Recent results from seismic tomography reveal that configurations of the subducted slabs are varied; some of them lie horizontally on the boundary between the upper and the lower mantles, and others penetrate into the lower mantle. In this study, a two-dimensional model which gives the velocity boundary condition is constructed to investigate temperature distribution in and around the horizontally lying slabs. The model includes the effect of flow of the ambient mantle induced by the subducting slab. The length of the horizontally lying portion of the slab tends to be proportional to the subducting velocity, and to approach a constant value with increasing dip angle. These suggest that the length of the horizontally lying portion of the slab is subject to the thermal parameter. P-wave velocity anomalies converted from the calculated temperature distribution nearly at steady state show region with very high velocity anomaly, more than 10%, within the slab, which is different from the results of seismic tomography. This indicates that our assumption that the mantle material is composed of olivine (Mg
0.89Fe
0.11)
2SiO
4 may not be correct, or the approximation of the used equations of state may not be so rigorous. We also found that the horizontally lying slabs calculated in this study exist at the region with high velocity anomalies in the seismic tomography. Furthermore, our result indicates that the viscous heating in the ambient mantle should be necessary to keep the mantle wedge hot permanently under the condition without upwelling and/or inflow of hot material.
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