Growing correlation length of moderate-sized earthquakes prior to two great earthquakes near Sumatra Island

Seismic correlation length for moderate earthquakes prior to two great earthquakes in the northern sea area of Sumatra Island (Mw9.1 in 2004 and Ms8. 6 in 2012) has been studied, using method of Single-Link-Cluster (SLC) analysis, and found to show a power-law growth about two years before their occurrences. No such growth was found for a magnitude 7 earthquake in the same area. This result suggests the occurrence of a physical process of critical-point characteristics in the source area before the great earthquakes