DOCSLIB.ORG

2. Fault Mechanics: Some Basic Aspects

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
2. Fault Mechanics: Some Basic Aspects 15 2. Fault mechanics: some basic aspects The behavior of rocks in the shallow crust (fig. Coulomb criteria (JAEGER & COOK, 1979; 7) has been extensively investigated with rock SIBSON, 1998). Three failure modes of intact mechanics laboratory experiments. The rock have been recognized (ENGELDER, 1999; results of experiments on the failure of intact SIBSON, 1998): tensional fracturing, transitio- rocks are graphically expressed using Mohr nal-tensional fracturing (also called in literatu- diagrams that relate principal stresses acting re extensional-shear fracturing, e.g., SIBSON, on a rock volume to shear stresses acting on 1998) and compressional failure (also called in planes differently oriented within the body. literature compressional shear failure, e.g., In Mohr diagrams (figs. 8, 9, 10), the composi- SIBSON, 1998). The first two failure modes te failure envelope for intact isotropic rock is occur when the effective minimum stress is contructed by merging the Griffith and tensional and are generally considered to occur only for fluid pressures greater than lithostatic in thrust regimes or at shallow depths in normal fault regions (SIBSON, 1998). Tensional fracturing mainly controls the deve- lopment of extensional fractures in rocks, whereas the compressional failure applies to development of faults and is governed by the Coulomb fracture criterion: t=C+sm where t is the shear stress, C is the cohesive shear stress, s is the normal stress and m is the angle of rock internal friction. The slope of the Coulomb envelope is controlled by the coeffi- cient of internal friction of rocks involved in Fig. 7 - Plumose structure on a fracture in lavas at Colcuc the deformation. Laboratory strength tests on (Dolomites). Note on the left the center of nucleation of the fracture. a wide range of rock types have shown that 16 Structural Style & Dolomites Field Trip the internal friction coefficient ranges bet- intact rocks at an angle of about 30° to s1 (fig. ween 0.5 and 1.0 (e.g., JAEGER & COOK, 1979). 11). ANDERSON (1905) used the Coulomb- It has been shown that in isotropic bodies Mohr theory to explain conjugate faults and (quite a rare situation in the Earth's crust), the different mean dip of the various types of thrust faults are most likely to form from faults. The Anderson's theory applies close to the Earth's surface, where one of the principal stresses needs to be vertical and the two remai- ning horizontal (due to the fact that, being a solid-air interface, the Earth's surface cannot sustain shear stresses). The main compressio- nal stress s1 is vertical in extensional regimes and consequently normal faults normally develop with high (dip around 60°) angle, whereas it is horizontal in contractional areas and thrust faults consequently develop with low angle (around 30°). In strike slip settings s2 is vertical and strike-slip faults are mainly subvertical. Important classes of faults that appear to contradict the Anderson's theory are low angle normal faults and high angle reverse faults. Fluid (e.g., water and hydrocarbons) pressure affects significantly the mechanics of faulting (fig. 12). High fluid pressures (caused by rapid Fig. 8 - Mohr diagram showing the state of effective stress at failure for various experiments (varying the confining and the burial of impermeable strata, thermal water axial load) with intact Fredrick Diabase. Each circle represents pressuring and dehydration reactions occur- the state of stress at failure at a different mean stress ring during burial and metamorphism) reduce ([s1+s2+s3]/3). The locus of stress states that bounds the field of stable and unstable stresses is called the Mohr envelo- drastically the stress needed to generate rock pe (after SUPPE, 1985). fracturing and formation of faults, since it sup- ports part of the normal stress that would otherwise act across rock grain boundaries. The