Remotely triggered earthquakes in south-central tibet following the 2004 Mw9.1 Sumatra and 2005 Mw8.6 Nias earthquakes

Abstract

We conduct a systematic search for remotely triggered earthquakes in South-Central Tibet following the 2004 December 26 Mw 9.1 Sumatra and 2005 March 28 Mw 8.6 Nias earthquakes. We apply a Network Waveform Matched Filter Technique (NWMFT) to continuous seismic data recorded by the Hi-CLIMB array to obtain more complete earthquake catalogues in this region. Local earthquakes with magnitudes up to 4 were triggered during the large-amplitude surface waves, and most of them occurred in Gaize immediately north of the Bangong-Nujiang Suture Zone separating the Lhasa and Qiangtang Terranes. The triggered seismicity lasted 50 hr following the Sumatra and a few hours following the Nias main shocks, respectively. The difference in triggering durations could be explained by the fact that the Sumatra main shock excited long-duration surface waves with cumulative energy density 15 times more than that of the Nias main shock. In both cases, the transient increase in seismicity is followed by a moderate transient decrease, likely reflecting a 'dynamic shadow effect', where there is a temporary lack of seismic events following the remotely triggered seismicity. In comparison, we do not find any clear evidence of dynamic triggering (with a magnitude of completeness Mc = 1.7) in the Zhongba region, where a Mw 6.3 normal faulting earthquake occurred 10 d after the 2005 Nias event.