Seismological evidence for the existence of serpentinized wedge mantle

• Published in: Geophysical research letters Vol. 27; no. 6; pp. 819 - 822
• Main Authors: Kamiya, Shin'ichiro, Kobayashi, Yoji
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 15.03.2000; American Geophysical Union
• Subjects: Earth sciences; Earth, ocean, space; Earthquakes, seismology; Exact sciences and technology; Internal geophysics; Solid-earth geophysics, tectonophysics, gravimetry; Far East; Honshu; Japan; serpentinite; seismology; S-waves; Poisson's ratio; epicenters; earthquakes; tomography; mantle; oceanic crust; seismic waves; models; metaigneous rocks; P-waves; serpentinization; igneous rocks; velocity; metamorphic rocks; anomalies; subduction; ductility; Asia; plutonic rocks; travel time; ultramafics; peridotites
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/1999GL011080

Serpentinized peridotite is detected seismologically by mapping Poisson's ratio beneath the Kanto district, central Japan, because serpentinite has a higher Poisson's ratio than other rocks in the crust and upper mantle. We determine three‐dimensional P and S wave velocity models using travel time tomography and then construct a three‐dimensional map of Poisson';s ratio. The models show low velocity anomalies near the upper boundary of the slab in a depth range from 20 to 70 km. In the low velocity region, there is an area with Poisson's ratio greater than 0.3 at depths of 20–45 km, which we attribute to serpentinized peridotite. The rest of the low velocity region is interpreted as descending oceanic crust with a Poisson's ratio of about 0.25. The high Poisson's ratio area is associated with low seismicity and weak interplate coupling, which is consistent with the ductility of serpentinite.