From Coseismic Offsets to Fault-Block Mountains

Total Page:16

File Type:pdf, Size:1020Kb

From Coseismic Offsets to Fault-Block Mountains From coseismic offsets to fault-block mountains George A. Thompsona,1 and Tom Parsonsb,2 aDepartment of Geophysics, Stanford University, Stanford, CA 94305; and bUnited States Geological Survey, Menlo Park, CA 94025 Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved August 8, 2017 (received for review June 29, 2017) In the Basin and Range extensional province of the western United pattern than the topography. Combined GPS and InSAR ob- States, coseismic offsets, under the influence of gravity, display servations (5, 6) show broad areas of uplift and subsidence in the predominantly subsidence of the basin side (fault hanging wall), with vicinity of a chain of magnitude (M) ∼ 7 earthquakes that struck comparatively little or no uplift of the mountainside (fault footwall). A central Nevada between 1915 and 1954 (7, 8). The areal extent of few decades later, geodetic measurements [GPS and interferometric vertical deformation observed over this period spans across both synthetic aperture radar (InSAR)] show broad (∼100 km) aseismic uplift basins and ranges and can be 100–200 km in width (Fig. 2). symmetrically spanning the fault zone. Finally, after millions of years However, a different deformation mode is observed during and hundreds of fault offsets, the mountain blocks display large uplift individual earthquakes (coseismic period). Highly concentrated and tilting over a breadth of only about 10 km. These sparse but subsidence (10–15 km wide) of the basins is observed (9–13) robust observations pose a problem in that the coesismic uplifts of whereas the ranges are stable, or rise very slightly (Fig. 3). the footwall are small and inadequate to raise the mountain blocks. To These observations are based on leveling surveys recorded in address this paradox we develop finite-element models subjected to Nevada before and after the 1954 M = 7.2 Fairview Peak and extensional and gravitational forces to study time-varying deforma- M = 6.5 Dixie Valley earthquakes, and in Idaho before and tion associated with normal faulting. Stretching the model under grav- after the 1983 M = 6.9 Borah Peak earthquake. Clearly, the evo- ity demonstrates that asymmetric slip via collapse of the hanging wall lution from seismic slip on faults to the final topographic signature is a natural consequence of coseismic deformation. Focused flow in the of crustal extension passes through different temporal phases. We upper mantle imposed by deformation of the lower crust localizes develop a physical hypothesis based on isostasy and crustal litho- uplift, which is predicted to take place within one to two decades after spheric rheology, and test it using finite-element models. each large earthquake. Thus, the best-preserved topographic signature of earthquakes is expected to occur early in the postseismic period. Conceptual Model Conceptually, the process begins with elastic rebound, which in rifting | finite-element modeling | earthquakes | crustal deformation | normal faulting requires a horizontal withdrawal of mass from Basin and Range the fault zone and thus an unloading of the footwall (14, 15) (Fig. 4). Isostatic forces and inflow of lower crust and upper mantle then ith its repeating series of parallel ranges rising sharply cause a postseismic upward-directed bulging, focused initially near Wabove deep valleys, the Basin and Range province is one the fault zone and later, after several decades, becomes broader. of Earth’s most distinctive terranes (Fig. 1). However, this active The basin side is repeatedly dropped with each large earthquake. ∼10–15-Ma-old (1) landscape bears little resemblance to present- Isostasy in the Earth’s crust means that its shallowest elastic day measures of deformation. During earthquakes, the basins drop parts float in the denser, hotter, and more ductile substrate below. (2), but the ranges show little or no rise. Satellite ranging [GPS, These floating masses find their equilibrium heights over time, with interferometric synthetic aperture radar (InSAR)] shows areas of that duration depending on the rheology of the substrate. Basic broad uplift and subsidence that do not directly correspond with isostatic calculations, wherein the sudden mass change after an topography. We