Papers by Jean-Pierre Gratier
How the Earth’s upper crust deforms in a viscous or brittle manner and how these behaviors interact and evolve over time: the crucial role of pressure solution creep and sealing processes
Revue française de géotechnique, 2023
Microstructural study of the partition between seismic and aseismic deformation along the North Anatolian Fault zone, Turkey
AGUFM, Dec 1, 2014
AGUFM, Dec 1, 2009
Mineral precipitation in the pores of a rock may exert a force, which is called crystallization p... more Mineral precipitation in the pores of a rock may exert a force, which is called crystallization pressure. This process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems. Cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride, at 30 or 45 °C, under axial normal stress in the range 0.02-0.26 MPa. The fluid was allowed to rise in the core samples by capillary forces, up to a controlled height where evaporation and precipitation occurred. The uniaxial deformation of the samples was measured using high-resolution displacement sensors. The samples were characterized using computed X-ray tomography, allowing therefore imaging in 3D the intensity and localization of the damage. Two kinds of damage could be observed. Firstly, small rock fragments were peeled from the sample surface. Secondly, and more interestingly, fracture networks developed, by nucleation of microcracks at the interface where evaporation occurred, and propagation to the free surface. Two families of fractures could be identified. A first set of sealed fracture parallel to the evaporation front is directly induced by crystallization pressure. A second fracture network, perpendicular to the evaporation front, accommodates the first set of fractures. An analytical model where fluid flow is coupled to evaporation, vapour transport, and localization of mineral precipitation explains the shape of this fracture network.
La déformation des roches par dissolution-cristallisation : aspects naturels et expérimentaux de ce fluage avec transfert de matière dans la croûte supérieure
Fast and slow temporal evolution of the upper crust ductile rheology: the role of fluid-rock interactions
EGUGA, Apr 1, 2013
Luminescence Studies of Age and Thermometric Properties of a SAFOD Phase III Core Sample: Initial Findings
AGUFM, Dec 1, 2009
This study aims to assess whether luminescence emission from trapped charge within silicate miner... more This study aims to assess whether luminescence emission from trapped charge within silicate minerals from SAFOD fault gouge samples can be used to determine the age distribution of deformation microstructures. Such age determination could help constrain some of the proposed micromechanical models for shear localization in fault gouge. A limited number of studies have attempted to determine the absolute age of gouge components. Among these include the application of trapped charge dating techniques to fault gouge minerals, including electron spin resonance (ESR), thermoluminescence (TL) and optically stimulated luminescence (OSL) dating methods. In all trapped charge dating techniques, sample age is determined by assessing the amount of charge accumulated since the traps were emptied or reset to zero. The mechanism by which previous trapped charge is reset in minerals in fault gouge is thought to be a combination of frictional heating and mechanical deformation, and these processes may be localized to grain surfaces. An added dating complexity for SAFOD samples is the high ambient temperature conditions, which acts as a barrier to charge storage in lower energy trapping sites. In this work a cube-shaped sample (~2.3x1.9x1.6 cm) of SAFOD Phase III core was obtained for analysis. Initial luminescence measurements have been conducted on 212-250 mum polymineral grains prepared from a ~2 mm surface slice. The natural luminescence signal without preheat treatment is absent in infrared and blue stimulated luminescence, which may be a result of annealing due to the geothermal gradient or from sample surface light exposure during core processing prior to sample acquisition. In contrast, a weak but measurable TL signal is evident. After laboratory beta radiation doses, both infrared and blue stimulated luminescence are dominated by high specific luminescence emission with slow decay. The TL signal comprises a single broad peak suggesting a quasi-continuous trap distribution. These luminescence features are all characteristic of feldspatic minerals. Such luminescence properties are not only encouraging for trapped charge dating studies but also allow assessment of thermal exposure of the silicate lattice during frictional heating and mechanical deformation. These initial findings and dating studies of minerals from slices taken from the core sample interior will be discussed.
