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  • Articles  (6)
  • 04.06. Seismology  (6)
  • 2020-2024  (6)
  • 2020  (6)
  • 1
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    Stick-slip vs. stable sliding fault behaviour: A case-study using a multidisciplinary approach in the volcanic region of Mt. Etna (Italy) (2020)
    Elsevier
    Details
    Publication Date: 2023-10-26
    Description: In active volcanic zones, fault dynamics is considerably fast but it is often difficult to separate the pattern of nearly continuous large-scale volcanic processes (inflation/deflation processes, flank instability) from impulsive episodes such as dyke intrusions or coseismic fault displacements. At Etna, multidisciplinary studies on active faults whose activity does not strictly depend on volcanic processes, are relatively few. Here we present the case-study of the San Leonardello fault, an active structure located in the eastern flank of Mt. Etna characterised by a well-known seismic history. This fault saw renewed activity in May 2009, when pre-seismic creeping along the southern segment preceded an MW 4.0 earthquake in the northern segment, followed by some twenty-five aftershocks. Later, in March–April 2016, creep events reactivated the southern section of the same fault. Both the seismic and aseismic phenomena were recorded by the seismic and GNSS networks of INGV-Osservatorio Etneo, and produced surface faulting that left a footprint in the pattern of ground deformation detected by the InSAR measurements. We demonstrate that the integration of multidisciplinary data collected for volcano surveillance may shed light on different aspects of fault dynamics, and allow understanding how coseismic slip and creep alternate in space and time along the strike. Moreover, we use findings from our independent datasets to propose a conceptual model of the San Leonardello fault, taking into account behaviour and previous constraints from fault-based seismic hazard analyses. Although the faulting mechanisms described here occur at a very small scale compared with those of a purely tectonic setting, this case-study may represent a perfect natural lab for improving knowledge of seismogenic processes, also in other fault zones characterised by stick slip vs. stablesliding fault behaviour.
    Description: Published
    Description: 228554
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Fault ; Earthquake ; Creep ; Seismotectonics ; Behaviour ; Mt. Etna volcano ; 04.07. Tectonophysics ; 04.06. Seismology ; 04.03. Geodesy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Are normal fault earthquakes due to elastic rebound or gravitational collapse? (2020)
    Istituto Nazionale di Geofisica e Vulcanologia
    Details
    Publication Date: 2023-05-22
    Description: We discuss two competing models for explaining the ground deformation associated with normal faulting earthquake in the brittle elastic upper crust. The classic elastic rebound theory is usually applied for all tectonic settings. In normal fault earthquakes, this model would predict a horizontal stretching eventually responsible for the elastic rebound at the earthquake. However, volumes mostly subside vertically during an extensional earthquake and the collapsed ground in the hanging wall is about one order of magnitude larger than the uplifted volumes of the surrounding hanging wall and footwall. The elastic rebound model would explain this asymmetry with a high horizontal elastic compressibility of the hanging wall and footwall absorbing the coseismic push. We rather suggest that the force activating normal fault earthquakes is mostly dictated by the sliding of the hanging wall, owing gravitational potential. The much larger coseismic subsidence with respect to the uplift can be explained by the closure at depth of a diffuse network of microfractures developed during the interseismic period. Since the horizontal stretching does not exist below ~1 km of depth, with the minimum horizontal stress tensor becoming positive below that depth, the development of a normal fault can be activated only by the vertical maximum stress tensor, i.e., the lithostatic load. The common fluids expulsion at the coseismic stage requires diffuse secondary permeability in the upper crust, in agreement with the presence of a diffuse network of microfractures.
