Figure 1: Earthquakes and subducted slabs beneath the Tonga–Fiji area. | Nature

Figure 1: Earthquakes and subducted slabs beneath the Tonga–Fiji area.

From: Tiny triggers deep down

Figure 1

The subducting slab and detached slab are defined by the historic earthquakes in this region: the steeply dipping surface descending from the Tonga Trench marks the currently active subduction zone, and the surface lying mostly between 500 and 680 km, but rising to 300 km in the east, is a relict from an old subduction zone that descended from the fossil Vitiaz Trench. The locations of the mainshocks of the two Tongan earthquake sequences discussed by Tibi et al.2 are marked in yellow (2002 sequence) and orange (1986 series). Triggering mainshocks are denoted by stars; triggered mainshocks by circles. The 2002 sequence lies wholly in the currently subducting slab (and slightly extends the earthquake distribution in it), whereas the 1986 mainshock is in that slab but the triggered series is located in the detached slab, which apparently contains significant amounts of metastable olivine8,9. (Modified from ref. 13 with permission of the American Geophysical Union.)

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