HR: 11:05h
AN: U22A-03    [Abstracts]
TI: The Spatio-temporal Context of the December 26, 2004 Aceh-Andaman Earthquake
AU: * Rajendran, C
EM: cp_r@vsnl.com
AF: Centre for Earth Science Studies, Akkulam, Trivandrum, 695031 India
AU: Rajendran, K
EM: kusala@seires.net
AF: Centre for Earth Science Studies, Akkulam, Trivandrum, 695031 India
AU: Earnest, A
EM: anil@seires.net
AF: Centre for Earth Science Studies, Akkulam, Trivandrum, 695031 India
AB: The available seismic history of the Andaman-Nicobar region indicates that in terms of size and fault length (1300 km), the M 9.3 December 26, 2004 earthquake is unprecedented in the region. A tsunamigenic earthquake (M ~7.5) is known to have occurred off Car Nicobar in 1881, reportedly defining a 300- km-long segment. Another event occurred in 1941 ruptured 300-400 km of the subduction interface, extending from middle to south Andamans. Available tide gauge data and eyewitness accounts suggest that the 1941 event, unlike the 1881 earthquake, may not have generated any tsunami. An earlier one occurred in the Andaman offshore on 28 January 1679 with its far-field felt area similar to the 1941 event. Historical data and estimations based on convergence rate from the Andaman-Nicobar region indicate a recurrence period of 200+-50 yr for the large earthquakes (M 7.5-8.0). Our field observations on coseismic uplift at various locations of the Andaman-Nicobar arc and the sites on the east coast of India, however, argue for a longer recurrence interval for the giant tsunamigenic earthquakes. The available age data of the coral terraces indicate that two major onshore uplift events (about 1 m) around 1000 and 3000 yr-BP. Historical information and stratigraphic context of suspected tsunami deposits from an archaeological site (7-12th century A.D) located in the east coast of India hint at the possible occurrence of a great tsunami around 900 A.D. From the available data, it appears that the 2004-type, megathrust events may be rare, aperiodical events. The temporal irregularity of such events vis-a-vis the more frequent segment-specific large events (e.g. 1679, 1881, and 1941), may be characteristic specific to the subduction zone. The northern segment between the North Andamans and the Burmese Coast (the Irrawady delta) is the most potential segment that remains to be broken. Historically this segment is quiescent, but we observed indications of previous liquefaction in the geological record in that region, whose size and timing need to be worked out.
DE: 3010 Gravity and isostasy (1218, 1222)
DE: 4804 Benthic processes, benthos (0408)
DE: 7209 Earthquake dynamics (1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Union [U]
MN: Fall Meeting 2005