The source lengths of the 2004 earthquake estimated
from various data are somewhat different. Seismological
analyses indicate that the 2004 rupture started at the
epicenter off the west coast of Sumatra, then propagated
toward north through Nicobar and Andaman Islands in
about 500 seconds with a total length of 1200 to 1300
km. The fault slip was largest, 20 to 30 m, off the
coast of northern Sumatra, followed by ~5 m slip off
Nicobar Island. The fault slip around the Andaman
Islands was estimated to be small and was speculated to
be slow. The analysis of tsunami waveforms recorded on
tide gauge stations showed a shorter, up to 900 km,
source of the tsunami. Satellite image analyses and
ground-truth field investigations indicated that
the coseismic coastal sea level change extended from
Sumatra through North Andaman Island with a total
length of 1600 km. Some of the northern slip is attributed
to afterslip on the fault plane which occurred up
to 40 days.