Regionality of crust and upper mantle structure around Japan as derived from large explosions at sea

Tectonophysics,

130 @ Elsevier Scientific

Publishing Company,

Amsterdam

56 (1979)

130

- Printed in The Netherlands

REGIONALITY OF CRUST AND UPPER MANTLE STRUCTURE AROUND JAPAN AS DERIVED FROM LARGE EXPLOSIONS AT SEA

RESEARCH Earthquake

GROUP FOR EXPLOSION Research

Institute,

University

SEISMOLOGY of Tokyo

l-l-l

Yayoi,

Bunkyo-ku,

Tokyo

(Japan) (Received

July 18, 1978)

ABSTRACT

Two large explosions (54on) in the Sea of Japan were carried out in July 1976 to study the crust and upper mantle structure around Japan. Seismic waves generated by these explosions were observed at about 50 temporary as well as about 60 permanent stations in Japan up to a distance of about 800 km. Analysis of these data based on the previous information gives the following: (1) The low P,-velocity, 7.5 km/s, beneath northeastern Honshu and the normal P,-velocity beneath the Sea of Japan, 8.1 km/s, were ascertained. (2) In four profiles the crust and upper mantle structure was derived by taking previous results and gravity data into account. (3) There is a possibility that anisotropy of P,-velocity is present beneath Honshu on the Sea of Japan side.