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  • 1
    Electronic Resource
    Electronic Resource
    Earthquake rupture dynamics frozen in exhumed ancient faults (2005)
    [s.l.] : Nature Publishing Group
    Nature 436 (2005), S. 1009-1012 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Most of our knowledge about co-seismic rupture propagation is derived from inversion and interpretation of strong-ground-motion seismograms, laboratory experiments on rock and rock-analogue material, or inferred from theoretical and numerical elastodynamic models. However, additional ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03910
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Friction falls towards zero in quartz rock as slip velocity approaches seismic rates (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 427 (2004), S. 436-439 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] An important unsolved problem in earthquake mechanics is to determine the resistance to slip on faults in the Earth's crust during earthquakes. Knowledge of coseismic slip resistance is critical for understanding the magnitude of shear-stress reduction and hence the near-fault acceleration ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02249
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  • 3
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    Fault lubrication and earthquake propagation in thermally unstable rocks (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-01-01
    Description: 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 coefficient {micro} decays exponentially from peak values (mp {approx} 0.8, in the Byerlee's range), to extremely low steady-state values ({micro}ss {approx} 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 flash temperatures that are large enough to activate chemical and physical processes, e.g., decarbonation reactions (T = 550 {degrees}C). During steady state (d [≥] Dw), shear strength is very low and not dependent upon normal stresses, suggesting that pressurized fluids (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 fluids 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 Colfiorito (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.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    Earthquake Nucleation Size: Evidence of Loading Rate Dependence in Laboratory Faults (2019)
    Details
    Publication Date: 2020-10-27
    Description: Recent Global Positioning System observations of major earthquakes such as the 2014 Chile megathrust show a slow preslip phase releasing a significant portion of the total moment (Ruiz et al., 2014, https://doi.org/10.1126/science.1256074). Despite advances from theoretical stability analysis (Rubin & Ampuero, 2005, https://doi.org/10.1029/2005JB003686; Ruina, 1983, https://doi.org/10.1029/jb088ib12p10359) and modeling (Kaneko et al., 2017, https://doi.org/10.1002/2016GL071569), it is not fully understood what controls the prevalence and the amount of slip in the nucleation process. Here we present laboratory observations of slow slip preceding dynamic rupture, where we observe a dependence of nucleation size and position on the loading rate (laboratory equivalent of tectonic loading rate). The setup is composed of two polycarbonate plates under direct shear with a 30‐cm long slip interface. The results of our laboratory experiments are in agreement with the preslip model outlined by Ellsworth and Beroza (1995, https://doi.org/10.1126/science.268.5212.851) and observed in laboratory experiments (Latour et al., 2013, https://doi.org/10.1002/grl.50974; Nielsen et al., 2010, https://doi.org/10.1111/j.1365-246x.2009.04444.x; Ohnaka & Kuwahara, 1990, https://doi.org/10.1016/0040-1951(90)90138-X), which show a slow slip followed by an acceleration up to dynamic rupture velocity. However, further complexity arises from the effect of (1) rate of shear loading and (2) inhomogeneities on the fault surface. In particular, we show that when the loading rate is increased from 10−2 to 6 MPa/s, the nucleation length can shrink by a factor of 3, and the rupture nucleates consistently on higher shear stress areas. The nucleation lengths measured fall within the range of the theoretical limits Lb and urn:x-wiley:jgrb:media:jgrb53198:jgrb53198-math-0001 derived by Rubin and Ampuero (2005, https://doi.org/10.1029/2005JB003686) for rate‐and‐state friction laws.
    Description: Published
    Description: 689-708
    Description: 2T. Sorgente Sismica
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Keywords: 04.01. Earth Interior
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Mechanical behaviour of fluid-lubricated faults (2020)
    Details
    Publication Date: 2020-10-27
    Description: Fluids are pervasive in fault zones cutting the Earth's crust; however, the effect of fluid viscosity on fault mechanics is mainly conjectured by theoretical models. We present friction experiments performed on both dry and fluid-permeated silicate and carbonate bearing-rocks, at normal effective stresses up to 20 MPa, with a slip-rate ranging between 10 μm/s and 1 m/s. Four different fluid viscosities were tested. We show that both static and dynamic friction coefficients decrease with viscosity and that dynamic friction depends on the dimensionless Sommerfeld number (S) as predicted by the elastohydrodynamic-lubrication theory (EHD).Under favourable conditions (depending on the fluid viscosity (η), co-seismic slip-rate (V), fault geometry (L/H02) and earthquake nucleation depth (∝σeff)), EHD might be an effective weakening mechanism during natural and induced earthquakes. However, at seismic slip-rate, the slip weakening distance (Dc) increases markedly for a range of fluid viscosities expected in the Earth, potentially favouring slow-slip rather than rupture propagation for small to moderate earthquakes.
