Delayed Subevents During the MW6.2 First Shock of the 2016 Kumamoto, Japan, Earthquake

Abstract

AbstractEarthquakes have been considered mostly to generate concentric rupture starting from the hypocenter. On the other hand, delayed subevents occurring after the first passage of rupture front have been found in the recent earthquakes, for example, the 2011 Tohoku earthquake. They potentially cause a long duration of ground motions. We study a source rupture process during the Mw6.2 first shock of the 2016 Kumamoto, Japan, earthquake, which may include the delayed subevent. The source model with three segments (S1, S2, and S3) is estimated from the near source records by using Bayesian inference, Markov chain Monte Carlo method. The maximum a posteriori solution well explains the near source records, and its layout of S1 and S2 segments are consistent with the previous studies. The posterior distribution suggests that location of S1 and S3 segments spatially overlaps with a time interval of about 6–7 s. Therefore, the S3 segment is accepted as the delayed subevent in this event. The first rupture on S1 concentrically propagates to trigger the second rupture on S2, and the second rupture then causes the dynamic triggering of S3 segment. Physical background how the delayed subevents can release the stress is needed to investigate in the future.