The 1881 Nicobar Islands earthquake occurred at about 07:49 local time (01:49 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.[1]
Tectonic setting
The Nicobar Islands are a series of volcanic islands that are part of an active volcanic arc, formed above the subduction zone where the Indo-Australian plate passes beneath the Burma plate. The convergence along this plate boundary is highly oblique, with the plate vector running at a low angle to the boundary. Most of the strike-slip component of the convergence is accommodated by the Great Sumatran fault, which passes northwards into the Andaman Sea spreading centre.[1] This plate boundary has been the location of many historical megathrust earthquakes. The 1881 rupture area lies almost entirely within that for the Template:M 9.2 2004 Indian Ocean earthquake, while rupturing less than a third of its down-dip width.[2]
Damage
The Andaman and Nicobar Islands suffered some damage, although the only masonry buildings affected were in Port Blair, including an infantry barrack and a chimney, both of which suffered severe cracking. On Car Nicobar, the coconut plantations and native huts were extensively damaged and sand volcanoes were observed.[1] There were no reported casualties associated with either the earthquake or the subsequent tsunami.[3]
Characteristics
| Selected EMS-98 intensities | ||
| Intensity | Locations | |
|---|---|---|
| Template:EMS-98 | Car Nicobar | |
| Template:EMS-98 | Port Blair | |
| Template:EMS-98 | Chennai | |
| Template:EMS-98 | Banda Aceh, Colombo | |
| Template:EMS-98 | Kolkata | |
| Template:EMS-98 | Kathmandu, Mangalore | |
| Template:Harvnb | ||
Earthquake
The earthquake was very widely felt with reports from many parts of mainland India, Burma and Sumatra, a total area of Template:Convert.[1] 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.[2] The larger, and more southerly, measured 150 km x 60 km dipping about 20° to the east with a displacement of Template:Convert and a smaller area to the north dipping 15° to the east with a displacement of Template:Convert. The larger gives an estimated Template:M 7.9 event and the smaller a Template:M 7.0 event.[2]
Tsunami
The tsunami was recorded by eleven of a series of continuous tide gauges around the Bay of Bengal that had recently been deployed by the Great Trigonometric Survey of India.[1] 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 Template:Convert at Nagapattinam.[1]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Source area and rupture parameters of the 31 December 1881 Mw = 7.9 Car Nicobar earthquake estimated from tsunamis recorded in the Bay of Bengal. Journal of Geophysical Research({Template:Year).
- ↑ 2.0 2.1 2.2 Partial and Complete Rupture of the Indo-Andaman Plate Boundary 1847–2004. Seismological Research Letters({Template:Year).
- ↑ Significant Earthquake Information. NOAA National Centers for Environmental Information.