1. Adisorn Foongkajorn Chiang Mai Seismic Station

2. Abstract A drop of number of seismicity is a seismic precursor (Bath,1979). During 1960-2005, earthquakes in Sumatra-Andaman seismic belt had occurred continually. After deployment of the World Wide Standardized Seismograph Network (WWSSN) in 1960’s, instrumentally seismic data of the region has been collected systematically. According to this study more than 3000 of the earthquakes of magnitude  5 in the Sumatra- Andaman seismic belt were analyzed and mapped. About 10% decline of seismicity was found in 1990’s. Then the most destructive event of the region occurred on 26 December 2004 with consequently high seismicity.

3. Scope of the study

4. http://elvis.engr.wisc.edu/UER/uer96/author3/fig2.gif Seismic Precursors

5. Seismic precursors - Decreasing Vp/Vs (10-20% change) Electrical resistivity (15% change) Number of seismicity - Increasing (geodetic measurements) Tilt Vertical motion Volumetric strain (Bath, 1979:298)

6. First Episode of the Great Sumatra Earthquake

7. Indian Plate that has played an important roll in the Sumatra- Andaman Seismic Belt

8. Panoramic Scene of the Sumatra- Andaman seismic belt

9. Origin of Volcanic Island Arc as Andaman and Nicobar were originated

10. Epicentral Distribution in Sumatra-Andaman seismic belt during 1960-2005

12. Number of the Earthquakes in Sumatra- Andaman Seismic Belt during 1960-2005 YearNo.Change(%) 1960-1969259 1970-1979 *541 + 108.88 1980-1989585 + 8.13 1990-1999529 - 9.57 2000-20051238 +134.03 * Development of highly sensitive seismograph Total 3152

13. Number of the Earthquakes in Sumatra-Andaman Seismic Belt during 1960-2005

14. MagnitudeNumber  91  81  717  6186  52947 Magnitude of the Earthquakes in Sumatra-Andaman seismic belt during 1960-2005 Total 3152

15. Magnitude of the Earthquakes in Sumatra-Andaman seismic belt during 1960-2005

16. Depth Distribution of the Earthquakes in Sumatra-Andaman seismic belt during 1960-2005

17. Cumulative Depth Distribution of the Earthquakes in Sumatra-Andaman seismic belt during 1960-2005 1960-19691960-1979 1960-19891960-1999 1960-2005

18. Cumulative Depth Distribution of the Earthquakes in Sumatra-Andaman seismic belt during 1960-2005

19. Depth Contour of the Earthquakes in Sumatra- Andaman seismic belt during 1960-2005

20. Depth of the Earthquakes in Sumatra- Andaman seismic belt during 1960-2005

21. Rupture, surface wave propagation and co-seismic displacements measured by GPS of the great Sumatra earthquake on 26 December 2005

22. Aftershock Distribution of the great Sumatra earthquake on 26 December 2005

23. Magnitude of the Earthquakes in Sumatra- Andaman Seismic Belt on 26 December 2004

24. Depth of the Earthquakes in Sumatra- Andaman Seismic Belt on 26 December 2004

25. Major and Great Earthquakes in Sumatra- Andaman Seismic Belt during 1960-2005

26. Major Earthquakes in Sumatra-Andaman Seismic Belt during 1900-1959

27. Major Earthquakes in Sumatra-Andaman Seismic Belt during 1900-2005

32. Conclusions According to the study more than 3000 of the earthquakes of magnitude  5 in the Sumatra- Andaman seismic belt during 1960-2005 were analyzed and mapped. About 10% decline of seismicity was found in 1990’s. Then the most destructive event of the region occurred on 26 December 2004 with consequently high seismicity. The drop of number of seismicity is precursory potential for earthquake prediction.

33. Thank you very much