Regional Seismic Activity after 2012 M8.6 Sumatra Earthquake

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 Lank

Radioactive and Non-Radioactive Element Analysis of Dorado Gas Discovery of Sri Lanka and Their Influence on Natural Environment

Naturally-occurring radionuclides deposited beneath the earth, which are referred to as "NORM" and other toxicnon-radioactive elements transported to the earth surface with the oil and gas production. Hence, knowledge of the prevailing background levels of these elements in the subsurface reservoir formations is valuable to all stakeholders, most notably to regulatory authorities of the country. The drill cuttings obtained within depth range 3025m to 3095m of reservoir sand section in the deep water exploratory well (CLPL- Dorado 91 H/1z) drilled in the Mannar Basin offshore Sri Lanka were subjected to high-resolution Gamma-ray spectrometry and X-ray fluorescence (XRF) spectrometry.As test results revealed activity concentration of 40K varies from 0.338 Bq/g to 0.514 Bq/g, 210Pb from 0.007 Bq/g to 0.015 Bq/g, 226Ra from 0.012 Bq/g to 0.0145 Bq/g while 232Th levels are between 0.030 Bq/g to 0.040 Bq/g. According to the XRF testing levels of significantly hazardous non-radioactive elements are considerably lower, except for the level of the Barium. The Pb level varies between the 48 ppm to 22 ppm. The Thorium level varies between 9.6 ppm to 10.1 ppm. Manganese has a range of 5,173ppm to 653ppm.The barium levels are between 118,666 ppm to 24,400 ppm. NORM concentration of the tested section were on the lower side when results matched with the IAEA published data on NORM concentration in oil, gas and there byproducts and therefore there will be low level of NORM contaminations when the Dorado gas discovery proceeds to the production stage. Further there is no harmful public exposure from NORM by disposing these drill cuttings to environment or storing at any site location. But the disposal of the drilling mud and handling of the drilling mud should be conducted with cautious since extremely high Ba levels can potentially cause health problems.Keywords: NORM, drill-cuttings, oil, gas, Sri Lanka, XR