Vol.54-2 CONTENTS

Yoshiyuki TANAKA, Hiroaki SAITA, Jun SUGAWARA, Kazumi IWATA, Tomoo TOYODA, Hideaki HIRAI, Tamotsu KAWAGUCHI, Shigeru MATSUZAKA, Yuki HATANAKA, Mikio TOBITA, Yuki KUROISHI and Tetsuro IMAKIIRE

The Geographical Survey Institute published a new geodetic datum (the Japanese Geodetic Datum 2000, JGD2000) in April 2002. The JGD2000 is a static geocentric datum compliant with the International Terrestrial Reference Frame 1994 at the first epoch, January 1997, in which coordinates of control points are unchanged with time. Therefore, in order to keep the datum from becoming distorted, relative coordinate changes of markers due to crustal deformations caused by earthquakes and the steady plate motion must be corrected. So far, the changes induced by earthquakes have been revised with surface displacements detected by actual GPS observations. However, a large earthquake that occurs in a plate boundary such as the 2003 Tokachi-Oki event (M8.0) will cause deformation covering several hundred square kilometers, and resurveying all the relevant control points would be prohibitively expensive. On the other hand, the strain accumulation caused by the steady plate motion has been neglected since public projects have focused on local surveys using small networks (baselines < 10 km). However, this leads to significant positioning errors in the recently introduced Network RTK-GPS which needs larger networks (> 30-100 km). To cope with these two assignments, we develop crustal movement models to obtain coordinate corrections. With these models, we show that (1) an interpolation of observed displacements effectively reproduces co-seismic deformations without dense measurements and (2) the same method is valid for correcting the inter-seismic strain accumulation. For the latter, we show the validity of semi-dynamic datum correction already adopted in New Zealand. Combining these methods with the advanced GPS network enables us to efficiently and effectively maintain the JGD2000 for modern surveys.

1. Introduction - geodetic datum and its errors due to crustal deformation
2. Observational networks
  2.1 Continuous GPS observation network
  2.2 Campaign GPS observation network
  2.3 Other networks
3. Model of earthquake-induced crustal deformation
  3.1 Overview
  3.2 Model
  3.3 PatchJGD
  3.4 Application to other earthquakes
4. Model of inter-seismic crustal deformation
  4.1 Inter-seismic deformation and relative error
  4.2 Semi-dynamic datum
  4.3 Model
  4.4 Effect of semi-dynamic datum
  4.5 Standardization of crustal movement correction in Network RTK-GPS
5. Conclusion
References