摘要：A Sacks-Evertson borehole volumetric strainmeter (SE strainmeter) at a site located 105 km from the epicenter of the mainshock recorded a clear slow strain event following the 2003 M w 8.0 Tokachi-oki earthquake (September 25, 2003, 19:50:06 UTC).This consisted of an episode of contraction for 4 days followed by expansion for 23 days.GPS sites in southeastern Hokkaido also recorded displacement changes during the same time interval.We use quasi-static calculations to generate synthetic waveforms for the measured quantities.All the data are satisfied by a propagating line source 2-stage model of slow reverse slip, uniform amplitude of 50 cm, with rupture propagation velocities of constant 9 cm/s (first stage) and exponentially decreasing from 3 to 0.7 cm/s (second stage).This post-seismic slip event is taken to be coplanar with the main shock rupture on the upper plane of the double Wadati-Benioff seismic zone (DSZ), and largely overlaps the seismic rupture.Regular earthquakes release only about 30% of the plate motion in this section of the subduction zone; post-seismic slip appears to account for at least some of the deficit. Key words Post-seismic slip event volumetric strainmeter 2003 Tokachi-oki earthquake aftershock activity state space approach.
