A comprehensive model of the deformation process in the Nagamachi-Rifu Fault Zone

Iio, Yoshihisa; Sagiya, Takeshi; Umino, Norihito; Nishimura, Takuya; Takahashi, Kyoko; Homma, Takashi

doi:10.1186/bf03353359

Cited by 8 publications

(6 citation statements)

References 16 publications

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“…Hence, it is likely that partially molten materials are distributed at this depth, thereby causing anomaly (1). The two-dimensional finite element modeling by Iio et al (2004b) showed that the observed surface deformations by GPS can be explained by models with a weak zone in the lower crust, leading these authors to suggest that this weak zone plays an important role in the stress accumulation process on the NRF. Anomaly (1) could act like such a zone.…”

Section: Deep Structure Around the Nagamachi-rifu Faultmentioning

confidence: 99%

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

et al. 2006

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An M=5 earthquake occurred on September 15, 1998, in the Nagamachi-Rifu fault (NRF), northeastern Japan. In the aftermath of this event, many seismograph stations were constructed temporarily around the fault, forming a dense network of stations with a spatial separation of 5 km. We report here our estimation of the threedimensional velocity structures of the P and S waves using arrival-time data recorded at these stations with the aim of understanding the heterogeneous structure around the NRF. Low-Velocity and high Poisson's ratio anomalies are imaged in the lower crust beneath the volcanic area, which are probably associated with the partially molten materials conveyed through the upwelling flow in the mantle wedge. A distinct low-velocity anomaly, which is explainable by the existence of H 2 O-filled pores, is observed in the mid crust at the deeper extension of the NRF. Two low-velocity anomalies that are probably associated with the remnants of magmatic activity that formed the Shirasawa caldera and with the existence of thick late-Cenozoic sedimentary layers are observed at depths shallower than 10 km in the hanging wall of the NRF. Our results successfully characterize the major features of the complex velocity structure around the NRF, with implications for the existence of fluid-rich regions in the mid to lower crust.

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Section: Deep Structure Around the Nagamachi-rifu Faultmentioning

confidence: 99%

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

et al. 2006

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“…For example, Cailleau et al [] investigated the accumulation of stress between volcanoes that causes intraplate earthquakes in Nicaragua. Iio et al [] developed a 2‐D finite element model along a cross section oriented near‐normal to the Nagamachi‐Rifu fault zone, northern Japan, in order to clarify the stress accumulation process on an intraplate earthquake fault. Cho and Kuwahara [] investigated 3‐D crustal deformation in the Japanese Islands considering a viscoelastic crustal structure with linear Maxwell material.…”

Section: Introductionmentioning

confidence: 99%

Heterogeneous stress state of island arc crust in northeastern Japan affected by hot mantle fingers

et al. 2016

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By considering a thermal structure based on dense geothermal observations, we model the stress state of the crust beneath the northeastern Japan island arc under a compressional tectonic regime using a finite element method with viscoelasticity and elastoplasticity. We consider a three‐layer structure (upper crust, lower crust, and uppermost mantle) to define flow properties. Numerical results show that the brittle‐viscous transition becomes shallower beneath the Ou Backbone Range compared with areas near the margins of the Pacific Ocean and the Japan Sea. Moreover, several elongate regions with a shallow brittle‐viscous transition are oriented transverse to the arc, and these regions correspond to hot fingers (i.e., high‐temperature regions in the mantle wedge). The stress level is low in these regions due to viscous deformation. Areas of seismicity roughly correspond to zones of stress accumulation where many intraplate earthquakes occur. Our model produces regions with high uplift rates that largely coincide with regions of high elevation (e.g., the Ou Backbone Range). The stress state, fault development, and uplift around the Ou Backbone Range can all be explained by our model. The results also suggest the existence of low‐viscosity regions corresponding to hot fingers in the island arc crust. These low‐viscosity regions have possibly affected viscous relaxation processes following the 2011 Tohoku‐oki earthquake.

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“…It is therefore likely that rheological heterogeneities in the crust beneath the seismic source region would control the localized crustal deformation due to anelastic deformation under E-W compressional regional stress (e.g., Hasegawa et al 2005). Iio et al (2004) anticipated that uplift with slight contraction occurs above the weakened lower crust based on models having different assumptions of the viscosity, which can explain the vertical crustal deformation within the range of several tens of kilometers on different time scales in the Southeast Tohoku district. Additionally, in the source region of the earthquake swarms, the stress regime is estimated to vary with depth from normal fault type at shallow depths to thrust or strike-slip fault type at greater depths (Yoshida et al 2015b).…”

Section: Discussionmentioning

confidence: 99%

Localized extensional tectonics in an overall reverse-faulting regime, Northeast Japan

Umeda

2015

Geosci. Lett.

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In Northeast Japan, it has been recognized that trench-normal compressional stresses, aligned in the approximate direction of plate convergence, tend to dominate stress fields over a broad region. However, a particularly notable event was the shallow, normal-faulting earthquake swarms with a T-axis oriented in the E-W or NW-SE directions that occurred immediately after the 2011 Tohoku-Oki earthquake near the Pacific coast in the Southeast Tohoku district. The stress tensor inversion represents the pre-Tohoku-Oki earthquake stress field in this area as a normal-faulting stress regime with the minimum principal horizontal stress oriented in a roughly NW-SE direction. Additionally, the stress regime varies with depth from normal faulting at shallow depths (<15 km) to thrust faulting at greater depths. Seismic tomography and magnetotelluric soundings defined a geophysical anomaly with low seismic velocity and low resistivity clearly visible beneath the swarm activity, strongly supporting the existence of an interconnected network with fluid-filled porosity. The upper boundary of the conductor is in good agreement with an extensionalcompressional stress transition zone. A plausible explanation for these drastic changes in the stress regime is upward flexure of the upper crust due to partly anelastic deformation in the weakened lower crust. Additionally, remarkable upwarping and localized extensional tectonics during the late Pleistocene reflect the long-term rheological heterogeneities in the crust beneath the seismic source region.

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A comprehensive model of the deformation process in the Nagamachi-Rifu Fault Zone

Cited by 8 publications

References 16 publications

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

Heterogeneous stress state of island arc crust in northeastern Japan affected by hot mantle fingers

Localized extensional tectonics in an overall reverse-faulting regime, Northeast Japan

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