 40(f /f ref)0.45, is used to describe the anelastic crustal attenuation in the region, consistently with the independent results of Akinci and Eyidogan (1996, 2000). Excitation terms are well matched by using a Brune spectral model with stress drop Dr ! 10 MPa (taken from the recent literature, Grosser et al., 1998). An effective high-frequency, distance-independent rolloff spectral parameter, jeff ! 0.02 sec, is obtained in this study. Peak ground acceleration predictions based on these parameters show a much more rapid decrease with distance than the relations usually used in Turkey, indicating that our results should only be applied to the Erzincan region itself.

Description: This study has been supported by Istituto Nazionale di Geofisica e Vulcanologia, INGV, Internal Project: “Attenuazione e leggi di scala nei paesi dell’area Mediterranea” (internally funded). R. B. Herrmann’s participation was supported by INGV and by the Earthquake Engineering Research Centers Program of the National Science Foundation under Award Number EEC-9701785.

Description: Published

Description: 1446-1455

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: A large data set of ground-velocity time histories from earthquakes that occurred in Friuli-Venezia Giulia (northeastern Italy) was used to define regional predictive relationships for ground motion, in the 0.25- to 14.0-Hz frequency band. The bulk of the data set was provided by the seismic network run by Centro Ricerche Sismologiche (CRS), a department of the Istituto Nazionale di Oceanografia e Geofisica (OGS). A collection of 17,238 selected recordings from 1753 earthquakes was compiled for the years 1995–1998, with magnitudes ranging from Mw !1 to 5.6. Ninety-six three-component strong-motion waveforms belonging to the largest events of the 1976–1977 Friuli seismic sequence were also taken from the ENEAENEL accelerogram database and included in our data set. For the strongest event, which occurred on 6 May 1976 at 20:00 local time, an average local magnitude ML 6.6 was computed by Bonamassa and Rovelli (1986). The inclusion of a large number of acceleration time histories from this earthquake and six others, from magnitudes from Mw 5.2 to magnitude Ms 6.1 (three of them of Ms !6.0), extends the validity of the predictive relationships proposed in this study up to the highest magnitude ever recorded in the region. A total of 10,256 vertical-component and 6982 horizontal-component seismograms were simultaneously regressed for excitation and site characteristics, as well as for the crustal propagation, in the hypocentral distance range 20–200 km. Results are given in terms of excitation, attenuation, and specific site for the vertical ground motion, together with a horizontal-to-vertical ratio for each existing horizontalcomponent seismometer. The regional propagation was modeled in the 0.5- to 14.0- Hz frequency band by using a frequency-dependent piece wise continuous linear (in a log–log space) geometrical spreading function and a frequency-dependent attenuation parameter: Q( f ) ! 260( f /1.0)0.55 The excitation spectra of larger events were modeled by using the regional propagation, a single-corner frequency Brune spectral model characterized by an effective stress parameter, Dr ! 60 MPa, and by a regional estimate of the near-surface, distance-independent, networkaveraged attenuation parameter j0 ! 0.045 sec that was estimated from the rolloff of the empirical source spectra obtained from the regressions. Other studies (De Natale et al., 1987; Cocco and Rovelli, 1989; Singh et al., 2001) suggested large stress drops (Dr ! 30–100 MPa,) to explain the highfrequency amplitude levels of the seismic radiation of the largest quakes of the 1976 sequence. Predictions for peak ground acceleration (PGA) and pseudo–spectral velocity (PSV) (5% damping) were computed through the use of the random vibration theory (RVT), with the parameters obtained from the regressions of this study.

Description: This study was supported by the Gruppo Nazionale Difesa dai Terremoti, (GNDT) through the project Terremoti probabili in Italia tra l’anno 2000 e il 2030: elementi per la definizione di priorita` degli interventi di riduzione del rischio sismico, task 3.1. The contribution of R. B. Herrmann was supported in part by the Earthquake Engineering Research Center’s Program of the National Science Foundation under Award No. EEC-9701785.

Description: Published

Description: 2186-2204

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: Explosion-quake seismograms recorded at Stromboli show that seismic phases with a high-amplitude and high-frequency content propagate with a velocity of approximately 330 m/s - the sound speed. The analysis of seismograms, recorded at a distance of 500 m from one of the three active vents, shows for the first onset a low frequency and particle motion characteristics of a p-wave, which loses its longitudinal polarization with the onset of the air-wave. Recording the explosion-quake simultaneously with a microphonewe would ascertain that the high frequency onset coincides with the air-wave's. In order to better understand the seismic wavefield generated by the atmospheric pressure, we performed a controlled source experiment at Stromboli using a seismic gun. Seismograms with the same two phases and particle motions comparable with the volcanic seismic data were obtained. A second experiment demonstrated, that the air-wave propagates at least in the uppermost 1m of the gound. We suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p- and air-waves are both generated in the same point and at the same time.

