Abstract

The giant Sumatra-Andaman earthquake of December 26, 2004 (Mw 9.3) ruptured the Sunda Arc from northern end of Sumatra to Andaman for a length of 1300 km. March 28, 2005 (Mw 8.7) rupture occurred south of it in north Sumatra. We studied seismic characteristics and energy release of the aftershock sequences of these two earthquakes. The energy released in aftershocks of 2004 and 2005 earthquakes was 0.135% and 0.365% of the energy of the respective mainshocks while the strain release in aftershocks was 39% and 71% for the two earthquakes, respectively. The b-value (slope of the frequency-magnitude relation), the p value (decay rate of aftershocks) and strain energy release are computed for both aftershock sequences.