Detailed horizontal crustal movements associated with the 1923 Kanto earthquake as deduced from network adjustment of old data including the third order triangulation stations

The crustal movements associated with the 1923 Kanto, Japan, earthquake of magnitude 7.9 are deduced from the results of network adjustments with the pre-seimic and post-seismic geodetic data including up to the third order triangulation. The average spacing of the third triangulation is 4 km of higher density as compared with the first order triangulation and the second order triangulation, so we can expect to find much more detailed behavior of the released crustal strain. The main rupture of the 1923 Kanto earthquake that had occurred in the Sagami Bay has been estimated from the crustal deformations deduced from repetition of the first order triangulation and the second order triangulation, while the detailed deformations associated with the secondary faulting are deduced for the first case from the repeated third order triangulation. We find evidence for the secondary faultings in the south Kanto district, Japan, mainly from the pattern of the released strain with the order of 10⁻⁴ and some of them are associated with the surface breakages. We carefully investigate whether these secondary faultings had originated with fracturing at the depth or not. We cannot find any evidence for deep fracturing, though we find remarkable high earth strain release along some secondary faultings. This is mainly due to the fact that the area of high released strain is very limited and narrow along the direction perpendicular to the faulting.