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Faulting Normal / Reverse / Transverse What is Faulting? ● Weakness in the earth's crust caused by earth ● ● ● ● ● ● ● ● movements Leads to fractures in the earth's crust Convection currents in mantle Faults force land up, down or sideways Down - normal fault (pulling apart) Up - reverse fault (pushing together) Sideways - Transform fault (sideways) Rock may slip very little each time (1-5 cm per year) In geological time (slippage = 100s of kilometres) Normal Fault ● Tension (Pulling Apart) ● Crust falls relative to other sections of crust ● Slope is known as a "scarp" ● The section that falls is known as a rift valley ● East African Rift Valley ○ many deep lakes due to faulting ○ New plate will form in millions of years East African Rift Valley African Plate Fault Line Somalian Plate (will break away from African plate in millions of years) Normal Fault Block Mountain Fault Scarp Rift Valley Normal Fault Normal Faults can lead to block mountains ● where a section of crust slips down and leaves a middle section above the two sides ● Looks likes a plateau or mountain with straight sides ● Example - Ben Bulben, Co. Sligo Normal faults & block mountains Block Mt Rift Valley Ben Bulben (Block Mountain) Reverse Fault ● Compression caused by earth movements ● also known as thrust faults ○ section of crust is pushed over another section ○ one section of crust is buried ● can occur together with normal faults ● lead to fold mountains, e.g. Armorican fold mountains in Munster (Caha & Galtee Mountains) ● Sandstone pushed over limestone Reverse Fault Diagram Galtee Mountains Transform / Transverse Diagram San Andreas Fault San Andreas Fault ● Pacific Plate moving northwest ● American Plate moving south ● Movement is about 5 cm per year ● Lateral motion (sideways) and not up or down ● May lead to earthquakes