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Morelli, Andrea
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Morelli, Andrea
Email
andrea.morelli@ingv.it
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staff
ORCID
Scopus Author ID
55724939200
Researcher ID
F-2486-2016
88 results
Now showing 1 - 10 of 88
- PublicationRestrictedGroup velocity of Rayleigh waves in the Antarctic regionWe analyzed dispersion of intermediate and long period surface waves, recorded at permanent observatories in the Antarctic region, in a tomographic study based on group velocity. We considered Rayleigh waves from available records of all events which occurred during years 1991-1995, with latitude lower than 40°S and magnitude M≥5.0. We performed classic single-station dispersion analysis on the surface wave train to measure group velocity of the Rayleigh fundamental mode in the period range between 30 and 120 s. We iteratively applied two different techniques of filter analysis: a multiple-filter [Dziewonski et al., 1969] and a phase-matched filter algorithm [Herrin, and Goforth, 1977]. We used such dispersion measurements to compute two-dimensional maps of velocity anomalies in the region. We parameterized group velocity with linear splines, and inverted the linear system by means of singular value decomposition. Results are in significant agreement with earlier studies, but reach a considerably higher detail. Our model differentiates well among geologically different regions, such as the old East Antarctica craton, the accreted terranes of West Antarctica, and the oceanic lithosphere surrounded by the ring of mid-ocean ridges. We image slow areas corresponding to hot-spot regions, including a broad anomaly corresponding to recent volcanism in the Ross Sea, where the existence of a mantle plume has been proposed.
43 1 - PublicationRestrictedFull-waveform seismic tomography of the Vrancea, Romania, subduction regionThe Vrancea region is one of the few locations of deep seismicity in Europe. Seismic tomography has been able to map lithospheric downwelling, but has not been able yet to clearly discriminate between competing geodynamic interpretations of the geological and geophysical evidence available. We study the seismic structure of the Vrancea subduction zone, using adjoint-based, full-waveform tomography to map the 3D vP and vS structure in detail. We use the database that was built during the CALIXTO (Carpathian Arc Lithosphere X-Tomography) temporary experiment, restricted to the broadband sensors and local intermediate-depth events. We fit waveforms with a cross-correlation misfit criterion in separate time windows around the expected P and S arrivals, and perform 17 iterations of vP and vS model updates (altogether, requiring about 16 million CPU hours) before reaching stable convergence. Among other features, our resulting model shows a nearly vertical, high-velocity body, that overlaps with the distribution of seismicity in its northeastern part. In its southwestern part, a slab appears to dip less steeply to the NW, and is suggestive of ongoing – or recently concluded – subduction geodynamic processes. Joint inversion for vP and vS allow us to address the vP/vS ratio distribution, that marks high vP/vS in the crust beneath the Focsani sedimentary basin – possibly due to high fluid pressure – and a low vP/vS edge along the lower plane of the subducting lithosphere, that in other similar environment has been attributed to dehydration of serpentine in the slab. In spite of the restricted amount of data available, and limitations on the usable frequency pass-band, full-waveform inversion reveals its potential to improve the general quality of imaging with respect to other tomographic techniques – although at a sensible cost in terms of computing resources. Our study also shows that re-analysis of legacy data sets with up-to-date techniques may bring new, useful, information.
172 4 - PublicationRestrictedSeismic moment tensors of the April 2009, L'Aquila (Central Italy), earthquake sequence(2010-01)
; ; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekstrom, G.; Lamont-Doherty Earth Observatory Columbia University NY USA ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; ; On 2009 April 6, the Central Apennines were hit by an Mw= 6.3 earthquake. The region had been shaken since 2008 October by seismic activity that culminated in two foreshocks with Mw > 4, 1 week and a few hours before the main shock. We computed seismic moment tensors for 26 events with Mw between 3.9 and 6.3, using the Regional Centroid Moment Tensor (RCMT) scheme. Most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively. The focal mechanisms are all extensional, with a variable and sometimes significant strike-slip component. This geometry agrees with the NE–SW extensional deformation of the Apennines, known from previous seismic and geodetic observations. Events group into three clusters. Those located in the southern area have larger centroid depths and a wider distribution of T-axis directions. These differences suggest that towards south a different fault system was activated with respect to the SW-dipping normal faults beneath L’Aquila and more to the north.240 24 - PublicationRestrictedThe Moho depth map of the Antarctica region(2013)
