Late Quaternary and coseismic crustal deformation across the focal area of the 2008 Iwate-Miyagi Nairiku earthquake

We investigated late Quaternary and coseismic crustal deformation rates in the 2008 Iwate-Miyagi Nairiku earthquake (2008 IMEQ) focal area. We identified five fluvial terraces and used tephrochronology and 14C dating to correlate them with marine isotope stages (MISs) 6-5, slightly younger than 5.3-5.2, 4-5, 2-1, and 1. The late Quaternary uplift rates calculated from the relative heights of the MIS 6-5 (120-140 ka) and 2-1 (10 ka) terrace surfaces were 0.18-0.21 ± 0.13 m/ky and 0.62-0.74 ± 0.13 m/ky on the downthrown and upthrown sides of the 2008 IMEQ fault, respectively. We developed a fault model that reflected the coseismic vertical displacements and surface ruptures. This model had a fault plane dipping to the west at 40° with slip of 4.4 m on the deep (10-3 km depth) part of the fault plane and of 0.3 m on the shallow (3-0 km depth) part. The late Quaternary and coseismic deformation pattern of the ground surface roughly agree. Furthermore, the recurrence interval (2.9-4.2 ky) calculated from the late Quaternary vertical offset and coseismic vertical deformation roughly agrees with the findings of a previous trenching study. Thus, the slip on the fault of the 2008 IMEQ was a characteristic earthquake event.