|casualties = none reported
}}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 Mw = 9.2 2004 Indian Ocean earthquake, while rupturing less than a third of its down-dip width.[1]
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.[2]
Characteristics
Selected EMS-98 intensities |
Intensity | Locations |
---|
VII (Damaging) | Car Nicobar |
VI (Slightly damaging) | Port Blair |
V (Strong) | Chennai |
IV (Largely observed) | Banda Aceh, Colombo |
III (Weak) | Kolkata |
|
II (Scarcely felt) | Kathmandu, Mangalore |
{{harvnb|Martin|Szeliga|2010}} |
Earthquake
The earthquake was very widely felt with reports from many parts of mainland India, Burma and Sumatra, a total area of {{convert|2000000|sqmi|km2}}.[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.[1] The larger, and more southerly, measured 150 km x 60 km dipping about 20° to the east with a displacement of {{convert|2.7|m|ft}} and a smaller area to the north dipping 15° to the east with a displacement of {{convert|0.9|m|ft|abbr=on}}. The larger gives an estimated {{M|w|link=y}} = 7.9 event and the smaller a {{M|w}} = 7.0 event.[3]
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 {{convert|1.22|m|ft|abbr=on}} at Nagapattinam.[1]
See also
- List of historical earthquakes
- List of historical tsunamis
References
1. ^1 2 3 4 5 {{cite journal|last=Ortiz|first=M.|author2=Bilham R.|year=2003|title=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=Journal of Geophysical Research|publisher=American Geophysical Union|volume=108|issue=B4|page=2215|doi=10.1029/2002JB001941|url=http://ciresweb.colorado.edu/~bilham/Andaman.pdf|bibcode=2003JGRB..108.2215O}}
2. ^{{cite web|url=http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=2310&t=101650&s=13&d=22,26,13,12&nd=display|title=Comments for the Significant Earthquake|last=NGDC|accessdate=2 November 2010}}
3. ^1 2 3 {{cite journal|last=Bilham|first=R.|author2=Engdahl R., Feldl N. & Satyabala S.P.|year=2005|title=Partial and Complete Rupture of the Indo-Andaman Plate Boundary 1847–2004|journal=Seismological Research Letters|volume=76|issue=3|pages=299–311|doi=10.1785/gssrl.76.3.299|url=http://cires.colorado.edu/~bilham/IndonesiAndaman2004_files/AndamanSRL4Mar.pdf|accessdate=20 November 2010}}