A finite-frequency P-wave tomographic model: images of subducted slabs stagnant above, penetrating through and trapped below the 660-km discontinuity
Abstract
We constructed a new P-wave tomographic model of the mantle using more than ten millions of travel time data. The finite frequency effect of seismic ray was taken into account by calculating banana-donut kernels at 2 Hz for all the first arrival data and at 0.1 Hz for the broadband differential travel time data. Based on this model, a systematic survey was made for subducted slab images around the circum Pacific including Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America. This survey clarified a progressive lateral variation of slab configuration along the arc or through the arc to arc, where a subducted slab is in general in one or two of the following four stages: I. slab stagnant above the 660, II. slab penetrating the 660, III. slab trapped in the uppermost lower mantle (660 to ∼1000 km in depth), and IV. slab descending well into the deep lower mantle. The majority of the slab images are either at stage I or III. We interpret I to IV as the successive stages of slab subduction through the transition region with the 660 at the middle, where I and III are relatively stable or neutral stages and II and IV are relatively unstable, transient stages. In particular, we emphasize III as a distinct stage of slab subduction, through which the slab once softened by the phase transition may progressively recover its hardness. Alternatively, the mantle viscosity may not increase stepwise across the 660 but increase gradually throughout the uppermost lower mantle. Plots of hypocentral distribution on tomographic slab images show that deep shocks at depths greater than ∼620 km are a good measure of slab penetration at stage either II or III.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMDI11A2390F
- Keywords:
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- 8124 TECTONOPHYSICS / Earth's interior: composition and state;
- 7208 SEISMOLOGY / Mantle;
- 7240 SEISMOLOGY / Subduction zones;
- 8162 TECTONOPHYSICS / Rheology: mantle