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II. Methods in Morphotectonics 1- Identification of Active Faults 2 Determination of slip-rate on strike-slip faults 3- Determination of fold growth and shortening rates across a thrust fault system 4- Determinations of vertical deformation and extension rate across a rift system 5. Dating techniques
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1.c Reverse and Thrust faults
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Satellite Mosaic and topography of Central Asia
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Note a clear fault cutting alluvial surfaces The lobate geometry of the fault trace suggest thrust faulting (in addition to being associate with an anticline) (Eastern termination of Tugulu antocline, North Tian Shan piemont, Dzoungar basin)
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Fault-bend fold (flat-ramp system)
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Thrust Fault are often blind Fault-tip fold
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Foreland fold-and-thrust belt North Tien Shan
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Satellite Mosaic and topography of Central Asia
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Rivers entrenching a growing fold above an active thrust fault, China
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Satellite Mosaic and topography of Central Asia
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Drainage is either force to entrench into the rising fold or is diverted Growing fold above an active reverse fault, China
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Seismic ruptures of thrust faults
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~90 mm/yr GPS measurement of interseismic strain across Taiwan (Yu et al, 1997; Hsu et al, 2003)
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TheMw, 7.6, ChiChi Earthquake 1999 (Western Taiwan) Surface ruptures extends over about 80km, with up to 12m of coseismic slip.
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Mw, 7.6, ChiChi Earthquake 1999 (Taiwan)
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A closer look Chichi
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Scarp landforms (from a study of the 1988 Armenian earthquake)
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The Mw, 7.6, ChiChi Earthquake 1999 (Western Taiwan) Surface ruptures extends over about 80km, with up to 12m of coseismic slip.
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The “Big Bend” Reverse fault in a strike-slip setting
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(Ekstrom and Stein, 1992, Stein and Ekstrom, 1992, Gusofski et al, 2007) New Idria, 1982, Mw, 5.5 Coalinga 1983, Mw, 6.5 Kettelman Hills, 1985, Mw, 6.1
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Gusofski et al, 2007
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From JPL’s SRTM mission The 1987 Whitier Narrow and 1994 Northridge earthquakes alerted us to the presence of active blind thrusts within the metro region 1994 1987
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The city of Tripoli, in Lebanon, is built on an active thrust, forming an about 60m-high surface scarp Photo from M. Daeron Irregular, sinuous, smooth topographic escarpment, Tripoli
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Reverse faults: Irregular, sinuous, smooth topographic escarpment (because collapse) Most active reverse faults are blind (partly because they have a low dip- angle fault plane) Yet, they are commonly associated to surface folding; such folding commonly forces rivers to deviate from their original course
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