; ; ;Baranov, A. ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Different tectonic units cover the Antarctic territory: platform, orogens and depression structures. This structural variability is reflected both in thickness and physical properties of the crust.We present a new Moho map for the Antarctica, derived from geophysical data selected from the literature. Themodel covers thewhole Antarctic region, from the South Pole out to the continental margin, including the Antarctic Peninsula. TheMoho depth is represented with a resolution of 1°×1° on a Cartesian grid obtained by an equidistant azimuthal geographical projection. A large volume of new data has been analyzed: mostly seismic experiments, as well as receiver functions and geological studies. In general,we can identify three large domainswithin the Antarctic continental crust. The oldest Archean and Proterozoic crust of East Antarctica has a thickness of 36–56 km (with an average of about 41 km). The continental crust of the Transantarctic Mountains, the Antarctic Peninsula and Wilkes Basin has a thickness of 30–40 km (with an average Moho of about 30 km). The youngest rifted continental crust of the West Antarctic Rift System has a thickness of 16–28 km (with an average Moho of about 26 km). The mean Moho depth of the whole model is 33.8 km. The new Moho model exhibits some remarkable disagreements at places with respect to global model CRUST 2.0. Difference between these two models may range up to −10/+24 km. The new model is available for download in digital format. We plan to update the model in the near future by including new data, particularly in the most poorly covered regions.330 66 - PublicationOpen AccessSeismic Anisotropy Analysis in the Victoria Land Region (Antarctica)(2010-05)
; ; ; ; ;Salimbeni, Simone; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Pondrelli, Silvia; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Danesi, Stefania; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, Andrea; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; We present shear-wave splitting results obtained from analysis of core refracted teleseismic phases recorded by permanent and temporary seismographic stations located in the Victoria Land region (Antarctica). We used eigenvalue technique to linearize the rotated and shifted shear-wave particle motion, in order to determine the best splitting parameters. A well-scattered distribution of single shear-wave measurements has been obtained. Average values show clearly that dominant fast axis direction is NE-SW oriented, accordingly with previous measurements obtained around this zone. Only two stations, OHG and STAR show different orientations, with N-S and NNWSSE main directions. On the basis of the periodicity of single shear-wave splitting measurements with respect to back-azimuths of events under study, we inferred the presence of lateral and vertical changes in the deep anisotropy direction. To test this hypothesis we have modelling waveforms using a cross-convolution technique in one and two anisotropic layer’s cases. We obtained a significant improvement on the misfit in the double layer case for the cited couple of stations. For stations where a multi-layer structure does not fit, we looked for evidences of lateral anisotropy changes at depth through Fresnel zone computation. As expected, we find that anisotropy beneath the Transantarctic Mountains (TAM) is considerably different from that beneath the Ross Sea. This feature influences the measurement distribution for the two permanent stations TNV and VNDA. Our results show a dominant NESW direction over the entire region, but other anisotropy directions are present and find an interpretation when examined in the context of regional tectonics.122 94 - PublicationOpen AccessAn atlas of Mediterranean seismicity(2004)
; ; ; ; ; ; ;Vannucci, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Argnani, A.; Geologia Marina, ISMAR-CNR, Bologna, Italy ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gasperini, P.; Dipartimento di Fisica, Università degli Studi di Bologna, Italy ;Boschi, E.; Dipartimento di Fisica, Università degli Studi di Bologna, Italy; ; ; ; ; 295 380 - PublicationOpen AccessPractical Issues in Monitoring a Hydrocarbon Cultivation Activity in Italy: The Pilot Project at the Cavone Oil Field(2021-11)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In this paper we describe the results of an experimental implementation of the recent guidelines issued by the Italian regulatory body for monitoring hydrocarbon production activities. In particular, we report about the pilot study on seismic, deformation, and pore pressure monitoring of the Mirandola hydrocarbon cultivation facility in Northern Italy. This site hosts the Cavone oil field that was speculated of possibly influencing the 2012 ML 5.8 Mirandola earthquake source. According to the guidelines, the monitoring center should analyse geophysical measurements related to seismicity, crustal deformation and pore pressure in quasi real-time (within 24–48 h). A traffic light system would then be used to regulate underground operations in case of detecting significant earthquakes (i.e., events with size and location included in critical ranges). For these 2-year period of guidelines experimentation, we analysed all different kinds of available data, and we tested the existence of possible relationship between their temporal trends. Despite the short time window and the scarce quantity of data collected, we performed the required analysis and extracted as much meaningful and statistically reliable information from the data. We discuss here the most important observations drawn from the monitoring results, and highlight the lessons learned by describing practical issues and limitations that we have encountered in carrying out the tasks as defined in the guidelines. Our main goal is to contribute to the discussion about how to better monitor the geophysical impact of this kind of anthropogenic activity. We point out the importance of a wider seismic network but, mostly, of borehole sensors to improve microseismic detection capabilities. Moreover, the lack of an assessment of background seismicity in an unperturbed situation -due to long life extraction activities- makes it difficult to get a proper picture of natural background seismic activity, which would be instead an essential reference information for a tectonically-active regions, such as Northern Italy.1137 46 - PublicationOpen AccessSeismic Anisotropy of the Victoria Land region, Antactica(2010-04-13)
; ; ; ; ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Danesi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; We present shear-wave splitting results obtained from the analysis of core refracted teleseismic phases recorded by permanent and temporary seismographic stations located in the Victoria Land region (Antarctica). We use an eigenvalue technique to isolate the rotated and shifted shear-wave particle motion, in order to determine the best splitting parameters. Average values show clearly that dominant fast axis direction is NE-SW oriented, in accordance with previous measurements obtained around this zone. Only two stations, OHG and STAR show different orientations, with N-S and NNW-SSE main directions. On the basis of the periodicity of single shear-wave splitting measurements with respect to back-azimuths of events under study, we infer the presence of lateral and vertical changes in the deep anisotropy direction. To test this hypothesis we model waveforms using a cross-convolution technique for the cases of one and two anisotropic layers. We obtain a significant improvement on the misfit in the double layer case for the two stations. For stations where a multi-layer structure does not fit, we investigate lateral anisotropy changes at depth through Fresnel zone computation. We find that anisotropy beneath the Transantarctic Mountains (TAM) is considerably different from that beneath the Ross Sea. This feature influences the measurement distribution for the two permanent stations TNV and VNDA. Our results show a dominant NE-SW direction over the entire region, but other anisotropy directions are present and maybe interpreted in the context of regional tectonics.268 498 - PublicationOpen AccessEllipticity of Rayleigh waves in basin and hard-rock sites in Northern ItalyWe measure ellipticity of teleseismic Rayleigh waves at 95 seismic stations in Northern Italy, for wave period between 10 and 110 s, using an automatic technique and a large volume of high-quality seismic recordings from over 500 global earthquakes that occurred in 2008– 2014. Northern Italy includes a wide range of crustal structures, from the wide and deep Po Plain sedimentary basin to outcropping sedimentary and crystalline rocks in the Northern Apennines and Alps. It thus provides an excellent case for studying the influence of shallow earth structure on polarization of surface waves. The ellipticity measurements show excellent spatial correlation with geological features in the region, such as high ellipticity associated with regions of low seismic velocity in the Po Plain and low ellipticity values in faster, hard rock regions in the Alps and Apennine mountains. Moreover, the observed ellipticity values also relate to the thickness of the basement, as highlighted by observed differences beneath the Alps and the Apennines. Comparison between observations and predicted ellipticity from a reference crustal model of the region show substantial fit, particularly for T ∼ 38 s data. Discrepancy for shorter wave period suggests that slight modifications of the model are needed, and that the ellipticity measurements could help to better constrain the shallow crustal structure of the region. Predictions for the Po Plain are larger than the observations by a factor of four or more and transition from retrograde to prograde Rayleigh wave motion at the surface for periods of T ∼ 10–13 s is predicted for seismic stations in the plain. Analysis of corresponding real data indicates a possible detection of teleseismic prograde particle motion, but the weak teleseismic earthquake signals are mixed with ambient noise signals at the predicted, short, transition periods. Detection of the period of polarity inversion from the joint analysis of earthquake and ambient noise ellipticity measurements may provide further, stringent, constraints on the structure of sedimentary basins.
271 173 - PublicationOpen AccessDuties and Responsibilities of the INGV-Centre for Monitoring Underground Anthropic Activities(2019-07)
; ; ; ; ; ; ; ; ; ; ; In 2014, the Italian Ministry of Economic Development published monitoring guidelines (ILG) describing in detail the governmental regulations for geophysical monitoring in areas interested by exploitation of underground potentials. The ILG prescribe the monitoring of microseismicity, ground deformation and pore pressure near the industrial activities, and direct the application of a four-stage traffic light protocol, depending on the magnitude, peak ground velocity and peak ground acceleration. In case the prescribed threshold values are exceeded, different alert levels have been scheduled, up to the limit of reduction or interruption of industrial operations. In a three-years test phase, the ILG will now be applied in a few areas involved in different exploitation activities, such as gas storage, hydrocarbon extraction and waste water reinjection, geothermal energy production. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) has recently been charged to realize multi-parametric monitoring systems in at least three of the aforementioned test areas and to provide indications about the applicability of these guidelines. INGV instituted specifically a Centre for monitoring underground anthropic activities, entrusted with the duties and responsibilities to implement the ILG at the test sites. The presentation gives a general overview about the state of the art, trying to emphasize critical situations as e.g. the problems in the magnitude calculation or the significance of the traffic light thresholds, especially in areas with multiple mining rights.94 14