use numerical modeling techniques constrained earthquake (1-m slip event) is treated in theoretical floating ver- with observations over three periods: coseismic (deformation tical columns, predict an upward directed force of ∼70 MPa during earthquakes), postseismic (deformation after earthquakes), and multiseismic (topography resulting from repeated earth- Significance quakes). We further constrain our models with the concept of isostasy, the gravitational equilibrium that must ultimately result Observations at different times during extensional faulting ’ from any vertical change to the Earth s surface. The addition of cycles show dramatically different deformation. Available this constraint allows us to produce a single unifying model that coseismic and postseismic observations bear little resemblance explains variations in fault-related deformation over time. to the topography of rifted zones, yet this topography is the end result of repeated earthquakes. During earthquakes, and Observations during periods decades later, there is little evidence of rift The Basin and Range province topography was built in response to flank, or range-front deformation, yet strong bending and broad crustal extension between the Sierra Nevada ranges to the uplift of these features ultimately define extended terranes. west, and the Colorado Plateau to the east. Repeated earthquakes Numerical modeling incorporating gravity and the principle of on dipping (45°–60°) faults offset crystalline bedrock ranges (fault isostatic balance predicts strong vertical forces during the first footwalls) against basins filled with sediment (fault hanging walls) decade after a significant earthquake that are preferentially (Fig. 1), meaning that roughly half of the resulting deformation is focused beneath range fronts. We conclude these forces are vertical. Cumulative slip on these faults (faults that accommodate responsible for characteristic rift topography. This hypothesis is extension are called normal faults) can be up to ∼10 km in mag- testable with intermediate period geodetic observations that nitude, and is the result of many hundreds of earthquakes. We thus are rare for extensional earthquakes. term this deformation as multiseismic. Observations and modeling results show mountain blocks that are tilted or bent upward over a Author contributions: G.A.T. and T.P. designed research, performed research, analyzed width of about 10 km (Fig. 1). Wider mountain blocks (∼20 km) data, and wrote the paper. display more bending, which requires permanent rock deformation, The authors declare no conflict of interest. probably in part expressed by myriad minor faults and joints (3, 4). This article is a PNAS Direct Submission. Deformation measured over the span of decades (postseismic 1Deceased May 12, 2017. period) using remote sensing methods shows a very different 2To whom correspondence should be addressed. Email: [email protected]. 9820–9825 | PNAS | September 12, 2017 | vol. 114 | no. 37 www.pnas.org/cgi/doi/10.1073/pnas.1711203114 Downloaded by guest on September 24, 2021 -120˚ -118˚ -116˚ 5 Warner Range Surprise Valley 0 Depth (km) 40˚ -5 0510 15 Distance (km) e g e 38˚ n a g R n a e l R a 3.4 g e B uneroded surface B’ n v i t a 2.8 h w VE 2.5:1 g i h a 2.2 N S B B’ 1.6 Elevation (km) 1.0 Syncline axis Normal Dip fault Dir. 0102030 Distance (km) Fig. 1. Characteristic basin and range topography, with narrow chains of ranges interspersed by basins. (Upper, Inset) Cross-section model of the Warner Range and its bent range front (3, 35). (Lower) The range blocks are bent as a result of repeated faulting along their fronts rather than being tilted. In this example, a single block is faced on either side by normal faults, has no significant internal faulting, and both sides are bent upward (36). applied across the narrow zone of postfaulting mass change (Fig. responsible for the signature deformation that characterizes the 4). Additionally, stress transferred from primary earthquake slip Bain and Range province and other rift zones. (16) onto the continuation of a shear zone into the deep crust can cause afterslip and additional deformation (17). Numerical Model A distinction regarding continental dip–slip faults that cause ele- A numerical model that is allowed to freely respond to forces vation changes emerges because of isostasy. Faults form and fail as a