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.
21-580: BFZ may refer to Blanco Fracture Zone off the coast of Oregon, United States Brawley Fault Zone near the Salton Sea in Southern California, United States Brothers Fault Zone in the state of Oregon, United States Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title BFZ . If an internal link led you here, you may wish to change
42-458: 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, the result of extensional stresses from the two nearby spreading centers. Most large events in this zone occur on
63-569: A left-step-over to create a pull-apart basin. This is illustrated in the accompanying figures. A regional strike slip fault is referred to as a principle displacement zone (PDZ). Connecting the tips of step over faults to the opposite fault are bounding basin sidewall faults. The tectonic subsidence of strike-slip basins is mainly episodic, short lived (typically less than 10 Ma), and end abruptly with commonly very high tectonic subsidence rates (greater than 0.5 km/Ma) compared to all other basin types. Recent sandbox models have shown that
84-533: 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; 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
105-450: A swarm of nine earthquakes took place, the maximum magnitude being 5.6. Pull-apart basin In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crustal extension undergoing tension , which causes
126-529: The Vienna Basin . The Dead Sea has been studied extensively and thinning of the crust in pull-aparts may generate differential loading and instigate salt diapirs to rise, a frequent trap for hydrocarbons. Likewise intense deformation and rapid subsidence and deposition in pull-aparts creates numerous structural and stratigraphic traps, enhancing their viability as hydrocarbon reservoirs . The shallow extensional regime of pull-apart basins also facilitates
147-400: The shear motion is oblique. Pull-apart basins form in extensional to transtensional environments along fault bends or between two adjacent left-lateral faults or two right-lateral faults. The step-over or bend in the fault must be the same direction as sense of motion on the fault otherwise the area will be subject to transpression. For example, two overlapping left lateral fault must have
168-494: 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 the Blanco Ridge. Typically this activity is consistent with normal faulting , although interference with the Cascadia Depression spreading center changes
189-608: 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 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
210-543: 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 the East Blanco Depression from the final major depression, the West Blanco Depression. The West Blanco Depression is shallow in the south, reaching only
231-491: 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 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
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#1732855410494252-702: The basin provide a timeline of activity along the fault. The Salton Trough is an active pull-apart located in a step-over between the dextral San Andreas Fault and the Imperial Fault . Displacement on the fault is approximately 6 cm/yr. The current transtensional state generates normal growth faults and some strike slip motion. The growth faults in the region strike N15E, have steep dips (~70 deg), and vertical displacements of 1–4 mm/yr. Eight large slip events have occurred on these faults with throw ranging from 0.2 to 1.0 meters. These produce earthquakes greater than magnitude six and are responsible for
273-516: The basin to sink down. Frequently, the basins are rhombic or sigmoidal in shape. Dimensionally, basins are limited to the distance between the faults and the length of overlap. The inhomogeneity and structural complexity of continental crust causes faults to deviate from a straight course and frequently causes bends or step-overs in fault paths. Bends and step-overs of adjacent faults become favorable locations for extensional and compressional stress or transtension and transpression stress, if
294-524: 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 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
315-479: 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 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
336-572: The geometry and evolution of pull-apart basins varies greatly in pure-strike slip situations versus transtensional settings. Transtensional settings are believed to generate greater surface subsidence than pure-strike slip alone. Famous localities for continental pull-apart basins are the Dead Sea , the Salton Sea , and the Sea of Marmara . Pull-apart basins are amenable to research because sediments deposited in
357-634: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=BFZ&oldid=962772050 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Blanco Fracture Zone The Blanco Transform Fault Zone 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
378-523: The majority of extension in the basin and consequently thermal anomalies, subsidence, and localization of rhyolite buttes such as the Salton Buttes . Pull-apart basins represent an important exploration target for oil and gas, porphyry copper mineralisation, and geothermal fields. The Matzen fault system in the Matzen oil field has been recast as extensional grabens produced by pull-apart basins of
399-444: 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 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
420-433: 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 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
441-658: 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 a period of a few days, some reached magnitudes of 5.8. In December 2021, a swarm of earthquakes occurred on the northwest portion of the Blanco Fracture Zone, with multiple being stronger than magnitude 5. On June 15, 2022,
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