Abstract
The Sumatra subduction zone, one of the most active plate tectonic margins in the world, is characterised by the Indo-Australia Plate subducting beneath the Sunda plate and Andaman micro plate, causing seismic activity along the plate boundary. There had been five major earthquakes of magnitude greater than 8.0 in this region from 2004 to 2014. Three of them are dip-slip and rest of the two is strike-slip type events. Regional earthquake activity after the occurrence of those five events was analyzed. Hypocentral data obtained from the Data Management Center at the Incorporated Research Institutions for Seismology for the period from January 2000 to December 2014 of magnitude 3.0 were used for the analysis. A statistical analysis was carried out to know whether earthquake activity has increased after the major five events and the analysis was carried out both qualitatively and quantitatively. The results of the analysis show that the number of earthquakes in the region has increased considerably after the occurrence of April, 2012 magnitude 8.6 and 8.2 strike-slip events. Further results show that there is no change in the regional earthquake activity after the occurrence of other three major dip-slip type events. Present study results reasonably agree with the results obtained by the other studies carried out with different methods. In the context of Sri Lanka, strike-slip type focal mechanism of the 2012 two major events may be the reason for increasing of activity in the region, especially in Eastern part of Sri Lanka near Maduruoya, Highland-Wijayan boundary and Wadinagala area of Ampara District. Keywords: seismology, Sumatra subduction zone, regional seismicity, earthquake, Sri Lanka
Highlights
Earthquakes are one of the most destructive natural phenomena of the Earth and it is a sudden movement of Earth releasing accumulated energy over a long period of time
The number of earthquakes of M>4 has increased after the occurrence of earthquake on 11th April 2012
The major earthquakes of magnitude greater than four which are considered in the analysis are occurred on the dates 26th December 2004, 28th March 2005, 12th September 2007 and 11th April 2012
Summary
Earthquakes are one of the most destructive natural phenomena of the Earth and it is a sudden movement of Earth releasing accumulated energy over a long period of time. The study of earthquakes has been providing a major significance for better understanding of the plate tectonics and the internal structure of the Earth. The tectonic plates move continuously due to the convectional currents of the Lithosphere. The plate velocity is different from plate to plate and is around 0-3cm/year (Read and Watson, 1975) and these motion cause plates to collide with each other. In Subduction zones plates collide with each other and one plate subducts under the other, these zones are down going limbs of the mantle convection system, where cold oceanic plates formed at mid ocean ridges return to the deep mantle (Stein and Stein, 1996; Gamage et al, 2009)
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