Description: Published

Description: 65-68

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: The persistent occurrence of long period (LP) events at Mt Etna became apparent with the installation of the first fixed broad-band seismic network in late 2003. Repeating similar LP events from Nov. ‘03 to Sept. ‘04 indicate a non-destructive source process. We perform moment tensor (MT) inversions on a stacked high S/N ratio representative LP signal, conducting a grid search for the source geometry and L2-inversion for the source time function. Results indicate a NNW-SSE oriented resonating sub-vertical crack as the most probable source. This result is consistent with deformation and GPS observations. Crucial to this result are constraints imposed by detailed 3D full waveform numerical simulations in a heterogeneous tomographic model with topography, and in particular a detailed assessment of the influence of very near surface velocity structure on LP signals. Pulsating gas injection is hypothesised as the most likely LP trigger.

Description: Published

Description: L22316

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: Between December 2004 and August 2005, more than 50,000 long-period events (LP) accompanied by very-long period pulses (VLP) were recorded at Mt. Etna, encompassing the effusive eruption which started in September 2004. The observed activity can be explained by the injection of a gas slug formed within the magmatic column into an overlying cavity filled by either magmatic or hydrothermal fluids, thus triggering cavity resonance. Although a large number of LP events exhibit similar waveforms before the eruption, they change significantly during and after the eruption. We study the temporal evolution of the LP-VLP activity in terms of the source movement, change of the waveforms, temporal evolution of the dominant resonance frequencies and the source Q factor and changes in the polarization of the signal. The LP source locations before and after the eruption, respectively, do not move significantly, while a slight movement of the VLP source is found. The intensity of the LP events increases after the eruption as well as their dominant frequency and Q factor, while the polarization of the signals changes from predominantly transversal to pure radial motion. Although in previous studies a link between the observed LP activity and the eruption was not found, these observations suggest that such a link was established at the latter end of the eruptive sequence, most likely as a consequence of a reestablishment of the pressure balance in the plumbing system, after it was undermined due to discharge of large amounts of resident magma during the eruption. Based on the polarization properties of the signal and geological setting of the area, a fluid- filled crack is proposed as the most likely source geometry. The spectral analysis based on the autoregressive-models (SOMPI) is applied to the signals in order to analyse the resonance frequencies and the source Q-factors. The results suggest water and basalt with the low gas volume fraction as the most likely fluids involved in the source process. Using theoretical relations for the “slow waves” radiated from the fluid-filled crack, we also estimate the crack size for both fluids, respectively.

Description: In press

Description: 3.6. Fisica del vulcanismo

Description: JCR Journal

Description: open

Description: Following the installation of a broadband network on Mt. Etna, sustained Long-Period (LP) activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004–2005 effusive episode. From about 56000 events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th, 2003–September 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the 0.5–10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters, and extending to a maximum depth of ≈ 800 m beneath the surface. No causal relationships are observed between LP, VLP and tremor activities and the onset of the 2004–2005 lava effusions, thus indicating that magmatic overpressure played a limited role in triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods, and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system.

Description: Published

Description: 340-354

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: We estimated the attenuation laws of high-frequency seismic waves in the shallow crust (depth 5 km) and earthquake source parameters by using a selected data set of 320 shallow events (2.6 MD 4.2), recorded at Mt. Etna volcano during the last two flank eruptions occurring in 2001 and 2002–2003. The quality factor (Q) was estimated from spectra of P and S waves for 24 stations of the local permanent network by applying a spectral ratio technique. The results show variations in both QP and QS as a function of frequency, according to the power law Q Q0 f n, with n ranging between 0.3 and 1.3 for P waves and between 0.2 and 0.9 for S waves. As typical of volcanic environments, strong azimuthal variations of QP were also found, suggesting the presence of local strong lateral heterogeneities and/or of fluid-filled cracked volumes. After correction for attenuation, we estimated the source parameters (seismic moment, source radius, and stress drop) of a subset of 66 shallow events, under the assumption of a circular dislocation. The estimated seismic moments M0 range from 1013 to 1015 N m. The source radii (r) are confined between 100 and 1000 m and stress drop (Dr) ranges between 0.2 MPa and about 4 MPa. Combining the source parameters obtained in this study with those calculated by Patane` et al. (1997) for an old data set of smaller microearthquakes (109 M0 1014 N m) recorded in the same area, we re-evaluated the scaling relationship between seismic moment (M0) and corner frequency ( fc) for the earthquakes with M0 ranging between 1013 and 1015 N m. We confirm that microearthquakes at Mt. Etna seem not to obey a scaling relationship, as generally observed for moderate to 3 M f 0 c large earthquakes, as the slope of the scale dependence about 4.3 or higher. Assuming that this dependence is real, within the uncertainty in the results, a departure from the self-similarity exists for the volcanotectonic earthquakes at Mt. Etna.

