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Structural Geology I: Folds & FaultsStructural Geology I: Folds & Faults2006 Lecture 20, J. Steven Kite, West Virginia University2006 Lecture 20, 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.
Quiz 7 Due TodayQuiz 7 Due Today4 April4 April
SeeSee
http://www.geo.wvu.edu/%7Ekite/2006Geol101_Quiz%207_GlacialRockyShores.htm
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Strike & DipStrike & Dip
Strike
Strike
Strike & Dip Strike & Dip SymbolsSymbols
N
Strike & Dip Strike & Dip SymbolsSymbols
N
Dip Dip DirectionDirection
3
Strike & Dip Strike & Dip SymbolsSymbols
N
30 = Dip = Dip Angle in Angle in DegreesDegrees
Stress vs. StrainStress vs. Strain
LowLow Temperature, PressureTemperature, Pressure-- Brittle Rocks Brittle Rocks -- FaultingFaulting
HighHigh Temperature, Pressure Temperature, Pressure
-- Ductile Rocks Ductile Rocks -- FoldingFolding
Force vs. ResponseForce vs. Response
StressStress
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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
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Types of FoldsTypes of Folds
Anticline Syncline Monocline
Eroded (or Breached) FoldsEroded (or Breached) Folds
Anticline Syncline Monocline
Erosion Surface
Older Rx
Younger Rx
Other Types of FoldsOther Types of Folds
Anticlinorium Synclinorium large foldsGeanticline Geosyncline larger folds
Dome Basin closed folds
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Strike & Dip Strike & Dip SymbolsSymbols
N
30 = Dip = Dip Angle in Angle in DegreesDegrees
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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
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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
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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
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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
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Progression of FoldingProgression of Folding
Symmetrical Asymmetrical OverturnedRecumbantThrust Fault
Overturned FoldOverturned Fold
Up-Side-Down (Overturned) Limb
RecumbantRecumbant FoldFold
Recumbant Limb
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ThrustThrust--Faulted FoldFaulted Fold
Thrust Fault
Earthquakes & FaultsEarthquakes & Faults
Stress: Force AppliedStrain: Response to Force
Stress vs. StrainStress vs. Strain
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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
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Fault PartsFault Parts
Normal Fault
Before
After
Stress
Tension = Pull-Apart
Normal FaultNormal FaultTension
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Tension Normal FaultNormal Fault
Normal FaultsNormal Faults
Tension
DownDown--Dropped Dropped
Block Block Bounded Bounded by by Two Two Normal Normal FaultsFaults
Graben
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GrabenGraben, Death Valley, CA, Death Valley, CA
Reverse Fault
Before
After
Stress
Compression= Squeezing
Reverse FaultReverse Fault
Compression
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Reverse FaultReverse Fault
Thrust FaultThrust FaultLow-Angle (<30o) Reverse FaultMay Have Great Displacement
DisplacementDisplacement
ReverseReverse FaultFaultCompression
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Thrust Fault, Eastern
Pennsylvania
StrikeStrike--Slip MotionSlip Motion
Lateral Fault
RightRight--Lateral FaultLateral Fault
Map View - Before
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RightRight--Lateral FaultLateral Fault
Map View - After
Stream Offset on
San Andreas
Fault Lineament
LeftLeft--Lateral FaultLateral Fault
Before After
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Types of Faults
Oblique Fault
Before
After
Stress
Tension +Shear
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
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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
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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
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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
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Earthquakes & FaultsEarthquakes & FaultsElastic Rebound
Earth Earth quakequake
ElasticElastic ReboundRebound
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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?
26
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
27
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
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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
29
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
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Roll of Fluids as LubricantsRoll of Fluids as Lubricants
WaterNuclear Wastes in Colorado
Quiz 8 Due in Class on 6 April Quiz 8 Due in Class on 6 April
http://www.geo.wvu.edu/%7Ekite/2006GEOL101Quz8Structures.htm
Quiz 9 Due in Class on 18 April Quiz 9 Due in Class on 18 April (Test III)(Test III)
Quiz 9 Due on 18 April - Plate Tectonics - Admission Ticket for 10:35 Time Slot on Test III
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What Develops in Rock What Develops in Rock Under Under CompressionCompression??
Brittle Rocks: Reverse Faults
Ductile Rocks: Folds
Reverse FaultReverse Fault
Compression of Compression of Ductile Rocks: Ductile Rocks:
FoldsFolds
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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
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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
34
SlatySlaty Cleavage in RocksCleavage in Rocks
Sandstone (Joints) & Shale (Slaty Cleavage
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