DOCSLIB.ORG

Geology of the Earthquake Source: an Introduction

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read 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. fault zones are reviewed in this introduction. A con- Reading this record, Sibson has added significantly ceptual fault-zone model building on previous to our understanding of how faults work. His intui- review works (e.g. Sibson 1983; Scholz 2002) that tive ability to relate structures in exhumed rocks to is based on observations of the depth-distribution seismological observations of active deformation of fault rocks, inferred variability in deformation has contributed significantly to bridging the gap mechanism, fault strength and frictional stability between how geologists and geophysicists think with depth is also described. It is explained how about fault mechanics, and has led to the develop- this model provides basic controls on the depth ment of earthquake science as a truly interdisciplin- limits of the crustal seismogenic zone. Earthquake ary field. This volume celebrates Rick Sibson’s size and scaling parameters, in relation to interpret- career by bringing together a collection of papers ing data from different scales and methods, are also that present innovative studies spanning a range briefly reviewed; and, finally, the chapters in this of topics within the field of earthquake geology. Special Publication are outlined. Included are descriptions of fault-zone rocks from active and ancient faults, rock deformation exper- iments at seismic slip rates, and theoretical treat- Earthquake mechanism and frictional ments of fault initiation and slip. stability In this introduction the mechanism of earthquake faulting – generally accepted to be the release of Faults slip at a range of speeds, including slow creep tectonic elastic strain energy stored in a rock at plate tectonic rates (order of 1–10 cm year21), volume – by fast slip on a pre-existing or new fault fast frictional sliding (c.1ms21) during earthquake (Brace & Byerlee 1966) is discussed. Also included slip and displacement at a range of recently discov- is a short discussion on how rate- and state-variable ered, intermediate slip rates (such as slow slip and frictional stability may affect the rate at which fault low-frequency earthquakes: see the review by slip occurs (Dieterich 1972, 1979). The deformation Peng & Gomberg 2010 and references therein). mechanisms likely to be active at different con- The mechanisms of fault creep and slip at intermedi- ditions within a fault zone, which may lead to ate velocities are not yet obvious, but earthquake seismic or aseismic deformation, are outlined, and slip is generally thought to arise from ‘stick–slip’ From:Fagereng,A˚ ., Toy,V.G.&Rowland, J. V. (eds) Geology of the Earthquake Source: A Volume in Honour of Rick Sibson. Geological Society, London, Special Publications, 359, 1–16. DOI: 10.1144/SP359.1 0305-8719/11/$15.00 # The Geological Society of London 2011. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 2 A˚ . FAGERENG & V. G. TOY frictional instability on a pre-existing fault (Brace & (Dieterich 1972, 1979; Scholz et al. 1972; Ruina Byerlee 1966) or, less commonly, by failure on a 1983; Marone 1998; Scholz 1998). Rate- and state- new fault surface. In this model, based on the variable effects on fault friction include an increase elastic rebound theory first suggested by Reid in ms with loading time, t, related to an increase (1911), elastic strain accumulates in rock surround- in real contact area with time under an applied ing the existing or potential fault surface (Fig. 1a), normal stress (Dieterich 1972). In addition, the until the resultant shear stress on the plane exceeds dynamic friction (mk), the sliding resistance experi- its frictional strength and failure occurs. Thus, earth- enced on a fault after slip has initiated, appears to quake faulting is a frictional process, where rupture vary with slip velocity, v (Fig. 1b) (Scholz et al. initiation depends on frictional resistance on the 1972). Although there are several forms of a consti- existing or potential fault plane. The shear stress tutive equation fitting laboratory observations of at failure, tf, is commonly approximated by the rock friction, a commonly used description of the empirical Amontons’ law: time and velocity dependence of friction is the Dieterich–Ruina law (Beeler et al. 1994): = + − tf C0 ms(sn Pf ) (1) = + + m m0 a ln(v/v0) b ln(v0u/D); where C is cohesive strength, m is the static coeffi- (2) 0 s du/dt = 1 − uv/D cient of friction, sn is normal stress and Pf is fluid pressure. Equation (1) indicates the shear stress con- ditions at which a fault will slip; however, it does not where m0 is the coefficient of friction at a reference define at what rate this slip occurs. slip velocity (v0), D is the critical slip distance, inter- Experimental studies of fault friction, generally preted as the slip increment needed for renewal of in homogeneous rock samples, have indicated that surface contacts (Dieterich 1979), a and b