that represent our best understanding of those acting in the result of differences in the magnitudes and directions of the principal Earth’s crust can yield revealing results provided the solutions stresses in the crust, typically at a frictionally dependent angle in- are not overly guided, or overly sensitive to parameter choices. clined 30°–60° to the least compressive stress direction (18). In Gravity is the driving force acting on the crust, and the primary compressional (thrust) faulting, the least stress is vertically inclined, feature of extensional terranes is that their boundaries can ex- and the greatest stress is oriented horizontally, whereas strike–slip pand laterally, enabling the crust to collapse under its weight. We faulting regimes have horizontally directed greatest and least stresses. develop a simple finite-element model under these conditions In extensional settings,
Recommended publications
  • Lesson 3 Forces That Build the Land Main Idea
    Lesson 3 Forces That Build the Land Main Idea Many landforms result from changes and movements in Earth’s crust. Objectives Identify types of landforms and the processes that form them. Describe what happens when an earthquake occurs. Vocabulary fault focus aftershock seismic wave epicenter seismograph magnitude vent What forces change Earth’s crust? At transform boundaries, the pieces of rock rub together in a force called shearing, like the blades of a pair of scissors, causing the rock to break. At convergent boundaries, plates collide and this force is called compression, squeezing the rock together. At divergent boundaries, plates separate causing tension, making the crust longer and thinner eventually breaking and creating a fault. Faults are usually located along the boundaries between tectonic plates. Three Kinds of Faults Shearing forms strike-slip faults. Tension forms normal faults. The rock above the fault moves down. Compression forms reverse faults. The rock above the fault moves up. Uplifted Landforms Folded mountains are mostly made up of rock layers folded by being squeezed together. Fault-block mountains are made by huge, tilted blocks of rock separated from the surrounding rock by faults. The Colorado Plateau was formed when rock layers were pushed upward. The Colorado River eventually formed the Grand Canyon. Quick Check Infer Why are faults often produced along plate boundaries? Forces act on the crust most directly at plate boundaries, because these locations are where plates are moving, relative to each other. Critical Thinking Why do some mountains form as folded mountains and others form as fault-block mountains? Compression forces form folded mountains, and tension forms fault- block mountains.
    [Show full text]
  • Part 3: Normal Faults and Extensional Tectonics
    12.113 Structural Geology Part 3: Normal faults and extensional tectonics Fall 2005 Contents 1 Reading assignment 1 2 Growth strata 1 3 Models of extensional faults 2 3.1 Listric faults . 2 3.2 Planar, rotating fault arrays . 2 3.3 Stratigraphic signature of normal faults and extension . 2 3.4 Core complexes . 6 4 Slides 7 1 Reading assignment Read Chapter 5. 2 Growth strata Although not particular to normal faults, relative uplift and subsidence on either side of a surface breaking fault leads to predictable patterns of erosion and sedi­ mentation. Sediments will fill the available space created by slip on a fault. Not only do the characteristic patterns of stratal thickening or thinning tell you about the 1 Figure 1: Model for a simple, planar fault style of faulting, but by dating the sediments, you can tell the age of the fault (since sediments were deposited during faulting) as well as the slip rates on the fault. 3 Models of extensional faults The simplest model of a normal fault is a planar fault that does not change its dip with depth. Such a fault does not accommodate much extension. (Figure 1) 3.1 Listric faults A listric fault is a fault which shallows with depth. Compared to a simple planar model, such a fault accommodates a considerably greater amount of extension for the same amount of slip. Characteristics of listric faults are that, in order to maintain geometric compatibility, beds in the hanging wall have to rotate and dip towards the fault. Commonly, listric faults involve a number of en echelon faults that sole into a low­angle master detachment.
