Studies on Three-Dimensional Seismic Velocity and Attenuation Structures in the Chubu and Kinki Regions, and Their Tectonic Implications

(1)利用120个浅层和中等深度地震的7500个P波到达时间，应用一种反演技术研究了日本中部地区的三维P波速度结构。结果清楚地揭示了日本中部活动海沟下方和俯冲板块上方的显著低速体。(2)提出了一种除横向非均质性外检测三维速度各向异性的新方法，并将其应用于日本中部的P波走时数据。(3)从地震活动性和地震震源机制出发，结合地质构造背景，研究了日本本州岛中部平田地区的地震构造特征。详细讨论了赤川断裂的不均匀地震活动及其最深地震活动的剧烈变化，以及该地区工作的压应力来源。(4)3…利用从大量局部地震中获得的2500个P波走时数据，用瑟伯方法反演了日达地区的多维上地壳结构。结果表明，在北国中部，特别是沿阿多舒川断裂的西段，存在高速区，低速带延伸至日达山活动涡旋下的中地壳。(5)用AVOVE方法，利用北国地区发生的278次局部地震，得到了北国地区的三维上地壳结构。结果表明，在北东-南西方向存在3公里以下的高速带。(6)利用反演技术得到了近海中北部地区的三维上地壳结构，并与该地区的地震活动性进行了对比。速度结构的最大变化在8%以内，但在该地区的大部分地区都不到4%。最深的地震活动似乎是从西南向东北方向加深的。较少

(1) 3-D P-wave velocity structure beneath central Japan has been investigated by applying an inversion technique, using 7,500 P-wave arrival times from 120 shallow and intermediate depth earthquakes. The results clealy reveal prominent low-velocity bodies just beneath active colcanoes in central Japan and above the subducting plates.(2) A new method to detect 3-D velocity anisotropy in addition to lateral heterogeneities has been proposed, and applied to P-wave travel time data in central Japan. No significant P-wave anisotropy was detected where shear wave anisotropy has been revealed.(3) Seisomotectionc features of the Hida region, central Honshu, Japan has benn investigated on the basis of seismicity and focal mechanism of earthquakes, with reference to the geological and tectonic setting. The non-uniform seismicity along the Atotsugawa fault, and its sharp variations of deepest seismicity, and the source of the compressive stress working in this region are discussed in detail.(4) 3 … More -D upper crustal structure in the Hida region has been derived by Thurber's inversion method applying to 2,500 P-wave travel time data obtained from a large number of local shocks. It has been found that high-velocity regions exist in the central part particularly along the western part of the Atotsugawa fault, and that low-velocity zones extend over the middle crust beneath active volvanoes in the Hida mountains.(5) 3-D upper crustal structure in the Hokuriku region has been derived from the avove method, using 278 local shocks that occurred around thei region. The results show that there is high-velocity zone trending in the NE-SW direction down to a depth of 3 km.(6) 3-D upper crustal structure in the central to northern Kinki region has been derived by the inversion technique, and compared with seismicity in this region. The largest variations in the velocity structure are found to be within 8 %, but less than 4 % in most part of the region. The deepest seismicity appears to become deeper from the SW to NE direction. Less