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35-527: The North Luzon Trough formed as a result of the oblique convergence between the Eurasian and Philippine Sea plates. The Philippine Sea Plate is subducting beneath the Eurasian Plate at a rate of approximately 80 millimeters per year (3.1 inches per year). This oblique convergence creates a complex tectonic setting, with both compressional and extensional forces acting on the crust. The trough itself

70-443: A VSP (of which there are many types) is that either the energy source, or the detectors (or sometimes both) are in a borehole . In the most common type of VSP, hydrophones , or more often geophones or accelerometers , in the borehole record reflected seismic energy originating from a seismic source at the surface. There are numerous methods for acquiring a vertical seismic profile (VSP). Zero-offset VSPs (A) have sources close to

105-420: A salt-sediment interface near a wellbore by using a source on top of a salt dome away from the drilling rig. Drill-noise VSPs (F), also known as seismic-while-drilling (SWD) VSPs, use the noise of the drill bit as the source and receivers laid out along the ground. Multi-offset VSPs (G) involve a source some distance from numerous receivers in the wellbore. A vertical seismic profile is constructed to identify

140-437: A tectonic response to the process of slab roll-back that moves the trench seaward) and slab fold (i.e. buckling of subducting slab due to phase transition ) may also occur. Moreover, collision of two plates leads to strike slip deformation of the forearc , thus forming a series of features including forearc slivers and strike slip fault systems that are sub-parallel to ocean trenches . In addition, oblique subduction

175-455: A value known as a source wavelet. This is useful when it comes to a process known as deconvolution. Deconvolution allows for a more readable and more focused VSP. The idea is that the VSP reports any abnormal seismic activity and deconvolution allows for a more focused profile on these abnormal activities. VSPs are used to measure a seismic signal at depth and with that measurement the wavelength at

210-466: Is a forearc basin , which is a depression that develops in front of an island arc system. The subducting plate releases fluids and sediments, which accumulate in the forearc basin. These sediments can be uplifted and incorporated into the island arc, contributing to its growth. The trough is a well-developed basin with active subduction into the Manila Trench system with complexities stemming from

245-490: Is a stub . You can help Misplaced Pages by expanding it . This tectonics article is a stub . You can help Misplaced Pages by expanding it . Oblique subduction Oblique subduction is a form of subduction (i.e. a tectonic process involving the convergence of two plates where the denser plate descends into Earth's interior) for which the convergence direction differs from 90° to the plate boundary . Most convergent boundaries involve oblique subduction, particularly in

280-422: Is accommodated by localized shear zones (short-term deformation) or trench parallel strike slip fault systems (long-term deformation) in the overriding plates. Likewise, this component commonly leads to the formation of forearc slivers. The trench normal component is taken up by thrust structures. These thrusts are generally discontinuous and their geometries change progressively. Short-term deformation

315-652: Is associated with the closure of ancient ocean, tsunami and block rotations in several regions. Forearc slivers are partly detached continental blocks of the overriding plates. They are bounded by the trenches and trench parallel strike slip fault systems. The motion of forearc slivers depend on the obliquity of the subducting slabs. Moreover, some forearc slivers occur in the absence of well defined strike-slip fault systems, and sliver motions are not purely strike-slip. Trench parallel strike-slip faults are deformational products contributed by trench parallel component of strain partitioning . They are located between

350-429: Is mainly elastic and acts at human time scale (i.e. perceptible during a human lifetime, unlike changes that take place on a geologic time scale ). When the denser plate subducts beneath the upper plate, they are coupled at the interface (i.e. plate coupling). The process of plate coupling thus generates tectonic force that follows the subduction direction. The orientation of tectonic force gradually rotates toward

385-585: Is observed. This caused tectonic extension in Taupo Volcanic Zone and tectonic shortening in northwestern South Island , for example the Buller region. In addition, the block rotation accommodates 25% to 65% of the trench parallel component from oblique subduction. Therefore, high rate trench parallel strike slip faults are absent in the North Island . In the oblique subduction zone,

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420-594: Is part of the Andean oblique subduction zone that was formed as a result of oblique subduction between the sinking Nazca Plate and the South American Plate . The current subduction direction is at east-north-east (see the summary below). However, geological record shows southeast subduction direction in Late Cretaceous period. Four major trench parallel strike slip faults are identified in