Description: Published

Description: 184-197

Description: 3.1. Fisica dei terremoti

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: In this study, we simulate and compare ground motion shaking in the city of Lisbon and surrounding counties (metropolitan area of Lisbon (MAL)), using two possible earthquake models: the onshore source area of Lower Tagus Valley, M5.7 and M4.7 and the offshore source area, Marques de Pombal Fault, M7.6, one of the possible source of the 1755 Lisbon earthquake. The stochastic and a new hybrid stochastic-deterministic approach (DSM) are used in order to evaluate the ground shaking and to characterize its spatial variability. Results are presented in terms of response acceleration spectra (PSA) and peak ground acceleration (PGA) with respect to bedrock and surface. Site effects are evaluated by means of equivalent stochastic non-linear one-dimensional ground responses analysis, performed for a set of stratified soil profile units properly designed to cope with the soil site conditions of MAL region. A sensitive study is carried out using different input parameters and different approaches in order to give the basic information to evaluate the range of uncertainty in seismic scenarios.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: We simulated strong motion records from the Umbria-Marche, Central Italy earthquake (Mw 6) of September 1997 using a frequency-dependent S-wave radiation function. We compared the observed acceleration spectra, from strong-motion instruments located in the near field and at regional distances, with those simulated using the stochastic modeling technique of Beresnev and Atkinson (1997, 1998), and modified to account for a frequency dependent radiation pattern correction. By using the frequency-dependent radiation function previously obtained by Castro et al. (2006) we reduced the overall fitting error of the acceleration spectra by about 9%. In general, we observed that the frequency-dependent radiation pattern correction has a small effect on the spectral amplitudes compared with site effects, which is an important factor controlling the strong-motion records generated by the 1997 Umbria-Marche earthquake. In addition, we modeled the observed ground-motion records using the dynamic corner frequency model of Motazedian and Atkinson (2005) to reproduce the directivity effects, reducing the average error of the spectral amplitudes by 24%. We concluded that although the frequency-dependent radiation pattern correction affects the frequency content of the spectral amplitudes simulated, site and directivity effects are more relevant.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: open

Description: Nel luglio 2006, nell’ambito della campagna di ricerche PRO.ME.TH.E.US (PROgram of Mediterranean Exploration for THermal Energy Use), l’OBS Lab dell’Osservatorio Geofisico di Gibilmanna dell’INGVCNT, ha deposto un prototipo di OBS/H sulla sommità del vulcano sottomarino Marsili (39° 16,383’ lat. Nord, 14° 23,588’ long. Est.) alla profondità di 790 m (D’Anna et alii, 2007); lo strumento ha registrato l’attività sismica del vulcano dal 12 al 21 luglio 2006. L’OBS/H era equipaggiato con un sismometro Trillium 40s della Nanometrics e un idrofono OAS E-2PD. La digitalizzazione è stata effettuata da un convertitore A/D a 21 bit a quattro canali (SEND Geolon MLS) e i segnali sono stati campionati ad una frequenza di 200 c/s (D’Anna et alii, 2007).In una prima fase di studio D’Alessandro et alii (2006) hanno individuato, nel segnale acquisito, la presenza di una elevata attività sismica (oltre 1000 eventi registrati in 9 giorni) legata probabilmente all’attività del vulcano Marsili oltre a eventi tettonici e forme d’onda transitorie di origine non sismica. In base ad analisi spettrali non parametriche, l’attività registrata era stata suddivisa in: eventi noti in letteratura come VT-B (Volcanic-Tectonic event, type B) che si manifestano in sciami, eventi ad alta frequenza legati a probabile attività idrotermale ed eventi classificabili come “Tornillo” o LPE (Long- Period Event) probabilmente generati da fenomeni di risonanza legati ad attività magmatica (Chouet, 1996). Al fine di caratterizzare con idonei parametri quantitativi i segnali appartenenti ai gruppi individuati e fare delle ipotesi sui diversi meccanismi sorgente, sono state successivamente eseguite analisi spettrali parametriche e di polarizzazione, che sono oggetto di questo lavoro. Rispetto all’analisi di Fourier, l’analisi spettrale parametrica permette di ottenere una migliore risoluzione, quando il segnale da analizzare presenta breve durata. Noi abbiamo applicato tale tipo di analisi agli eventi classificabili come Tornillo. Tali eventi sono generalmente quasi-monocromatici e presentano un inizio di tipo impulsivo, seguito da un lento e graduale decadimento in ampiezza. La descrizione delle frequenze di oscillazione di un Tornillo è di fondamentale importanza per stimare le caratteristiche della sorgente. Un metodo ad alta risoluzione spettrale basato sulle proprietà di un sistema dinamico è stato sviluppato da Kumazawa et alii (1990). Questo metodo chiamato Sompi è stato successivamente esteso da Yokoyama et alii (1997) alle equazioni AR non omogenee. Noi abbiamo utilizzato quest’ultimo metodo, implementando la procedura di Nakano et alii (1998), per analizzare i Tornillo ed attribuirgli una frequenza complessa.L’analisi di polarizzazione, risolvendo il problema agli autovalori associato alla matrice di covarianza dei segnali relativi alle tre componenti del moto, permette di definire l’orientazione e la lunghezza degli assi dell’ellissoide di polarizzazione associato alla finestra temporale del segnale sismico presa in esame. Al fine di migliorare la stima degli attributi di polarizzazione, la matrice di covarianza è stata corretta per la presenza di rumore sismico, sotto l’ipotesi di stocasticità e stazionarietà del rumore stesso. L’analisi di polarizzazione è stata applicata a oltre 200, tra gli eventi VT-B con maggiore energia, per individuare attraverso la direzione di polarizzazione delle fasi P (linearmente polarizzate) eventuali direzioni prevalenti di provenienza e quindi l’esistenza e ubicazione di volumi sismogenetici.

