WEPP2 -Global P-wave velocity model-

Model WEPP2 is an update of the P-velocity tomographic model for the Western Pacific WEPP1 by Fukao et al. [1992]. About 2,000,000 P first arrival times are used from the selected 12,000 earthquakes in the bulletins of the International Seismological Centre for a period of 28-years from 1964 to 1991. The whole mantle structure are parameterized by blocks with finer ones in the western Pacific. The mantle is divided into 32, 64, and 16 basic blocks in latitude, longitude, and radius, respectively. Beneath the western Pacific, the basic blocks are subdivided into smaller blocks. The size of the smallest block is 1/4 of a basic block in latitude and longitude and 1/2 in depth.

Obayashi, M., T. Sakurai, and Y. Fukao, Comparison of recent tomographic models (abstract), International Symposium on New Images of the Earth's Interior through long-term ocean-floor observations, 29, Tokyo, 1997.
Fukao, Y., S. Widiyantoro and M. Obayashi, Stagnant slabs in the upper and lower mantle transition region, Rev. of Geophys., 2001.

Slowness anomalies of each layer. The red and blue colors indicate slow and fast anomalies, respectively. The scale is 2.0% for the top 4 layers and 1.0% for the other layers.

The parameters of the basic blocks are converted to the coefficients of the spherical harmonics (up to 24-degree) for each of the 16 layers . Definition of the spherical harmonics is the same as Dziewonski [1984].
Coefficients of the spherical harmonics:
layer 1 layer 2 layer 3 layer 4
layer 5 layer 6 layer 7 layer 8
layer 9 layer 10 layer 11 layer 12
layer 13 layer 14 layer 15 layer 16
All layers

For the high resolution region (western Pacific) ----Figures

W-Pac: High resolution models of slowness perturbations (%) in the Western Pacific region defined by the parallels at latitudes 16.875S and 61.875N and meridians at 95.625E and 163.125E. For ease of parameterization this region is uniformly divided into 56 x 48 (latitude x longitude) finest blocks, although the actual blocks have three different sizes. This data set begins with slowness perturbation (%) of the block at the bottom left (southwest end) of the map for the top layer (layer #1), goes upward to the northwest end and then starts again from the southern end but with one block aside to the east. Once this process is completed for layer #1, it proceeds to the deeper layers (up to#32).

For communication regarding this page, please contact:
Masayuki Obayashi