岡山大学 地球科学研究報告
Published by Okayama University Earth Science Reports Editorial Committee

西南日本の地殻及び上部マントルの三次元P波速度構造

田中 猛士
小田 仁 岡山大学理学部地球学科
Thumnail ESR_4_1.pdf 898 KB
抄録
Trevel-time data of the P wave were inverted to study three-dimensional structure of the P wave velocity in the upper mantle and crust beneath the Shikoku and Chugoku districts, southwest Japan. Low-velocity and high-velocity regions were found in the upper crust of the eastrn and western regions in the Shikoku district, respectively. The activity of crustal earthquakes is high in the eastern region. Moreover a significant high-velocity region exists in the uppermost mantle, where the activity of small earthquakes is very high. A low-velocity region with velocity of 7.0km/s was found just above the descending Philippine Sea plate with high velocity of 8.0 km/s. This region is continued to oceanic crust in the vicinity of the Nankai trough and its velocity is nearly equal to the P wave velocity (6.7 km/s) of oceanic crust. Thus the low velocity is interpreted as the oceanic crust. A high-velocity region is found below the depth of 50km in the Shikoku district. This region suggests the Philippine sea plate lying horizontally from the Shikoku districts to the ocast of the Seto Inland Sea of the Chugoku district. A low-velocity zone suggesting the volcanic front is found around the depth of 50km at the coast of the Japan Sea of the Chugoku distrit.
キーワード
Three-dimenrsional structure
P wave
Crust
Upper mantle
Philippine Sea plate
ISSN
1340-7414
NCID
AN10506284