    Description: Published
    Description: 1274
    Description: 3T. Sorgente sismica
    Description: 2IT. Laboratori analitici e sperimentali
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Structural Complexity and Mechanics of a Shallow Crustal Seismogenic Source (Vado di Corno Fault Zone, Italy) (2021)
    Wiley Agu
    Details
    Publication Date: 2021-01-25
    Description: The mechanics and seismogenic behavior of fault zones are strongly influenced by their internal structure. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (VCFZ, Central Apennines, Italy) was quantified by combining high-resolution structural mapping with 3-D fault network analysis over ∼2 km along fault strike. The fault zone was exhumed from ∼2 km depth in carbonate rocks, accommodated 1.5–2 km of extensional throw since Early Pleistocene, and cuts through the Pliocene Omo Morto Thrust Zone (OMTZ) with partial reactivation in extension. The exceptional exposure of the footwall block allowed us to reconstruct in detail the geometry of the OMTZ and quantify the spatial arrangement of master/subsidiary faults and fault zone rocks within the extensional VCFZ. The combination of the structural map and the 3-D fault network with kinematic and topological analyses pointed out the crucial role of the older thrust geometry (i.e., lateral ramps) in controlling the along-strike segmentation and slip distribution of the VCFZ. These observations were discussed in the framework of regional extension through a slip tendency analysis and a simplified mechanical model, which suggest the activation of oblique inherited structures during the lateral propagation of the VCFZ segments. The interaction of the VCFZ with the OMTZ generated along strike and possibly downdip mechanical asperities. Considering the exhumed VCFZ as an analog for the shallow structure of other seismic sources in the Central Apennines, similar settings could play first-order control on the spatio-temporal evolution and rupture heterogeneity of earthquakes in the region
    Description: European Research Council Consolidator Grant Project (NOFEAR) 614705 MSCA-IF DAMAGE 839880
    Description: Published
    Description: e2019JB018926
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Keywords: Fault ; Earthquakes ; Carbonates ; Rock damage ; Central Apennines ; Earthquake mechanics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Fault gouge graphitization as evidence of past seismic slip (2018)
    Details
    Publication Date: 2021-03-09
    Description: One moderate- to large-magnitude earthquake (M 〉 6) nucleates in Earth’s crust every three days on average, but the geological record of ancient fault slip at meters-per-second seismic velocities (as opposed to subseismic slow-slip creep) remains debated because of the lack of established fault-zone evidence of seismic slip. Here we show that the irreversible temperature-dependent transformation of carbonaceous material (CM, a constituent of many fault gouges) into graphite is a reliable tracer of seismic fault slip. We sheared CM-bearing fault rocks in the laboratory at just above subseismic and at seismic velocities under both water-rich and water-deficient conditions and modeled the temperature evolution with slip. By means of micro-Raman spectroscopy and focused-ion beam transmission electron microscopy, we detected graphite grains similar to those found in the principal slip zone of the A.D. 2008 Wenchuan (Mw 7.9) earthquake (southeast Tibet) only in experiments conducted at seismic velocities. The experimental evidence presented here suggests that high-temperature pulses associated with seismic slip induce graphitization of CM. Importantly, the occurrence of graphitized fault-zone CM may allow us to ascertain the seismogenic potential of faults in areas worldwide with incomplete historical earthquake catalogues.
