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Probabilistic seismic hazard assessment for offshore structures in Andaman Sea
Published in Stein Haugen, Anne Barros, Coen van Gulijk, Trond Kongsvik, Jan Erik Vinnem, Safety and Reliability – Safe Societies in a Changing World, 2018
Deformation of the overriding plate leads to larger complexities in plate motions. Sumatra sits at the southwestern edge of the Sunda plate (Bird 2003), which moves at a few millimeters per year to a centimeter per year eastward relative to Eurasia (Chamot-Rooke & Le Pichon 1999, Bock et al. 2003) (Figure 1). The resulting convergence between the Sunda plate and the oceanic plates to the southwest is somewhat slower than it would be relative to Eurasia. The rate and direction of subduction of the lithosphere under the Sunda forearc, however, are further modified by the independent motion of the forearc. Fitch (1972) explained the presence of the Sumatran fault and other similar faults inboard subduction zones by the process now known as slip partitioning. That is, in some cases of oblique subduction where the two plates do not converge at a right angle to the strike of the trench, it requires smaller overall shear force to share the shearing (trench-parallel) component of the relative motion between two separate faults instead of on one fault. In the case of partitioning, one fault is the subduction thrust, which takes up all of the trench-normal slip (the dip-slip component) and some fraction of the trench-parallel slip (the strike-slip component). A second fault, within the overriding plate and commonly strike-slip in nature, takes up a portion of the trench-parallel motion. The subduction thrust and strike-slip fault isolate a wedge of forearc called the sliver plate. The slip rates on the separate faults can be inferred from their geometries and knowledge of the overall convergence.
Tectonics and Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Thick sedimentary piles are stacked rn the form of accretionary prisms in the forearcs. As the subduction zone migrates towards the sea the forearc sediments are successively thrust upwards (Fig. 7.8). Small sedimentary basins may develop over these accretionary prisms. Those lying between the volcanic arc and the trench slope break are generally very wide (50–100 km). These are the forearc or outer-arc basins. Behind the volcanic arc occur the back-arc basins.
Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
Suzuki, K., Ebinuma, T. & Narita, H. 2009 :Features of Methane Hydrate-bearing Sandy-sediments of the Forearc Basin along the Nankai Trough: Effect on Methane Hydrate-Accumulating Mechanism in Turbidite, Journal of Geography, 118(5): 899-912 (in Japanese).
Ordovician Macquarie Arc and turbidite fan relationships, Lachlan Orogen, southeastern Australia: stratigraphic and tectonic problems
Published in Australian Journal of Earth Sciences, 2018
C. L. Fergusson, G. P. Colquhoun
In the reconstruction of Fergusson (2009), polarity of the Macquarie Arc is shown for Phase 1 activity as facing northwards and changing gradually to the west as the arc rotated anticlockwise around an Euler pole located near its western terminus. This geometry would imply active extension was occurring southwest of this pole. Similar plate boundary geometry occurs on the northwest boundary of the Caroline plate in the western Pacific Ocean north of West Papua, south of Palau (Bird, 2003). For Phase 1 igneous activity in the Macquarie Arc, the location of the subduction is not clear as no evidence remains to uniquely locate it. The simplest assumption following from its later location (Figure 17) would be that the arc faced to the NNW with a SSE-dipping subducting slab. A difficulty with analysing long-lived island arcs in the ancient record is that subduction processes operate in the longer term to remove evidence of subduction polarity. The dominant process in subduction zones is subduction erosion rather than subduction accretion (Stern, 2011) and thus forearcs can be lost over time resulting in much reduced forearc widths and the loss of potential subduction polarity indicators including high-P metamorphic rocks, subduction complexes and forearc basins.
Subduction erosion: contributions of footwall and hanging wall to serpentinite mélange; field, geochemical and radiochronological evidence from the Eocene HP-LT belt of New Caledonia
Published in Australian Journal of Earth Sciences, 2021
The andesite-basalt pillow lavas and diorite dykes of the Haute Néhoué Unit and Ouehat-Ougne peaks occur within the Intermediate Mélange and are (tectonically) associated with EMORB and BABB likely derived from PTB. These lavas and dykes have no equivalent in the Poya Terrane (lower plate) and clearly differ from IAT dolerites of the Peridotite Nappe (upper plate), which are much more depleted (Figure 7a) and are also older (55–54 Ma vs 50–47 Ma). It is suggested that they represent a small supra-subduction basin formed immediately after subduction inception and most likely resulting from incipient forearc extension.