    [Show full text]
  • THE JOURNAL of GEOLOGY March 1990
    VOLUME 98 NUMBER 2 THE JOURNAL OF GEOLOGY March 1990 QUANTITATIVE FILLING MODEL FOR CONTINENTAL EXTENSIONAL BASINS WITH APPLICATIONS TO EARLY MESOZOIC RIFTS OF EASTERN NORTH AMERICA' ROY W. SCHLISCHE AND PAUL E. OLSEN Department of Geological Sciences and Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 ABSTRACT In many half-graben, strata progressively onlap the hanging wall block of the basins, indicating that both the basins and their depositional surface areas were growing in size through time. Based on these con- straints, we have constructed a quantitative model for the stratigraphic evolution of extensional basins with the simplifying assumptions of constant volume input of sediments and water per unit time, as well as a uniform subsidence rate and a fixed outlet level. The model predicts (1) a transition from fluvial to lacustrine deposition, (2) systematically decreasing accumulation rates in lacustrine strata, and (3) a rapid increase in lake depth after the onset of lacustrine deposition, followed by a systematic decrease. When parameterized for the early Mesozoic basins of eastern North America, the model's predictions match trends observed in late Triassic-age rocks. Significant deviations from the model's predictions occur in Early Jurassic-age strata, in which markedly higher accumulation rates and greater lake depths point to an increased extension rate that led to increased asymmetry in these half-graben. The model makes it possible to extract from the sedimentary record those events in the history of an extensional basin that are due solely to the filling of a basin growing in size through time and those that are due to changes in tectonics, climate, or sediment and water budgets.
    [Show full text]
  • A Parametric Method to Model 3D Displacements Around Faults with Volumetric Vector Fields G
    A parametric method to model 3D displacements around faults with volumetric vector fields G. Laurent, G. Caumon, A. Bouziat, M. Jessell To cite this version: G. Laurent, G. Caumon, A. Bouziat, M. Jessell. A parametric method to model 3D displace- ments around faults with volumetric vector fields. Tectonophysics, Elsevier, 2013, 590, pp.83-93. 10.1016/j.tecto.2013.01.015. hal-01301478 HAL Id: hal-01301478 https://hal.archives-ouvertes.fr/hal-01301478 Submitted on 23 Jul 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. A parametric method to model 3D displacements around faults with volumetric vector fieldsI Gautier Laurenta,b,∗, Guillaume Caumona,b, Antoine Bouziata,b,1, Mark Jessellc, Gautier Laurenta,b,∗, Guillaume Caumona,b, Antoine Bouziata,b,1, Mark Jessellc aUniversit´ede Lorraine, CRPG UPR 2300, Vandoeuvre-l`es-Nancy,54501, France bCNRS, CRPG, UPR 2300, Vandoeuvre-l`es-Nancy, 54501, France cIRD, UR 234, GET, OMP, Universit´eToulouse III, 14 Avenue Edouard Belin, 31400 Toulouse, FRANCE Abstract This paper presents a 3D parametric fault representation for modeling the displacement field associated with faults in accordance with their geometry. The displacements are modeled in a canonical fault space where the near-field displacement is defined by a small set of parameters consisting of the maximum displacement amplitude and the profiles of attenuation in the surrounding space.
    [Show full text]
  • Garlock Fault: an Intracontinental Transform Structure, Southern California
    GREGORY A. DAVIS Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 B. C. BURCHFIEL Department of Geology, Rice University, Houston, Texas 77001 Garlock Fault: An Intracontinental Transform Structure, Southern California ABSTRACT Sierra Nevada. Westward shifting of the north- ern block of the Garlock has probably contrib- The northeast- to east-striking Garlock fault uted to the westward bending or deflection of of southern California is a major strike-slip the San Andreas fault where the two faults fault with a left-lateral displacement of at least meet. 48 to 64 km. It is also an important physio- Many earlier workers have considered that graphic boundary since it separates along its the left-lateral Garlock fault is conjugate to length the Tehachapi-Sierra Nevada and Basin the right-lateral San Andreas fault in a regional and Range provinces of pronounced topogra- strain pattern of north-south shortening and phy to the north from the Mojave Desert east-west extension, the latter expressed in part block of more subdued topography to the as an eastward displacement of the Mojave south. Previous authors have considered the block away from the junction of the San 260-km-long fault to be terminated at its Andreas and Garlock faults. In contrast, we western and eastern ends by the northwest- regard the origin of the Garlock fault as being striking San Andreas and Death Valley fault directly related to the extensional origin of the zones, respectively. Basin and Range province in areas north of the We interpret the Garlock fault as an intra- Garlock.
