Structural Geology I: Folds & FaultsStructural Geology I: Folds & Faults2009 Lect. 18, J. Steven Kite, West Virginia University2009 Lect. 18, J. Steven Kite, West Virginia University

Steeply dipping axial plane cleavage. These folded sedimentary layers exposed near Sullivan River in southeastern British Columbia dramatically illustrate the awesome forces constantly at work reshaping the features of the earth.

Photo by R.A. Price

2 Apr

Strike & DipStrike & Dip

Strike

Strike

Strike & Dip Strike & Dip SymbolsSymbols

N

Strike & Dip Strike & Dip SymbolsSymbols

N

Dip Dip DirectionDirection

Strike & Dip Strike & Dip SymbolsSymbols

N

30 = Dip = Dip Angle in Angle in DegreesDegrees

Stress vs. StrainStress vs. Strain

Force vs. ResponseForce vs. Response

Rock BehaviorRock Behavior

LowLow Temperature, PressureTemperature, Pressure-- Brittle Rocks Brittle Rocks -- FaultingFaulting

HighHigh Temperature, Pressure Temperature, Pressure

-- Ductile Rocks Ductile Rocks –– Folding or Folding or PullPull--Apart Apart (Silly Putty or Taffy)(Silly Putty or Taffy)

Varies with TemperatureVaries with Temperature

StressStress(Force)(Force)Red ArrowsRed Arrows

Ductile Strain Ductile Strain (Response) Boxes(Response) Boxes

FOLDSFOLDS

Compression

FOLDSFOLDS

Compression

Rails Compressed During 1964 Earthquake Alaska

National Earthquake Information Centerneic.usgs.gov/neis/eqlists/USA/1964_03_28_pics_1.html

Types of FoldsTypes of Folds

Anticline Syncline Monocline

Eroded (or Breached) FoldsEroded (or Breached) Folds

Anticline Syncline Monocline

Erosion Surface

Older Rx

Younger Rx

Anticlines (A) & Synclines (S)Anticlines (A) & Synclines (S)

Photo by R.A. Price

AAAA AA SSSSSS

?

?

Strike & Dip Strike & Dip SymbolsSymbols

N

30 = Dip = Dip Angle in Angle in DegreesDegrees

Ant

iclin

e

Ant

iclin

e

Sync

line

Home

Grandmother’s House

The

Woo

ds

The

Riv

er

Parts of a Fold

LimbAxis = Line of Symmetry

Plural = Axes

Parts of a Fold

LimbAxis = Line of Symmetry

Axial Plane

Parts of a Fold

LimbAxis = Line of Symmetry

Axial Plane

Parts of a Fold

Axial Planes

NonNon--Plunging vs. Plunging FoldsPlunging vs. Plunging FoldsDipping AxesHorizontal Axes

Plunging FoldPlunging Fold

Breached (Eroded) Folds & Age of Rocks. Superposition:

Youngest on Top

Where are older rocks exposed at the surface? Younger Rocks

Younger RocksOlder Rocks

MD Geological Survey Photo: www.mgs.md.gov/esic/features/ gif/sidel.jpg

Younger RocksYounger Rocks

Older RocksOlder Rocks

Older RocksOlder Rocks

Where are Older Rocks, Younger Rocks?Where are Older Rocks, Younger Rocks?Remember Remember ““SuperpositionSuperposition””

Symmetrical Symmetrical SynclineSyncline

AsymmetricalAnticline

Asymmetrical Asymmetrical SynclineSyncline

AsymmetricalAnticline

Progression of FoldingProgression of Folding

Symmetrical Asymmetrical OverturnedRecumbantThrust Fault

Overturned FoldOverturned Fold

Up-Side-Down (Overturned) Limb

RecumbantRecumbant FoldFold

Recumbant Limb

ThrustThrust--Faulted FoldFaulted Fold

Thrust Fault

Earthquakes & FaultsEarthquakes & Faults

Stress: Force AppliedStrain: Response to Force

Stress vs. StrainStress vs. Strain

FaultFault

Plane of Weakness Along Which Movement Has Occurred

JointJointBreak Without Significant Movement

Go to this site to see animations of different fault types:

http://www.iris.edu/gifs/animations/faults.htmCheck Out Fig 15.21 in Plummer Text Book, 10th Ed.

