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WVU GEOL 341 - Faults and Faulting

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1Faults and FaultingGeol341-3422011Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004Topics• Faults on outcrop, maps, and cross sections• Fault zones and fault rocks• Types of faults and terminology• Slip vs. separation• Faults in wells• Fault propagationFaults, fault zones, shear zonesTerminologyHanging wallFoot wallFault Zone in Granitic GneissFault scarp after an earthquake- Nevada2Plate Boundary-San Andreas FaultFaultFenceFault zone, Brooks Range, AKFault zone in Quartzites-Brooks RangeSmall Normal FaultsPhoto: EL MillerSmall Thrust Fault – Moss Beach, CaPhoto: EL MillerTypes of fault3Oblique slipFault Striations- SlikenlinesRegional StrainTypes of Fault and the Principal StressesNormal ThrustStrike-slipFaults are shear fracturesin an elastic solid4Fault Propagation• Right-lateral Coulomb stress change on planes parallel to the main fault (Stein and Lisowski, 1983).The longer a fault, the more displacementit hasFault rocks with depthFault Rocks• Gauge: non-cohesive, fine grain• Breccia: coarse angular fragments• Cataclasite: cohesive fragments• Mylonite: ductile-brittle fault zone• Fault Melt (pseudotachylite): due to frictionDepthFault zone brecciain QuartziteBrooks Range, AK5Hydrothermal Fault BrecciaFault MeltMylonitesUndeformed granite DeformedLow angle fault- Whipple Mts, CAYoung Mountains-Active Fault –Basin and Range ProvinceEvolution of an ActiveMountain Front6Slot Canyon, Faulted Alluvial Fan- Death ValleyFaults Symbols in Map ViewNormal FaultsThrust FaultsDecorations are on the hanging wallStrike-slipFault on a Geological MapWhat kind of fault is this?NorthMap View of FaultsSlip vs. SeparationBlock Diagram7Separation : 2DIf layers are tilted, the map may be deceivingHow is this possible?Some Faults are Almost flatFaults in Seismic Reflection Data- Hope Basin, AKInterpreted Seismic Data3 km0Map view of normal fault(Fossen, 2010)8Faulted structure contour mapNormal faults from well dataWell LoggingSP Log (Spontaneous Potential)Electrical logsSpontaneous PotentialElectrical Resistivity9Thrust Fault in a WellThrust Fault in a Well(after Nelson, 2001)no scaleUNION OOLITEDEPI #5639 (047DEPI #5639 (047--055055--00226) Gamma Ray log00226) Gamma Ray logUNION OOLITE(Hanging wall)UNION OOLITE(Foot wall)100’PILOT KNOB THRUST FAULT228’ vertical displacementCrossCross--section A section A --AA’’A A’0-500-1000-1500PILOT KNOBARISTANWSEScale:500’500’5645564456395646303512715128961236652344473093UNIONPICKAWAYDENMARLITTLELIMEPRICETake Home Points• Relationship of type of fault to principal stresses• Types of fault rocks vs. depth• Fault slip vs. separation• Recognizing faults in outcrop and in wells– Normal faults omit section– Thrust faults repeat section• Faults don’t go on for ever they are elastic


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