normal stress is then reduced to a lower effective normal stress. Extremely high pore fluid pressure will promote hydrofracturing (a process normally induced in oil wells to increase the permeability of reservoir rocks) and vein development. Normally, faults are associated with hydrothermal extensional vein systems (fig. 13). Veins are mainly horizontal when associated to thrust faults and subverti- Fig. 9 - Generic Mohr diagram showing a composite Griffith- cal for normal faults. Coulomb failure envelope for intact rocks. The three shown cri- Reactivation of existing faults accounts for tical stress circles represent different failure modes: tensional most of the deformation within the frictional fracturing, transitional-tensional fracturing (also called in lite- rature extensional-shear fracturing) and compressional failure seismogenic crust (fig. 14). In Mohr diagrams, (also called in literature compressional shear failure). the frictional failure envelope follows the FAULT MECHANICS 17 linear Amonton's law and, for faults characte- with respect to s1 pre-existing normal faults rised by cohesive strength, is a form of the are expected to remain unsheared and new Coulomb envelope (fig. 15). The slope of the fault planes may develop. Domino tilting of Amonton envelope is controlled by the sli- faults in extensional and compressional areas ding coefficient of friction of the fault, which may progressively rotate the active fault plane has been shown to have typical values as high so that they may acquire an unfavourable as 0.85 in the shallow crust (BYERLEE, 1978). orientation for re-shearing, may lock-up and The frictional resistence along pre-existing be abandoned. Further deformation will planes is expressed by the Byerlee's law: require the nucleation of new, favourably t=0.85s. The Byerlee's law is broadly litho- oriented faults. logy-insensitive. Fault surfaces that contain a Most of the theory on fault mechanics is based layer of gouge also obey Byerlee's law and dis- on the assumption of isotropic rock. This play a frictional behavior similar to clean rock assumption is largely inconsistent with the surfaces involving either strong and weak observations both in sedimentary and base- lithologies. The only silicatic minerals that ment rocks, where stratification, schistosity display significant lower friction than and other metamorphic and igneous foliations Byerlee's law are montmorillonite, vermiculi- occur. In strongly anisotropic rocks, the te and illite. Other platy minerals (e.g., chlori- orientation of the forming fractures is gene- te, kaolinite and serpentine) display normal rally influenced by the foliation. Only in case frictional properties. of planes of anisotropy nearly perpendicular The existence of near optimally oriented faults to the s1 direction, unisotropy is unimpor- (at an angle close to 30° from s1) normally tant in localizing fractures (fig. 16). inhibits the development of new planes by The displacement distribution along normal brittle failure. As the orientation of existing and thrust faults is maximum at the fault cen- faults becomes less favourable, reactivation ter and dies out to the fault margins. The occurs for increasingly higher effective stresses thickness of the fault gouge is direct function until the angle of frictional lockup is reached of total slip along the surface (fig. 17). and Coulomb mode rupture is expected to The mechanics of thrust faulting has been the occur (HANDIN, 1969). For example, in com- subject of animated discussion since when pressional settings characterised by pre-exi- large thrust sheets were recognized. The sting normal faults unfavourably oriented mechanical problem is that thrust sheets are σ1 τ Mohr envelope θ θ σ3 σ3 τ0 φ 2θ σn σ3 σ1 σ σ 1 + 3 σ 2 1 Fig. 10 - Mohr-Coulomb failure criterion for isotropic intact rocks (left panel). The point of tangency of the Mohr circle represents the state of stress on the plane which is at an angle Q from the s1 axis of the right panel. 