Description: Published

Description: Rome

Description: 2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini

Description: open

Description: Within the Italian Project S3 (DPC-INGV) “Shaking seismic scenarios in area of strategic and/or priority interest” the urban area of Gubbio has been chosen as a test site for the calculation of ground shaking scenarios for forecasting purposes. The area has been selected because the urban and / or geomorphologic characteristics of the town of Gubbio and its surrounding are good representatives of many areas in Central Italy: an historical centre of high cultural and artistic value founded on a rocky hillside with new residential and industrial areas developed on the alluvial plain. A great deal of effort has been put in the seismic characterisation of the Gubbio basin, since the general purpose of this work has been the quantification of site effects in intra-mountain basins. Recent studies have shown in fact that significant site effects take place in the Eugubina plain, as evidenced by the generation of surface waves. In particular, the strong motions recorded at the accelerometric station GPB, belonging to the RAN (Rete accelerometrica italiana), installed within the alluvial basin, shows strong amplification and lengthening of significant duration respect to rock sites (Pacor et al; 2007). Several investigations with active and passive seismic survey techniques have been planned and carried out in the plain, also favoured by the intense seismic activity typical of the area (see PS3-Deliverable 21). All data are collected in a GIS herewith enclosed (section 7). The estimates of the empirical transfer functions in the basin have been related to the monitoring activities of 4 temporary transects of seismometric stations (Figure 1.1), operating between June 2005 and May 2006 and described in this Deliverable. The velocemetric records are collected in PS3-Deliverable D26 The amplitude transfer functions for sites corresponding to the stations installed in the basin have been determined by applying three different methods, namely the horizontal-to-vertical spectral ratio (H/V), the standard spectral ratio (SSR) and the generalized inversion technique (GIT).

Description: Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico” (coord. F.Pacor e M. Mucciarelli).

Description: Published

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: Abstract The source parameters of 523 aftershocks (0.5 ML 5.9) of the 1999 Kocaeli earthquake are determined by performing a two-step spectral fitting procedure. The source spectrum, corrected for both site and propagation effects, is described in terms of a standard x-square model multiplied by an exponential term of frequency. The latter term is introduced to estimate the high-frequency (f 12 Hz) fall-off of the acceleration source spectra by computing the j parameter. The seismic moments obtained range between 1.05 1014 and 2.41 1017 N m, whereas the Brune stress drops are between 0.002 and 40 MPa. The j value varies between 0.00 and 0.08 sec, indicating a decay of the acceleration level at the higher frequency part of the spectrum greater than that assumed by the x 2 model. Both the stress drop and the j parameter show the tendency of increasing with aftershock magnitude. No evidence of self-similarity breakdown is observed between the source radius and M0. Finally, both the seismic moment and the moment magnitude are compared with the local magnitude to derive new moment–magnitude relationships for the area.

