1,721,058 research outputs found
Recorded displacements in a landslide slope due to regional and teleseismic earthquakes
No full textRegional and teleseismic earthquakes can induce displacements along joints in a landslideinvolved rocky slope in Central Italy. The rarity of these effects is due to specific physical properties of the seismic signals associated with: (i) the energy content, (ii) the distribution of relative energy and peak of ground acceleration related to the ground motion components and (iii) the spectral amplitude distribution in the frequency domain; these properties allow the triggering earthquakes to be distinguished from the others. The observed effects are relevant when compared to the direction of the landslide movement and the dimensions of the involved rock mass volume. The landslide movement is less constrained in the direction parallel to the dip of the slope and the landslide dimensions are associated with characteristic periods that control the landslide deformational response in relation to the spectral content of the ground motion. The earthquake-induced displacements are significant because they have the same order of magnitude as the average annual cumulative displacement based on a decade of strain measurements within the slope. © The Author 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society
Engineering geological zonation of a complex landslide system through seismic ambient noise measurements at the Selmun Promontory (Malta)
No full textThe cliff slope of the Selmun Promontory, located in the Northern part of the island of Malta (Central Mediterranean Sea) close to the coastline, is involved in a landslide process as exhibited by the large block-size talus at its bottom. The landslide process is related to the geological succession outcropping in the Selmun area, characterized by the overposition of a grained limestone on a plastic clay, that induces a lateral spreading phenomenon associated with detachment and collapse of different-size rock blocks. The landslide process shapes a typical landscape with a stable plateau of stiff limestone bordered by an unstable cliff slope. The ruins of Ghajn Hadid Tower, the first of the 13 watchtowers built in 1658 by the Grand Master Martin de Redin, stand out on the Selmun Promontory. The conservation of this important heritage site, already damaged by an earthquake which struck the Maltese Archipelago on 1856 October 12, is currently threatened by a progressive retreat of the landslide process towards the inland plateau area. During 2015 and 2016, field surveys were carried out to derive an engineering geological model of the Selmun Promontory. After a highresolution geomechanical survey, the spatial distribution of the joints affecting the limestone was obtained. At the same time, 116 single-station noise measurements were carried out to cover inland and edge of the limestone plateau as well as the slope where the clays outcrop. The obtained 1-hour time histories were analysed through the horizontal to vertical spectral ratio technique, as well as polarization and ellipticity analysis of particle motion to define the local seismic response in zones having different stability conditions, that is, related to the presence of unstable rock blocks characterized by different vibrational modes. The results obtained demonstrate the suitability of passive seismic geophysical techniques for zoning landslide hazard in case of rock slopes and prove the relevance of anisotropies in conditioning the polarization of vibrational modes for dislodged rock masses. © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society
Experiment of an innovative nanoseismic monitoring applied to gravity-induced slope instabilities in a karstified rock mass
No full textThe Peschiera Springs slope (RI), which hosts the drainage plant of the Rome's aqueduct, is affected by a gravitational slope deformation process, that is responsible for a rock-mass lateral spreading, associated to several landforms including sinkholes, subvertical scarps and trenches. An experiment, based on an innovative method of monitoring, was carried out to record microseismic events generated by underground instabilities such as failures and collapses. At this aim a SNS (Seismic Navigation System) array was installed during the year 2013 inside a the tunnel of the drainage plant in order to carry out a continuous monitoring. The nanoseismic monitoring, allowed to record 37 microseismic events. The seismic records were managed by NanoseismicSuite software that allowed to identify and characterize two different typologies of events: 19 underground collapses and 18 underground failures. The locations of these events are in good agreement with the evolutionary geological model of the ongoing gravitational slope deformation, i.e. with the spatial distribution of the main trenches and scarps on the slope. © Società Geologica Italiana, Roma 2015