18 Structural Style & Dolomites Field Trip σ 3 σ2 30° σ1 σ1 σ2 σ3 σ1 60° σ2 σ3 σ3 σ2 σ1 σ 90° 2 σ1 σ3 Fig. 11 - Anderson's theory of faul- ting. The struc- tures associated to fault planes σ3 (i.e., stylolites, extensional frac- σ1 tures and veins) σ2 are also shown. FAULT MECHANICS 19 very thin relative to their apparent frictional weight; 5) mountain belts may be modelled as resistence. When thrust faulting is reduced to critical tapers, similar to the deformed wedges the elementary physics problem of pushing a of snow or sand developing in front of a bull- rigid block over a rigid base, the force with dozer. which the thin sheet has to be pushed deter- At present the two more accepted explana- mines stresses that are even an order of magni- tions invoke the role of fluids and the critical tude larger than the yield stress of commun taper behavior of thrust faults. Two lines of rocks. evidence suggest that fluid pressures play a Several solutions were proposed to solve this significant role: 1) pumping of fluids in reser- enigma: 1) the basal resistence is not expressed voirs near active faults produces small earth- by Coulomb friction but is viscous or plastic quakes; 2) fluid pressure measurements in acti- (i.e., lower than expected); 2) thrusts are not ve regions show that major thrusts are confi- pushed from behind but slide along dipping ned to overpressured rock volumes. planes; 3) fluid pressures may lower the fric- The critical taper theory suggests that fold- tional resistence along the basal surface and and-thrust belts and accretionary prisms are enhance thrusting; 4) mountain belts are pla- first characterised by internal deformation and stic masses that flow outward under their own development of a topographic gradient Fig. 12 - Mohr stress diagram showing the effects of pore fluid pressure on the state of stress of a rock volume. An increase of pore fluid pressure p lowers the principal stresses acting on the body and shifts the corresponding Mohr circle to the left.
Load more

Recommended publications
  • Systematic Variation of Late Pleistocene Fault Scarp Height in the Teton Range, Wyoming, USA: Variable Fault Slip Rates Or Variable GEOSPHERE; V
    Research Paper THEMED ISSUE: Cenozoic Tectonics, Magmatism, and Stratigraphy of the Snake River Plain–Yellowstone Region and Adjacent Areas GEOSPHERE Systematic variation of Late Pleistocene fault scarp height in the Teton Range, Wyoming, USA: Variable fault slip rates or variable GEOSPHERE; v. 13, no. 2 landform ages? doi:10.1130/GES01320.1 Glenn D. Thackray and Amie E. Staley* 8 figures; 1 supplemental file Department of Geosciences, Idaho State University, 921 South 8th Avenue, Pocatello, Idaho 83209, USA CORRESPONDENCE: thacglen@ isu .edu ABSTRACT ously and repeatedly to climate shifts in multiple valleys, they create multi­ CITATION: Thackray, G.D., and Staley, A.E., 2017, ple isochronous markers for evaluation of spatial and temporal variation of Systematic variation of Late Pleistocene fault scarp height in the Teton Range, Wyoming, USA: Variable Fault scarps of strongly varying height cut glacial and alluvial sequences fault motion (Gillespie and Molnar, 1995; McCalpin, 1996; Howle et al., 2012; fault slip rates or variable landform ages?: Geosphere, mantling the faulted front of the Teton Range (western USA). Scarp heights Thackray et al., 2013). v. 13, no. 2, p. 287–300, doi:10.1130/GES01320.1. vary from 11.2 to 37.6 m and are systematically higher on geomorphically older In some cases, faults of known slip rate can also be used to evaluate ages landforms. Fault scarps cutting a deglacial surface, known from cosmogenic of glacial and alluvial sequences. However, this process is hampered by spatial Received 26 January 2016 Revision received 22 November 2016 radionuclide exposure dating to immediately postdate 14.7 ± 1.1 ka, average and temporal variability of offset along individual faults and fault segments Accepted 13 January 2017 12.0 m in height, and yield an average postglacial offset rate of 0.82 ± 0.13 (e.g., Z.