Mostly Up and Down

DipDip--Slip MotionSlip Motion

Fault PartsFault Parts

Normal Fault

Before

After

Stress

Tension = Pull-Apart

Normal FaultNormal FaultTension

Tension Normal FaultNormal Fault

Normal FaultsNormal Faults

Tension

DownDown--Dropped Dropped

Block Block Bounded Bounded by by Two Two Normal Normal FaultsFaults

Graben

GrabenGraben, Death Valley, CA, Death Valley, CA

Reverse Fault

Before

After

Stress

Compression= Squeezing

Reverse FaultReverse Fault

Compression

Reverse FaultReverse Fault

Thrust FaultThrust FaultLow-Angle (<30o) Reverse FaultMay Have Great Displacement

DisplacementDisplacement

ReverseReverse FaultFaultCompression

Thrust Fault, Eastern

Pennsylvania

StrikeStrike--Slip MotionSlip Motion

Lateral Fault

RightRight--Lateral FaultLateral Fault

Map View - Before

RightRight--Lateral FaultLateral Fault

Map View - After

Stream Offset on

San Andreas

Fault Lineament

LeftLeft--Lateral FaultLateral Fault

Before After

Types of Faults

Oblique Fault

Before

After

Stress

Tension +Shear

L'Aquila, Italy Earthquake: 6.3L'Aquila, Italy Earthquake: 6.3April 6th 2009 earthquake in Central Italy occurred as a result of normal faulting on a NW-SE oriented structure in the central Apennines. Focus was only 5 km (3 mi) depth.http://www.youtube.com/watch?v=qJFwtSoH0qM&feature=related

Sound –http://www.youtube.com/watch?v=TeEXjrQse4Q&feature=related

http://maps.google.com/maps?f=q&hl=en&q=42.4037,13.3236(M6.3+-+Central+Italy+-+2009+April+6+01%3A32%3A42+UTC)&t=h&z=7

Seismologist Was Forced to Remove Italy Earthquake Warning From the Internethttp://blogs.wsj.com/digits/2009/04/06/seismologist-was-forced-to-remove-italy-earthquake-warning-from-the-internet/

Active vs. Inactive FaultsActive vs. Inactive Faults

Active Faults: Moved at Least Once in Last 10,000 years OR

Twice or More in Last 250,000 years

2 Apr

Expected Earthquake IntensityExpected Earthquake Intensity

3 New Madrid 3 New Madrid Quakes Quakes 18111811--18121812

Modified Richter (Total Energy) Magnitude ScaleModified Richter (Total Energy) Magnitude Scale

Sumatra 2004

MercalliMercalli(Surface Intensity)(Surface Intensity)

ScaleScaleFig 16.11Fig 16.11

Focus: Point of FaultingFocus: Point of Faulting

Epicenter: Point on Surface Above Focus

What Causes Damage?What Causes Damage?No Opening of Earth & Gobbling up Cities

Little Damage From Fault Offset

Most Damage Caused by Seismic Waves (Including Tsunamis) & Landslides

Elastic Rebound theoryElastic Rebound theory

Developed after 1906 SF Quake

Earthquakes & FaultsEarthquakes & Faults

At Great Depths, Rock Does Not Fully Snap Back... At Great Depths, Rock Does Not Fully Snap Back...

Earthquakes & FaultsEarthquakes & FaultsElastic Rebound

Earthquakes & FaultsEarthquakes & FaultsElastic Rebound

Earth Earth quakequake

ElasticElastic ReboundRebound

Marin County, 1906

http://neic.usgs.gov/neis/eqlists/USA/1906_04_18_pics_2.html

USGS Photo by G.K. Gilbert

Offset Fence Shows Strike Slip Motion

Right or Left Lateral?

