Abstract
The fate of lithospheric slabs descending along island arcs is an important issue on mantle dynamics. The slab penetration into the lower mantle implies the flow of upper mantle material into the lower mantle. Travel time anomalies observed from deep-focus earthquakes suggest the extension of the high velocity slabs into the lower mantle in the western Pacific subduction zones. The depth extent of the slabs is not definitely determined by using only travel time data, because the path coverage of body waves is bad in the lower mantle below subduction zones. Observations of anomalously broad and complex S waveforms from deep-focus earthquakes are consistent with the lower mantle slab penetration hypothesis. Lower mantle slab models which quantitatively explain the observed waveform broadening have not been derived. Appropriate methods for calculation of theoretical seismograms in strongly heterogeneous media such as subduction zones are required to analyze the observed waveforms and confirm the hypothesis. Deployments of global network of broadband seismographs with wide dynamic range are also essential to reveal the lower mantle slab structure.
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Schedule a callMore From: Zisin (Journal of the Seismological Society of Japan. 2nd ser.)
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