Fumiaki Kimata, Kazuro Hirahara, and Naoyuki Fujii Graduate School of Environmental Studies,

1. Interplate Coupling Model in the Tokai region, Japan, Estimated from the Ground Deformation by Leveling, Tide Gauge, and GPS Measurements in 1996-2000. Fumiaki Kimata, Kazuro Hirahara, and Naoyuki Fujii Graduate School of Environmental Studies, Nagoya Univ.

2. Overview of the Presentation Interplate Coupling Model in the Tokai Region Back Slip Model estimated from GPS by Sagiya (1999). Conversion Rate of 2 cm/yr at Suruga Trough by Heki & Miyazaki (2001) Back slip Model estimated from vertical movements (Kimata et al.,2002) Back Slip Model constrained by conversion rate of 2 cm/yr at Suruga T. Episodic change of the coupling 2001 Slow Slip Event Ground Deformation referred to GujyoHachiman in GIS GPS networks

3. Backslip model in the Tokai region estimated from GPS measurements By Sagiya(1999) • Estimated backslip rates more than 3 cm/yr • Underestimation of the vertical movements

4. Subsidence of 8mm/yr at Omaezaki for late 40 years -10 cm -20 cm -30 cm 40 years

5. Backslip Model estimated from vertical movementsby Kimata et al.,2002 Rigid coupling is started under not Suruga trough but Omaezaki and extended to Mikawa Bay area.

6. Time Series of E-W component on GPS measurements referred to GujyoHachiman(Gifu) in 1996-2002

7. N-S comp. U-D comp. Time Series of E-W component on GPS measurements referred to GujyoHachiman (Gifu) in 1996-2002

8. Observed in 1996-2000 Calculated 2cm 2cm Ground deformation observed and calculated fixed

9. Comparing the deformation observed by measurements and calculated by model 2 cm/yr Calculated Observed Fig.2 Correlation of observed and calculated displacement rates of N-S and E-W comportments.

10. Episodic DeformationStable deformation in 1996-2000 by Sagiya (2001)

11. fixed Ground deformation in every year in 1996-2001(except May.2000 – Dec.2000) The ground deformations, horizontal vectors and vertical movements as a contour of 1 mm/yr are shown in whole period and in every year since 1996 t0 2001. We fix the coordinates at GujyoHachiman as same discussion as Sagiya 19999. The horizontal vectors at the sites in the Izu Peninsula are also shown in the figures. The figures make clear that, firstly, the horizontal vectors are stable until April 2000, and observed vertical deformation is not stable to discuss the movements yearly, as same as Sagiya’s discussion in 2001. It is very defined that the horizontal displacements in 2001 are different. The horizontal vectors toward west-northwestward are disappeared in the western Tokai region, except at Omaezaki in 2001.Additionally, the horizontal displacements detected at Hamaoka sites are different with that observed at around sites, and horizontal displacements at the western part of the around at Hamamatsu are decreasing of the vectors in 1999.

12. 2ｃｍ 2ｃｍ Ground Deformation observed in 1996-2000/2001 2001 Tokai Slow Slip Event Disappearing the northwestward displacements and uplifting of 2 cm in the western Tokai region. Residual Deformation in 2001-(1996-2000) 2ｃｍ Obs(01/01-02/01)

13. 2ｃｍ 15 cm 15 cm Observed and Estimated the 2001 Tokai Slow Slip Pure Slow Slip only Total Deformation Observation Model 70 km x 20 km x 15 cm

14. Summary Interplate Coupling Model and its Episodic Change in the Tokai Region Estimated from GPS Measurements 1. Interplate coupling model estimated from the GPS measurements in 1996-2000. Our coupling model is accountable the horizontal and vertical movements in 80% of observation. The convergent rate at the Suruga Trough and the back slip rates between the plates are within 2 cm/yr maximally. 2.Episodic Changes of the Interplate Coupling since 1996. Tokai Slow Slip Event in 2001 is undergoing as the deformation of the horizontal displacements to the south-east and the upheaval of 2 cm in the western Tokai region, centered on Hamamatsu. We estimate the slow slip event as the forward slip of 15 cm toward southeastward of the fault with the size 70 km x 20 km.