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De Paola, N.
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- PublicationOpen AccessRock and fault rheology explain differences between on fault and distributed seismicityAnalysis of seismicity can illuminate active fault zone structures but also deformation within large volumes of the seismogenic zone. For the Mw 6.5 2016-2017 Central Italy seismic sequence, seismicity not only localizes along the major structures hosting the mainshocks (on-fault seismicity), but also occurs within volumes of Triassic Evaporites, TE, composed of alternated anhydrites and dolostones. These volumes of distributed microseismicity show a different frequency-magnitude distribution than on-fault seismicity. We interpret that, during the sequence, shear strain-rate increase, and fluid overpressure promoted widespread ductile deformation within TE that light-up with distributed microseismicity. This interpretation is supported by field and laboratory observations showing that TE background ductile deformation is complex and dominated by distributed failure and folding of the anhydrites associated with boudinage hydro-fracturing and faulting of dolostones. Our results indicate that ductile crustal deformation can cause distributed microseismicity, which obeys to different scaling laws than on-fault seismicity occurring on structures characterized by elasto-frictional stick-slip behaviour.
24 6 - PublicationRestrictedCalibration and validation of reservoir models: the importance of high resolution, quantitative outcrop analogues(2009)
; ; ; ; ; ; ; ; ; ;Jones, R. R.; Geospatial Research Limited, University of Durham ;McCaffrey, K. J. W.; University of Durham ;Imber, J; University of Durham ;Wightman, R.; University of Durham ;Smith, S. A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Holdsworth, R. E.; University of Durham ;Clegg, P.; GeoPressure Technology Ltd. ;De Paola, N.; University of Durham ;Healy, D.; University of Durham; ; ; ; ; ; ; ; Rapidly developing methods of digital acquisition, visualization and analysis allow highly detailed outcrop models to be constructed, and used as analogues to provide quantitative information about sedimentological and structural architectures from reservoir to subseismic scales of observation. Terrestrial laser-scanning (lidar) and high precision Real-Time Kinematic GPS are key survey technologies for data acquisition. 3D visualization facilities are used when analysing the outcrop data. Analysis of laser-scan data involves picking of the point-cloud to derive interpolated stratigraphic and structural surfaces. The resultant data can be used as input for object-based models, or can be cellularized and upscaled for use in grid-based reservoir modelling. Outcrop data can also be used to calibrate numerical models of geological processes such as the development and growth of folds, and the initiation and propagation of fractures.165 24 - PublicationRestrictedFault lubrication and earthquake propagation in thermally unstable rocks(2011)
; ; ; ; ; ; ;De Paola, N.; Durham University, ;Hirose, T.; Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe-otsu, Kochi 783-8502, Japan ;Mitchell, T.; Experimental Geophysics Laboratory, Institute for Geology, Mineralogy, and Geophysics, Ruhr-University Bochum, D-44780 Bochum, Germany ;Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Viti, C.; Dipartimento di Geoscienze, Università degli Studi di Padova, Via Giotto 1, Padua 35137, Italy ;Shimamoto, T.; Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 1-3-1, Kagami-yama, Higashi-Hiroshima 739-8526, Japan; ; ; ; ; Experiments performed on dolomite or Mg-calcite gouges at seismic slip rates (v > 1 m/s) and displacements (d > 1 m) show that the frictional coeffi cient μ decays exponentially from peak values (mp ≈ 0.8, in the Byerlee’s range), to extremely low steady-state values (μss ≈ 0.1), attained over a weakening distance Dw. Microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products (periclase and lime or portlandite) were produced in the slip zone during the transient stage (d < Dw). These observations, integrated with CO2 emissions data recorded during the experiments, suggest that particle interaction in the slip zone produces fl ash temperatures that are large enough to activate chemical and physical processes, e.g., decarbonation reactions (T = 550 C). During steady state (d ≥ Dw), shear strength is very low and not dependent upon normal stresses, suggesting that pressurized fl uids (CO2) may have been temporarily trapped within the slip zone. At this stage a continuous layer of nanoparticles is developed in the slip zone. For d >> Dw, a slight