Description: Published

Description: 655-660

Description: 3.3. Geodinamica e struttura dell'interno della Terra

Description: JCR Journal

Description: partially_open

Description: Uno dei principali obiettivi degli studi di pericolosità sismica è la quantificazione della risposta di sito, che può modificare in maniera significativa il moto registrato in superficie durante un terremoto rispetto al moto osservato su sito rigido. In questo lavoro si presentano i risultati di uno studio finalizzato alla determinazione della risposta sismica del bacino di Gubbio, ottenuti nell’ambito del Progetto INGV-DPC S3 (2005-2007) “Scenari di scuotimento sismico in aree strategiche e/o prioritarie”. In tale area, infatti, recenti studi, basati sull’analisi di registrazioni della stazione accelerometrica GBP, installata nella piana e della stazione vicina GBB, localizzata su sito rigido, hanno evidenziato la presenza di effetti locali legati al bacino alluvionale. Nella piana sono state programmate e svolte molteplici indagini sperimentali sia di sismica attiva che passiva, finalizzate alla determinazione di un modello di riferimento del bacino ed alla stima della risposta di sito. In particolare è stata svolta un’attività di monitoraggio con l’installazione di 4 transetti temporanei di stazioni sismometriche, che hanno operato da Giugno 2005 fino a Maggio 2006. Due transetti sono stati posizionati in direzione trasversale all’asse della piana, uno in direzione longitudinale e l’ultimo presso il centro storico di Gubbio. Durante l’esperimento, grazie all’intensa attività sismica della zona, sono stati registrati più di 300 terremoti locali e regionali, con una magnitudo massima pari a M 4.7. Con un data set selezionato, sono state valutate le funzioni di amplificazione empiriche utilizzando diverse tecniche spettrali. In particolare sono stati applicati il metodo SSR basato sul rapporto spettrale delle componenti orizzontali o verticali rispetto ad un sito di riferimento e la tecnica di inversione generalizzata GIT. Inoltre è stata utilizzata la tecnica H/V, consistente nel rapporto spettrale tra la componente orizzontale e verticale registrata da una singola stazione, per la stima delle frequenze di risonanza. I risultati hanno mostrato che i metodi basati sui rapporti spettrali rispetto ad una stazione di riferimento su roccia (SSR) evidenziano impressionanti effetti di bacino 2D-3D, mentre i rapporti spettrali H/V forniscono utili indicazioni sulla risposta 1D del bacino. Le risposte di sito ottenute nella piana con il GIT e la tecnica SSR sono infatti caratterizzate da elevatissime amplificazioni con ampiezze fra 5 e 20 in una ampia banda di frequenze compresa fra 0.2-0.3Hz fino a 3–4 Hz, in accordo con il contenuto spettrale delle onde di superficie generate localmente. Viceversa, dal picco principale del rapporto H/V, è possibile stimare solo la frequenza fondamentale di risonanza dei siti e, congiuntamente ad altre informazioni sulle velocità delle onde S, gli spessori dei sedimenti.

Description: Published

Description: Roma

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: In the recent years, two Italian research projects have been devoted to the simulation of ground shaking scenarios in different areas. A large part of the activities has been performed in the Umbria region and was in particular related to the 1997 Colfiorito earthquake. In general the statistical-deterministic approach was adopted for evaluating the scenarios for strong motion parameters (peak values, spectral ordinates, signal integral quantities, and so on) associated with the occurrence of a characteristic earthquake on a given fault. This approach is based on the realistic occurrence of a single earthquake related to the fracture of an a priori well identified active fault. According to the characteristic earthquake model, an earthquake rupture can repeatedly occurs along the same fault (or fault system) with an almost constant geometry, mechanism and seismic moment, these parameters being mainly related to the direction and intensity of the large scale tectonic stress regime. These ideas are supported by numerous paleoseismic studies of active faults in different tectonic environments [e.g., Pantosti and Valensise, 1990]. On the other hand, each faulting process may not repeat the same style of nucleation, propagation and arrest during successive rupture episodes occurring along a given fault zone, depending these characteristics on the pre-fracturing conditions of rock strength and/or yielding stress along the fault zone. It is therefore assumed that the large scale source characteristics (i.e., fault size and position, focal mechanism and seismic moment) are a priori known as the result of previous geological, geophysical and historical seismicity investigations. The variability of the rupture process is expected to produce variable strong ground motions at the earth surface, depending on the distribution of the kinematic parameters (final slip distribution, rupture velocity, slip duration …) along the faulting surface. In order to account for the possible variation of the source process from one rupture event to another, a large number of synthetic seismograms should be computed for different (and possible) rupture histories occurring along the characteristic fault selected, so to provide a representative set of strong motion records to be used for hazard estimation. By this strategy, the massive computation of synthetics for different possible rupture models does not provide a single earthquake scenario (as for the standard deterministic approach) but a set of possible scenarios whose variability substantially reflects the heterogeneity of the source process. The advantage of this approach is that the variability of the selected strong ground motion parameter at a given site can be described by the statistical quantities inferred from the large number of simulations available. The earthquake scenario can then be represented, for example, by a couple of maps, one describing the spatial distribution of the mean value of the considered ground motion parameter and the other representing the associated variability for example in terms of standard deviation.

Description: Published

Description: Roma, Università degli Studi Roma TRE

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: open

Description: Within the framework of four research projects (RISK-EU, EUROSEISRISK, SRM_LIFE and LESSLOSS) extensive calculations were carried out assessing the seismic hazard in the Thessaloniki and surrounding area. The main results were derived from probabilistic and deterministic approaches taking into account rock site conditions for each examined site in the Metropolitan area of Thessaloniki. The expected strong-ground motions were calculated applying different methodologies. Two different groups worked for the assessment of the seismic hazard, the first one constituted of the INGV (Istituto Nazionale di Geofisica e Vulcanologia, Italy) and LSMF (Laboratory of Soil Mechanics and Foundation Engineering, Thessaloniki, Greece) and the second one of LSMF and ITSAK (Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki, Greece).

