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TheMendocino fracture zone is afracture zone andtransform boundary over 4000 km (2500 miles) long,[1] starting off the coast ofCape Mendocino in far northernCalifornia. It runs westward from a triple junction with theSan Andreas Fault and theCascadia subduction zone for about 300 km to the southern end of theGorda Ridge. It continues on west of its junction with the Gorda Ridge, as an inactive remnant section which extends for about 4,000 km to approximately 35°N 175°W.[2]
Technically, a fracture zone is not a transform fault, but in the case of the Mendocino, the term has been loosely applied to theactive fault segment east of the Gorda Ridge as well as to the true fracture zone segment west of it. Manyseismologists refer to the active segment as theMendocino Fault orMendocino fault zone. The fault section demarcates the boundary between the northwestward-movingPacific plate and the eastward-movingGorda plate. The Gorda plate is subducting beneath theNorth American plate just offshore of Cape Mendocino. Where the Mendocino Fault intersects the undersea trench of the subduction zone, it also meets the San Andreas Fault. This seismically active intersection is called atriple junction, and specifically theMendocino triple junction.
Intsunami studies, energy focusing around the fracture zone has been noted, leading to increased wave heights in the area aroundCrescent City, California. The fracture zone is referred to as theMendocino escarpment in these studies, descriptively rather than named from its geological origin.[3]
Robert W. Pease observed in 1965 that the alignment of a transverse tectonic zone extending fromMount Lassen to theWalker Lane at the north end ofHoney Lake Fault, suggests it was once the continental terminus of the Mendocino Fault. It forms the boundary of theModoc Plateau andColumbia Plateau provinces with theGreat Basin. Where it meets Honey Lake Fault, it bends to trend northeast across the northwest corner of Nevada, where it accompanies the geologicaltrough that formsBlack Rock Desert.[4]