Rock Mass Characterization Coupled with Seismic Noise Measurements to Analyze the Unstable Cliff Slope of the Selmun Promontory (Malta)
No full textIn the Mediterranean area, cliff slopes represent widespread high-risk landforms as they are highly frequented touristic places often interested by landslide processes. Malta represents a significant case study as several cliffs located all around the island are involved in instability processes, as evidenced by wide block-size talus distributed all along the coast line. These diffused instabilities are related to the predisponding geological setting of Malta Island, i.e. the over-position of grained limestone on plastic clay deposits, that induces lateral spreading phenomena associated to falls and topples of different-size rock blocks and is responsible for a typical landscape with stable plateau of stiff rocks bordered by unstable cliff slopes. The ruins of GLatin small letter h with strokeajn adid Tower, the first of the thirteen watchtowers built in 1658 by the Gran Master Martin de Redin, stand out in the Selmun area. Currently the safety of this important heritage site, already damaged by an earthquake on October 12th 1856, is threaten by a progressive moving of the landslide process towards the stable plateau area. During autumn 2015, a field-campaign was realized to characterize the jointed rock mass. A detailed engineering-geological survey was carried out to reconstruct the geological setting and to define the mechanical properties of the rock mass. Based on the surveyed joint spatial distribution, 58 single-station noise measurements were deployed to cover both the unstable zone and the stable area. The obtained 1-hour records were analyzed in the frequency domain for associating vibrational evidences to different instability levels, i.e. deriving the presence of already isolated blocks by the local seismic response. The here presented results can be a useful contribute to begin to asses defense strategies for the Selmun Promontory, in the frame of managing the landslide risk in the study area and preserving the local historical heritage. © 2017 The Authors
High-resolution geological model of the gravitational deformation affecting the western slope of Mt. Epomeo (Ischia)
No full textThe recent geological history of Ischia Island is characterized by slope-scale gravitational deformations closely related to volcano-tectonic dynamics of the Mt. Epomeo resurgent caldera. This study focuses on the gravitational deformation that involves alkali-trachytic lava and trachytic ignimbrite flow-units of Mt. Nuovo, located in the western portion of Mt. Epomeo. A preliminary, high-resolution engineering-geological model was obtained through geological, geomorphological and geophysical surveys and reveals a complex morpho-structure with geomorphological evidence of gravitational instability. The complexity of the ongoing slope deformations is confirmed by field geo-structural evidences that led to the identification of a multiple compound mechanism with a main rupture surface which is about 200 m deep. This geometry was better constrained by passive seismic investigations consisting in noise measurements, focused on resonance frequencies of the soil (i.e. based on H/V Nakamura approach). In addition, a close relationship between the outcrop of Mt. Epomeo Green Tuff breccia layers and the distribution of hydrothermal emissions and gas vent can be inferred, as it is related to the higher permeability of the breccia layers with respect to the main Mt. Epomeo Green Tuff flow unit, where the ascent path of deep hydrothermal fluids developed along faults and fracture networks. © Società Geologica Italiana, Roma 2015
Integrated seismic monitoring system in a major aqueduct infrastructure
No full textAn integrated monitoring system is operative in the Peschiera Springs slope (Central Apennines, Italy) to manage the landslide risk related to the plant of Rome aqueducts. Since 2008, an accelerometric network has been operating in order to integrate the stress-strain monitoring system. Nowadays about 1300 microseismic signals due to instabilities have been recorded; these events can be distinguished in failures and collapses. Whereas the failures are related to the rock mass deformation, the collapses are mainly associated with the aquifer discharge changes (about 16-21 m3/s). A Control Index (CI), based on the frequency of occurrence and the cumulative energy of the recorded local instabilities was tested for providing three levels of alert. In 2014, a nanoseismic array (Seismic Navigation System) was installed inside the drainage plant that is contributing to identify sequences of microseismic prefailure events, allowing to assess the related landslide hazard. © 2016 Associazione Geotecnica Italiana, Rome, Italy
Detection of nanoseismic events related to slope instabilities in the quarry district of coreno ausonio (Italy)
