西南日本合同地震観測データを用いたレシーバ関数解析

Abstract

2000年鳥取県西部地震の余震地域を含んだ西南日本において，大学合同地震観測のデータを用いてレシーバ関数解析を行った。得られた地下構造と地震分布を比較して以下の結果を得た。1）四国東部地域における深さ40kmまでの地震は，上部マントルではなくて，海洋性地殻で発生している可能性があること，2）2000年鳥取県西部地震地域のモホ不連続面は，深さ約30kmであり，深さ約60kmに存在する不連続面が，プレートの延長である可能性があること，3）地殻内の地震発生層の最下部付近に，不連続面が存在すること。

We imaged S wave velocity discontinuities by analyzing Ps converted waves in receiver functions with data from the Joint Seismic Observation of Japan Universities in Southwest Japan. The source area of the 2000 Western Tottori Earthquake is located in the observation area. The Moho discontinuity is clearly imaged in the result. It is possibly deduced that the clear Moho discontinuity in the Shikoku district is the continental Moho discontinuity rather than the oceanic one. Furthermore, earthquakes may occur at the boundary of the Philippine Sea Plate (PHP) or in the oceanic crust rather than in the uppermost mantle of the oceanic plate. The Moho discontinuity is located at ～30 km deep in the northern Chugoku district. A discontinuity was also found at ～60 km in the region. This discontinuity may be an extension of the PHP. Discontinuities in the crust are intermittent and they seem to be located just below the seismogenic zone.