Skip to main content

Density structure inferred from gravity anomalies in the eastern area of the Itoigawa-Shizuoka Tectonic Line, central Japan

Abstract

A gravity survey was conducted between October 2002 and December 2003 in and around the eastern area of the Itoigawa-Shizuoka Tectonic Line (ISTL). The total number of measurement points amounted to about 436 and 326 stations were taken at the same points as the seismic survey points. The location and altitude were decided by differential GPS and the accuracy is thought to be within several ten-centimeters. The data was compiled from existing data (Geological Survey of Japan, 2000), so the total number of compiled gravity maps is about 3,540 points. All measured gravity data were referred to the International Gravity Standardization Net 1971 (IGSN71) and the normal gravity values were estimated according to the gravity formula of 1980. Terrain corrections were conducted within a range of 60 km by approximating the real topography to an assemblage of annular prisms interpolated by mesh terrain data and random terrain data of the gravity points. The effect of the sinking of the topography due to the Earth’s curvature was taken into consideration. Bouguer corrections within a range of 60 km in arc distances were made using a spherical cap crust formula. The density for both terrain correction and Bouguer corrections was chosen to be 2,670 kg/m3, because the mean surface density of the whole area is estimated to be a slightly large density by the CVUR method. The features of Bouguer anomalies is characterized by a low anomaly in Omachi city, in the northern parts of Matsumoto basin, and a high anomaly in the central highlands, Central Uplift Zone, about 10 km west of Ueda city. The low anomaly shows that the thickness of the sedimentary layer is more than 1 km from 2D/3D automatic analysis.

References

  1. Geological Survey of Japan, 1:500,000 Geological Map / KANAZAWA (2nd ed.), 1974.

    Google Scholar 

  2. Geological Survey of Japan, 1:200,000 Geological Map / TAKAYAMA, 1989.

    Google Scholar 

  3. Geological Survey of Japan, 1:200,000 Geological Map / NAGANO, 1998.

    Google Scholar 

  4. Geological Survey of Japan, Gravity CD-ROM of Japan, DGM P-2, 2000.

    Google Scholar 

  5. Ikami, A., T. Yoshii, S. Kubota, Y. Sasaki, A. Hasemi, T. Moriya, H. Miyamachi, R. S. Matsu’ura, and K. Wada, A seismic-refraction in and around Nagano Prefecture, central Japan, J. Phys. Earth, 34, 457–474, 1986.

    Article  Google Scholar 

  6. Imai, T., T. Iwasaki, T. Takeda, T. Kawanaka, and H. Sato, Detailed upper crustal structure across the Itoigawa-Shizuoka Tectonic Line from the 2002 Seismic Expedition, Proceedings of the Second International Symposium on Slip and Flow Processes in and below the Seismogenic Region, 2–5, 2) 1–6, 2004.

    Google Scholar 

  7. Komazawa, M. A gravimetric terrain correction method by assuming annular prism model, J. Geod. Soc. Japan, 34, 11–23, 1988 (in Japanese with English abstract).

    Google Scholar 

  8. Komazawa, M., Gravimetric analysis of Aso Volcano and its interpretation, J. Geod. Soc. Japan, 41, 17–45, 1995.

    Google Scholar 

  9. Okubo, S., Y. Ikeda, T. Kumamoto, G. Seta, N. Matuta, H. Chiba, and Y. Arai, 2-D and 3-D subsurface density structure in the northern part of the Itoigawa-Shizuoka Tectonic Line derived by gravity surveying, J. Geod. Soc. Japan, 46, 177–186, 2000.

    Google Scholar 

  10. Sato, H., T. Iwasaki, S. Kawasaki, Y. Ikeda, N. Matsuta, T. Takeda, N. Hirata, and T. Kawanaka, Formation and shortening deformation of a back-arc rift basin revealed by deep seismic profiling, central Japan, Tectonophysics, 388, 47–58, 2004.

    Article  Google Scholar 

  11. Woollad, G. P., The new gravity system—changes in international gravity base values and anomaly values, Geophysics, 44, 1352–1366, 1979.

    Article  Google Scholar 

  12. Yano, T., Late Cenozoic geohistory in the northern Fossa Magna Region, Central Japan, J. Sci. Hiroshima Univ., Ser. C,9, 81–132, 1989.

    Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to Masao Komazawa.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Komazawa, M. Density structure inferred from gravity anomalies in the eastern area of the Itoigawa-Shizuoka Tectonic Line, central Japan. Earth Planet Sp 56, 1309–1314 (2004). https://doi.org/10.1186/BF03353355

Download citation

Key words

  • Itoigawa-Shizuoka Tectonic Line
  • Omine belt
  • CVUR method
  • 3-D gravity basement
  • Central Uplift Zone
  • fold structure