    [Show full text]
  • Geology of the Earthquake Source: an Introduction
    Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 Geology of the earthquake source: an introduction A˚ KE FAGERENG1* & VIRGINIA G. TOY2 1Department of Geological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa 2Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand *Corresponding author (e-mail: [email protected]) Abstract: Earthquakes arise from frictional ‘stick–slip’ instabilities as elastic strain is released by shear failure, almost always on a pre-existing fault. How the faulted rock responds to applied shear stress depends on its composition, environmental conditions (such as temperature and pressure), fluid presence and strain rate. These geological and physical variables determine the shear strength and frictional stability of a fault, and the dominant mineral deformation mechanism. To differing degrees, these effects ultimately control the partitioning between seismic and aseismic defor- mation, and are recorded by fault-rock textures. The scale-invariance of earthquake slip allows for extrapolation of geological and geophysical observations of earthquake-related deformation. Here we emphasize that the seismological character of a fault is highly dependent on fault geology, and that the high frequency of earthquakes observed by geophysical monitoring demands consider- ation of seismic slip as a major mechanism of finite fault displacement in the geological record. Rick Sibson has, throughout his career, pointed out the geological and physical parameters likely to that earthquakes occur in rocks (e.g. Sibson 1975, control their prevalence discussed. The mechanisms 1977, 1984, 1986, 1989, 2002, 2003). This simple by which rocks were deformed can be inferred from fact implies that fault rocks exert a critical control their textures (Knipe 1989); these relationships for on earthquake nucleation and propagation, and the typical fault rocks encountered in exhumed should contain an integrated record of earthquakes.
    [Show full text]
  • Along-Strike Growth of a Crustal Fault Controls the Modern Corinth Rift
    Geophysical Research Abstracts Vol. 20, EGU2018-12264, 2018 EGU General Assembly 2018 © Author(s) 2018. CC Attribution 4.0 license. Along-strike growth of a crustal fault controls the modern Corinth Rift David Fernández-Blanco, Gino de Gelder, Robin Lacassin, and Rolando Armijo Sorbonne Paris Cité, Univ Paris Diderot, CNRS, Institut de Physique du Globe de Paris, Lithosphere Tectonics and Mechanics, Paris, France ([email protected]) The Corinth Rift is the worldwide fastest-extending subaerially-exposed continental region, and thus an outstand- ing natural laboratory for research on fault and young rift mechanics. Here we address two of the rift’s most foundational and discrepant questions: whether the Corinth Rift formed; (i) as a “long” lived feature (∼5 Ma) by basinward fault migration, or as a short-lived feature (<1 Ma) by a single fault system; and by (ii) a north-dipping low angle detachment fault in the upper-to-middle crust or a steep normal fault affecting the entire crust. We re- assess available data and integrate it into a new map of the rift and use DEM-based analysis together with key concepts of fault mechanics and fluvial geomorphology to unravel the evolution of the master fault from onset to present. Footwall relief denotes that the master fault, composed at the surface of several segments, is at depth a single fault system >90 km in length. This finding implies that the Corinth Rift master fault reaches at least basal crustal depths. This crustal master fault initiated around the present rift centre and grew laterally by linkage and inclusion of younger individual fault segments along strike and has very high slip (and derived uplift) rates all along its strike.
    [Show full text]
  • Evolving Flexure Recorded in Continental Rift Uplifting Landscapes - Corinth Rift, Greece
    [Non Peer-Reviewed Earth ArXiv Preprint – Originally submitted to Geology, preparing resubmission to GRL] Evolving flexure recorded in continental rift uplifting landscapes - Corinth Rift, Greece David Fernández-Blanco1, Gino de Gelder1, Sean Gallen2, RoBin Lacassin1 & Rolando Armijo1 1 Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France 2 GeoloGical Institute, Swiss Federal Institute of TechnoloGy (ETH), 8092 Zü rich, Switzerland Abstract Elastic flexure of the lithosphere is commonly used to model crustal mechanics, rheoloGy and dynamics. However, accurate characterizations of flexure in nature at the spatiotemporal scale of active continental riftinG (tens of km; 104-106 yr) are scant. We use exceptionally preserved Geomorphic evidence in the asymmetric, younG and fast-extendinG Corinth Rift, central Greece, to document the combined effect of proGressive uplift and footwall flexure throuGhout its upliftinG marGin. Across the rift marGin, footwall lonGitudinal river profiles and topoGraphy define uplift increasinG exponentially towards the boundinG fault. AlonG the rift marGin, geomorphic proxies for fault’s footwall relief, slip rate and uplift rate show parabolic distributions decayinG alonG strike away from the fault center. Conspicuous drainage reversals where the topoGraphic expression of elastic flexure is most prominent similarly suGGest that maximum slip rates occur at the rift center. Overall, the geomorphic evidence for flexure implies disruptive Middle Pleistocene onset of a highly-localized, master fault system of crustal scale controllinG the Growth of the modern Corinth Rift. Similar hiGhly-localized strain and associated elastic flexure of the lithosphere may have occurred elsewhere, includinG old and/or slow-extendinG rifts and areas of intracontinental extension lackinG adequate Geomorphic evidence.
