North of New Zealand, the Pacific Plate is obliquely subducted beneath the Indo-Australian plate at the Tonga-Kermadec trench. The Alpine Fault Zone along the western South Island of New Zealand is an example of an obliquely convergent transform plate boundary separating two zones of subduction with opposite polarity. The lithosphere is thinner beneath the San Andreas fault system than for normal continental lithosphere. Other segments are undergoing slow, continuous deformation or creep. In such segments, built-up strain may finally be rapidly released, producing an earthquake. Some segments of the San Andreas and other major faults in the San Andreas fault system are locked. Changes in their orientation and relay stepping of faults result in localized dilatation or contraction. The San Andreas Fault is the main transcurrent or strike-slip fault within a broad deformation zone that comprises hundreds of minor faults along western California. South of this triple junction, the Rivera Plate is subducted beneath North America. It terminates at the Rivera triple junction in the southern Gulf of California (junction between the Rivera, Pacific and North American plates). The San Andreas fault system steps through a series of oblique spreading ridges and transform faults in the Gulf of California. The easterly moving Gorda –Juan de Fuca plate is subducted beneath the American plate north of the San Andreas fault system termination forming the Cascade Range. Here the North American and Pacific plates intersect the Gorda –Juan de Fuca plate. In the north, the San Andreas fault system terminates at the Mendocino triple junction where it intersects the Mendocino Fracture Zone and Cascadia subduction. Western California, part of the Pacific Plate, comprises exotic terranes translated northwards and rotated through angles up to 90 degrees along the margin of the North American plate. The northwards-moving Pacific plate is subducted at the Aleutian trench and at western Pacific island arcs. The best-known transform plate boundary is the San Andreas fault system, which accommodates the right-lateral displacement between the North American and Pacific plates. Detailed studies of piercing points show the San Andreas Fault has experienced over 225 km of movement in the last 20 million years, and this movement occurred at three different fault traces.A transform plate boundary is a margin between two lithospheric plates that constitutes a regional-scale transform fault. The best type of piercing point includes unique patterns that are used to match the parts of a geological feature separated by fault movement. Other types of faults-normal and reverse -tend to be more destructive, obscuring or destroying these features. Transform faults are unique because their horizontal motion keeps a geological feature relatively intact, preserving the record of what happened. Piercing points are very useful for recreating past fault movement, especially along transform boundaries. When a geological feature is cut by a fault, it is called a piercing point. The fault can be seen about halfway down, trending left to right, as a change in the topography. This is caused by the San Andreas Fault cutting roughly perpendicular to the creek, and shifting the location of the creek over time. Note as the creek flows from the northern mountainous part of the image, it takes a sharp right (as viewed from the flow of water), then a sharp left. \): Wallace (dry) Creek on the Carrizo Plain, California.
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