Twenty Years of Subduction Zone Science: Subduction Top to Bottom 2 (ST2B-2)
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This research is about the distribution of earthquake in subduction zone and calculation of subduction angle in the central Sumatera period 1967-2016. The data used in this research is earthquake data period January 1, 1967 until December 31, 2016 associated with the subduction zone. Research region consist of West Sumatera, Riau and North Sumatera. This region is made by following the slope of the subduction zone using GMT 5. Graphic of the relation between distance and depth every earthquake event is processed using polynomial method to be able to know the trend of subduction zone in this region. While, to find out the subduction angle in this region, calculation with the first derivative of the parabolic equation have been do. The results show that the subduction trend within 50 years is calculated in 10 years interval, the displacement that occurs is not too visible. But, it shows that the longer, the more subdued. While the angle of subduction at 50 km, 100 km, 150 km and 200 km respectively is 22.68°, 35.73°, 42.89° and 47.72°. This shows that the deeper, the larger subduction angle is formed.
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Abstract The Sumatra subduction zones have been known to produce large destructive earthquakes and tsunami, such as the 26 December 2004 M9 earthquake at the western offshore of Aceh. This large destructive earthquake usually occurred at the shallow portion of the subduction zone between 10 – 35 km depth, while the intermediate-to-deep earthquake usually occurred at the greater depth, deeper than 65 km along the subduction, which produces small to moderate earthquake with a magnitude between M3-5. Thus, these deep events along the subduction zone usually being neglected. However, the recent study has shown that an anomalous large ground movement associated with a deep earthquake at the subduction zone has been observed along the forearc region while in the backarc or at its epicenter, it remains low. Hence, the characteristics of the body-wave at these regions are different, which could be utilized for hazard mitigation. For this reason, this study aims to identify the body-wave characteristics between the forearc and backarc regions at the Sumatra subduction zone. Several selected deep regional earthquake records with a depth greater than 100 km provided by the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) were analyzed. The finding indicates that the body-waves recorded in the forearc region are significantly different, with the main characteristics are; 1. Amplitude: preserve high amplitude, 2. Arrival time: shows a delayed signal of P- and S-waves, and 3. Spectral: conserve energy at low to high frequency and shows as a dispersion. These findings suggest that the signal recorded at the forearc region travel within the subducting slab, and the late arrival of the signal indicates that the seismic waves record at forearc travel at the top of the subducting slab, i.e., the oceanic crust, which is having lower velocity to the surrounding mantle.
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Subduction initiation is one of the main unclear aspect of plate tectonics. When studying subduction processes,
subduction initiation is therefore generally avoided as it constitutes a problem in itself. The easiest way to avoid this
problem in numerical models is to start the simulations with either a pre-existing subduction zone or a pre-existing
weak suture zone. In the Wilson cycle, as subduction initiation is often supposed to correspond to the first stage
when an oceanic lithosphere formed during extension turn in compression, we here present 2D thermo-mechanical
models of continental rifting followed by compression. While some of the models evolve toward subduction(s),
they often do not occur at the expected location. This poster aims to discuss the results obtained in such models
and the consequences of prescribing initial weak suture zones in the numerical models.
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Historic earthquake sequences on subduction zones that are similar to the Cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern United States. Based on systematic comparisons of several physical characteristics, including physiography and seismicity, subduction zones that are deemed most similar to the Cascadia subduction zone are those in southern Chile, southwestern Japan, and Colombia. These zones have all experienced very large earthquake sequences, and if the Cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length, then earthquakes of very large size (M_w > 8 1/2) must be considered. Circumstantial evidence is presented that suggests (but does not prove) that large subduction earthquakes along the Cascadia subduction zone may have an average repeat time of 400 to 500 yr.
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Subduction is the phenomenon of movement of one lithospheric plate under another, arising in connection with the heterogeneity of both geometrical and physical parameters of the lithospheric plates approaching each other. Such phenomena can occur in land, ocean and coastal areas. Active boundaries of the plates are divided into two types – subduction and collision ones. Collision processes are peculiar to the interaction of continental lithospheric plates and lead mainly to the twisting and generation of new mountains, while the subduction ones tend to cause earthquakes. By subduction, a part of the ocean floor sinks beneath the land plate. At great depth this part melts and due to the spreading it spreads and forms new crust both under the land and under the ocean. Subduction zones were discovered and described by the seismologist Benioff. Earthquakes occur most frequently in these zones. Benioff called them seismic focal zones, now they are called Benioff zones. There are attempts to explain the reasons for such properties of the Benioff zones, but they are not based on rigorous mechanical and mathematical approaches and are not convincing. The starting earthquakes are studied in the sone of subduction.
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Flat subduction can significantly influence the distribution of volcanism, stress state, and surface topography of the overriding plate. However, the mechanisms for inducing flat subduction remain controversial. Previous two-dimensional (2-D) numerical models and laboratory analogue models suggested that a buoyant impactor (aseismic ridge, oceanic plateau, or the like) may induce flat subduction. However, three-dimensional (3-D) systematic studies on the relationship between flat subduction and buoyant blocks are still lacking. Here, we use a 3-D numerical model to investigate the influence of the aseismic ridge, especially its width (which is difficult to consider in 2-D numerical models), on the formation of flat subduction. Our model results suggest that the aseismic ridge needs to be wide and thick enough to induce flat subduction, a condition that is difficult to satisfy on the Earth. We also find that the subduction of an aseismic ridge parallel to the trench or a double aseismic ridge normal to the trench has a similar effect on super-wide aseismic ridge subduction in terms of causing flat subduction, which can explain the flat subduction observed beneath regions such as Chile and Peru.
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