1881 Nicobar Islands earthquake

UTC) on 31 December, with an epicentre beneath Car Nicobar. It occurred as two separate ruptures, the largest of which had an estimated magnitude of 7.9 on the moment magnitude scale and triggered a tsunami that was observed around the Bay of Bengal. It is probably the earliest earthquake for which rupture parameters have been estimated instrumentally.^[3]

2004 Indian Ocean earthquake, while rupturing less than a third of its down-dip width.^[1]

sand volcanoes were observed.^[3] There were no reported casualties associated with either the earthquake or the subsequent tsunami.^[4]

Burma and Sumatra, a total area of 2,000,000 square miles (5,200,000 km²).^[3] The rupture area, and therefore the magnitude, has been calculated by modelling the observed tsunami arrival times and heights. Two rupture areas have been identified.^[1] The larger, and more southerly, measured 150 km x 60 km dipping about 20° to the east with a displacement of 2.7 metres (8.9 ft) and a smaller area to the north dipping 15° to the east with a displacement of 0.9 m (3.0 ft). The larger gives an estimated M_w 7.9 event and the smaller a M_w  7.0 event.^[1]

Great Trigonometric Survey of India.^[3] The ten gauges on the Indian mainland were synchronised using a telegraph to Madras (Chennai) time, while that at Port Blair was set by a chronometer linked to local time. The maximum recorded wave height was 1.22 m (4.0 ft) at Nagapattinam.^[3]