Good Friday 1964 Alaska Earthquake, Magnitude 9.2National Earthquake Information CenterNational Earthquake Information Center

neic.usgs.gov/neis/eqlists/USAneic.usgs.gov/neis/eqlists/USA//1964_03_28_pics_1.html1964_03_28_pics_1.html

This side rose 5 m (16 ft)Dip-slip motion

Fault Scarp

Earthquake Damage: Landslides

National Earthquake Information Centerneic.usgs.gov/neis/eqlists/USA/1964 03 28 pics 1.html

Anchorage Elementary School Destroyed

Earthquake Damage: Landslides1964 Alaska RR Near Anchorage

National Earthquake Information Centerneic.usgs.gov/neis/eqlists/USA/

1964_03_28_pics_1.html

Earthquake Damage: Tsunami= Seismic Sea Wave

(A.K.A. “Tidal Wave”)

National Earthquake Information Centerneic.usgs.gov/neis/eqlists/USA/1964_03_28_pics_1.html

Logging Truck Wrapped Around Tree by TsunamiNational Earthquake Information Center

neic.usgs.gov/neis/eqlists/USA/1964_03_28_pics_1.html

18 April 1906 Quake Damage18 April 1906 Quake DamageSan Francisco City HallSan Francisco City Hall

http://neic.usgs.gov/neis/eqlists/USA/1906_04_18_pics_2.html

StanfordUniversity

1906

http://neic.usgs.gov/neis/eqlists/USA/1906_04_18_pics_2.html

USGS California Seismic

Risk Map

USGS W.Va. USGS W.Va. Seismic Risk MapSeismic Risk Map

Largest Earthquake in West Virginia: 1969 November 20, Magnitude 4.5

Historic EarthquakesSouthern West Virginia

1969 11 20 01:00:09.3 UTC (Local 11/19) Magnitude 4.53 Intensity VI

Largest Earthquake in West Virginia Minor damage occurred in Giles County, Virginia, at Glen Lyn and Rich Creek, and

at three towns in southern West Virginia. At Glen Lyn, a few bricks were knocked from a chimney, windows were broken, and plaster was broken from most of the walls in an old house. At Rich Creek, plaster cracked and fell and windows were broken. A cornice reportedly was shaken from one building in Henry County, at Collinsville, Virginia. Windows also were broken in southern Mercer County, West Virginia, at Lerona, Oakvale, and Elgood. Felt over all or parts of nine States: Georgia, Kentucky, Maryland, North Carolina, Ohio, South Carolina, Tennessee, Virginia, and West Virginia.

Abridged from Seismicity of the United States, 1568-1989 (Revised), by Carl W. Stover and Jerry L. Coffman, U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, Washington: 1993.

At Some Point (T, P)At Some Point (T, P) Earthquakes Are Earthquakes Are Impossible Impossible Because Rock Is Not ElasticBecause Rock Is Not Elastic

Roll of Fluids as LubricantsRoll of Fluids as Lubricants

WaterNuclear Wastes in Colorado

Quiz 7 Due in Class on 9 April Quiz 7 Due in Class on 9 April

http://www.geo.wvu.edu/~kite/2009GEOL101Quiz7Structures.pdf

What Develops in Rock What Develops in Rock Under Under CompressionCompression??

Brittle Rocks: Reverse Faults

Ductile Rocks: Folds

Reverse FaultReverse Fault

Reverse FaultReverse Fault

Compression of Compression of Ductile Rocks: Ductile Rocks:

FoldsFolds

What Develops in Rock What Develops in Rock Under Tension?Under Tension?

Brittle Rocks: Normal Faults

Normal FaultsNormal Faults

Tension

What Develops in Rock What Develops in Rock Under Tension?Under Tension?

Ductile Rocks: Boudinage

Boudinage

11 Apr

BoudinageBoudinage

Force Force Nature of RockNature of RockBrittle Brittle DuctileDuctile

Tension Normal Faults * Boudinage

Compression Reverse Faults Folds *

* Why Are Normal Faults & Folds Most Common?

Slaty Cleavage in RocksFirst Step in

Metamorphic Foliation

SlatySlaty Cleavage in RocksCleavage in Rocks

Sandstone (Joints) & Shale (Slaty Cleavage

InterpetationInterpetation of Structures: of Structures: Simple CaseSimple Case

Horizontal Rocks (Law of Original Horizontality)

Folded Rocks --> Deformation (Compression)

Modern Topography Almost Always Is Related to Differential Erosion