Repeating aftershocks of the great 2004 Sumatra and 2005 Nias earthquakes

• Published in: Journal of Asian earth sciences 2013-05, Vol.67-68, p.153-170
• Main Authors: Yu, Wen-che, Song, Teh-Ru Alex, Silver, Paul G.
• Format: Article
• Language: English
• Subjects: 2004 Sumatra–Andaman earthquake; 2005 Nias–Simeulue earthquake; High-precision earthquake location determination; Post-seismic afterslip; Repeating earthquakes
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2013.02.018

•Similar waveforms and master event algorithm achieve precise earthquake relative location.•Slip estimated from repeaters is similar to GPS displacement time series.•Temporal decay rate of repeaters follows power-law decay and conforms to Omori’s law.•Repeating aftershocks are governed by post-seismic afterslip. We investigate repeating aftershocks associated with the great 2004 Sumatra–Andaman (Mw 9.2) and 2005 Nias–Simeulue (Mw 8.6) earthquakes by cross-correlating waveforms recorded by the regional seismographic station PSI and teleseismic stations. We identify 10 and 18 correlated aftershock sequences associated with the great 2004 Sumatra and 2005 Nias earthquakes, respectively. The majority of the correlated aftershock sequences are located near the down-dip end of a large afterslip patch. We determine the precise relative locations of event pairs among these sequences and estimate the source rupture areas. The correlated event pairs identified are appropriately referred to as repeating aftershocks, in that the source rupture areas are comparable and significantly overlap within a sequence. We use the repeating aftershocks to estimate afterslip based on the slip-seismic moment scaling relationship and to infer the temporal decay rate of the recurrence interval. The estimated afterslip resembles that measured from the near-field geodetic data to the first order. The decay rate of repeating aftershocks as a function of lapse time t follows a power-law decay 1/tp with the exponent p in the range 0.8–1.1. Both types of observations indicate that repeating aftershocks are governed by post-seismic afterslip.