Fault model of the 2007 Noto Hanto earthquake estimated from coseismic deformation obtained by the distribution of littoral organisms and GPS: Implication for neotectonics in the northwestern Noto Peninsula

Yoshihiro Hiramatsu,Takahiro Kamiya,Michio Kato,Kazuyoshi Moriya,Takuya Nishimura

doi:10.1186/bf03352846

Yoshihiro Hiramatsu, Takahiro Kamiya + Show 3 more

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https://doi.org/10.1186/bf03352846

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Abstract

AbstractWe investigate the coseismic vertical crustal movement along the northern and western coast of the Noto Peninsula caused by the Noto Hanto earthquake on March 25, 2007, from the distribution of supra-, mid- and infra-littoral organisms. The highest uplift of 44 cm is observed at Akakami and the maximum subsidence of 8 cm at Fukami. We construct a rectangular fault model with a uniform slip in elastic half-space using both the coseismic vertical displacement estimated from the distribution of these organisms and the coseismic crustal deformation obtained by GPS. The model shows a reverse fault with a right-lateral slip of 1.3 m in a 18.6 km×14.5 km area. The seismic moment is 1.0×1019 N m (MW6.6) using a rigidity of 30 GPa. The geometry of the source fault is consistent with the distribution of aftershocks and active faults, and the fault is restricted to the central area of the aftershock area. Relationships among the fault, the distribution of aftershocks, active faults, and geological blocks around the source area suggest that geological structures restrict the fault size of the earthquake. By considering an inclined altitudinal distribution of marine terraces and the coseismic vertical crustal deformation detected in this study, we estimate that the recurrence of earthquakes during the past 120 kyr would produce a vertical crustal deformation of ≈12 m and the background tectonic uplift would reach ≈28 m.

Highlights

The Noto Hanto earthquake (MJMA 6.9) occurred at 9:41(JST) March 25, 2007 at a depth of 11 km beneath the west coast of the Noto Peninsula, central Japan (Fig. 1)
We report our measurements of coseismic vertical displacement using the distribution of supra, mid, and infralittoral organisms and construct a fault model from these measurements together with the coseismic crustal deformation obtained by continuous GPS observation
The length of the fault, 18.6 km along the strike, is slightly shorter than that estimated by the inversion of the GPS data with fixed fault dip and strike based on the aftershock distribution (Tobita et al, 2007; Ozawa et al, 2008) and slightly longer than that estimated by the coastal vertical crustal deformation with a fixed fault dimension based on the aftershock distribution (Awata et al, 2008)

Summary

Introduction

(JST) March 25, 2007 at a depth of 11 km beneath the west coast of the Noto Peninsula, central Japan (Fig. 1) This is historically the first M ∼ 7 earthquake that has hit the Peninsula and historically the first earthquake that has caused strong ground motion, with the Japan Meteorological Agency (JMA) measuring seismic intensity in 6 upper in the Peninsula. The source mechanism of the earthquake is estimated to be a reverse fault with a right-lateral slip from the moment tensor inversion of long-period seismic waves (Hoshiba, 2007; Takeda et al, 2007). This fault movement caused the coseismic crustal deformation, as reported by the Geographical Survey Institute (GSI) from continuous GPS observation (GSI, 2007a). This crustal deformation is confirmed by synthetic aperture radar interferometric analysis (InSAR) (Fukushima et al, 2008; Ozawa et al, 2008) and leveling results (GSI, 2007b)

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