When slabs collide: A tectonic assessment of deep earthquakes in the Tonga-Vanuatu region

Dynamics of subduction initiation with different evolutionary pathways

“…The New Hebrides subduction zone initiated through a polarity reversal at ∼10–12 Ma [ Greene et al , 1994]. Here, a slab segment beneath the North Fiji Basin is characterized by an unusual group of more than 100 earthquakes located at ∼600 km depth [ Hamburger and Isacks , 1987; Okal and Kirby , 1998; Richards et al , 2011]. This detached slab segment may have broken off the subducted Australian plate at ∼5 Ma ago according to the structural interpretation of Richards et al [2011].…”

“…Here, a slab segment beneath the North Fiji Basin is characterized by an unusual group of more than 100 earthquakes located at ∼600 km depth [ Hamburger and Isacks , 1987; Okal and Kirby , 1998; Richards et al , 2011]. This detached slab segment may have broken off the subducted Australian plate at ∼5 Ma ago according to the structural interpretation of Richards et al [2011]. Consequently, the segmentation would have occurred ∼5–7 Myrs after subduction initiation of the Australian plate.…”

Mantle constraints on the plate tectonic evolution of the Tonga–Kermadec–Hikurangi subduction zone and the South Fiji Basin region

“…A clear example of this is the North Fiji backarc Basin, which has a wedgeshaped geometry and is generally interpreted to have opened during clockwise rotation of the New Hebrides arc (e.g. Auzende et al 1988;Schellart et al 2002Schellart et al , 2006Richards et al 2011). The North Fiji Basin has a very complex backarc spreading pattern with multiple spreading ridges that strike sub-parallel to sub-perpendicular to the strike of the New Hebrides arc and trench (Figure 1).…”

Deep Earth Structure - Subduction Zone Structure in the Mantle Transition Zone

“…Note that the deepest seismic zone here apparently splits into two, one extending at a very shallow dip and the other dipping very steeply. More detailed studies of the deep seismicity and focal mechanisms (e.g., Bonnardot et al, 2009;Brudzinski and Chen, 2005;Richards et al, 2011) suggest that the shallowly dipping seismic zone represents either the northern segment of the slab from the Tonga trench or the slab from the Vanuatu trench and that the steeply dipping seismic zone represents the southern segment of the slab from the Tonga trench. Fukao and Obayashi (2013) interpreted these two seismic zones as an indication of juxtaposition of two separate slabs, rather than a doubly thickened slab: one is stagnant above the 660-km discontinuity and the other is deflecting subhorizontally just below the discontinuity, as observed in northern Kermadec (Figure 7(b)).…”