    [Show full text]
  • Faulted Joints: Kinematics, Displacement±Length Scaling Relations and Criteria for Their Identi®Cation
    Journal of Structural Geology 23 (2001) 315±327 www.elsevier.nl/locate/jstrugeo Faulted joints: kinematics, displacement±length scaling relations and criteria for their identi®cation Scott J. Wilkinsa,*, Michael R. Grossa, Michael Wackera, Yehuda Eyalb, Terry Engelderc aDepartment of Geology, Florida International University, Miami, FL 33199, USA bDepartment of Geology, Ben Gurion University, Beer Sheva 84105, Israel cDepartment of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA Received 6 December 1999; accepted 6 June 2000 Abstract Structural geometries and kinematics based on two sets of joints, pinnate joints and fault striations, reveal that some mesoscale faults at Split Mountain, Utah, originated as joints. Unlike many other types of faults, displacements (D) across faulted joints do not scale with lengths (L) and therefore do not adhere to published fault scaling laws. Rather, fault size corresponds initially to original joint length, which in turn is controlled by bed thickness for bed-con®ned joints. Although faulted joints will grow in length with increasing slip, the total change in length is negligible compared to the original length, leading to an independence of D from L during early stages of joint reactivation. Therefore, attempts to predict fault length, gouge thickness, or hydrologic properties based solely upon D±L scaling laws could yield misleading results for faulted joints. Pinnate joints, distinguishable from wing cracks, developed within the dilational quadrants along faulted joints and help to constrain the kinematics of joint reactivation. q 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction impact of these ªfaulted jointsº on displacement±length scaling relations and fault-slip kinematics.
    [Show full text]
  • Mechanics, Structure and Evolution of Fault Zones
    Pure appl. geophys. 166 (2009) 1533–1536 Ó Birkha¨user Verlag, Basel, 2009 0033–4553/09/101533–4 DOI 10.1007/s00024-009-0509-y Pure and Applied Geophysics Mechanics, Structure and Evolution of Fault Zones YEHUDA BEN-ZION and CHARLES SAMMIS 1. Introduction The brittle portion of the Earth’s lithosphere contains a distribution of joints, faults and cataclastic zones that exist on a wide range of scale-lengths and usually have complex geometries including bends, jogs, and intersections. The material around these complexities is subjected to large stress concentrations, which lead during continuing deformation to the generation of new fracture and granular damage with an associated evolution of the elasticity, permeability and geometry of the actively deforming regions. The evolving material and geometrical properties within and around the fault zone can lead, in turn, to evolution of various aspects of earthquake and fault mechanics. The geometrical complexity, material heterogeneities and wide range of effective space-time scales make the quantification of properties and processes associated with fault zones extremely challenging. Many fundamental questions concerning the mechanics, structure and evolution of fault zones remain unanswered despite consider- able research spanning over 100 years. The fourteen papers in this volume provide recent theoretical and observational perspectives on fault zones. Topics include damage and breakage rheologies, development of instabilities, fracture and friction, dynamic rupture experiments, analysis of geodetic data, and geological and laboratory characterizations of fault traces, fault surfaces, fracture zones, and particles in rock samples from fault zone environments. FINZI et al. present computer simulations of the evolution of geometrical and elastic properties of large strike-slip fault zones and associated deformation fields, using a model with a seismogenic upper crust governed by a continuum damage rheology.