    [Show full text]
  • The Late Bajocian-Bathonian Evolution of the Oseberg-Brage Area, Northern North Sea
    Sedimentation history as an indicator of rift initiation and development: the Late Bajocian-Bathonian evolution of the Oseberg-Brage area, northern North Sea RODMAR RAVNÅS, KAREN BONDEVIK, WILLIAM HELLAND-HANSEN, LEIF LØMO, ALF RYSETH & RON J. STEEL Ravnås, R., Bondevik, K., Helland-Hansen, W., Lømo, L., Ryseth, A. & Steel, R. J.: Sedimentation history as an indicator of rift initiation and development: the Late Bajocian-Bathonian evolution of the Oseberg-Brage area, northem North Sea. Norsk Geologisk Tidsskrift, Vol. 77, pp. 205-232. Oslo 1997. ISSN 0029 -196X. The Tarbert Formation in the Oseberg-Brage area consists of shoreline sandstones and lower delta-plain heterolithics which basinward interdigitate with offshore sediments of the lower Heather Formation and landward with fluvio-deltaic deposits of the upper Ness Formation. The Late Bajocian-Tarbert and lower Heather Formations form three wedge-shaped, regressive-transgressive sequences which constitute offset, landward-stepping shoreline prisms. Initial gentle rotational extensional faulting occurred during the deposition of the uppermost Ness Formation and resulted in basinfloor subsidence and flooding across the Brent delta. Subsequent extensional faulting exerted the major control on the drainage development, basin physiography, the large-scale stacking pattem, i.e. the progradational-to-backstepping nature of the sequences, as well as on the contained facies tracts and higher-order stacking pattem in the regressive and transgressive segments. Progradation occurred during repetitive tectonic dormant stages, whereas the successive transgressive segments are coupled against intervening periods with higher rates of rotational faulting and overall basinal subsidence. Axial drainage dominated during the successive tectonic dormant stages. Transverse drainage increased in influence during the intermittent rotational tilt stages, but only as small, local (fault block) hanging-wall and footwall sedimentary lobes.
    [Show full text]
  • 4. Deep-Tow Observations at the East Pacific Rise, 8°45N, and Some Interpretations
    4. DEEP-TOW OBSERVATIONS AT THE EAST PACIFIC RISE, 8°45N, AND SOME INTERPRETATIONS Peter Lonsdale and F. N. Spiess, University of California, San Diego, Marine Physical Laboratory, Scripps Institution of Oceanography, La Jolla, California ABSTRACT A near-bottom survey of a 24-km length of the East Pacific Rise (EPR) crest near the Leg 54 drill sites has established that the axial ridge is a 12- to 15-km-wide lava plateau, bounded by steep 300-meter-high slopes that in places are large outward-facing fault scarps. The plateau is bisected asymmetrically by a 1- to 2-km-wide crestal rift zone, with summit grabens, pillow walls, and axial peaks, which is the locus of dike injection and fissure eruption. About 900 sets of bottom photos of this rift zone and adjacent parts of the plateau show that the upper oceanic crust is composed of several dif- ferent types of pillow and sheet lava. Sheet lava is more abundant at this rise crest than on slow-spreading ridges or on some other fast- spreading rises. Beyond 2 km from the axis, most of the plateau has a patchy veneer of sediment, and its surface is increasingly broken by extensional faults and fissures. At the plateau's margins, secondary volcanism builds subcircular peaks and partly buries the fault scarps formed on the plateau and at its boundaries. Another deep-tow survey of a patch of young abyssal hills 20 to 30 km east of the spreading axis mapped a highly lineated terrain of inactive horsts and grabens. They were created by extension on inward- and outward- facing normal faults, in a zone 12 to 20 km from the axis.
