A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics . Lithospheric plates on either side of an active transform fault move in opposite directions; here, strike-slip activity occurs. Fracture zones extend past the transform faults, away from the ridge axis; are usually seismically inactive (because both plate segments are moving in the same direction), although they can display evidence of transform fault activity, primarily in the different ages of the crust on opposite sides of the zone.
25-696: The Hunter Fracture Zone is a sinistral (left-lateral) transform faulting fracture zone , that to its south is part of a triple junction with the New Hebrides Trench , and the North Fiji Basin Central Spreading Ridge. The Hunter Fracture Zone, with the Hunter Ridge , an area with recent volcanic activity to its north, is the southern boundary of the North Fiji Basin . This boundary area in
50-733: A maximum depth of 3300 m and only measuring at 5 km across. It is connected through the Parks Plateau fault to the Cascadia Depression. A small sill connects the Surveyor Depression to the East Blanco Depression, a broad basin which is composed of a series of small deeps ranging from 3600 m to 3700m. Small intermediate ridges rise up a few hundred meters to separate these local ravines. A larger sill rises up to 2900 m depth to separate
75-562: A total of 350 km to the west. The section of the Mid-Atlantic Ridge between the two fracture zones is seismically active. The flow of major North Atlantic currents is associated with this fracture zone which hosts a diverse deep water ecosystem. The Heirtzler Fracture Zone was approved by the Advisory Committee on Undersea Features in 1993. The Mendocino Fracture Zone extends for over 4,000 km off
100-646: A transform fault zone. In March and April 2008, a swarm of moderate earthquakes occurred both near and within the Blanco zone. The swarm began on March 30 when over 600 measurable tremors began occurring north of the zone within the Juan de Fuca plate . On April 23, activity moved to the Blanco fault zone itself, near its junction with the Gorda Ridge . Another series of earthquakes occurred in June 2015. Spread out over
125-535: Is 125 km long and 15 km wide. Blanco Fracture Zone The Blanco Fracture Zone or Blanco Transform Fault Zone (BTFZ) is a right lateral transform fault zone, which runs northwest off the coast of Oregon in the Pacific Northwest of the United States, extending from the Gorda Ridge in the south to the Juan de Fuca Ridge in the north. The Blanco Transform Fault Zone
150-480: Is also evidence of active seafloor spreading in this zone, indicating that the Cascadia Depression likely became separated from one of the spreading ridges that border the Blanco Transform Fault Zone. The western part of the zone is made up of a series of depressions separated by transform fault ridges. The Surveyor Depression is the shallowest and smallest of these depressions, reaching
175-464: Is an approximately 350 km long zone that varies in width between 20 and 75 km. The Blanco Fracture Zone starts about 150 km off Cape Blanco , and extends northwest to about 500 km off of Newport . It consists of a series of deep basins interrupted by transform faults. The western part of the fracture zone, from the Cascadia Depression to the Juan de Fuca Ridge, moves at 1.4 cm/a;
200-541: The Juan de Fuca Ridge and the Gorda Ridge . The dominating feature of the fracture zone is the 150 km long Blanco Ridge, which is a high-angle, right-lateral strike slip fault with some component of dip-slip faulting . The Charlie-Gibbs Fracture Zone consists of two fracture zones in the North Atlantic that extend for over 2000 km. These fracture zones displace the Mid-Atlantic Ridge
225-472: The Kadavu Islands immediately to its north. However some earlier work has postulated that the fault structures around Suva on Fiji itself are related and different authors have defined the zone variably. The western Hunter Fracture Zone is an area of fair shallow seismicity. Large (more than M w 6) earthquakes have occurred in historic times. It defines part of the plate boundary between
250-777: The New Hebrides and the Conway Reef microplate with the Australian plate , with the rest of the convergence being accommodated by subduction and rifting . The major present subduction and rifting is in an area where the Hunter Ridge is being split that is called the Monzier Rift.. This is active volcanically as part of a separate subduction system to the rest of the Vanuatu subduction zone that has been called
275-630: The Romanche Trench , this fracture zone separates the North Atlantic and South Atlantic oceans. The trench reaches 7,758 m deep, is 300 km long, and has a width of 19 km. The fracture zone offsets the Mid-Atlantic Ridge by more than 640 km. The Sovanco Fracture Zone is a dextral-slip transform fault running between the Juan de Fuca and Explorer Ridge in the North Pacific Ocean . The fracture zone
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#1732764841376300-463: The Blanco Ridge. Typically this activity is consistent with normal faulting , although interference with the Cascadia Depression spreading center changes the motion on some of the faults. Shallow earthquakes consistent with strike-slip faulting occur on the western side of the zone, but their large distribution indicates that multiple faults exist. Generally these faults run along the walls of
325-524: The East Blanco Depression from the final major depression, the West Blanco Depression. The West Blanco Depression is shallow in the south, reaching only a depth of 3400 m, but quickly reaches depth near the Juan de Fuca Ridge, dropping down to 4800 m. This basin is at a slightly different angle than the other western depressions, likely due to interference from the Juan de Fuca Ridge. All of these depressions are likely pull-apart basins,