    [Show full text]
  • Structural Analysis of Rock Canyon Near Provo, Utah
    Structural Analysis of Rock Canyon near Provo, Utah LAURA C. WALD, BART J. KOWALLIS, and RONALD A. HARRIS Department of Geological Sciences, Brigham Young University, Provo, Utah 84604 Key words: Utah, structure, Rock Canyon, thrust fault, folding, structural model ABSTRACT A detailed structural study of Rock Canyon (near Provo, Utah) provides insight into Wasatch Range tecton- ics and fold-thrust belt kinematics. Excellent exposures along theE-W trending canyon allow the use of digital photography in conjunction with traditional field methods for a thorough analysis of Rock Canyon’s structural fea- tures. Detailed photomontages and geometric and kinematic analyses of some structural features help to pinpoint deformation mechanisms active during the canyon’s tectonic history. Largescale images and these structural data are synthesized in a balanced cross section, which is used to reconstruct the structural evolution of this portion of the range. Projection of surficial features into the subsurface produces geometrical relationships that correlate well with a fault-bend fold model involving one or more subsurface imbrications. Kinematic data (e.g. slickenlines, fractures, fold axes) indicate that the maximum stress direction during formation of the fault-bend fold trended at approximately 120°. Following initial thrusting, uplift and development of a thrust splay produced by duplexing may have caused a shift in local stresses in the forelimb of the Rock Canyon anticline leading to late-stage normal faulting during Sevier compression. These normal faults may have activated deformed zones previously caused by Sevier folding, and reactivated early-stage decollements found in the folded weak shale units and shaley limestones. Movement on most of these normal faults roughly parallels stress directions found during initial thrusting indicating that these extensional features may be coeval with thrusting.
    [Show full text]
  • Fault Segmentation and Controls of Rupture Initiation and Termination
    DEPARTMENT OF THE INTERIOR U. S. GEOLOGICAL SURVEY PROCEEDINGS OF CONFERENCE XLV Fault Segmentation and Controls of Rupture Initiation and Termination Palm Springs, California Sponsored by U.S. GEOLOGICAL SURVEY NATIONAL EARTHQUAKE-HAZARDS REDUCTION PROGRAM Editors and Convenors David P. Schwartz Richard H. Sibson U.S. Geological Survey Department of Geological Sciences Menlo Park, California 94025 University of California Santa Barbara, California 93106 Organizing Committee John Boatwright, U.S. Geological Survey, Menlo Park, California Hiroo Kanamori, California Institute of Technology, Pasadena, California Chris H. Scholz, Lamont-Doherty Geological Observatory, Palisades, New York Open-File Report 89-315 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 1989 TABLE OF CONTENTS Page Introduction and Acknowledgments i David P. Schwartz and Richard H. Sibson List of Participants v Geometric features of a fault zone related to the 1 nucleation and termination of an earthquake rupture Keitti Aki Segmentation and recent rupture history 10 of the Xianshuihe fault, southwestern China Clarence R. Alien, Luo Zhuoli, Qian Hong, Wen Xueze, Zhou Huawei, and Huang Weishi Mechanics of fault junctions 31 D J. Andrews The effect of fault interaction on the stability 47 of echelon strike-slip faults Atilla Ay din and Richard A. Schultz Effects of restraining stepovers on earthquake rupture 67 A. Aykut Barka and Katharine Kadinsky-Cade Slip distribution and oblique segments of the 80 San Andreas fault, California: observations and theory Roger Bilham and Geoffrey King Structural geology of the Ocotillo badlands 94 antidilational fault jog, southern California Norman N.