    [Show full text]
  • Joints, Folds, and Faults
    Structural Geology Rocks in the Crust Are Bent, Stretched, and Broken … …by directed stresses that cause Deformation. Types of Differential Stress Tensional, Compressive, and Shear Strain is the change in shape and or volume of a rock caused by Stress. Joints, Folds, and Faults Strain occurs in 3 stages: elastic deformation, ductile deformation, brittle deformation 1 Type of Strain Dependent on … • Temperature • Confining Pressure • Rate of Strain • Presence of Water • Composition of the Rock Dip-Slip and Strike-Slip Faults Are the Most Common Types of Faults. Major Fault Types 2 Fault Block Horst and Graben BASIN AND Crustal Extension Formed the RANGE PROVINCE Basin and Range Province. • Decompression melting and high heat developed above a subducted rift zone. • Former margin of Farallon and Pacific plates. • Thickening, uplift ,and tensional stress caused normal faults. • Horst and Graben structures developed. Fold Terminology 3 Open Anticline – convex upward arch with older rocks in the center of the fold (symmetrical) Isoclinal Asymmetrical Overturned Recumbent Evolution Simple Folds of a fold into a reverse fault An eroded anticline will have older beds in the middle An eroded syncline will have younger beds in middle Outcrop patterns 4 • The Strike of a body of rock is a line representing the intersection of A layer of tilted that feature with the plane of the horizon (always measured perpendicular to the Dip). rock can be • Dip is the angle below the horizontal of a geologic feature. represented with a plane. o 30 The orientation of that plane in space is defined with Strike-and- Dip notation. Maps are two- Geologic Map Showing Topography, Lithology, and dimensional Age of Rock Units in “Map View”.
    [Show full text]
  • Uplift of Earth's Crust
    Standards—7.3.4: Explain how heat flow and movement of material within Earth causes earthquakes and vol- canic eruptions and creates mountains and ocean basins. 7.3.7: Give examples of some changes in Earth’s surface that are abrupt, such as earthquakes and volcanic eruptions, and some changes that happen very slowly, such as uplift and wearing down of mountains and the action of glaciers. Also covers: 7.2.7 (Detailed standards begin on page IN8.) Uplift of Earth’s Crust Building Mountains One popular vacation that people enjoy is a trip to the mountains. Mountains tower over the surrounding land, often providing spectacular views from their summits or from sur- I Describe how Earth’s mountains rounding areas. The highest mountain peak in the world is form and erode. Mount Everest in the Himalaya in Tibet. Its elevation is more I Compare types of mountains. than 8,800 m above sea level. In the United States, the highest I Identify the forces that shape mountains reach an elevation of more than 6,000 m. There are Earth’s mountains. four main types of mountains—fault-block, folded, upwarped, and volcanic. Each type forms in a different way and can pro- The forces inside Earth that cause duce mountains that vary greatly in size. Earth’s plates to move around also are responsible for forming Earth’s Age of a Mountain As you can see in Figure 11, mountains mountains. can be rugged with high, snowcapped peaks, or they can be rounded and forested with gentle valleys and babbling streams.
