Shear wave polarization anisotropy observed in a rift zone in Japan

摘要: Abstract We have found polarization anisotropy in shear waves from small earthquakes both the upper crust and uppermost mantle beneath a rift zone Central Kyushu, Japan. recognized two different directions of faster waves: about E-W at three stations located zone, N-S possibly outside close to edge zone. The former case (E-W) is consistent with hypothesis that shear-wave splitting caused by vertical cracks or fractures striking direction which formed under present tectonic stress inside extending direction, maximum horizontal compressive minimum vertical. In contrast, latter (N-S) inconsistent above hypothesis. This inconsistency may be due complicated pattern crack distribution around Alternatively, it result regime within Arrival-time differences between slower split crustal are less than 0.12 s, while those events 0.25 s. relatively arrival-time respect their hypocentral distances could density lower compared crust.