    [Show full text]
  • Understanding the Process of Faulting: Selected Challenges and Opportunities at the Edge of the 21St Century
    Journal of Structural Geology 21 (1999) 985±993 www.elsevier.nl/locate/jstrugeo Understanding the process of faulting: selected challenges and opportunities at the edge of the 21st century R.A. Schultz Geomechanics±Rock Fracture Group, Department of Geological Sciences, Mackay School of Mines/172, University of Nevada, Reno, NV 89557, USA Received 18 March 1998; accepted 12 January 1999 Abstract Displacement distributions along fault surfaces are a record of the processes of fault nucleation, slip, linkage, and propagation. Because several disparate processes can collectively in¯uence the fault displacements, the relative contributions of these processes can be challenging, but are therefore necessary, to decipher. Continued advances in the mechanics of discontinuous slip surfaces in rock masses, when combined with appropriate ®eld studies, should determine the roles of cohesive end zones, fault interaction, and propagation direction in shaping the displacement distributions. Studies of faults on other planetary surfaces provide a window into the role of a broad range of environmental conditions that can in¯uence the faulting process. More inroads need to be made into traditional strain-based classes in structural geology so that mechanically sound concepts of fault analysis can become better utilized in the curriculum and by the non-specialist geological community. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction otherwise homogeneous, isotropic, linearly elastic ma- terial (Linear Elastic Fracture Mechanics, LEFM) has The past decade has witnessed explosive growth in provided a ®rst-order understanding of how geological our understanding of faults. Focused studies on the fractures accommodate displacement, concentrate process of faulting have largely supplanted a reliance stresses, interact, and propagate (see Pollard and on various classi®cation schemes that have been in use Segall, 1987 and Engelder et al., 1993 for clear treat- during this century (e.g.
    [Show full text]
  • Geology of the Eastern Part Beaty Butte Four Quadrangle, Oregon
    G r OF THE EASTERN PART BEATY BUTTE FOUR QUADRANGLE, OR S ON by Neil Joseph Maloney A THESIS submitted to OR ON STATE COLLEGE in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE June 1961 APPROVED: Redacted for Privacy Instructor of Geology in Charge of Major Redacted for Privacy Chairman of Department of Geology Redacted for Privacy Chairman of School Graduate Committee Redacted for Privacy. Dean of Graduate School Date thesis is presented 3 /910 Typed by Verna Blaine ACIC to 3 I am very grateful to Mr. D. O. Cochran who supervised and assisted the work in a great many ways. I am grateful to Drs. I. S. Allison and D. A. Bostwick for critically reviewing the manuscript. I would like to thank all of the faculty for advice and suggestions con. corning the thesis, especially Dr. Bostwick for aid in preparation of the plates, Dr. J. C. Cummings for sugges- tions concerning structural geology, and Mr. J. R. Snook for the axial angle of the anorthoolase. I gratefully acknowledge the many conversations and patient good humor of Daniel Johnson and Prank Blair who were co-workers in the field. TABLE OF CONTENTS NTRODUCTION . Page 1 Location and Accessibility......... .... .. ... 1 Previous Work 1 Present Worki14101100.00041 . *di . 0000**080090000041 3 Geography.. .... ... ... ***** . * . ***** ....... 4 STRATIGRAPHY." ............... ***** 5 Regional Stratigraphy 5 Local Stratigraphy ... 7 Steens Basalt....... "4'. ** 7 Lithology......,... ** . * ............ 10 Origin................... 13 Lone Mountain Formation.......... * ... 13 Lithology-Vitrophyres .... 16 Lithology-Felsites"a.... ... 19 Origin ... ***** ......" .0.. 23 Danforth CO Formation.. 25 Lithology......... * .... ... a ... ... 26 Origin................ .... ......... 27 Thousand Creek 01 Formation...
