The 2004 Indian Ocean tsunami: description of the event and estimation of length of the tsunami source region based on data from Indian tide gauge

Abstract

The Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauges along the coast of India. The tsunami struck the Indian east coast around 0330 UTC. The amplitude was 2.0 m above the tide at Chennai and Paradip, 1.5 m at Visakhapatnam and less than a metre at Tuticorin. The tsunami propagated into the Arabian Sea from the south and Kochi was hit at 0541 UTC. The maximum amplitude had decayed to about 80 cm at Kochi and it was less than 10 cm at Okha in Gujarat. All these tide gauges are to the west of the earthquake zone and the detided sea levels show first a rise in sea level with the arrival of the tsunami, and then a sharp decrease. Spectral and wavelet analysis of the residuals shows that the maximum amplitude was at a period of 35-45 min, with another maximum around 20 min. Along the Indian east coast, however, there is another broad peak between 1-2 hours within the first few hours after the first tsunami wave. Numerical simulation of this event is critically dependent on the initial perturbation used to force the model. The extent of the tsunami source region remains a key bottleneck. Arrival times recorded on the tide gauges provide additional constraint on the northern extent of the tsunami source location. Using the newly available tide-gauge data from Paradip, the northernmost station along the Indian east coast and therefore the most critical constraint on the northern extent of the tsunami source region, we investigate the northern extent of the source region of the Indian Ocean tsunami. Using backward ray tracing, it is shown that the tsunami travel times as recorded on the tide gauges at Paradip, Vishakhapatnam, and Chennai imply that the tsunami source region extends to approx. ~11 degrees N, implying a source region about 900 km long, about 30% greater than earlier estimates.