Detection of 12th September 2007 Sumatra Tsunami at Goa and Kavaratti Island

Subsurface pressure based real-time reporting and Internet-accessible coastal sea-level stations designed and established by the Indian National Institute of Oceanography (NIO) reported the 12^th September 2007 Sumatra tsunami waves from Goa (west coast of India) and Kavaratti Island (Lakshadweep archipelago) in the Arabian Sea. The sea-level stations sampled and transmitted the subsurface pressure data to the Internet server (IS) via GPRS cellular network at 5-minutes intervals. The subsurface pressure data received at the IS are converted to sea-level data and then the observed, predicted, and residual sea-levels in graphical format are displayed in real time on Internet. The graphical display from our sea-level station at Goa provided an indication of the presence of a distinct signal of tsunami periodicity. Spectral analysis of this data clearly reveals a dominant period of about 43 minutes. The tsunami wave arrived at the Goa site at ~00 hr: 45 minutes 1^ST on 13 September 2007, after traveling for ~8 hr from the tsunami source region (Sumatra). The first wave was negative (trough). The observed and the maximum trough-to-crest wave height was 29 cm. The tsunami wave which arrived at Kavarathi Island at 22 hr 1^ST on 12^th September 2007 was less prominent (trough-to-crest wave height ~5 cm) relative to that observed in Goa. Thus, tsunami signal at Goa was ~ 6-fold larger than that at Kavarastti Island. Arrival of a detectably large tsunami signal first at Kavaratti Island and 2 hr: 45 minutes later at the shallower Goa coastal region of the mainland shows the importance of having real-time monitoring and Internet-accessible sea-level stations on India´s island locations for effective tsunami warning purposes.