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Aftershocks and Seismotectonic Implications of the 13 September 2002 Earthquake (M_w 6.5) in the Andaman Sea Basin

Geological Survey of India
Central Geophysics Division
27, J.L. Nehru Road
Calcutta 700 016, India
jr_kayal{at}hotmail.com
(J.R.K., O.P.S.)

Geological Survey of India
Central Region
Nagpur, India
(S.G.G.)

Geological Survey of India
Eastern Region
Kolkata, India
(G.K.C.)

A medium-size earthquake mainshock (M_w 6.5) occurred on 13 September 2002 (22 h 28 m 31 s UTC) in the Andaman Sea, about 20 km offshore Diglipur, north Andaman Island. The epicenter at 13.087° N and 93.112° E and centroid depth at 31 km were estimated by the U.S. Geological Survey (USGS). The main shock was a reverse-faulting event. Four digital seismograph stations were established in the Andaman Islands to monitor aftershocks. About 200 aftershocks (M_d 1.0) were recorded during a period from 19 September to 7 October 2002. The epicenter map shows a northwest-southeast-trending aftershock cluster in an area of about 140 x 70 km², which reflects the rupture area of the mainshock. The aftershocks occurred mostly at a depth range of 5-20 km, except one at 38 km. The moment tensor solutions (USGS) of the mainshock and the largest aftershock (M_w 5.8), which occurred 22 hr after the mainshock, revealed consistent reverse faulting. The northeast-dipping northwest-southeast-trending nodal plane, which is comparable with the aftershock trend, is inferred to be the fault plane. The northeast-southwest compressional stress (P axis), obtained by the fault-plane solutions, is compatible with the north-northeast movement of the Indian plate. The mainshock and the two well-located largest aftershocks, located by the USGS, occurred within the subducted plate. One composite fault-plane solution is obtained for the shallower aftershocks recorded by the temporary network. The solution shows normal faulting with a northeast-southwest tensional (T) axis. These aftershocks occurred off the subducted plate at a much shallower depth (<10 km) and are due to local tension in the overriding plate.

This article has been cited by other articles:

				O. P. Mishra, J. R. Kayal, G. K. Chakrabortty, O. P. Singh, and D. Ghosh Aftershock Investigation in the Andaman-Nicobar Islands of India and Its Seismotectonic Implications Bulletin of the Seismological Society of America, January 1, 2007; 97(1A): S71 - S85. [Abstract] [Full Text] [PDF]