Reservoir-Seal-Fault Systems Leakage Evolution Though Time and Space
AGU Fall Meeting Abstracts, Dec 1, 2011
漸新世以降における,西アルプスの半時計回り回転 古地磁気データによる新たな知見
Tectonics, 2002
Modeling Fluid Transfer Along Californian Faults When Integrating Pressure Solution Crack-Sealing and Compaction Processes
AGU Fall Meeting Abstracts, Dec 1, 2001
Quaternary International, May 1, 2017
Active and fossil endogenic travertine mounts scattered along the Little Grand Wash fault are stu... more Active and fossil endogenic travertine mounts scattered along the Little Grand Wash fault are studied as records of Quaternary CO 2 -enriched fluid leakage. This study focusses on a particular area where a fossil mount formed in a near-surface setting by successive circulation/sealing episodes from Late Pleistocene to Mid-Holocene and where a modern surface travertine is still being formed by a CO 2 -enriched fluid source. The fossil mount is composed of horizontal and vertical veins whereby the vertical veins recorded numerous cycles of circulation/sealing/dissolution events and were used as conduits for the CO 2enriched fluid circulation from the depth to the surface or along sub-horizontal fractures where successive precipitation events are recorded. The modern travertine is being built at the surface by successive eruption of Crystal Geyser, an anthropic geyser active since the 1930's. d 13 C and d 18 O signatures and U/Th datings, ranging from 11.5 ky till present-day allows calibrating in detail the CO 2 enriched fluid leakage along a single fault segment and in a post glacial context, as last glaciations in the study area took place 15 ky ago. The dataset shows a high decrease of the oxygen stable isotope values till about 6 ky, then the variations reflect a constant range until present-day. This tends to restrain the period of local increase of the meteoric water input in the aquifer that is sourcing the CO 2enriched water. The fossil travertine represents a 7 ky-long record of CO 2 leakage above a natural reservoir, from Late Pleistocene to Mid-Holocene. The flux of CO 2 leakage through time and the total escaping volume have been computed and appears to be low in comparison with an anthropogenic leak provoked, for instance, by a non-sealed well.
Earth and Planetary Science Letters, Apr 1, 2017
Observations of coseismic pulverization in porous sedimentary rocks in fault damage zones are sca... more Observations of coseismic pulverization in porous sedimentary rocks in fault damage zones are scarce, in contrast to coseismic pulverization of crystalline rocks. Also, juxtaposition of stiff crystalline rocks and compliant porous rocks across a fault often yields an asymmetric damage zone geometry, with less damage in the more compliant side. In this study, we argue that such asymmetry near the sub-surface occurs because of a different response of lithology to similar transient loading conditions. Uniaxial unconfined high strain rate loadings with a split Hopkinson pressure bar were performed on dry and water saturated Rothbach sandstone core samples. Bedding anisotropy was taken into account by coring the samples parallel and perpendicular to the bedding. The results show that pervasive pulverization below the grain scale, such as observed in crystalline rock, does not occur in the sandstone samples for the explored strain rate range (60-150 s -1 ). Damage is mainly restricted to the scale of the grains, with intragranular deformation occurring only in weaker regions where compaction bands are formed. The presence of water and the bedding anisotropy mitigate the formation of compaction bands and motivates intergranular dilatation. The competition between inter-and intragranular damage during dynamic loading is explained with the geometric parameters of the rock in combination
Slip localization by cataclasis and fluid-rock interaction in seismogenic crustal faults (Gole Larghe Fault, Italy)
At nucleation depths of earthquakes in the continental crust (7-15 km), cataclastic processes and... more At nucleation depths of earthquakes in the continental crust (7-15 km), cataclastic processes and fluids interact in a complex way, affecting the mechanical properties, deformation mechanisms and fabric of fault rocks. In this study, we analyzed the effects of cumulative displacement, fault orientation and slip localization on the fabric of low-displacement cataclasite-pseudotachylyte-bearing faults in granodiorite and discuss the feedbacks between deformation mechanisms potentially controlling the transition to unstable slip.The samples were stem from a well-exposed outcrop of the Gole Larghe Fault Zone (Southern Alps, Italy), which was active 30 Ma ago as a dextral transpressive fault at depths of earthquake nucleation (9-11 km, 250-280°C). Faults and shear fractures were digitized from an orthorectified photomosaic over an area of about 65 m2 to quantify their spatial arrangement. Samples were stem from faults and shear fractures which accommodated increasing cumulative displacements from 0 to 4.8 m, with strikes ranging from N074 to N125. Samples were characterized by means of microstructural (field emission scanning electron microscope, optical cathodoluminescence), mineralogical (X-Ray powder diffraction), geochemical (Energy Dispersive X-Ray Spectroscopy, EMPA) and image analysis (clast size distribution and shape parameters) investigations.Although fractures are uniformly distributed in the analyzed outcrop, 69% of the total displacement is accommodated along two main pseudotachylyte-bearing fault strands. Cataclasites consist of fragments of the wall rock (quartz, plagioclase and K-feldspar), in a matrix of K-feldspar, chlorite and epidote. With increasing displacement, the average grain size of quartz and plagioclase clasts decreases, the fractal dimension of the clast size distribution increases (from 1.6 to 2.8 in two dimensions) and the faults develop multiple domains of foliated cataclasites and non-foliated, highly comminuted ultracataclasites. If ultracataclasites or pseudotachylytes are present in the fault rocks, an increase of the displacement/thickness ratio suggests strain localization. The boundaries of quartz and plagioclase clasts in cataclasites are generally jagged, and clasts with equivalent diameters of less than 5 μm are rare, suggesting partial corrosion of the clast’s boundaries and dissolution of the smallest fragments. Elongated clasts are often oriented at an acute angle with fault boundaries, forming foliated cataclasite domains. Their iso-orientation is more intense in faults having a higher resolved normal stress (assuming a constant far-field stress tensor), i.e., the P-shears. Foliation is associated with an incipient mineral segregation of the matrix minerals, with epidote and titanite aligned along the foliation surfaces and K-feldspar and chlorite in low-strain sites.In agreement with experimental results, once slip localizes along highly comminuted horizons, slip appears to be further localized along it, suggesting slip weakening behavior associated with cataclastic flow. Diffusive mass transfer processes enhanced by comminution and fluid ingression allow a residual part of the displacement to be accommodated by frictional-viscous mechanisms (creep), especially at high driving stresses.
