Oblique subduction

[5] Subduction zones with high obliquity angles include Sunda trench (ca.

[6][7] 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.

[10] In addition, oblique subduction is associated with the closure of ancient ocean, tsunami and block rotations in several regions.

[10] Vertical strike slip fault systems are generally accepted by the early literature of oblique subduction.

[24][25] The result shows that the trench parallel slip component of at least 32 mm per year is left.

This attributes to the decline of trench parallel component when the force leaves the plate coupling zone.

[30] Under continuous oblique subduction, the aforementioned frontal part of the upper plate permanently accommodates the trench parallel component.

Yukinobu et al., (2018) suggested that oblique subduction was the primary reason leading to the occurrence of the tsunami.

[11] It obscures trench parallel strike slip fault and the topographic ridge of the wedge.

[12] Examples of oblique subduction-induced block rotation are identified in North Island, Cascadia and New Guinea.

[12] 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 is observed.

[12] In addition, the block rotation accommodates 25% to 65% of the trench parallel component from oblique subduction.

[12] Therefore, high rate trench parallel strike slip faults are absent in the North Island.

[12] In the oblique subduction zone, the sinking slab is characterized by the Hikurangi plateau in the south.

[12] In the southern trench, thick oceanic plateau induces high collisional resistance forces that cripples the subduction process.

[13] Geological and geochemical analysis suggest that there was an ocean basin between the plates and it was part of the Paleo-Tethys Ocean[40] Tectonic features of oblique subduction, for example a right lateral strike-slip thrust belt are identified in the tectonic zone.

[41] However, geological record shows southeast subduction direction in Late Cretaceous period.

[42] Four major trench parallel strike slip faults are identified in the oblique subduction zone.

[50] It was formed during the Mid to Late Jurassic period as a left-lateral fault due to oblique subduction of the Phoenix Plate.

Simplified model of oblique subduction. The oblique subduction motion is composed of motion vectors that are parallel and orthogonal to plate boundary . [ 1 ] The obliquity of plate convergence is compensated by the relative motion between forearc sliver and the remaining overriding plate. [ 1 ] In this way, the relative motion between the overriding plate and the subducting plate is almost perpendicular to the plate boundary. [ 1 ] Adapted from Westbrook, 2005. [ 1 ]
Oblique subduction model with the development of forearc sliver and margin parallel strike slip fault. Forearc sliver is a microplate bounded by the oceanic trench and strike slip fault . [ 14 ] Trench parallel strike slip fault develops when the forearc sliver moves away from stable continent. [ 14 ] Adapted from Haq and Davis, 2010. [ 14 ]
A vertical strike slip fault model. The red line indicates the vertical fault. The fault extends from surface down to the subducting slab. [ 10 ]
A mega splay fault system model. The strike slip fault is suggested to be one of the branches in the mega splay fault, which also links thrust faults in the forearc . [ 21 ] The mega splay fault is subparallel to the subducting plate at depth. [ 21 ] Modified from Tsuji et al., 2014. [ 21 ]
A curved strike slip fault model. Adapted from Ormeño. et al., 2017 [ 19 ]
USGS map of the 2012 M w 8.6 earthquake in Indian Ocean . The star represents the location of epicentre . Adapted from USGS, 2012
Model of trench parallel strike slip fault in subducting slab. Trench parallel component in this setting is accommodated by strike slip faults both in the upper plate and the outer trench region of the sinking slab. [ 24 ] Adapted from Ishii et al., 2013. [ 24 ]
Top view of short term deformation model. The initial direction of tectonic force follows oblique subduction direction. [ 27 ] Decline of trench parallel component causes gradual rotation of tectonic force. [ 27 ] Therefore, only the forearc wedge, instead of the whole upper plate, is dragged. [ 27 ] Adapted from Hoffmann-Rothe et al., 2006. [ 27 ]
Top view of long term deformation model. The frontal part of upper plate permanently accommodates the trench parallel component of strain partitioning . [ 27 ] As a result, tectonic force rotates gradually toward the trench parallel direction. [ 27 ] The frontal part detaches from upper plate under enormous tectonic force, forming trench parallel strike slip fault system and forearc sliver. [ 27 ] Adapted from Hoffmann-Rothe et al., 2006. [ 27 ]
Bird's eye view of the accretionary wedge in Ryukyu oblique subduction zone. The inferred slide mass is outlined by the grey dotted line. Modified from Yukinobu et al., 2018. [ 11 ]
Simplified evolution diagram of the oblique subduction-induced tsunami. Stage 1 : Formation of trench parallel strike slip fault owing to oblique subduction of the Philippine Sea Plate . The fault extended and reached the Ryukyu Trench . Stage 2 : Movement of fault weakened the strength of the seaward slope. Resulting in several slope failures around the tip of the fault. [ 11 ] Stage 3 : Ongoing slope failures further weakened the slope. A large seaward block then collapsed and slid. [ 11 ] During earthquake, the ground shaking caused the landward block to collapse seaward. [ 11 ] Resulting in the great tsunami. [ 11 ] Modified from Yukinobu et al., 2018. [ 11 ]
Tectonic setting of North Island oblique subduction zone. It was formed by the collision of the Pacific Plate and the Indo-Australian Plate . [ 12 ] The convergence rate is about 45 mm per year. [ 12 ] Figure made with GeoMapApp (www.geomapapp.org) (Ryan et al., 2009). [ 38 ]
Locations of four major trench parallel strike slip fault in South America. Adapted from Hoffmann-Rothe et al., 2006. [ 27 ] Figure made with GeoMapApp (www.geomapapp.org) (Ryan et al., 2009). [ 38 ]
Location of Chiloe Microplate. The Chiloe Microplate is bounded by the northwest striking Lanalhue Fault in Arauco Peninsula in the north and Chile Triple Junction in the south. [ 58 ] Figure made with GeoMapApp (www.geomapapp.org) (Ryan et al., 2009). [ 38 ]