ROCK PHYSICS AND NATURAL HAZARDS PDF
Preview ROCK PHYSICS AND NATURAL HAZARDS
Rock Physics and Natural Hazards Edited by Sergio Vinciguerra Yves Bernabé Birkhäuser Basel · Boston · Berlin Reprint from Pure and Applied Geophysics (PAGEOPH), Volume 166 (2009) No. 5 – 7 Editors Sergio Vinciguerra Yves Bernabé Sezione di Sismologia e Dept. Earth, Atmosphere Tettonofisica & Planetary Sciences Istituto Nazionale di Geofisica e Massachussets Institute of Technology Vulcanologia (INGV) 77, Massachussets Ave. Via di Vigna Murata 605 Cambridge, MA 02139 00143 Roma USA Italy Email: [email protected] Email: [email protected] Library of Congress Control Number: 2009930008 Bibliographic information published by Die Deutsche Bibliothek: Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data is available in the Internet at <http://dnb.ddb.de> ISBN 978-3-0346-0121-4 Birkhäuser Verlag AG, Basel · Boston · Berlin This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustra- tions, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. For any kind of use, permission of the copyright owner must be obtained. © 2009 Birkhäuser Verlag AG Basel · Boston · Berlin P.O. Box 133, CH-4010 Basel, Switzerland Part of Springer Science+Business Media Printed on acid-free paper produced from chlorine-free pulp. TCF ∞ Cover graphic: Based on a graphic from the article “Axial and Radial Permeability Evolutions of Compressed Sandstones: End Effects and Shear-band Induced Permeability Anisotropy” by J. Dautriat, N. Gland, J. Guelard, A. Dimanov and J. L. Raphanel. Printed in Germany ISBN 978-3-0346-0121-4 e-ISBN 978-3-0346-0122-1 9 8 7 6 5 4 3 2 1 www.birkhauser.ch Pureappl.geophys.166(2009)737–739 (cid:3)Birkha¨userVerlag,Basel,2009 0033–4553/09/050737–3 Pure and Applied Geophysics DOI10.1007/s00024-009-0507-0 Introduction SERGIO VINCIGUERRA1 and YVES BERNABE´2 Natural hazards events such as earthquakes or volcanic eruptions involve activation of coupled thermo-hydro-chemo-mechanical processes in rocks. The 7th Euro-Conference of Rock Physics and Geomechanics, sponsored by the Italian Istituto Nazionale di GeofisicaeVulcanologia(INGV),theFrenchCentreNationaldeRechercheScientifique (CNRS) and Exxon-Mobil, was held September 25 to 30, 2007, in Erice (Italy), to explore how rock physics experiments and models can facilitate understanding and constraint of natural hazards’ mechanisms, and, to foster cross-disciplinary collabora- tions. The Erice Conference was organized around six sessions: 1) fault healing, sealing and rupture process, 2) rock deformation and coupled processes in rocks, 3) fault structure and mechanics, from laboratory to exploratory drilling of major faults, 4) fracture and flow in volcanic and geothermal areas, and physical properties of volcanic rocks, 5) reservoir characterization and stimulation, 6) scaling laws, applications to rupture mechanicsandfluidflow.Thepresenttopicalissue originatedfrom thedesireto assemble in a single volume unpublished contributions to the Erice Conference. This volumepresentsnewlaboratorydata,theoreticalandnumericalrockphysicsmodelsand field observations relevant to the study of natural hazards. The bulk of this topical issue is devoted to questions related to rock failure and earthquake source mechanisms. BIZZARRI presents a review of various competing mechanismswhichcontroldynamicfailureduringlargeearthquakesandattemptstoinfer arealisticearthquakesourcemodelfromthem.GROBetal.advancethefactthat,despite the huge reduction in scale, laboratory experiments sometimes display phenomena strikingly similar to field observations and can therefore provide insight into natural phenomena.Here,thetemporal andspatialdistributions ofevents during interface crack propagation suggest that dynamic fracture propagation is controlled by elastic interac- tions between structural heterogeneities. At the laboratory scale, NASSERI et al. explore the relationship between fracture toughness and roughness in thermally (up to 850(cid:2)C) treated Westerlygranite,whileFORTINetal.,STANCHITSetal.andBAUDetal.investigate the relationship between competing deformation micro-mechanisms, as measured and 1 IstitutoNazionalediGeofisicaeVulcanologia, SezionediRoma1,ViadiVignaMurata605, 00143Rome,Italy. 2 Earth, Atmospheric and Planetary Sciences Department, Massachusetts Institute of Technology, Cambridge,MA02139,U.S.A. 738 S.VinciguerraandY.Bernabe´ Pureappl.geophys., characterized by acoustic emission activity and microstructural observations, and strain localization in sandstones and carbonates. The effect of a number of factors such as confining pressure, porosity, and the presence or absence of water is investigated. Pressure solution is another important example of a deformation mechanism involving coupledchemicalandmechanicalprocesses.BERNABE´ etal.presentmicroscalenumerical simulations of pressure solution creep, and attempt to interpret them via a commonly used, generic creep law. This creep law could be, in turn, incorporated into models of fault gouge healing during the seismic cycle. Mechanical and transport properties of rocks are known to be coupled in many field situations. In order to help constrain this typeofproblem,NASSERIetal.proposeaneffectivemedium-basedinversionschemeand employ it to infer the mechanical properties and permeability of thermally cracked Westerly granite under isostatic