Description: Published

Description: Thessaloniki (Greece)

Description: 4.2. TTC - Scenari e mappe di pericolosità sismica

Description: open

Description: This study presents the results of 90 seismic ambient noise measurements in Palermo, the main city of Sicily (Italy). The dataset has been processed using the horizontal-to-vertical spectral ratio (HVNSR) technique and interpreted in terms of local geology, which is characterized by the presence of alluvial sediments of two river-beds masked by urbanization since the 17th century. HVNSRs show significant variations in the study area: when the transition stiff-to-soft is crossed, a typical spectral peak appears in the HVNSRs, mostly in the frequency band 1 to 2 Hz, and exceeding a factor of 3 in amplitude. Using available information on sub-surface geological structure we compute theoretical 1- and 2-D transfer functions. The resonance frequencies of soft soils obtained by HVNSR are well reproduced by the fundamental frequencies from numerical modeling. The distribution of frequency peaks of HVNSR and their amplitudes are also compared with the local damage caused by historical earthquakes. Previous studies demonstrated that damage variations in Palermo were controlled more by near-surface geology than building vulnerability. A uniform vulnerability is an ideal condition to test statistical methods and their capability in seeking correlation between HVNSR and potential damage due to local geological conditions. We apply two well-established multivariate statistical methodologies (factor analysis and canonical correlation) to the HVNSR dataset and macroseismic data (damage grades of the European Macroseismic Scale). Through these analyses we quantify the significance of the correlation between the HVNSR peak in the low-medium frequency range (0.5-3 Hz) and the occurrence of the highest damage grades. This approach allows us i) to estimate the threshold value in the resulting linear combination of the HVNSR amplitudes which separates zones of light damage from zones of significant damage, and therefore ii) to improve the spatial definition of potentially high hazard zones through a denser grid of microtremor measurements.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: open

Description: In the text

Description: Published

Description: 67-76

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: 3.6. Fisica del vulcanismo

Description: JCR Journal

Description: reserved

Description: Seismic noise recorded by broad-band stations in the middle of and around the Colfiorito plain is analyzed in the frequency band 0.1 to 10 Hz. Small daily variations in noise amplitude are found, on the order of 2 for f 〉 1 Hz. In contrast, long-term amplitude variations due to weather conditions are significant throughout the analyzed frequency band; for f 〈 1 Hz, the amplitude increase can be as large as a factor of 50. In the low-frequency band, horizontal components vary much more than the vertical at both firm and soft sites. However, these noise variations at low frequencies do not contaminate significantly the 0.9-Hz peak of the H/V spectral ratio that fits the fundamental eigenfrequency of the sedimentary fill of the basin, resonating during earthquakes. Correlating the long-term variations of noise with different meteorological parameters, we find that wind speed best matches the low-frequency noise disturbances.

Description: Published

Description: reserved

Description: The report describes the methods used for retrieving data and selecting a suitable earthquakes dataset from the recordings of the seismic stations used by the INGV Rome team involved in the study of the influence of surface geology on ground motion. It describes also the programs used in the spectral analyses for computing spectral ratios both on earthquake and ambient seismic noise datasets.

Description: Istituto Nazionale di Geofisica e Vulcanologia

Description: Published

Description: open

Description: This study is aimed at predicting the strong ground shaking in the Phlegraen Fields area, in the western part of the city of Naples, by the use of synthetic simulations of the seismic radiation possibly produced by earthquakes occurring on active faults of the southern Apennines range. Given their distance, geometry and expected mechanism these faults have been selected as the potentially most dangerous ones for the city of Naples. We selected the seismogenic sources associated with earthquakes having caused intensity equal or above VII in the city of Naples and having occurred in the past 700 years (the most reliable time window for the historical earthquake catalogue). All seismogenic sources were taken from INGV’s DISS database. These faults are long and relatively shallow structures (length greater than 25 km and maximum depth within 13 km) having seismic moment and focal mechanism comparable to the 1980, M 6.9 Irpinia earthquake. According to the literature, the latter is included in our simulation study by considering the occurrence of three separate rupture processes along three distinct fault segments. A suite of synthetic seismograms at the basement rock in Naples for each considered fault has been generated by using the discrete wavenumber method proposed by Bouchon (1981) numerically implemented for the computation of complete wave field Green’s function in a flat-layered medium. We adopted a simplified source model (line source Haskell model) to simulate the kinematic rupture process along an extended source, allowing for rupture nucleation in the middle (bi-lateral) and at the edge (uni-lateral) of the Haskell line. This approach has been preliminary tested and validated with the comparison between synthetic and observed 10-Hz low-pass filtered 1980 Irpinia earthquake records. The investigated site is located in the eastern part of the Phlegraen caldera, a plain area filled with recent (〈 12,000 yr) pyroclastic soils. Several specific experiments were performed to evaluate the effect of surface geology on ground shaking. The experimental data used in this study come from a 2D active refraction seismic survey, from the spectral analysis of the shot-induced multichannel surface-waves (MASW), and from a 2D small-aperture array that recorded both natural earthquakes and ambient noise. Simultaneously, a firm-site reference station was also operating on an outcrop of yellow Neapolitan tuff (lithoid facies), about 1 km away from the array. These data, integrated with stratigraphy available from boreholes drilled in the plain, allowed us to reconstruct a 1D vertical profile of shear-wave velocities at the site of interest. This velocity model was mostly based on the inversion of the dispersion curves obtained from ambient noise measured at the array combined with MASW results from the refraction survey. The fundamental resonance frequency of the site was assessed around 1 Hz. At this frequency, the soft-to-firm spectral ratios computed from the recorded earthquakes are consistent with the theoretical transfer function of the model in terms of both predominant frequency and amplitude. The rock-site synthetic seismograms were then convolved by the site theoretical transfer function in a linear-equivalent approach, where shear-modulus and damping curves for the soft materials of the uppermost layers are taken from the literature. Acceleration and displacement response spectra were computed from the convolved synthetics. A comparison of the retrieved response spectra with those required by the Italian seismic code (Italian government ordinance PCM 3274 of 20 March 2003) suggests that our results are consistent with expectations at short-periods (T〈 2 s) but some discrepancies arise at longer periods, where our predictions exceed the spectral ordinates of the seismic codes. This finding stresses the need for more thorough investigations of intermediate-period surface waves

