Rupture characteristics of the 2016 Meinong earthquake revealed by the back projection and directivity analysis of teleseismic broadband waveforms

Abstract

AbstractThe 2016 Mw 6.4 Meinong earthquake struck a previously unrecognized fault zone in midcrust beneath south Taiwan and inflicted heavy causalities in the populated Tainan City about 30 km northwest of the epicenter. Because of its relatively short rupture duration and P wave trains contaminated by large‐amplitude depth phases and reverberations generated in the source region, accurate characterization of the rupture process and source properties for such a shallow strong earthquake remains challenging. Here we present a first high‐resolution MUltiple SIgnal Classification back projection source image by using both P and depth‐phase sP waves recorded at two large and dense arrays to understand the source behavior and consequent hazards of this peculiar catastrophic event. The results further corroborated by the directivity analysis indicate a unilateral rupture propagating northwestward and slightly downward on the shallow NE‐dipping fault plane. The source radiation process is primarily characterized by one single peak, ~7 s duration, with a total rupture length of ~17 km and average rupture speed of 2.4 km/s. The rupture terminated immediately east of the prominent off‐fault aftershock cluster about 20 km northwest of the hypocenter. Synergistic amplification of ground shaking by the directivity and strong excitation of sP and reverberations mainly caused the destruction concentrated in the area further to the northwest away from the rupture zone.