SLANT-STACK VELOCITY ANALYSIS FOR ONE-DIMENSIONAL UPPER-MANTLE STRUCTURE USING SHORT-PERIOD DATA FROM MAJO

In this paper, regional P-wave upper mantle structure is investigated using slant-stack velocity analysis of short-period earthquake data re corded at station MAJO (Matsushiro, Japan). Shallow earthquakes from 1 980-1986 within 35-degrees of MAJO are used to construct a common rece iver gather. Processing of the wavefield data includes focal depth and static time corrections, as well as deterministic deconvolution, in o rder to equalize pulse shapes and align wavelets on the first arrivals . The processed wavefield data are slant stacked and iteratively downw ard continued to obtain a regional upper mantle velocity model. The mo del includes a low velocity zone between 107 and 220 km. Beneath the L VZ, the velocity increases smoothly down to the discontinuity at 401 k m. In the transition zone, the velocity model again increases linearly , although there is some suggestion of further complexity in the downw ard continued wavefield data. At the base of the transition zone, a se cond velocity discontinuity occurs at 660 km, with a linear velocity g radient below. In addition to slant-stack analysis, travel times and s ynthetic seismograms are computed and compared with the processed and unprocessed wavefield data.