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Collettini, Cristiano
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Collettini, Cristiano
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cristiano.collettini@uniroma1.it
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- PublicationOpen AccessFluid overpressure as the triggering mechanism for the seismicity of the Northern Apennines: constraints from field and laboratory data(2007-09-25)
; ; ; ;De Paola, N.; Univ. Perugia, Italy ;Collettini, C.; Univ. Perugia, Italy ;Faulkner, D.; Univ. Liverpool, UK; ; ;; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italiasee Abstract Volume134 160 - PublicationOpen AccessPhysical properties of seismogenic Triassic evaporites in the northern Appennines (Central Italy)(2007-09-25)
; ; ; ; ;Trippetta, F.; Univ. Perugia, Italy ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Collettini, C.; Univ. Perugia, Italy ;Meredith, P.; UCL, UK; ; ; ; ; ; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bernabé, Y.see Abstract Volume115 596 - PublicationOpen AccessFabric controls fault stability in serpentinite gouges(2023)
; ; ; ; ; ; ; ; ; ; ; ; ;Serpentinites are polymineralic rocks distributed almost ubiquitously across the globe in active tectonic regions. Magnetite-rich serpentinites are found in the low-strain domains of serpen- tinite shear zones, which act as potential sites of nucleation of unstable slip. To assess the potential of earthquake nucleation in these materials, we investigate the link between me- chanical properties and fabric of these rocks through a suite of laboratory shear experiments. Our experiments were done at room temperature and cover a range of normal stress and slip velocity from 25 to 100 MPa and 0.3 to 300 μm s −1 , respecti vel y. We show that magnetite-rich serpentinites are ideal materials since they display strong sensitivity to the loading rate and are susceptible to nucleation of unstable slip, especially at low forcing slip velocities. We also aim at the integration of mechanical and microstructural results to describe the underlying mechanisms that produce the macroscopic behaviour. We show that mineralogical composi- tion and mineral structure dictates the coexistence of two deformation mechanisms leading to stable and unstable slip. The weakness of phyllosilicates allows for creep during the interseis- mic phase of the laboratory seismic cycle while favouring the restoration of a load-bearing granular framework, responsible of the nucleation of unstable events. During dynamic slip, fault zone shear fabric determines the mode of slip, producing either asymmetric or Gaussian slip time functions for either fast or slow events. We report rate/state friction parameters and integrate our mechanical data with microstructural observations to shed light on the mech- anisms dictating the complexity of laborator y ear thquakes. We show that mineralogical and fabric heterogeneities control fault slip behaviour.87 11 - PublicationOpen AccessOn the evolution of elastic properties during laboratory stick-slip experiments spanning the transition from slow slip to dynamic rupture(2016-12)
; ; ; ; ; ; ; ; ; ; ; The physical mechanisms governing slow earthquakes remain unknown, as does the relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes and related quasi‐dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration. We reproduced the full spectrum of slip behavior, from slow to fast stick slip, by altering the elastic stiffness of the loading apparatus (k) to match the critical rheologic stiffness of fault gouge (kc). Our experiments show an evolution from stable sliding, when k > kc, to quasi‐dynamic transients when k ~ kc, to dynamic instabilities when k < kc. To evaluate the microphysical processes of fault weakening we monitored variations of elastic properties. We find systematic changes in P wave velocity (Vp) for laboratory seismic cycles. During the coseismic stress drop, seismic velocity drops abruptly, consistent with observations on natural faults. In the preparatory phase preceding failure, we find that accelerated fault creep causes a Vp reduction for the complete spectrum of slip behaviors. Our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults, depending on frictional properties. In agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by Vp changes during the seismic cycle. The observed reduction in Vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high‐resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors.400 132 - PublicationRestrictedThe mechanical paradox of low-angle normal faults: Current understanding and open questions(2011)