350-1091: The Matthew and Hunter subduction zone. The Hunter Ridge and Hunter Fracture Zone are the south eastern terminus of the Vanuatu subduction zone 's subduction and its associated slab edge. From 3 million years ago the southernmost Central Spreading Ridge of the North Fiji Basin propagated southward and has now intersected with the New Hebrides Trench and the Hunter fracture zone to form the current triple junction. Fracture zone In actual usage, many transform faults aligned with fracture zones are often loosely referred to as "fracture zones" although technically, they are not. They can be associated with other tectonic features and may be subducted or distorted by later tectonic activity. They are usually defined with bathymetric , gravity and magnetic studies. Mid-ocean ridges are divergent plate boundaries. As
375-423: The bathymetric basins, but near the Juan de Fuca ridge they become distorted, and rotate towards the ridge axis instead. On January 9, 1994, a large series or swarm of earthquakes occurred in the East Blanco Depression. Acoustic signals recorded during these events indicated that an eruption occurred in this zone. Further investigation revealed an active hydrothermal vent, the first of its kind to be discovered in
400-453: The coast of California and separates the Pacific plate and Gorda plate . The bathymetric depths on the north side of the fracture zone are 800 to 1,200 m shallower than to the south, suggesting the seafloor north of the ridge to be younger. Geologic evidence backs this up, as rocks were found to be 23 to 27 million years younger north of the ridge than to the south. Also known as
425-531: The eastern segment, from the Cascadia Depression to the Gorda Ridge moves at 3.9 cm/a. The whole zone averages a slip rate of 2.0 cm/a. Through it, Cascadia Channel passes. The principal feature of the eastern portion of the zone is the Blanco Ridge, a 150 km right lateral-moving fault that is responsible for the largest earthquakes in the region. The ridge itself varies between 3.5 and 7 km wide, and peaks between 600 and 1000 m above
450-406: The offset in the magnetic striping, one can then determine the rate of past plate motions. In a similar method, one can use the relative ages of the seafloor on either side of a fracture zone to determine the rate of past plate motions. By comparing how offset similarly aged seafloor is, one can determine how quickly the plate has moved. The Blanco Fracture Zone is a fracture zone running between
475-409: The plates on either side of an offset mid-ocean ridge move, a transform fault forms at the offset between the two ridges. Fracture zones and the transform faults that form them are separate but related features. Transform faults are plate boundaries, meaning that on either side of the fault is a different plate. In contrast, outside of the ridge-ridge transform fault, the crust on both sides belongs to
500-400: The result of extensional stresses from the two nearby spreading centers. Most large events in this zone occur on the Blanco Ridge, as the motion on this fault accounts for the majority of the plate movement. Strike slip faulting occurs in this region; motion on the fault is parallel to the motion of the plate. Tectonic activity in the central part of the zone is weaker and deeper than on
525-408: The same plate, and there is no relative motion along the junction. The fracture zone is thus the junction between oceanic crustal regions of different ages. Because younger crust is generally higher due to increased thermal buoyancy , the fracture zone is characterized by an offset in elevation with an intervening canyon that may be topographically distinct for hundreds or thousands of kilometers on
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#1732764841376550-486: The sea floor. As many areas of the ocean floor, particularly the Atlantic Ocean, are currently inactive, it can be difficult to find past plate motion. However, by observing the fracture zones, one can determine both the direction and rate of past plate motion. This is found by observing the patterns of magnetic striping on the ocean floor (a result of the reversals of Earth's magnetic field over time). By measuring
575-532: The seafloor. The ridge likely formed through extensive shearing and subsequent serpentinization from the intrusion of seawater. The Gorda Depression, a 10 km wide extensional basin , connects the eastern end of the Blanco Ridge to the Gorda Ridge. This basin is around 4400 m deep in the center, 11 km across in the NE-SW direction, and 18 km wide in the NW-SE direction. The Cascadia Depression connects
600-581: The south-western part of the Hunter Fracture Zone is associated with hot subduction, and a unique range of volcanic geochemistry. The Hunter Fracture Zone is located to the south and southwest of Fiji and starts where the southern part of the New Hebrides Trench ends due to the increasing obliqueness of convergence lending to more strike slip faulting than subducting. It terminates around the International Date Line , with
625-513: The two halves of the Blanco Transform Fault Zone. The depression is elongated, around 20 km in the NE-SW direction, but only about 8 km in the NW-SE direction. Roughly 500 m of sediments line the floor of the depression, mostly turbidites . Channels cut through the southern end of the depression are remnants of turbidity flows originating from the Missoula floods , but there are also signs of more recent, local turbidity currents . There
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