The 1997 Kagoshima (Japan) earthquake doublet: A quantitative analysis of aftershock rate changes

[1] We quantitatively map relative rate changes for the aftershock sequence following the second mainshock of the 1997 earthquake doublet (MW = 6.1, MW = 6.0) in the Kagoshima province (Japan). Using the spatial distribution of the modified Omori law parameters for aftershocks that occurred during the 47.8 days between the two mainshocks, we forecast the aftershock activity in the next 50 days and compare it to the actually observed rates. The relative rate change map reveals four regions with statistically significant relative rate changes three negative and one positive. ‘‘Our analysis suggests that the coseismic rate changes for off-fault aftershocks could be explained by changes in static stress. However, to explain the activation and deactivation of on-fault seismicity, other mechanism such as unusual crustal properties and the presence of abundant crustal fluids are required.’’