but abrupt increase in shear strength is observed and interpreted as due to fl uids escaping the slip zone. At this stage, dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone. Experimentally derived seismic source parameter Wb (i.e., breakdown work, the energy that controls the dynamics of a propagating fracture) (1) matches Wb values obtained from seismological data of the A.D. 1997 M6 Colfi orito (Italy) earthquakes, which nucleated in the same type of rocks tested in this study, and (2) suggests similar earthquake-scaling relationships, as inferred from existing seismological data sets. We conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms, which are activated or inhibited by physicochemical reactions in the slip zone.152 22 - PublicationRestrictedFault weakening due to CO2 degassing in the Northern Apennines: short- and long-term processes(2008)
; ; ; ; ; ; ;Collettini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita` 1, 06100 Perugia, Italy ;Cardellini, C.; Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita 1, 06100 Perugia ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;De Paola, N.; 1Dipartimento di Scienze della Terra, Universita` di Perugia, Piazza dell’Universita1, 06100 Perugia ;Holdsworth, R. E.; Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK ;Smith, S. A. F.; Reactivation Research Group, Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK; ; ; ; ; The influx of fluids into fault zones can trigger two main types of weakening process that operate over different timescales and facilitate fault movement and earthquake nucleation. Short- and long-term weakening mechanisms along faults require a continuous fluid supply near the base of the brittle crust, a condition satisfied in the extended/extending area of the Northern Apennines of Italy. Here carbon mass balance calculations, coupling aquifer geochemistry to isotopic and hydrological data, define the presence of a large flux (c. 12 160 t/day) of deep-seated CO2 centred in the extended sector of the area. In the currently active extending area, CO2 fluid overpressures at 85% of the lithostatic load have been documented in two deep (4–5 km) boreholes. In the long-term, field studies on an exhumed regional low-angle normal fault show that, during the entire fault history, fluids reacted with fine-grained cataclasites in the fault core to produce aggregates of weak, phyllosilicate-rich fault rocks that deform by fluid assisted frictional–viscous creep at sub-Byerlee friction values (m , 0.3). In the short term, fluids can be stored in structural traps, such as beneath mature faults, and stratigraphical traps such as Triassic evaporites. Both examples preserve evidence for multiple episodes of hydrofracturing induced by short-term cycles of fluid pressure build-up and release. Geochemical data on the regional-scale CO2 degassing process can therefore be related to field observations on fluid rock interactions to provide new insights into the deformation processes responsible for active seismicity in the Northern Apennines234 37 - 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 - PublicationRestrictedFault lubrication during earthquakes(2011-03-24)
; ; ; ; ; ; ; ; ; ;Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Han, R.; Korea Inst Geosci & Mineral Resources, Taejon 305350, South Korea ;Hirose, T.; JAMSTEC, Kochi Inst Core Sample Res, Kochi 7838502, Japan ;De Paola, N.; Univ Durham, Dept Earth Sci, Durham DH1 3LE, England ;Nielsen, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mizoguchi, K.; Cent Res Inst Elect Power Ind, Civil Engn Res Lab, Chiba 2701194, Japan ;Ferri, F.; Univ Padua, Dipartimento Geosci, I-35131 Padua, Italy ;Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Shimamoto, T.; China Earthquake Adm, Inst Geol, Beijing 100029, Peoples R China; ; ; ; ; ; ; ; The determination of rock friction at seismic slip rates (about 1 m s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip(1). Given the difficulty in determining friction by seismological methods(1), elucidating constraints are derived from experimental studies(2-9). Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built(4-6), quartz-built(3) and carbonate-built(7,8)) rocks and non-cohesive rocks (clay-rich(9), anhydrite, gypsum and dolomite(10) gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger(11,12) a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates(13,14) suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.253 47 - PublicationOpen AccessLithological and stress anisotropy control large-scale seismic velocity variations in tight carbonates(2021-05-04)