Description: Unpublished

Description: Vienna

Description: open

Description: On October 2002 a seismic swarm occurred on the eastern flank of Mt. Etna. One of the strongest events caused severe damage, up to EMS intensity of VIII that contrasts with its local magnitude of 4.4. The occurrence of significant damage at such small magnitude is repeatedly observed in the Mt. Etna area and is traditionally attributed to the shallow source of volcanic earthquakes. Strong-motion accelerograms and broad-band seismograms recorded during the swarm demonstrate that there is a more cogent cause for the severe damage, i.e. an anomalously strong low-frequency (0.1 〈 f 〈 1 Hz) radiation deviating from the conventional Brune (1970) spectral scaling. Therefore, these earthquakes cause unexpectedly large ground displacements and long ( 20 sec) durations of shaking. The integration of digital accelerograms recorded on October 2002 yields a maximum peak ground displacement as large as 1.8 cm at a distances of 18 km, out of the largest damage zone. Based on the sharp local attenuation of ground motion amplitudes observed during the Mt. Etna earthquakes, we infer that displacements near the epicentres can have attained 10 cm. So large displacements are consistent with the maximum observed damage. Moreover, the frequency cutoff below 1.25 Hz in the Wood-Anderson response attenuates the peak-to-peak amplitudes used to assess local magnitudes. This instrumental deamplification at low frequency yields underestimated values of local magnitude that are not representative of the real ground shaking. Since a prompt, correct magnitude (and potential damage) assessment is crucial for efficient Civil Protection actions, a procedure is proposed which, in near-real-time, can be successful in identifying potentially damaging earthquakes of Mt. Etna through the computation of response spectra. The procedure provides a magnitude value that is derived on a statistical basis from the Housner (1952) spectral intensity computed in the low-frequency band. This parameter is a suitable near-real-time indicator of large earthquake-induced building shaking and could also be applied for a preliminary determination of the epicentral macroseismic intensity of volcanic events of Mt. Etna through consolidated relationships established for tectonic earthquakes in Italy.

Description: Submitted

Description: open

Description: Following the installation of a broadband network on Mt. Etna, sustained Long- Period (LP) activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004–2005 effusive episode. From c. about 56000 events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th, 2003–September 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the 0.5–10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters, and extending to a maximum depth of ≈800 m beneath the surface. No causal relationships are observed between LP, VLP and tremor activities and the onset of the 2004–2005 lava effusions, thus indicating that magmatic overpressure played a limited role in triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods, and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system.

