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

Abstract

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.