; ; ; ; ; ; ; ; ; ; ; Our knowledge of subsurface structures often derives from seismic velocities that are measured during seismic acquisition surveys. These velocities can greatly change due to lithological, fracture frequencies and/or effective pressure/temperature variations. However, the influence of such intrinsic lithological properties and environmental conditions at the large scale is poorly understood due to the lack of comprehensive datasets. Here, we analyze 43 borehole-derived velocity datasets of 3 end-member tight carbonate sequences from Central Italy, including massive pure limestone (Calcare Massiccio, CM), thick-layered (20-50 cm) pure limestone (Maiolica, MA), and thin-layered (2-20 cm) marly limestone (Calcareous Scaglia, CS). Our results show that the main rock parameters and environmental conditions driving large scale velocity variations are bedding and paleostresses, while mineralogical composition and current tectonic stress also play a role. For each of the 3 end-members, measured VP values vary differently with depth, as the thin-layered CS units show a clear increase in Vp, while velocity slightly increases and remains constant for the thick-layered MA and massive CM units, respectively. Such observations show that velocities are affected by specific characteristics of lithological discontinuities, such as the thickness of bedding. Counterintuitively, larger Vp values were recorded in the deformed mountain range than in the undeformed foreland suggesting that higher paleo-stresses increase velocity values by enhancing diagenesis and healing of discontinuities. Our results thus demonstrate that large scale velocity variations are strictly related to variation of lithological properties and to the geological and tectonic history of an area. We suggest that such lithological and environmental controls should be taken into account when developing velocity and mechanical models for tectonically active regions of the Mediterranean Area, where earthquakes mostly nucleate and propagate through carbonate formations, and for resource exploration in fractured carbonate reservoirs.40 14 - PublicationRestrictedThe geochemical signature caused by earthquake propagation in carbonate-hosted faults(2011)
; ; ; ; ; ; ;De Paola, N.; Rock Mechanics Laboratory, Earth Sciences Department, University of Durham, South Road, DH1 3LE Durham, UK ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Hirose, T.; Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan ;Cardellini, C.; Dipartimento di Scienze della Terra, Università di Perugia, Piazza Università, 06123 Perugia, Italy ;Caliro, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Shimamoto, T.; Institute of Geology, China Earthquake Administration, Beijing, China; ; ; ; ; Friction laboratory experiments have been performed at sub-seismic (≈ 0.01 m/s) to seismic slip rates (N1 m/s) on dolomite gouges of the Triassic evaporites, which hosted the five mainshocks (5bMw b6) of the 1997 Colfiorito earthquakes in the Northern Apennines (Italy). Experimental faults are lubricated as marked falls of the steady state sliding friction coefficients, μss≈0.2, are observed at seismic slip rates, as opposed to values of μss≥0.6 attained for sub-seismic slip rates. At seismic slip rates decarbonation reactions, triggered by frictional heating in the experimental slip zone, produced: 1) new fluid (CO2) and mineral phases (e.g. Mg-calcite, periclase/brucite, lime/portlandite); 2) isotopic fractionation between the reaction products and the reactant mineral phases. The variations of total dissolved inorganic carbon (TIDC) in concentration Δ(TDIC) and isotopic composition Δ(δ13CTIDC) in a carbonate aquifer, with geochemical parameters similar to those of an aquifer located in the seismic belt of the Northern Apennines, have been modelled after an input of earthquake-produced CO2. Modelling results show that variation in Δ(δ13CTIDC) can be detected in volumes of groundwater which are about three times larger than those calculated for the variations in Δ(TDIC). For amounts of CO2 produced by coseismic decarbonation of ≤5 wt.% of the slip zone gouge, modelling results show that a detectable geochemical anomaly is obtained if the produced CO2 is dissolved into volumes of water comparable to those of the shallower aquifers feeding the springs in the 1997 Colfiorito earthquakes area. We conclude that the integration of results from laboratory experiments, performed at seismic condition, and geochemical analyses can potentially aid in the calibration of monitoring strategies of geochemical properties of water in seismically active areas and provide insights into seismic fault zone processes (e.g. constraints on the temperature rise during earthquake propagation).223 37