Focal mechanisms of major earthquakes in southwest Japan and their tectonic significance.

Source mechanisms of subcrustal and upper mantle earthquakes around the northeastern Kyushu region, southwestern Japan, and their tectonic implications.

“…The stress state at subcrustal depths over an extensive region from the southern Chubu region to the Iyonada, northwestern Shikoku are characterized by systematic alignments of the tensional axis parallel to the leading edge of the subducting Philippine Sea plate (parallel extension). SHIONO (1977) and SHIONO et al (1980) also found that the tensional axis dips westwards and is approximately parallel to the dip of an inclined seismic zone under the Kyushu Island and the northern Ryukyu arc. In the inland Kyushu region, on the other hand, tensile stress working in an N-S direction appear to prevail at a shallow crust, in view of the focal mechanism with normal faulting type of relatively large earthquakes in central Kyushu (YAMASHINA and MURAI, 1975).…”

“…3A-E). These cross sections have been taken perpendicularly to iso-depth curves of subcrustal earthquakes suggested by MIZOUE (1977) and SHIONO (1977). It is obvious that the focal depths of the deepest earthquakes increase from the northern to southern region.…”

“…1. On the other hand, SHIONO (1977) suggested that the stress state in southwestern Japan may be classified into three categories on the basis of the locations of hypocenters and focal mechanisms of crustal and upper mantle earthquakes taking place there. One is the northwestward compressional stress working at shallow depths along the Nankai trough and in the Hyuganada region, which is inferred from low-angled thrust faulting earthquakes.…”

Stability of the regional stress field in central Japan during the late Quaternary inferred from the stress inversion of the active fault data

“…Blue crosses denote the locations of outcrops, trench sites, and seismicreflection profiles from where the fault-slip data were collected. Focal-mechanism solutions for historical surface-rupturing earthquakes are also shown by Shiono [1977] and Kikuchi and Kanamori [1996]: 1891 Nobi, 1927Kita-Tango, 1945Mikawa, 1948Fukui, and 1995 [Twiss and Gefell, 1990], improved by Sato [2006], that display the fault attitude and possible slip directions of the complete and sense-only data. A complete datum is denoted by an arrow plotted by a lower-hemisphere, equal-area projection; the pole of the fault plane is depicted in the stereogram by the position of the arrow, which itself indicates the slip direction of the footwall block (Figure 2d).…”

Seismic activity of subcrustal earthquakes and associated tectonic properties in the southeastern part of the Kinki district, southwestern Japan.

“…earthquakes with depths of 30 to 90 km are taking place. The configuration of the hypocentral distribution and the focal mechanism of these subcrustal earthquakes have been closely related to the subduction process of the Philippine Sea plate by many authors (see e.g., Kanamori and Tsumura, 1971;Shiono, 1977;Mizoue et al, 1983; Yamazaki and Ooida, 1985;Ishida and Hasemi, 1988).…”