    Description: Published
    Description: 979–982
    Description: 2T. Sorgente Sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Production of nanoparticles during experimental deformation of smectite and implications for seismic slip (2018)
    Details
    Publication Date: 2021-03-09
    Description: Nanoparticles and amorphous materials are common constituents of the shallow sections of active faults. Understanding the conditions at which nanoparticles are produced and their effects on friction can further improve our understanding of fault mechanics and earthquake energy budgets. Here we present the results of 59 rotary shear experiments conducted at room humidity conditions on gouge consisting of mixtures of smectite (Ca-montmorillonite) and quartz. Experiments with 60, 50, 25, 0 wt.% Ca-montmorillonite, were performed to investigate the influence of variable clay content on nanoparticle production and their influence on frictional processes. All experiments were performed at a normal stress of 5 MPa, slip rate of 0.0003 〈 V 〈 1.5 ms-1, and at a displacement of 3 m. To monitor the development of fabric and the mineralogical changes during the experiments, we investigated the deformed gouges using scanning and transmission electron microscopy combined with X-ray powder diffraction quantitative phase analysis. This integrated analytical approach reveals that, at all slip rates and compositions, the nanoparticles (grain size of 10–50 nm) are partly amorphous and result from cataclasis, wear and mechanical solid-state amorphization of smectite. The maximum production of amorphous nanoparticle occurs in the intermediate slip rate range (0.0003 〈 V 〈 0.1 ms-1), at the highest frictional work, and is associated to diffuse deformation and slip strengthening behavior. Instead, the lowest production of amorphous nanoparticles occurs at co-seismic slip rates (V 〉 0.1 ms-1), at the highest frictional power and is associated with strain and heat localization and slip weakening behavior. Our findings suggest that, independently of the amount of smectite nanoparticles, they produce fault weakening only when typical co-seismic slip rates (〉1.3 ms−1) are achieved. This implies that estimates of the fracture surface energy dissipated during earthquakes in natural faults might be extremely difficult to constrain.
    Description: Published
    Description: 221-231
    Description: 2T. Sorgente Sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Structural control on the directional amplification of seismic noise (Campo Imperatore, central Italy) (2018)
    Details
    Publication Date: 2021-05-17
    Description: Seismic signals propagating across a fault may yield information on the internal structure of the fault zone. Here we have assessed the amplification of seismic noise (i.e., ambient vibrations generated by natural or anthropogenic disturbances) across the Vado di Corno Fault (Campo Imperatore, central Italy). The fault zone is considered as an exhumed analogue of the normal faults activated during the L'Aquila 2009 earthquake sequence. Detailed structural geological survey of the footwall block revealed that the fault zone is highly anisotropic and is affected by a complex network of faults and fractures with dominant WNW–ESE strike. We measured seismic noise with portable seismometers along a ∼500 m long transect perpendicular to the average fault strike. Seismic signals were processed calculating the horizontal-to-vertical spectral ratios and performing wavefield polarization analyses. We found a predominant NE–SW to NNE–SSW (i.e., ca. perpendicular to the average strike of the fault-fracture network) amplification of the horizontal component of the seismic waves. Numerical simulations of earthquake-induced ground motions ruled out the role of topography in controlling the polarization and the amplitude of the waves. Therefore, the higher seismic noise amplitude observed in the fault-perpendicular direction was related to the measured fracture network and the resulting stiffness anisotropy of the rock mass. These observations open new perspectives in using measures of ambient seismic noise, which are fast and inexpensive, to estimate the dominant orientation of fracture networks within fault zones.
    Description: Published
    Description: 10-18
    Description: 4T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 10
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    Past seismic slip-to-the-trench recorded in Central America megathrust (2018)
    Details
    Publication Date: 2021-05-12
    Description: The 2011 Tōhoku-Oki earthquake revealed that co-seismic displacement along the plate boundary megathrust can propagate to the trench. Co-seismic slip to the trench amplifies hazards at subduction zones, so its historical occurrence should also be investigated globally. Here we combine structural and experimental analyses of core samples taken offshore from southeastern Costa Rica as part of the Integrated Ocean Drilling Program (IODP) Expedition 344, with three-dimensional seismic reflection images of the subduction zone. We document a geologic record of past co-seismic slip to the trench. The core passed through a less than 1.9-million-year-old megathrust frontal ramp that superimposes older Miocene biogenic oozes onto late Miocene–Pleistocene silty clays. This, together with our stratigraphic analyses and geophysical images, constrains the position of the basal decollement to lie within the biogenic oozes. Our friction experiments show that, when wet, silty clays and biogenic oozes are both slip-weakening at sub-seismic and seismic slip velocities. Oozes are stronger than silty clays at slip velocities of less than or equal to 0.01 m s–1, and wet oozes become as weak as silty clays only at a slip velocity of 1 m s–1. We therefore suggest that the geological structures found offshore from Costa Rica were deformed during seismic slip-to-the-trench events. During slower aseismic creep, deformation would have preferentially localized within the silty clays.
    Description: Published
    Description: 935–940
    Description: 2T. Sorgente Sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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