Geology, Aug 28, 2015
Natural deformation of rocks is commonly associated with development of mineralogical layering, l... more Natural deformation of rocks is commonly associated with development of mineralogical layering, leading to irreversible transformations of their microstructure. The mechanisms of such chemical differentiation processes during diagenesis, tectonics, metamorphism, or fault differentiation remain poorly understood, as they are difficult to reproduce experimentally due to the very slow kinetics involved. This paper shows that development of differentiated layering, similar to that observed in natural deformation, is stress driven and can be obtained from indenter experiments. Samples of (1) gypsum plaster mixed with clay, and (2) natural diatomite loosely interbedded with volcanic ash, saturated with aqueous solutions in equilibrium, were subjected to loading for several months at 40 °C and 150 °C, respectively. X-ray microtomography and scanning electron microscopy observations show that layering develops by a self-organized pressure solution process. Stress-driven dissolution of the soluble minerals (either gypsum or silica) is initiated in the areas initially richer in insoluble species (clay or volcanic ash), as diffusive mass transfer along the interface between soluble and insoluble minerals is much faster than along the healed boundaries of the soluble minerals. The passive concentration of the insoluble minerals amplifies the dissolution along layers oriented perpendicularly to the maximum compressive stress. Conversely, in areas with an initial low content of insoluble minerals and clustered soluble minerals, dissolution is slower. Consequently, these areas are less deformed; they host the re-deposition of the soluble species and act as rigid objects that concentrate both stress and dissolution near their boundaries, thus amplifying the differentiation and the development of layered microstructures.
Geophysical Research Letters, Jul 28, 2017
Postseismic recovery within fault damage zones involves slow healing of coseismic fractures leadi... more Postseismic recovery within fault damage zones involves slow healing of coseismic fractures leading to permeability reduction and strength increase with time. To better understand this process, experiments were performed by long-term fluid percolation with calcite precipitation through predamaged quartz-monzonite samples subjected to upper crustal conditions of stress and temperature. This resulted in a P wave velocity recovery of 50% of its initial drop after 64 days. In contrast, the permeability remained more or less constant for the duration of the experiment. Microstructures, fluid chemistry, and X-ray microtomography demonstrate that incipient calcite sealing and asperity dissolution are responsible for the P wave velocity recovery. The permeability is unaffected because calcite precipitates outside of the main flow channels. The highly nonparallel evolution of strength recovery and permeability suggests that fluid conduits within fault damage zones can remain open fluid conduits after an earthquake for much longer durations than suggested by the seismic monitoring of fault healing.
Are stylolitic surfaces inherently unstable surfaces? Insight from shape-minimization considerations
HAL (Le Centre pour la Communication Scientifique Directe), Dec 10, 2007
ABSTRACT
Implications of microstructural studies of the SAFOD gouge for the strength and deformation mechanisms in the creeping segment of the San Andreas fault
The San Andreas Fault zone (SAF) in the vicinity of the San Andreas Fault Observatory at Depth (S... more The San Andreas Fault zone (SAF) in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD)in central California is characterized by an average 21 mm/year aseismic creep and strain release through repeating M<3 earthquakes. Seismic inversion studies indicate that the ruptures occur on clusters of stationary patches making up 1% or less of the total fault surface area.
Journal of Structural Geology, Sep 1, 2018
. Stylolite formation depends on rock composition and structure, stress and fluids. . Stylolite g... more . Stylolite formation depends on rock composition and structure, stress and fluids. . Stylolite geometry, fractal and self-affine properties, network structure, are investigated. . The experiments and physics-based numerical models for their formation are reviewed. . Stylolites can be used as markers of strain, paleostress orientation and magnitude. . Stylolites impact transport properties, as function of maturity and flow direction.
Le fluage des roches par dissolution sous contrainte, dans la croute superieure
Bulletin De La Societe Geologique De France, 1993
Experimental layering development by indenter technique and application to fault rheology differentiation
AGUFM, Dec 1, 2014
Long term CO2 trapping and associated leakage efficiency: the role of active faults
AGUFM, Dec 1, 2010
Geological CO2 storage is viewed as a possible solution for the mitigation of increasing on-going... more Geological CO2 storage is viewed as a possible solution for the mitigation of increasing on-going global warming. Several pilot injection sites are already in place and numerous numerical scenarios are modeled. However, the remaining question is how effective the different kind of traps, caprocks and associated leakages are in the long term. One of the best keys to answer this
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Papers by Jean-Pierre Gratier