SIGNATURES OF PRE-2004 INDIAN OCEAN TSUNAMI EVENTS FROM SRI LANKA

Although several studies were carried to identify the pre-2004 large tsunamis generated at the India-Burma subduction boundary, still there are gaps and mismatches in records and hence recurrence interval of such events are not yet clear. Sri Lanka is located facing the northern section of the plate boundary and provide an ideal location for studying signatures such pre-2004 events generated at the above area. The 2004 tsunami itself, which left signatures in southern and eastern back-barrier environments of Sri Lanka, is an ideal modern analogue for such large events.

Sediment cores were collected from back barrier environments at Tangalla and Kumana, Devundara, Ratgama and Koggala of southwestern, southern, and southeastern coastal Sri Lanka

Textural, physical and chemical characteristics of sediment were used to distinguish paleo-tsunami layers. Radiocarbon dating of inorganic and organic materials of the sediments was used to determine the ages of recognized layers.

Based on proxy data, present study was able to identify 06 abrupt events of marine origin. Two events occurred 3000, 4000 yrs BP correlating among sites and can be considered as tsunami events. Another two layers, deposited around 4500 and 7000 yrs BP, correlate with previous records from Sri Lanka. When consider the tsunami wave propagation direction, these four events could be recognized as pre-2004 large trans-basin tsunami events generated at the northern section of plate boundary.