    [Show full text]
  • Long-Period Ground Motions in the Upper Mississippi Embayment from Finite-Fault, Finite-Difference Simulations
    University of Kentucky UKnowledge University of Kentucky Doctoral Dissertations Graduate School 2009 LONG-PERIOD GROUND MOTIONS IN THE UPPER MISSISSIPPI EMBAYMENT FROM FINITE-FAULT, FINITE-DIFFERENCE SIMULATIONS Kenneth A. Macpherson University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Macpherson, Kenneth A., "LONG-PERIOD GROUND MOTIONS IN THE UPPER MISSISSIPPI EMBAYMENT FROM FINITE-FAULT, FINITE-DIFFERENCE SIMULATIONS" (2009). University of Kentucky Doctoral Dissertations. 746. https://uknowledge.uky.edu/gradschool_diss/746 This Dissertation is brought to you for free and open access by the Graduate School at UKnowledge. It has been accepted for inclusion in University of Kentucky Doctoral Dissertations by an authorized administrator of UKnowledge. For more information, please contact [email protected]. ABSTRACT OF DISSERTATION Kenneth A. Macpherson The Graduate School University of Kentucky 2009 LONG-PERIOD GROUND MOTIONS IN THE UPPER MISSISSIPPI EMBAYMENT FROM FINITE-FAULT, FINITE-DIFFERENCE SIMULATIONS ABSTRACT OF DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Kenneth A. Macpherson Lexington, Kentucky Director: Dr. Edward W. Woolery, Professor of Geophysics Lexington, Kentucky 2009 Copyright c Kenneth A. Macpherson 2009 ABSTRACT OF DISSERTATION LONG-PERIOD GROUND MOTIONS IN THE UPPER MISSISSIPPI EMBAYMENT FROM FINITE-FAULT, FINITE-DIFFERENCE SIMULATIONS A 3D velocity model and 3D wave propagation code have been employed to simu- late long-period ground motions in the upper Mississippi embayment. This region is exposed to seismic hazard in the form of large earthquakes in the New Madrid seismic zone and observational data are sparse, making simulation a valuable tool for predicting the effects of large events.
    [Show full text]
  • Thrust-Fault Growth and Segment Linkage in the Active Ostler Fault Zone, New Zealand
    Journal of Structural Geology 27 (2005) 1528–1546 www.elsevier.com/locate/jsg Thrust-fault growth and segment linkage in the active Ostler fault zone, New Zealand Kenneth Davisa, Douglas W. Burbanka,*, Donald Fisherb, Shamus Wallacec,1, David Nobesc aDepartment of Geological Sciences, University of California at Santa Barbara, Santa Barbara, CA 93106, USA bDepartment of Geosciences, Pennsylvania State University, University Park, PA 16802, USA cDepartment of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Received 23 September 2003; received in revised form 19 April 2005; accepted 19 April 2005 Available online 6 July 2005 Abstract Thrust faulting is a fundamental mode of crustal deformation, yet many of the key geometrical attributes of thrust faults and the controls on fault rupture, growth, and linkage remain poorly resolved. Numerous surface-rupturing thrust faults cut through upper Quaternary glacial outwash terraces within the Ostler Fault zone, an active thrust system in the Southern Alps, New Zealand. We use these deformed marker surfaces to define the three-dimensional deformation field associated with their surface expression and to map displacement and length on w40 fault segments. Displacement transfer across two fault segment arrays occurs in distinctly different styles. In one, displacement is transferred between en e´chelon fault segments to produce a smooth, linear displacement gradient. In the other, large-scale folding and a population of small faults transfer displacement between two non-overlapping fault segments, with a residual displacement minimum within the transfer zone. Size distribution of fault-segment length and maximum displacement follow a power-law scaling relationship. Maximum displacement (Dmax) scales linearly with and represents w1% of segment trace length (L).
    [Show full text]