Description: Submitted

Description: open

Description: By using small-to-moderate-sized earthquakes located within ~200 km of San Francisco, we characterize the scaling of the ground motions for frequencies ranging between 0.25 and 20 Hz, obtaining results for geometric spreading, Q(f), and site parameters using the methods of Mayeda et al. (2005) and Malagnini et al. (2004). The results of the analysis show that, throughout the Bay Area, the average regional attenuation of the ground motion can be modeled with a bilinear geometric spreading function with a 30 km crossover distance, coupled to an anelastic function ! exp " #fr $Q( f ) % & ' ( ) * , where: Q(f)=180 f 0.42. A body-wave geometric spreading, g(r)= r -1.0, is used at short hypocentral distances (r 〈 30 km), whereas g(r)= r -0.6 fits the attenuation of the spectral amplitudes at hypocentral distances beyond the crossover. The frequency-dependent site effects at 12 of the Berkeley Digital Seismic Network (BDSN) stations were evaluated in an absolute sense using coda-derived source spectra. Our results show: i) the absolute site response for frequencies ranging between 0.3 Hz and 2.0 Hz correlate with independent estimates of the local magnitude residuals (dML) for each of the stations; ii) moment-magnitudes (MW) derived from our path and sitecorrected spectra are in excellent agreement with those independently derived using fullwaveform modeling as well as coda-derived source spectra; iii) we use our weak-motionbased relationships to predict motions region wide for the Loma Prieta earthquake, well above the maximum magnitude spanned by our data set, on a completely different set of stations. Results compare well with measurements taken at specific NEHRP site classes; iv) an empirical, magnitude-dependent scaling was necessary for the Brune stress parameter in order to match the large magnitude spectral accelerations and peak ground velocities with our weak-motion-based model.

Description: Submitted

Description: open

Description: On October 31st and November 1st, 2002 two moderate earthquakes of moment magnitude Mw=5.7 (INGV-Harvard European-Mediterranean Regional Centroid-Moment tensor project) occurred in southern Italy. After the mainshocks, felt in many municipalities of the Molise and Puglia region, a strong motion and a seismic temporary network were installed in the epicentral area and surrounding regions. The strong motion network was composed by 9 stations, integrating the accelerometers of the permanent Rete Accelerometrica Nazionale (RAN network), and operated until December 2003. The strong motion data set is composed by 195 recordings from 51 earthquakes (2.5〈Ml〈5.4) recorded by 29 accelerometers (Dipartimento della Protezione Civile et al., 2004). In addition to the strong motion network, several Italian research institutions (Istituto Nazionale di Geofisica e Vulcanologia, INGV; Istituto Nazionale di Oceanografia e Geofisica, INOGS; Dipartimento per lo studio del Territorio e delle sue Risorse, University of Genoa, Dip.Te.Ris) installed a temporary regional network, composed by 35 seismic stations. This network aimed at monitoring and studying the evolution in time and space of the seismic sequence. More than 1900 aftershocks were recorded in the period November 1st - December 5th, 2002 (Chiarabba et al., 2005). The unified velocity-acceleration data set has been considered to derive ground motion models for peak ground acceleration and peak ground velocity for both maximum horizontal and vertical components. The results obtained for the Molise area have been compared with the attenuation pattern of the Umbria-Marche region (central Italy), that was recently investigated by Bindi et al. (2006). The remarkable differences observed indicate the need of a regional attenuation relation for the area and the need of further investigations, to better identify the role of source characteristics, anelastic and geometric attenuation and site effects in the evaluation of peak ground motion values.

Description: Unpublished

Description: Geneva, Switzerland

Description: open

Description: To define more accurately the near field and the directivity effect, different methodologies of finite-fault modelling have been used to describe the behaviour of ground shaking based on deterministic, stochastic and hybrid stochastic-deterministic approaches as in the framework of the ongoing European project “LESSLOSS – Risk Mitigation for Earthquakes and Landslides”. In this study, we simulate and compare seismic scenarios obtained from the complex source characteristic of the 1980 Irpinia earthquake, M 6.9, Southern Italy, using models based on the source models hypothesized in Bernard and Zollo (1989) and in Valensise et al. (1990). Furthermore, two finite-fault numerical approaches are used: 1. The approach RSSIM [Carvalho et al., 2004] that is a non-stationary stochastic simulation method that synthesizes the ground motion due to an extended source; 2. The approach EXSIM [Motazedian and Atkinson, 2005] that is a new version of FINSIM [Beresnev and Atkinson, 1998] introducing a new variation based on a “dynamic corner frequency”. The shaking scenarios are computed in terms of Response Acceleration Spectra (PSA), time series, peak ground acceleration (PGA) at bedrock level. Source and path propagation parameters taken from other studies were tested and the computed shaking scenarios are compared to acceleration records to eight different stations. Preliminary results are here presented in terms of PGA maps for the Campania region (Southern Italy).

Description: Unpublished

Description: Geneva, Switzerland

Description: open

Description: A seismic rehabilitation program is being implemented to address the vulnerability of a large proportion of Italian building stock. A risk management framework, initially only for Italian school buildings, has been developed to assign priorities for the rehabilitation, and to give timescales within which retrofit or demolition must take place. Since it is not practical to carry out detailed assessment for around 60,000 Italian public schools, the framework is a multiplelevel procedure which aims to identify the highest-risk buildings based on filters of increasing detail, and reduces the size of the building inventory at each step. Finally, priorities and timescales are assigned based on vulnerability, seismic hazard and building occupancy, within a general framework with parameters which must be assigned by the relevant authorities. The methodology is transparent, technically-based, and flexible enough to be adapted for other building types or other regions.

Description: Submitted

Description: reserved