Migration Of Aftershocks Following M_w6.0 In Central Italy By MFT

Generally,a large crustal earthquake is often followed by a fair number of aftershocks.Through the statistical results on seismic data,people found some principles of aftershocks.However,it is still hard to explain the mechanism of earthquake triggering,which is important to figure out earthquake nucleation.Many low-magnitude earthquakes can be covered by the code of mainshock,so aftershock catalogues are incomplete and lose numerous early small events.The missing aftershocks contain crucial information of earthquake time-spatial evolution and migration,and these provide insight into earthquake triggering.Matched filter technique,based on that seismicity in same source region is closely related,can effectively detect the small events from noise,making catalogs more complete.An extensional Mw 6.0 earthquake struck the Central Italy on 24th August,2016.Two month later,another three large shocks-Mw 5.5,Mw 5.9 and Mw 6.5 occurred successively near the focal region of the Mw 6.0 earthquake.We adopt the matched-filter method to perform detection of aftershocks through continuous waveforms 80 days after the Mw 6.0 mainshock,and the total number of detection events is tens times than that listed in template catalog.Moreover,the magnitude of completeness of the new catalog consisting of both detection and template events is lower than before.According to the analysis on time-spatial evolution and migration of aftershocks,we conclude some points as followed:The migration of aftershock is different among three mainshocks.Early aftershocks of Mw 6.0 expend towards both sides of the fault,but postseismic of Mw 5.9 and Mw 6.5 migrates asymmetrically along the fault strike.From aftershocks distribution profiles of various depth,we can see that in shallow crust early aftershocks expend perpendicularly to fault strike and gather as clusters,due to the complex geological structure of source region.In deep crust,aftershocks distribute along the fault strike might be relate to the detachment below fault system.In view of activation of aftershocks at time,we observe aftershock migration speeds up on the week after Mw 6.0,and promote stress loading around the Mw 5.5.Besides,the early aftershock fronts expand with logarithm time since Mw 6.0 and Mw 5.5,indicating that the postseismic migration is driven by aseismic slip.