Co-seismic slip, post-seismic slip, and aftershocks associated with two large earthquakes in 1996 in Hyuga-nada, Japan

Abstract

We analyzed continuous GPS data to investigate the spatial distribution of post-seismic slip associated with two large earthquakes of October 19 and December 2, 1996, in Hyuga-nada, Japan. We found that the moment release due to post-seismic events was comparable to the co-seismic moment release during the two earthquakes. The source parameters of the first post-seismic event are as follows: the moment release = 1.7 × 1019 Nm; the maximum slip = 0.06 m at about 50 km northwest from the epicenter of the first earthquake; the characteristic decay time (= final slip/initial slope) = 15 days. For the second post-seismic event, the moment release = 2.0 × 1019 Nm; the maximum slip = 0.13 m at about 15 km northwest from the epicenter of the second earthquake; the characteristic time = 100 days. In both events, the slip vectors of the downgoing Philippine Sea (PHS) Plate on the SW-striking interplate boundary are directed west, in accordance with the co-seismic slip. It is also shown that the sites for co-seismic slip, post-seismic slip, and aftershocks do not overlap but complementarily share the plate boundary. This suggests that individual sites are characterized by their own constitutive laws, which may control modes of moment release as well as the entire sequence.