Similarities and Differences in the Rupture Processes of the 1952 and 2003 Tokachi‐Oki Earthquakes

Abstract

We investigated the similarities and differences between the rupture processes of the 1952 and 2003 Tokachi‐oki earthquakes (M_w ∼ 8) that occurred 51 years apart in the southernmost region of the Kuril subduction zone. This event pair is rare because seismic waveforms of both events were instrumentally recorded. We performed joint source inversion analyses of both earthquakes to better understand the rupture processes of this earthquake sequence. The dataset for the 1952 earthquake consists of teleseismic and strong motion data which were obtained by digitizing copies of analog seismograms. Two datasets were made for the 2003 earthquake to examine the effect of data limitation and to facilitate a comparison of the inversion results of the two earthquakes. One dataset consists of a large amount of teleseismic, strong motion, and geodetic data. The other dataset is similar to that of the 1952 earthquake. Our results show that the rupture propagation, slip areas, and maximum slip amounts were similar for the 1952 and 2003 earthquakes in the Tokachi‐oki region. However, there are two important differences: the 1952 earthquake was initiated by an M_w 6.1 subevent in the Tokachi‐oki region, and its rupture extended to the adjacent Akkeshi‐oki region. The similarity in the rupture pattern of the M8‐class earthquake pair suggests the persistence of asperities on the plate interface, while the differences imply a degree of variability in the initiation and termination of the cascading rupture process.