; ;Collettini, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, ItaliaLow-angle normal faults, LANF, (dip b 30°) have been proposed as key-structures for accommodating crustal Fault mechanics blocks affected by brittle processes. LANF act as preferential channels for fluid flow and in some cases they Seismicity promoted fluid overpressure. Fluid–rock interactions along some detachments favour the development of extension. In contrast, frictional fault reactivation theory predicts that slip on LANF is extremely unlikely: this prediction is consistent with the absence of moderate-to-large earthquakes on normal faults dipping less than 30°. In order to discuss this discrepancy I will analyse and integrate: 1) geological data from 9 LANF, 2) the dip- range of earthquake-ruptures in extensional environments, and 3) frictional fault mechanics. LANF fault zone structure is represented by two end members: a) a thick mylonitic shear zone superposed by cataclastic processes and some localization; 2) a discrete fault core separating hangingwall and footwall phyllosilicates that in general are characterised by low frictional strength, μb0.4, and inherently stable, velocity-strengthening frictional behaviour. The low friction coefficient of the phyllosilicates can explain movements on LANF and the velocity strengthening behaviour of the phyllosilicates implies fault creep and therefore can be used to explain the absence of moderate-to-large earthquakes on LANF in seismological records. However in my view, the integration of the three datasets does not provide a simple mechanical solution for the LANF paradox since it leaves two important open questions. First a widespread development of phyllosilicates does not seem to be a common feature for most of the exhumed LANF that on the contrary show the typical fault rocks of the brittle and seismogenic crust. Second, although some brittle detachments reactivated pre-existing ductile shear zones, others formed as gently dipping structures within a brittle crust characterised by a vertical σ1: a well constrained mechanical explanation for this second class of structures is lacking.136 38 - PublicationOpen AccessFault structure and slip localization in carbonate-bearing normal faults: An example from the Northern Apennines of Italy(2014)
; ; ; ; ; ; ; ; ; ;Collettini, C.; Dipartimento di Scienze della, Terra Università La Sapienza di Roma, ;Carpenter, B. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Viti, C.; Dipartimento di Scienze della Terra Università degli Studi di Siena, ;Cruciani, F.; Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, ;Mollo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Tesei, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Trippetta, F.; Uni Sapienza ;Valoroso, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Chiaraluce, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; ; ; ; ; ; ; ; Carbonate-bearing normal faults are important structures for controlling fluid flow and seismogenesis within the brittle upper crust. Numerous studies have tried to characterize fault zone structure and earthquake slip processes along carbonate-bearing faults. However, due to the different scales of investigation, these studies are not often integrated to provide a comprehensive fault image. Here we present a multi-scale investigation of a normal fault exhumed from seismogenic depths. The fault extends for a length of 10 km with a maximum width of about 1.5 km and consists of 5 sub-parallel and interacting segments. The maximum displacement (370e650 m) of each fault segment is partitioned along sub-parallel slipping zones extending for a total width of about 50 m. Each slipping zone is characterized by slipping surfaces exhibiting different slip plane phenomena. Fault rock development is controlled by the protolith lithology. In massive limestone, moving away from the slip surface, we observe a thin layer (<2 cm) of ultracataclasite, cataclasite (2e10 cm) and fault breccia. In marly limestone, the fault rock consists of a cataclasite with hydrofractures and smectite-rich pressure solution seams. At the micro-nanoscale, the slip surface consists of a continuous and thin (<300 mm) layer composed of coarse calcite grains (~5e20 mm in size) associated with sub-micrometer grains showing fading grain boundaries, voids and/or vesicles, and suggesting thermal decomposition processes. Micrometer-sized calcite crystals show nanoscale polysynthetic twinning affected by the occurrence of subgrain boundaries and polygonalized nanostructures. Investigations at the kilometres-tens of meter scale provide fault images that can be directly compared with high-resolution seismological data and when combined can be used to develop a comprehensive characterization of seismically active fault structures in carbonate lithologies. Micro and nanoscale investigations along the principal slipping zone suggest that different deformation processes, including plastic deformation and thermal decomposition, were active during seismic slip.392 602 - PublicationRestrictedAftershocks driven by a high-pressure CO2 source at depth(2004-02-19)
; ; ; ; ; ; ;Miller, S. A.; Institute of Geophysics, Swiss Federal Institute of Technology (ETH), 8093 Zu¨rich,Institute of Geophysics, Swiss Federal Institute of Technology (ETH), 8093 Zu¨rich,Switzerland ;Collettini, C.; Universita` degli Studi di Perugia, Perugia, 06100 Italy ;Chiaraluce, L.; Instituto Nazionale di Geofisica e Vulcanologia, Rome, 00143 Italy ;Cocco, M.; Instituto Nazionale di Geofisica e Vulcanologia, Rome, 00143 Italy ;Barchi, M.; Universita` degli Studi di Perugia, Perugia, 06100 Italy ;Kaus, B. J. P.; Geology Institute, Swiss Federal Institute of Technology (ETH), 8092 Zu¨rich,Switzerland; ; ; ; ; In northern Italy in 1997, two earthquakes of magnitudes 5.7 and 6 (separated by nine hours) marked the beginning of a sequence that lasted more than 30 days, with thousands of aftershocks including four additional events with magnitudes between 5 and 6. This normal-faulting sequence is not well explained with models of elastic stress transfer1,2, particularly the persistence of hanging-wall seismicity3 that included two events with magnitudes greater than 5. Here we show that this sequence may have been driven by a fluid pressure pulse