Surface Rupture of the 2008 Iwate-Miyagi Nairiku Earthquake Observed at Oshu and Ichinoseki Cities, Iwate Prefecture, Northeast Japan

Abstract

The 2008 Iwate-Miyagi Nairiku earthquake (Mw 6.9) struck an area where no active fault was known prior to the earthquake. The earthquake was shallow and large enough to produce scattered and discontinuous surface ruptures. To better understand the source processes and seismotectonic setting of the earthquake, we mapped the coseismic surface ruptures observed at Oshu and Ichinoseki Cities, Iwate Prefecture. The NNE-to NNW-trending surface ruptures appeared at three localities: (1) between Mochikorobashi and Ochiai, (2) Itagawa, and (3) southwest of Shinyu hot spring. Most of the surface ruptures are fold scarps up on the west, which are consistent with source fault models based on geodetic and seismological data. These surface ruptures appear to be associated with a reverse slip on west-dipping faults imaged by seismic reflection profiling, which originated as Miocene normal faults and have been reactivated as reverse faults since the Pliocene. Some of the ruptures appeared along preexisting tectonic scarps, although these scarps are short and discontinuous. Geomorphic expression of the causative faults of the 2008 earthquake is weak. Integration of geomorphic, geologic and geophysical data is necessary to identify active faults in areas where crustal strain is distributed to multiple fault strands and thus the tectonic landform of each fault is not well developed.

Single-station cross-correlation analysis of ambient seismic noise: application to stations in the surroundings of the 2008 Iwate-Miyagi Nairiku earthquake

“…1) measured a vertical acceleration of 3.95 g (Aoi et al 2008). Coseismic surface displacements of up to 1.2 m have been measured by InSAR (Takada et al 2009) and major surface ruptures were also reported (Tsutsumi et al 2010).…”

Coseismic and postseismic elastic wave velocity variations caused by the 2008 Iwate‐Miyagi Nairiku earthquake, Japan

“…InSAR measurements revealed coseismic surface displacements of up to 1.2 m caused by the earthquake [ Takada et al , 2009]. The surface ruptures associated with the earthquake were studied by Tsutsumi et al [2010]. The earthquake triggered an aseismic slow slip event on the Detana fault, northeast of the Iwate‐Miyagi Nairiku earthquake fault zone [ Iinuma et al , 2009].…”

High-resolution DEMs in the study of rainfall- and earthquake-induced landslides: Use of a variable window size method in digital terrain analysis

“…The geology of the Hanokidachi region comprises Tertiary sedimentary rocks, and is similar lithologically to the Izumozaki region. The Hanokidachi region suffered fewer landslides than the Kurikoma-dam region, although clear surface ruptures had been investigated (Tsutsumi et al, 2010).…”