![]() Our understanding of strike-slip faults has advanced with detailed field mapping, subsurface imaging, and numerical and analogue modelling. Convergent margins with oblique plate trajectories will also generate strike-slip faults in accretionary prisms, forearcs and backarcs. ![]() The characteristic zig zag dismembering of mid-ocean spreading ridges is caused by ridge transforms that accommodate the strain from oblique spreading. They form in oceanic and continental crust/lithosphere. Strike-slip faults occur in most plate tectonic settings, primarily at plate boundaries (like most other fault types). The present trajectory along Alpine Fault is also transpressional. Pacific plate trajectories at Hikurangi margin become increasingly oblique from north to south. The right-lateral Alpine Fault transform and its strike-slip fault splays (Marlborough fault system), in the context of other plate tectonic elements: the Hikurangi subduction zone that is linked to Alpine Fault via Hope Fault and the subduction zone at the south end of South Island where oceanic crust of the Australian Plate is subducting beneath the Pacific plate (opposite polarity to Hikurangi). But he was right… Jumping ahead a few years (and encapsulating several decades of science history in a single sentence), we now know this fault as the Alpine Fault, a dextral, or right-lateral transform strike-slip fault that also doubles as the boundary between the Pacific and Australian plates. Wellman’s hypothesis turned a few heads and invited its share of derision. The consensus at the time was that crustal movements were dominated by vertical displacements. The dislocation was the result of 600 km lateral shift along a major fault. In 1940 Harold Wellman and Dick Willett proposed that two groups of rocks at either end of the South Island of New Zealand, each having the same stratigraphic and lithologic characteristics, were at one time a single unit. The fault splays are clearly delineated by valleys. ![]() The intersection of splay faults that trend northeast indicated by black dots. ![]() The master fault is a prominent linear feature immediately left of the snow line (black arrow, bottom). Strike-slip fault - a fault on which the two blocks slide past one another. The San Andreas Fault is an example of a right lateral fault.Ī left-lateral strike-slip fault is one on which the displacement of the far block is to the left when viewed from either side.Ī right-lateral strike-slip fault is one on which the displacement of the far block is to the right when viewed from either side.An oblique view of Alpine Fault from the International Space Station. Reverse (thrust) fault - a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block. This type of faulting is common in areas of compression, such as regions where one plate is being subducted under another as in Japan. When the dip angle is shallow, a reverse fault is often described as a thrust fault. Normal fault - a dip-slip fault in which the block above the fault has moved downward relative to the block below. This type of faulting occurs in response to extension and is often observed in the Western United States Basin and Range Province and along oceanic ridge systems. The following definitions are adapted from The Earth by Press and Siever. A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.Įarth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults. Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse (thrust), depending on their motion. Faults which move horizontally are known as strike-slip faults and are classified as either right-lateral or left-lateral. Faults which show both dip-slip and strike-slip motion are known as oblique-slip faults. ![]()
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