    Description: Published
    Description: SE213
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Normal fault earthquakes; Graviquakes; Lithostatic load; Coseismic deformation; Fluid expulsion ; 04.07. Tectonophysics; ; 04.06. Seismology ; Tectonics ; Structural geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Crustal Thickness Beneath the Dinarides and Surrounding Areas From Receiver Functions (2020)
    Agu
    Details
    Publication Date: 2023-10-31
    Description: Knowledge about the crustal thickness is one of the key elements in the reconstruction of the regional tectonic history. The Dinaric mountain belt is one of the most enigmatic segments of the Alpine‐Mediterranean collision zone, characterized by large variations in crustal thickness and not studied sufficiently. We present a new Moho depth map for the wider Dinarides region which was created using teleseismic earthquake recordings from 87 permanent and temporary seismic stations in the region. Teleseismic data were analyzed using the receiver function method to extract converted P to S waves. The resulting Moho topography fits well within a structural framework comprising a thicker crust under the Dinarides, which gradually becomes thinner toward the Pannonian and Adriatic domains. The profiles crossing the northwestern Dinarides are marked by a relatively sharp decrease in crustal thickness north of the main thrust front. This transition is followed by significant crustal thinning toward the Pannonian basin. The Mohorovičić discontinuity lies the deepest in the central and southern Dinarides, at depths of over 55 km. Here similarly to the northwestern segment we observe a jump in the crustal thickness when transitioning toward the Internal Dinarides, which hints at possible underthrusting (or subduction) of the Adria plate in this region. Moho depths in the transition zone toward the Pannonian basin and in the Pannonian basin proper vary between 25 and 35 km. In the Adriatic domain, we find crustal thickness ranging from 30 km to more than 45 km around the Central Adriatic islands.
    Description: Published
    Description: e2019TC005872
    Description: 1T. Struttura della Terra
    Description: 2TR. Ricostruzione e modellazione della struttura crostale
    Description: JCR Journal
    Keywords: Mohorovičić discontinuity ; crustal thickness ; Adriatic microplate ; Dinarides ; receiver functions ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Seismicity induced by massive wastewater injection near Puerto Gaitán, Colombia (2020)
    Details
    Publication Date: 2023-11-14
    Description: This article has been accepted for publication in Geophysical Journal International ©:The Author(s) 2020. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Uploaded in accordance with the publisher's self-archiving policy. All rights reserved.
    Description: Seven years after the beginning of a massive wastewater injection project in eastern Colombia, local earthquake activity increased significantly. The field operator and the Colombian Geological Survey immediately reinforced the monitoring of the area. Our analysis of the temporal evolution of the seismic and injection data together with our knowledge of the geological parameters of the region indicate that the surge of seismicity is being induced by the re-injection of produced water into the same three producing reservoirs. Earthquake activity began on known faults once disposal rates had reached a threshold of ∼2 × 106 m3 of water per month. The average reservoir pressure had remained constant at 7.6 MPa after several years of production, sustained by a large, active aquifer. Surface injection pressures in the seismically active areas remain below 8.3 MPa, a value large enough to activate some of the faults. Since faults are mapped throughout the region and many do not have seismicity on them, we conclude that the existence of known faults is not the only control on whether earthquakes are generated. Stress conditions of these faults are open to future studies. Earthquakes are primarily found in four clusters, located near faults mapped by the operator. The hypocentres reveal vertical planes with orientations consistent with focal mechanisms of these events. Stress inversion of the focal mechanisms gives a maximum compression in the direction ENE-WSW, which is in agreement with borehole breakout measurements. Since the focal mechanisms of the earthquakes are consistent with the tectonic stress regime, we can conclude that the seismicity is resulting from the activation of critically stressed faults. Slip was progressive and seismic activity reached a peak before declining to few events per month. The decline in seismicity suggests that most of the stress has been relieved on the main faults. The magnitude of a large majority of the recorded earthquakes was lower than 4, as the pore pressure disturbance did not reach the mapped large faults whose activation might have resulted in larger magnitude earthquakes. Our study shows that a good knowledge of the local fault network and conditions of stress is of paramount importance when planning a massive water disposal program. These earthquakes indicate that while faults provide an opportunity to dispose produced water at an economically attractive volume–pressure ratio, the possibility of induced seismicity must also be considered.
