Source Characteristics Of The 2016 Meinong (M-L 6.6), Taiwan, Earthquake, Revealed From Dense Seismic Arrays: Double Sources And Pulse-Like Velocity Ground Motion

The 5 February 2016, Meinong, Taiwan, earthquake brought extensive damage to nearby cities with significant pulse-like velocity ground motions. In addition to the spatial slip distribution determination using filtered strong-motion data, we show that, with the advantage of the densely distributed seismic network as a seismic array, we can project the earthquake sources (asperities) directly using nearly unfiltered data, which is crucial to the understanding of the generation of the pulse-like velocity ground motions. We recognize that the moderate but damaging M-L 6.6 Meinong earthquake was a composite of an M-w 5.5 foreshock and an M-w 6.18 mainshock with a 1.8-5.0 s time delay. The foreshock occurred at the hypocenter reported by the official agency, followed by the mainshock with a centroid located at 12.3 km to the north-northwest of the hypocenter and at a depth of 15 km. This foreshock-mainshock composition is not distinguishable in the finite-fault inversion because it filtered the seismic data to low frequencies. Our results show that the pulse-like velocity ground motions are mainly attributed to the source of mainshock with its directivity and site effects, resulting in the disastrous damages in the city of Tainan. Although finite-fault inversion using filtered seismic data for spatial slip distribution on the fault has been a classic procedure in understanding earthquake rupture processes, using a dense seismic network as a seismic array for unfiltered records helps us delineate the earthquake sources directly and provide more delicate information for future understanding of earthquake source complexity.