455-484: The Indo-Australian Plate . A trench parallel strike slip fault system, North Island Dextral Fault Belt , was formed. Based on geological and geodetic data, five tectonic blocks are identified in the region. These blocks are separated by block-bounding faults. Based on GPS measurement, a clockwise rotation of microblocks at a rate of 0.5° to 3.8° per million year relative to the Indo-Australian Plate

490-645: The Phoenix Plate . The fault system has been inactive since the Miocene Period. The right lateral slip rate is estimated to be less than 1 mm per year since the Pliocene . The Precordilleran Fault , also known as the Domeyko fault , is composed of several anastomosing faults (i.e. branching and irregular faults) including Sierra Moreno Fault, West Fault and Limon Verde. Precordilleran Fault

525-559: The Ring of Fire including the Ryukyu , Aleutian , Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench (ca. 60°) and Ryukyu arc (ca. 50°). Obliquity in plate convergence causes differences in dipping angle and subduction velocity along the plate boundary. Tectonic processes including slab roll-back , trench retreat (i.e.

560-463: The Sumatra subduction zone , the trench parallel slip component is measured to be approximately 45 mm per year, the motion rate of northern Great Sumatra Fault ranges from 1 to 9 mm per year with the maximum rate of 13 mm per year. The result shows that the trench parallel slip component of at least 32 mm per year is left. On 11 April 2012, a M w 8.6 earthquake occurred in

595-405: The aforementioned trench parallel strike slip faults . Several models suggest that there are other slip accommodating mechanisms formed by oblique subduction as means to take up the remaining slip component. Ishii et al., (2013) suggested that the trench parallel strike-slip faults may appear in the obliquely subducting slabs to accommodate a portion of the trench parallel slip component. In

630-447: The forearc slivers and the remaining overriding plates. Vertical strike slip fault systems are generally accepted by the early literature of oblique subduction. However, modern technology, such as seismic profiling , reveals that the faults are not necessarily vertical. Several other models concerning the orientations of the faults are proposed. Trench parallel slip component from oblique subduction may not be fully accommodated by

665-667: The north to the Altiplano in the south. The continental boundary is located between the Western Cordillera and the Eastern Cordillera. Chiloe Microplate, also known as Chiloe Block, is a forearc sliver that detached along the Liquine Ofqui Fault . It is bounded by Arauco Peninsula and Chile Triple Junction . The sliver moves northward with a motion rate ranges from 32 mm per year in

700-416: The oblique subduction zone. Liquiñe-Ofqui Fault is a 1,200 km long fault that located in the southern Andes. Left lateral strike slip motion was active during Mesozoic period. In Pliocene period, strike slip motion of the fault system changed to right lateral motion to accommodate the trench parallel slip component from oblique subduction. The El Tigre Fault is observed in the central part of

735-500: The offshore extension of the Philippine Fault System into the trough. Multi-channel seismic data suggests that the basin's sedimentary deposits resulted from multiple periods of emplacement and erosion . Today, the trough contains a relatively stable zone and a deformation zone characterized by compressional deformation characteristic of past tectonic activity in the trough. This Philippines -related article

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770-455: The sinking slab is characterized by the Hikurangi plateau in the south. The thickness of this oceanic plateau ranges from 15 km to 10 km along the oceanic trench . The along strike thickness variation leads to differential subduction rate. In the southern trench , thick oceanic plateau induces high collisional resistance forces that cripples the subduction process. However,

805-528: The source of the seismic activity is easily found. With the measurement of the source wavelet, geophysicists can carry out deconvolution on the VSP and decrease the reports of all seismic activity and limit the reports to just abnormal or extreme changes in seismic activity. In recent years, using a VSP has become more popular in regards to reducing well placement risks as well as improving the monitoring of such wells. The advancement in technology for well monitoring has made VSPs more accurate and more precise with

840-560: The south to 13 mm per year in the north. This northward motion not only caused by the oblique subduction of the Nazca Plate , but also the oblique collision and spreading of the Chile Rise at the southern edge of the sliver. Vertical seismic profile In geophysics , vertical seismic profile ( VSP ) is a technique of seismic measurements used for correlation with surface seismic data. The defining characteristic of

