Adisorn FoongkajornChiang Mai Seismic Station

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.

Scope of the study

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

SeismicPrecursors

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)

First Episode of the Great Sumatra Earthquake

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

Panoramic Scene of the Sumatra-Andaman seismic belt

Origin of Volcanic Island Arc as Andaman and Nicobar were originated

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

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

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

Year No. Change(%)

1960-1969 259

1970-1979 *

541 + 108.88

1980-1989 585 + 8.13

1990-1999 529 - 9.57

2000-2005 1238 +134.03

* Development of highly sensitive seismograph

Total 3152

Number of the Earthquakes in Sumatra-Andaman Seismic Beltduring 1960-2005

Magnitude Number 9 1 8 1 7 17 6 186 5 2947

Magnitude of the Earthquakes in Sumatra-Andaman seismic beltduring 1960-2005

Total 3152

Magnitude of the Earthquakes in Sumatra-Andaman seismic beltduring 1960-2005

Depth Distribution of the Earthquakes in Sumatra-Andaman seismic beltduring 1960-2005

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

1960-1969 1960-1979

1960-1989 1960-1999

1960-2005

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

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

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

Rupture, surfacewave propagationand co-seismicdisplacements measured by GPS of the great Sumatra earthquake on 26 December 2005

Aftershock Distribution of the great Sumatra earthquake on 26 December 2005

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

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

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

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

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

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.

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