    Description: Servicio Geológico Colombiano (SGC)
    Description: Published
    Description: 777–791
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Keywords: Fracture and flow ; Earthquake dynamics ; Earthquake source observations ; Induced seismicity ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Pseudoprospective Evaluation of the Foreshock Traffic-Light System in Ridgecrest and Implications for Aftershock Hazard Assessment (2020)
    SSA
    Details
    Publication Date: 2023-11-16
    Description: The Mw 7.1 Ridgecrest earthquake sequence in California in July 2019 offered an opportunity to evaluate in near‐real time the temporal and spatial variations in the average earthquake size distribution (the b‐value) and the performance of the newly introduced foreshock traffic‐light system. In normally decaying aftershock sequences, in the past studies, the b‐value of the aftershocks was found, on average, to be 10%–30% higher than the background b‐value. A drop of 10% or more in “aftershock” b‐values was postulated to indicate that the region is still highly stressed and that a subsequent larger event is likely. In this Ridgecrest case study, after analyzing the magnitude of completeness of the sequences, we find that the quality of the monitoring network is excellent, which allows us to determine reliable b‐values over a large range of magnitudes within hours of the two mainshocks. We then find that in the hours after the first Mw 6.4 Ridgecrest event, the b‐value drops by 23% on average, compared to the background value, triggering a red foreshock traffic light. Spatially mapping the changes in b-values, we identify an area to the north of the rupture plane as the most likely location of a subsequent event. After the second, magnitude 7.1 mainshock, which did occur in that location as anticipated, the b‐value increased by 26% over the background value, triggering a green traffic light. Finally, comparing the 2019 sequence with the Mw 5.8 sequence in 1995, in which no mainshock followed, we find a b‐value increase of 29% after the mainshock. Our results suggest that the real‐time monitoring of b‐values is feasible in California and may add important information for aftershock hazard assessment.
    Description: Published
    Description: 2828-2842
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: 7T. Variazioni delle caratteristiche crostali e precursori sismici
    Description: 8T. Sismologia in tempo reale
    Description: JCR Journal
    Keywords: 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    Geophysical reconstruction of buried geological features and site effects estimation of the Middle Valle Umbra basin (central Italy) (2020)
    Elsevier
    Details
    Publication Date: 2023-11-14
    Description: The Middle Valle Umbra (central Italy) is a NW-SE 20 km long and 10 km wide Quaternary extensional basin located in the internal sector of the Apennine chain. This area historically experienced strong earthquakes that caused significant damages to the outstanding historical heritage. The same area has been recently hit by the 2016 seismic sequence of Amatrice-Visso-Norcia. With the aim to reconstruct the buried geological structures of the basin, a multi-technique geophysical approach was performed. An extended campaign of ambient noise measurements was carried out to investigate the subsurface setting, and to identify the main geological units. We performed three 2D passive arrays to analyze two different sites within the basin; their aperture was between 150 and 752 m for one site and of 48 m for the other site, to characterize the geological units in terms of sediment thickness and shear-wave velocity profile. Data collected were processed with f-k and MSPAC analysis to extract dispersion curves with good resolution in a frequency range of 0.5–10 Hz and 4.5–18 Hz for the two sites respectively. Spectral ratios were computed for every single station ambient noise measurement performed and for all the stations of the bigger array. Our final target is to extend these results to the whole valley, in order to retrieve the attitude of the main geological units and propose a reliable reconstruction of the subsurface geometry of the basin. Another point of this work is to evaluate the site response in the middle of the valley through the analysis of the earthquakes recorded by the accelerometric station IT.CSA (belonging to the Italian Civil Protection) and the corresponding recordings of the nearby rock station IT.ASS.
    Description: Published
    Description: id 105543
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: site effects ; seismic site characterization ; subsoil model ; spectral ratios ; Valle Umbra ; passive arrays ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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