875-527: The southwestern part of the Ryukyu arc . Yukinobu et al., (2018) suggested that oblique subduction was the primary reason leading to the occurrence of the tsunami. In the plate boundary, an approximately 80 km long and 30 km wide depression is observed. It obscures trench parallel strike slip fault and the topographic ridge of the wedge. Oblique subduction has led to rotation of microblocks about nearby poles of rotation (See also: Euler poles ) in some oblique subduction zones. In these regions,

910-467: The subducting plate (i.e. the Indo-Australian Plate ). Strike-slip seismicity was recorded in the earthquake. This infers strike slip fault systems are present in the descending slab and they may potentially accommodate slip component from oblique subduction. Strain partitioning is a form of deformation. In oblique subduction zone, strain partitioning is initiated into trench parallel component and trench normal component. The trench parallel component

945-556: The subduction zone. It is a relatively short strike slip fault (ca. 120 km) that located further landward. The slip rate of the fault system is approximately 1 mm per year. The Atacama Fault and the Precordilleran Fault are located in northern Chile . The Atacama Fault extends more than 1,000 km. It was formed during the Mid to Late Jurassic period as a left-lateral fault due to oblique subduction of

980-469: The thin oceanic crust in the north is subducted. This activated the tectonic block rotations about a nearby axis. The Qinling-Dabieshan orogen in central China consists of three separate plates, including the north China plate , the Qinling-Dabieshan microplate, and the south China plate . Geological and geochemical analysis suggest that there was an ocean basin between the plates and it

1015-418: The trench normal direction. This attributes to the decline of trench parallel component when the force leaves the plate coupling zone. In this way, only the frontal part, rather than the whole upper plate, is dragged by the subducting slab. Long-term deformation occurs at geological time scale . Under continuous oblique subduction, the aforementioned frontal part of the upper plate permanently accommodates

1050-479: The trench parallel strike slip fault systems are less prominent. This is because a portion of the trench parallel component is accommodated by the microblock rotation. Examples of oblique subduction-induced block rotation are identified in North Island , Cascadia and New Guinea . The North Island oblique subduction zone in New Zealand was established by the obliquely subducting Pacific Plate beneath

1085-410: The trench parallel component. In this way, the orientation of tectonic force rotates gradually toward the trench parallel direction. Strong and continuing tectonic force in trench parallel direction leads to the development of trench parallel strike slip fault system. The fault thus separate a portion of the forearc from the overriding plate, forming the forearc sliver. The tsunami occurred in

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1120-448: The use of very long baseline interferometry (VLBI). VLBI is an astronomical radio antenna technique that allows for high resolution imaging on a spatial scale. Therefore, using these techniques to create a seismic profile produces incredibly accurate images of wavelets and enhances determination of source wavelets. VSPs are more suitable than other seismic profiles to host the equipment for VLBI. The long vertical length required to create

1155-472: The wellbore directly above receivers. Offset VSPs (B) have sources some distance from the receivers in the wellbore. Walkaway VSPs (C) feature a source that is moved to progressively farther offset and receivers held in a fixed location. Walk-above VSPs (D) accommodate the recording geometry of a deviated well, having each receiver in a different lateral position and the source directly above the receiver. Salt-proximity VSPs (E) are reflection surveys to help define

1190-652: Was formed in the Late Eocene . In Neogene period, the fault system changed from left lateral to right lateral motion along with the uplift of the Precordillera . Two major forearc slivers are observed along the Peru-Chile Trench . The Peruvian Sliver, also known as Inca Sliver, has a width of 300 to 400 km and a total length of over 1,500 km. It extends from the Gulf of Guayaquil in

1225-554: Was part of the Paleo-Tethys Ocean Tectonic features of oblique subduction, for example a right lateral strike-slip thrust belt are identified in the tectonic zone. These evidence suggest that the south China plate was obliquely subducted to the northwest beneath the north China plate in the Early Mesozoic and led to the closure of the northeastern Paleo-Tethys Ocean . The Peru–Chile Trench

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