faults_part1 - Introduction to Faults I Basic Terminology A Fault a planar surface or narrow zone along which there is slip between the two blocks of

faults_part1 - Introduction to Faults I Basic Terminology A...

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52 Introduction to Faults I. Basic Terminology A. Fault: a planar surface or narrow zone along which there is slip between the two blocks of rock. 1. Fault = mode 1 or 2 "shear fracture" a. "Fault": > 1m or more b. "Shear Fractures": on centimeter scale c. "micro-fault": on order of micrometers, under scope (1) single mineral shear fractures 2. Fault = "brittle rock failure" + shear motion 3. Occurrences of Faults a. Fault: Single, discrete fault plane b. Fault Zone: Anastomosed network of branching faults c. Ductile Shear Zone: a zone of ductile deformation B. Fault Terminology 1. Fault Blocks: two masses of rock cut by fault 2. Hanging Wall: block of rock above fault plane 3. Footwall: block of rock below fault plane a. Vertical Faults: hanging wall/footwall do not apply 4. High angle Fault: > 45 degrees dip 5. Low angle Fault: < 45 degrees dip 6. Slip or Relative Displacement: net distance and direction the hanging wall block has moved with respect to the footwall block a. Throw: net vertical offset of marker horizon along fault b. Heave: net horizontal offset of marker horizon along fault C. Fault Classification 1. Dip-slip Faults: net slip parallel to dip direction of fault plane 2. Strike-slip Faults: net slip parallel to strike direction of fault plane 3. Oblique-slip Faults: net slip at some acute angle to strike and dip of fault plane a. strike-slip vector component + dip-slip vector component 4. Normal Faults: dip-slip fault in which hanging wall moves down relative to footwall 5. Reverse Faults: high-angle, dip-slip fault in which hanging wall moves up relative to footwall 6. Thrust Faults: low-angle, dip slip fault in which hanging wall moves up
53 relative to footwall 7. Strike Slip Faults: hanging wall and footwall offset along strike of fault plane (neither up or down) a. Dextral Strike Slip Faults = Right Lateral Strike-Slip Faults: when looking across fault plane, block on opposite side appears to move to the right b. Sinistral strike slip faults = left lateral strike slip faults: when looking across fault plane, block on opposite side appears to move to the left 8. Oblique Slip Faults a. Sinistral/Dextral Normal b. Sinistral/Dextral Reverse II. Recognition of Faults A. Intrinsic Features 1. Textures/structures imparted to rocks deformed by the fault process: a. Cataclasis: mechanical crushing/grinding of rocks along shear zone (1)

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