No full textNanoseismic monitoring is a passive geophysical technique used to identify and locate weak seismic events (down to local magnitudes, ML, around -3). This technique was applied in the open-pit quarry district of Coreno Ausonio (central Italy) to detect possible gravity-induced slope instabilities resulting from quarry rock blasting. After identifying an active quarry, an engineering-geological survey was carried out to characterise the jointed rock mass on an abandoned wall in front of the quarry. Four main joint sets were surveyed and their geometric and mechanical properties were measured in order to carry out stability analyses that evidenced scarce proneness to failure of the investigated wall. The analysis of seismic records obtained during three monitoring surveys, performed through the NanoseismicSuite software, made it possible to detect and characterise 15 blasts, of which 3 from the reference quarry and 12 from nearby quarries within the district, as well as 27 weak slope instability events (23 collapses and 4 failures). While failures originated from different areas of the quarry district, collapses occurred in a site characterised by an abandoned quarry having a wall more prone to gravity-induced instabilities than the one previously characterised. © Sapienza Università Editrice
Microseismicity related to gravity-induced slope deformations for risk management
No full textAn accelerometric array installed on 4 September 2008, has been used to manage the geological risk in the Peschiera Springs drainage plant of Rome's aqueduct, located in the Central Apennines approximately 80 km from Rome, Italy. The plant occupies a carbon-atic slope that is extensively involved in gravitational deformations, which are responsible for underground failures such as cracks and collapses of karst caves. To distinguish among different types of recorded events, an automated procedure was implemented taking into account duration, peak of ground acceleration (PGA) and its variation within the accelerometric array. The main sequence of underground failures so far recorded was related to the L'Aquila seismic sequence occurred in April 2009. Moreover, a very intense sequence of underground failures occurred in September 2011 that was not related to seismic events, i.e. only due to the gravitational processes affecting the slope. These evidences prove that the ongoing gravitational slope deformations have a key role in predisposing and/or causing the underground failures within the karst rock mass of the Peschiera Spring slope. A control index (CI) is daily computed as a function of sub-indexes which are derived from the rate of cumulative Arias intensity of underground failures, the frequency of underground failures and the frequency of earthquakes. The CI index identifies "ordinary", "alert" or "emergency" levels of attention and represents a fundamental tool for managing the geological risk associated with the deformational process affecting the drainage plant. © 2013 Sapienza Università Editrice
Preliminary results of vibration modes induced by forced dynamic shaking in a quarry rock wall
No full textSeismic response of the geologically complex alluvial valley at the "europarco business park" (rome - italy) through instrumental records and numerical modelling
No full textThe analysis of the local seismic response in the "Europarco Business Park", a recently urbanized district of Rome (Italy) developed over the alluvial valley of the "Fosso di Vallerano" stream, is here presented. A high-resolution geological model, reconstructed over 250 borehole log-stratigraphies, shows a complex and heterogeneous setting of both the local Plio- Pleistocene substratum and the Holocene alluvia. The local seismo-stratigraphy is derived by a calibration process performed through 1D numerical modelling, accounting for: i) 55 noise measurements, ii) 10 weak motion records obtained through a temporary velocimetric array during the August 2009 L'Aquila- Gran Sasso seismic sequence and iii) one cross-hole test available from technical report. Based on the reconstructed seismostratigraphy, the local seismic bedrock is placed at the top of a gravel layer that is part of the Pleistocene deposits and it does not correspond to the local geological bedrock represented by Plio-Pleistocene marine deposits. 1D amplifcation functions were derived via numerical modelling along three representative sections that show how in the Fosso di Vallerano area two valleys converge into a single one moving from SE toward NW. The obtained results reveal a main resonance at low frequency (about 0.8 Hz) and several higher resonance modes, related to the local geological setting. Nonlinear effects are also modelled by using strong motion inputs from the offcial regional dataset and pointed out a general down-shift (up to 0.5 Hz) of the principal modes of resonance as well as an amplitude reduction of the amplifcation function at frequencies higher than 7 Hz. © Sapienza Università Editrice
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