9614639 Lees This research involves the deployment of broadband portable seismometers from PASSCAL on the Kamchatka Peninsula to study the effect of upper mantle flow around the sharp transform-to- convergent transition in the Pacific/North-American plate boundary at the intersection of Kamchatka and the Aleutian Islands. The geology of the Kamchatka region has unusual features which may be related to asthenospheric flow around the slab edge, such as exceptionally high rates of arc magmatism involving both slab and mantle melts, and recent rifting and spreading of the Komandorskaya Basin. Using portable and nearby permanent stations, scientists from Yale University and the Russian Institute of Volcanology will investigate lateral variations in seismic velocity, anisotropy and Q using shear-wave splitting, surface-wave scattering, body wave reverberation, attenuation and diffraction observations, and regional seismicity. They will address whether trench-parallel flow exists below the Pacific plate, and whether Kamchatka volcanism is underlain by a low-velocity, low-Q upper-mantle wedge associated with mantle material pulled around and above the descending slab. Data from stations north of the Aleutian intersection, where island-arc volcanism has only recently ceased, will be used to determine whether a stalled, buoyant slab from the subduction of the young Komandorskaya Basin exists, or whether low-velocity upper mantle suggests the presence of a "slab window." Earthquakes in Japan and the Kurile arc have ideal geometry for measuring crustal dispersion, and hence crustal thickness variations, along the Kamchatka Peninsula. ***
