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Joints vs. Faults Diastrophism Deformation of the earth’s crust due to plate movement Landforms that are created when plates collide or separate are caused by diastrophism Columnar Joints No displacement of layers after cracking Faulting Fractures in bedrock in which movement HAS taken place Earth’s Plate Boundaries follow Fault Lines New Madrid Zone is a fault line that is an ancient plate boundary Fault or Joint? Hanging Wall Footwall Let’s look at those again & determine the Footwall and Hanging Wall A B A B B A A B MC Strike & Dip Dip Dip refers to the angle at which a fault plane DIPS into the earth’s crust This is a dip… This is also a dip… This is taking a dip… This is definitely a dip… Dip-Slip Faults Normal Dip-Slip Fault Slickenlines are fine scratches & show direction of slip… In a Normal Dip-Slip Fault the Hanging Wall has moved DOWN relative to the footwall Reverse Dip-Slip Fault Reverse Dip-Slip faults are often referred to as THRUST faults because they are cause by compression forces. The Footwall acts likes a wedge… In Reverse Dip-Slip the Hanging Wall has moved UP relative to the footwall Strike & Dip Strike is the compass direction where the fault meets the surface Strike-Slip Faults AKA: Lateral Fault Caused by SHEAR forces The San Andreas Fault is a Lateral or Strike-Slip Fault Oblique-Slip Faults Caused by tension forces Divergent Plate Boundary Graphics showing RIFTING Africa is being slowly torn apart by rifting and Oblique faults… Oblique-Slip Fault Rifting can lead to sea floor spreading as can be seen in the MidAtlantic Ridge. This is technically an Oblique Fault Ok, now it’s time to identify faults Normal Dip-Slip Reverse Dip-Slip Strike-Slip Oblique-Slip That was a Normal Dip-Slip! You’re good. That was a Strike-Slip Fault… That was an Oblique-Slip Fault… Did you get it? Yup. That was another Normal Dip-Slip (As opposed to an ABNORMAL one ) So, did you call that one a Reverse Dip-Slip? You’re right!! That was certainly another Reverse Dip-Slip You called it… Reverse Dip-Slip Strike-Slip… Reverse Dip-Slip… Enough of the Strike-Slip Faults already!
