VERTICAL CRUSTAL MOVEMENT IN THE BOSO PENINSULA, SOUTH KANTO, JAPAN, AS DEDUCED FROM THE ADJUSTMENT OF A GEODETIC NETWORK WITH SIGNALS

In the adjustment of a leveling network that is frequently resurveyed, we introduce corrections not only to the approximated heights of the stations but also to their rates of vertical movement, which are linear over time, as an unknown. Thus we can apply least-squares collocation to the problem, and have some cases corresponding to the rank deficiency of the design matrix in the observation equation. We have applied this method to the study of the vertical crustal deformation in the Kanto district, particularly to the Boso peninsula, Honshu, Japan. Rates of vertical crustal movement and their covariance matrices are deduced for two periods for the Kanto district (1) 1965-1978 and (2) 1978-1989, and for three periods for the Boso peninsula (1) 1965-1972, (2) 1973-1976 and (3) 1976-1988. The deduced rates range from - 10 mm/yr to + 10 mm/yr, and their standard deviations amount to +/- 11 mm/yr for the Kanto district. For the Boso peninsula, they range from - 22 mm/yr to + 6 mm/yr, and amount to +/- 5 mm/yr. This peninsula is very close to the convergent plate boundary between the Philippine sea plate and South Kanto, and the results of this analysis reveal the typical fluctuating behavior of the crustal movements associated with the subduction process during the interseismic period. The author interprets this episodic crustal movement as being due to intermittent creep dislocation along the deeper part of the interface between the Kanto district and the Philippine Sea plate.