    [Show full text]
  • Synclinal-Horst Basins: Examples from the Southern Rio Grande Rift and Southern Transition Zone of Southwestern New Mexico, USA Greg H
    Basin Research (2003) 15 , 365–377 Synclinal-horst basins: examples from the southern Rio Grande rift and southern transition zone of southwestern New Mexico, USA Greg H. Mack,n William R. Seagern and Mike R. Leederw nDepartment of Geological Sciences, New Mexico State University, Las Cruces, New Mexico, USA wSchool of Environmental Sciences, University of East Anglia, Norwich, Norfolk, UK ABSTRACT In areas of broadly distributed extensional strain, the back-tilted edges of a wider than normal horst block may create a synclinal-horst basin.Three Neogene synclinal-horst basins are described from the southern Rio Grande rift and southernTransition Zone of southwestern New Mexico, USA.The late Miocene^Quaternary Uvas Valley basin developed between two fault blocks that dip 6^81 toward one another. Containing a maximum of 200 m of sediment, the UvasValley basin has a nearly symmetrical distribution of sediment thickness and appears to have been hydrologically closed throughout its history.The Miocene Gila Wilderness synclinal-horst basin is bordered on three sides by gently tilted (101,151,201) fault blocks. Despite evidence of an axial drainage that may have exited the northern edge of the basin, 200^300 m of sediment accumulated in the basin, probably as a result of high sediment yields from the large, high-relief catchments.The Jornada del Muerto synclinal- horst basin is positioned between the east-tilted Caballo and west-tilted San Andres fault blocks. Despite uplift and probable tilting of the adjacent fault blocks in the latest Oligocene and Miocene time,sedimentwas transported o¡ the horst and deposited in an adjacent basin to the south.
    [Show full text]
  • Faults and Joints
    97 FAULTS Fractures are planar discontinuities, i.e. interruption of the rock physical continuity, due to stresses. The geological fractures occur at every scale so that any large volume of rock has some or many. These discontinuities are attributed to sudden relaxation of elastic energy stored in the rock. The geological fractures have their economic importance. The loss of continuity in intact rocks provides the necessary permeability for migration and accumulation of fluids such as groundwater and petrol. Fractured reservoirs and aquifers are typically anisotropic since their transmissivity is regulated by the conductive properties of fractures, which the local stress field partially controls. Geological fractures may be partially or wholly healed by the introduction of secondary minerals, often giving rise to ore deposits, or by recrystallization of the original minerals. Planar discontinuities along which rocks lose cohesion during their brittle behavior are: - joints if there is no component of displacement parallel to the plane (there may be some very small orthogonal parting; joints are extension fractures). - faults if rocks on both sides of the plane have moved relative to each other, parallel to the plane (faults are shear fractures). - veins if the fractures are filled with secondary crystallization. Joints and faults divide the rocks into blocks whose size and shape must be taken into consideration for engineering, quarrying, mining, and geomorphology. Fault terminology Definitions Faults separate two adjacent blocks of rock that have moved past each other because of induced stresses. The notion of localized movement leads to two genetically different classes of faults reflecting the two basic behaviors of rocks under stress: brittle and ductile.
    [Show full text]
  • And S-Wave Seismic Attenuation for Deep Natural Gas Exploration and Development DE-FC26-04NT42243
    Novel Use of P- and S-wave Seismic Attenuation for Deep Natural Gas Exploration and Development DE-FC26-04NT42243 Final Report October 1, 2004 to September 30, 2006 Issued: October 2006 Contributors Dr. Joel Walls* Dr. M. T. Taner* Richard Uden* Scott Singleton* Naum Derzhi* Dr. Gary Mavko** Dr. Jack Dvorkin** *Principal Contractor: Rock Solid Images 2600 S. Gessner Suite 650 Houston, TX, 77036 **Subcontractor: Petrophysical Consulting Inc. 730 Glenmere Way Emerald Hills, CA, 94062 Novel Use of P-wave and S-wave Seismic Attenuation for Deep Natural Gas Exploration and Development, Final Report DE-FC26-04NT42243 DISCLAIMER This report was prepared as an account of work sponsored by the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 2 Novel Use of P-wave and S-wave Seismic Attenuation for Deep Natural Gas Exploration and Development, Final Report DE-FC26-04NT42243 ABSTRACT Deeply buried gas reservoirs along the Gulf of Mexico shelf are an important future energy resource for the U.S.
    [Show full text]