1. Variations in GPS-derived displacements and stresses during the 2003 Miyagi earthquakes Ali O. Oncel and Omer Aydan Geological Survey of Japan Tokai University, Department of Marine Civil Engineering

3. Seismotectonic aspects of Japan (Oncel, Wilson and Nishizawa, JGR-2001) Negative Correlations :Stress suddenly released of larger magnitude seismicity on interconnected faults of larger total surface . . Positive Correlations: Stress is gradually released by lower magnitude seismicity on smaller fault strands. Tohoku Events: July 26 event (M=6.2) were located in a positive correlation (Area III) noted to be anomalously quiescent. 5.00 to 6.00 6.00 to 7.00 1998-2003 M=6.2 2003.07.26 M=5.5 2003.07.26

4. GPS Earth Observation Network (GEONET) displacement rate GPS stations almost 1000 stations in Japanese Islands daily measurement of location with accuracy of 1[cm] No spatial filtering to get rid of measurement noise FEM with triangle element

5. Variations in regional strain (Hori, 2003) displacement rate GPS stations volumetric max. shear

6. Variations in regional stress (Hori, 2003) displacement rate GPS stations volumetric max. shear

7. Miyagi Event and GPS-stations Directivity of inferred deformation for July 26 event (Mw=6.2)

8. Aftershocks AND GPS-local stations

10. stress rate tensor computed by using Hooke’s law from the computed strain rates for elastic materials. Maximum Shear Stress + Mean Stress Rate * = Disturbing Stress Rate Friction of coefficient ( =0.8) Lame’s constants, which are generally assumed to be 30 GPa [Fowler, 1990]. Stress rates (Aydan 2000, 2003)

11. Estimated displacements for about three months M6.1 M6.3 M6.1 M6.3 M6.1 M6.3 1.5cm 2.7 cm 2.7cm 3.4 cm 1.4 cm 0.7 cm 1.7cm 1.0cm Variations in Displacements

12. Variations in Stress Rates M6.1 M6.3

13. Disturbing stress changes and asperity

14. Changes in GPS measurement seems to be partially related to the fault patches of seismic (asperity) and aseismic (creep). Especially, GPS velocity vectors is smaller in northern strand of NAFZ indicating higher seismic hazard while observing larger in its southern strand. Suggested asperities and GPS