compression from experimental data. The transport propertiesofrocksare,ofcourse,primarilycontrolledbythegeometryoftheporespace. PAPE and CLAUSER propose a novel model linking the Nuclear Magnetic Resonance T1 andT2distributionstopermeabilityinrockswithfractalporespace.Contrarytoprevious models,whichassumethatporesareisolated,thenewmodelincludestheeffectofproton diffusioncouplingbetweenconnectedpores.BERNABE´ revisitsACflowofacompressible fluidthroughasingledeformablepipeandheterogeneouspipenetworks.TheseACflow waves may occur in open fractures, possibly causing resonance effects such as might be involved in volcanic tremors. Shear deformation in the Earth, ductile and/or brittle, is often associated with anisotropy of the rock physical properties. CIRRINCIONE et al. document microstructural evidence of this process in naturally deformed leuco-gneiss from an Alpine shear zone while CHEN et al. characterize the anisotropy of permeability in cores from the Chelungpu fault and assess the implications of their findings to fault models and weakening mechanisms inferred for the Chi-Chi Earthquake. At the laboratory scale, DAUTRIAT et al. and LOUIS et al. investigate stress-induced anisotropy and its possible control by the transport properties and pre-existing fabric, respectively. Finally, rock physics techniques and models can be applied or tested in geotechnical applications such as geothermal energy recovery or oil/gas production. The work of ZIMMERMANNetal.andBLO¨CHERetal.stresstheimportanceofhydro-mechanicalcoupling foroptimalreservoirmanagement.PAPEetal.estimaterockpermeabilityatthewell-bore and core scale, based on Nuclear Magnetic Resonance T1 and T2 measurements. Although most studies in this topical issue are not directly devoted to natural hazards, they present rock physics data and models that can be applied to the rock mechanisms and processes occurring during events such as earthquakes or volcanic eruptions. Acknowledgements Theguesteditorsarethankfultothecontributorsfortheircommitmentandenthusiasm andtoRenataDmowskaforprovidingeditorialguidance.Theyalsorecognizetheefforts of the colleagues who conscientiously performed critical reviews of the papers: M.Balme,P.Baud,P.Benson,Y.Bernabe´,P.Besuelle,A.Bizzarri,M.Cocco,C.David, Vol.166,2009 Introduction 739 G. Dresen, D. Faulkner, J. Fortin, P. Glover, J-P. Gratier, Y. Gue´guen, B. Haimson, M. Heap,H.Kern,I.Main,A.Maineult,C.Marone,P.Meredith,A.Niemeijer,D.Olgaard, T. Reuschle´, F. Rossetti, J. Rudnicki, A. Schubnel, S. Shapiro, S. Stanchits, T.-f. Wong, W. Zhu. Pureappl.geophys.166(2009)741–776 (cid:3)Birkha¨userVerlag,Basel,2009 0033–4553/09/050741–36 Pure and Applied Geophysics DOI10.1007/s00024-009-0494-1 WhatDoesControlEarthquakeRupturesandDynamicFaulting?AReview ofDifferent Competing Mechanisms ANDREA BIZZARRI Abstract—Thefaultweakeningoccurringduringanearthquakeandthetemporalevolutionofthetraction onaseismogenicfaultdependonseveralphysicalmechanisms,potentiallyconcurrentandinteracting.Recent laboratoryexperimentsandgeologicalfieldobservationsofnaturalfaultsrevealedthepresence,andsometime thecoexistence,ofthermallyactivatedprocesses(suchasthermalpressurizationofporefluids,meltingofgouge and rocks, material property changes, thermally-induced chemical environment evolution), elasto-dynamic lubrication,porosityandpermeabilityevolution,gougefragmentationandwear,etc.Inthispaper,byreviewing inaunifyingsketchallpossiblechemico–physicalmechanismsthatcanaffectthetractionevolution,wesuggest how they can be incorporated in a realistic fault governing equation. We will also show that simplified theoreticalmodelsthatidealisticallyneglectthesephenomenaappeartobeinadequatetodescribeasrealistically aspossiblethedetailsofbreakdownprocess(i.e.,thestressrelease)andtheconsequenthighfrequencyseismic waveradiation.Quantitativeestimatesshowthatinmostcasestheincorporationofsuchnonlinearphenomena has significant, often dramatic, effects on the fault weakening and on the dynamic rupture propagation.The range of variability of the value of some parameters, the uncertainties in the relative weight of the various competingmechanisms,andthedifferenceintheircharacteristiclengthandtimescalessometimeindicatethat the formulation of a realistic governing law still requires joint efforts from theoretical models, laboratory experimentsandfieldobservations. Keywords: Rheologyandfrictionofthefaultzones,constitutivelaws,mechanicsoffaulting,earthquake dynamics,computationalseismology. 1. Introduction Contrary to other ambits of physics, seismology presently lacks knowledge of exact physical law which governs natural faults and makes the understanding of earthquakes feasiblefromadeterministicpointofview.Inadditiontotheubiquitousignoranceofthe initial conditions (i.e., the initial state) of the seismogenic region of interest, we also ignoretheequationsthatcontrolthetractionevolutiononthefaultsurface;thishasbeen recently recognized as one of the grand challenges for seismology (http://www.iris.edu/ hq/lrsps/seis_lrp_12_08_08.pdf, December 2008). Indirect information comes from theoreticalandnumericalstudies,which,undersomeassumptionsandhypotheses,tryto reproduce real–world events and aim to infer some constraints from a systematic IstitutoNazionalediGeofisicaeVulcanologia,SezionediBologna,Italy.E-mail:[email protected]
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