generated from the coseismic release of a known deep source4 of trapped high-pressure carbon dioxide (CO2). We find a strong correlation between the high-pressure front and the aftershock hypocentres over a twoweek period, using precise hypocentre locations5 and a simple model of nonlinear diffusion. The triggering amplitude (10– 20MPa) of the pressure pulse overwhelms the typical (0.1– 0.2MPa) range from stress changes in the usual stress triggering models1,6. We propose that aftershocks of large earthquakes in such geologic environments may be driven by the coseismic release of trapped, high-pressure fluids propagating through damaged zones created by the mainshock. This may provide a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow.457 27 - PublicationRestrictedDevelopment of interconnected talc networks and weakening of continental low-angle normal faults(2009-06)
; ; ; ; ;Collettini, C.; University of Perugia ;Viti, C.; University of Siena ;Smith, S .A. F; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Holdsworth, R. E.; University of Durham; ; ; Fault zones that slip when oriented at large angles to the maximum compressive stress, i.e., weak faults, represent a signifi cant mechanical problem. Here we document fault weakening induced by dissolution of dolomite and subsequent precipitation of calcite + abundant talc along a low-angle normal fault. Within the fault core, talc forms an interconnected foliated network that deforms by frictional sliding along 50–200-nm-thick talc lamellae. The low frictional strength of talc, combined with dissolution-precipitation creep, can explain slip on low-angle normal faults. In addition, the stable sliding behavior of talc is consistent with the absence of strong earthquakes along such structures. The development of phyllosilicates such as talc by fl uid-assisted processes within fault zones cutting Mg-rich carbonate sequences may be widespread, leading to profound and long-term fault weakness.170 26 - PublicationRestrictedConnecting seismically active normal faults with Quaternary geological structures in a complex extensional environment: The Colfiorito 1997 case history (northern Apennines, Italy)(2005-01-15)
; ; ; ; ; ;Chiaraluce, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Barchi, M.; Geologia Strutturale e Geofisica, Dipartimento di Scienze della Terra, Universita` di Perugia, Perugia, Italy ;Collettini, C.; Geologia Strutturale e Geofisica, Dipartimento di Scienze della Terra, Universita` di Perugia, Perugia, Italy ;Mirabella, F.; Geologia Strutturale e Geofisica, Dipartimento di Scienze della Terra, Universita` di Perugia, Perugia, Italy ;Pucci, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; The northern Apennines of Italy are characterized by a complex Tertiary tectonic history, where superposed compressional and extensional deformation occurred. In such regions, characterized by low active extensional strain rate, the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between ‘‘geological’’ faults (i.e., faults which can be mapped at the surface) and ‘‘seismological’’ faults (i.e., faults which actually generate earthquakes). The availability of detailed geological mapping and high-resolution seismological data for the Colfiorito area, struck in 1997 by a sequence of six 5 < Mw 6 normal faulting earthquakes, allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological Quaternary faults and the activated structures. In map view, the earthquakes distribution reflects the fault pattern mapped at the surface, the length of activated and mapped faults is quite similar (7–10 km), the coseismic subsided region imaged by interferometric synthetic aperture radar data, is located in the hanging wall of the mapped normal faults that bound the Quaternary basins. In section view, there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth. Comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency. This study points out that the Quaternary tectonosedimentary evolution and the present-day geological and geomorphologic setting of the Colfiorito area can be interpreted as the result of repeated, extensional earthquakes, similar to the 1997 events, occurring on NW-SE trending normal faults. Our data also show that the main shocks of the Colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional/transpressional structures, which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size.275 24 - PublicationOpen AccessSlow-to-fast transition of giant creeping rockslides modulated by undrained loading in basal shear zones(2020)
; ; ; ; ; ; ; Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. They creep slowly for centuries and then can fail catastrophically posing major threats to society. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse remain elusive. We couple laboratory experiments on natural rockslide shear zone material and in situ observations to provide a scale-independent demonstration that short-term pore fluid pressure variations originate a full spectrum of creep styles, modulated by slip-induced undrained conditions. Shear zones respond to pore pressure increments by impulsive acceleration and dilatancy, causing spontaneous decel- eration followed by sustained steady-rate creep. Increasing pore pressure results in high creep rates and eventual collapse. Laboratory experiments quantitatively capture the in situ behavior of giant rockslides and lay physically-based foundations to understand the collapse of giant rockslides.66 5