are empiri- a rate- and state-variable friction law can describe cal material constants, and u is a state variable observed sliding behaviour on laboratory faults that evolves over time. Geological effects, such as time Elastic strain (a) Start of new cycle Interseismic strain Post-seismic accommodation (b) Slow Fast 0.07 0.06 T2 b2 0.05 0.04 ° T1 = quartz at 150 C, velocity weakening Δm 0.03 ° T2 = quartz at 600 C, velocity strengthening a2 0.02 0.01 a1 T b1 0.0 1 -0.01 0 2 4 6 8 10 Slip distance/D Fig. 1. (a) Fault movement by elastic rebound. Starting from a relaxed state at the beginning of a seismic cycle, the rock surrounding the fault accumulates elastic strain. When this strain reaches a value where the resultant shear stress on the fault exceeds its frictional strength, displacement occurs on the fault, releasing stored elastic strain in the wall rock. (b) Example of the velocity dependence of friction, using material properties (a and b) for quartz from Blanpied et al. (1995) and Equation (2), at temperatures of 150 8C (solid line) and 600 8C (dashed line). Note the different evolution of the frictional coefficient (m) predicted for velocity-weakening and velocity-strengthening conditions. Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 GEOLOGY OF THE EARTHQUAKE SOURCE 3 mineralogy, fluid pressure, dominant deformation by fluid presence between grains (Carter 1975). mechanism and rock structure, as well as environ- Because of high porosity and, commonly, high mental variables including temperature and pressure, fluid content, diagenetic chemical processes such are here included in the empirical material constants as cementation in pore spaces, recrystallization and a, b and D, and in the time-dependent state variable, u. fluid-assisted diffusional mass transfer into sites of Stick–slip instabilities, proposed by Brace & low stress are also likely to contribute to this sort Byerlee (1966) to result in earthquake slip, may of deformation (Maltman 1994). These chemical only occur where the fault material exhibits unstable processes are unlikely to accommodate much dis- or conditional frictional stability (Scholz 2002). placement but, rather, lead to an increase in cohe- Frictional stability depends on the empirical con- sion and rigidity, suppressing granular flow and stants a, b and D; where, if the difference (a 2 b) increasing the ability of the rock to store elastic is positive, the material is said to be ‘velocity strain. A shallow transition from continuous granu- strengthening’ and m increases with slip (Fig. 1b). lar flow to frictional, discontinuous deformation of Such material is inherently stable and cannot slip cohesive rock capable of elastic rebound may there- at seismic velocities (Dieterich 1979). However, if fore occur in response to increasing confining (a 2 b) is negative, friction decreases with slip pressure, and to mechanical and chemical cementa- (Fig. 1b) and the material is ‘velocity weakening’. tion (Moore & Saffer 2001). In this case, the material is either unstable or con- ditionally stable; earthquakes may only nucleate in Grain-size-sensitive creep the unstable regime but can propagate into con- ditionally unstable regions (Scholz 1998).
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]
  • 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]
  • The Mechanics of First Order Splay Faulting: the Strike-Slip Case
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Columbia University Academic Commons Journal of Structural Geology 32 (2010) 118–126 Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg The mechanics of first order splay faulting: The strike-slip case Christopher H. Scholz*, Ryosuke Ando1, Bruce E. Shaw Lamont-Doherty Earth Observatory, Palisades, NY, USA article info abstract Article history: First order splay faults, as defined here, are secondary faults that form at acute angles symmetrically on Received 11 February 2009 either side of a primary fault of the same sense of shear. We show that these faults form when the Received in revised form primary fault becomes critically misaligned with the principal stresses such that splay fault formation, on 24 August 2009 the optimum plane for faulting, is favored. First order splay faults, in distinction from other splay faults, Accepted 7 October 2009 are secondary only in the temporal sense – they are subsequent but not subordinate, in a tectonic sense, Available online 14 November 2009 to the primary fault. Here we analyze the case of strike-slip faults, and compare it with data for several continental transform fault systems, where we show that the splay faults form in the most favorable Keywords: Faulting direction: parallel to the plate motion vector. We also discuss and speculate on several outstanding Earthquakes problems with regard to first order splay faults: the placement of them in space, means by which Fault interactions primary faults become misoriented in the stress field, and the mechanics of first order splay fault- primary fault junctions, once formed.
    [Show full text]