Abstract
In contrast to common subduction, the young and thin part of the Antarctic Plate subducts first to the south of the Chile Triple Junction (CTJ), followed by the old and thick part, corresponding to wedge subduction. A finite element model was used to simulate the wedge subduction of the Antarctic Plate and to compare it with the slab subduction of the Nazca Plate. The results show that the CTJ is not only a wedge subduction boundary but also an important factor controlling the lithospheric thermal structure of the overriding plate. The computed heat flow curves are consistent with the data observed near the trench of the two selected profiles. The different slab dips to the north and south of the CTJ are considered to be caused by wedge subduction. When the slabs are young and at the same age, the deep dip of the Antarctic slab is 22° smaller than the Nazca slab. Southward from the CTJ, the slab age of the wedge subduction increases, which leads to a larger slab dip, a colder slab, and a wider seismogenic zone. The effect of the slab age of wedge subduction on the focal depth is smaller than that of the convergence rate. A 4.8-cm/year difference in convergence rate of the wedge subduction results in an 11-km difference in the width of the seismogenic zone and a 10-km difference in the depth of the downdip limit. Among these controlling factors, the convergence rate plays a major role in the different focal depths south and north of the CTJ.
Highlights
Fewer earthquakes occur to the south than the north of the Chile Triple Junction (CTJ) (Figure 1A), and the focal depths south of CTJ are much shallower
On the basis of the tomography (Figure 2) and previous numerical model settings for the CTJ and the comparison of different initial slab dips (Surface Heat Flow and Seismogenic Zone and Seismicity Data), the initial slab dips of Models 1–5 were set in a way in which it gradually increases with the depth from 0° at the trench to 30° at about 120-km deep
Due to the lack of observations of the slab dip south of the CTJ, we focused, in Slab Dip, on the effect of wedge subduction on slab dip
Summary
Fewer earthquakes occur to the south than the north of the Chile Triple Junction (CTJ) (Figure 1A), and the focal depths south of CTJ are much shallower. The effects of the plate age, wedge subduction, and convergence rate on the lithospheric thermal structure and the seismogenic zone of the CTJ area were studied. On the basis of the tomography (Figure 2) and previous numerical model settings for the CTJ (van der Hilst and de Hoop, 2005; Scherwath et al, 2006, 2009; Simmons et al, 2010; Völker et al, 2011; Maksymowicz et al, 2012) and the comparison of different initial slab dips (Surface Heat Flow and Seismogenic Zone and Seismicity Data), the initial slab dips of Models 1–5 were set in a way in which it gradually increases with the depth from 0° at the trench to 30° at about 120-km deep.
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