Caldera structure inferred from gravity anomalies west of Nagamachi-Rifu Fault, Northeast Japan

Komazawa, Masao; Mishina, Masaaki

doi:10.1186/bf03353300

Cited by 4 publications

(3 citation statements)

References 2 publications

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“…The effect can result in the hanging wall having a lower velocity than the footwall. The existence of thicker late Cenozoic sediments in the hanging wall is consistent with the low-Bouguer gravity anomaly (Komazawa and Mishina, 2002). Similar low-velocity anomalies probably related to the inversion tectonics have been imaged in the hanging wall of the Ishinomaki-wan fault (Okada, 2003), located approximately 50 km NE away from the NRF, and in the hanging wall of the fault where the 2004 Mid-Niigata prefecture earthquake (M=6.8) occurred (Okada et al, 2005).…”

Section: Deep Structure Around the Nagamachi-rifu Faultsupporting

confidence: 79%

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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 Faultsupporting

confidence: 79%

“…This results in a complex crustal struc- ture in this area. Low Bouguer gravity anomalies related to calderas have also been identified (Komazawa and Mishina, 2002).…”

Section: Seismotectonic Settingmentioning

confidence: 96%

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

et al. 2006

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“…These have included, crustal movement observations with a dense GPS array (Nishimura et al, 2004), resistivity structure surveys using the magnetoteluric (MT) method (Ogawa et al, , 2003, gravity survey (Komazawa and Mishina, 2002), reflection and refraction seismic surveys (Sato et al, 2002;Umino et al, 2002a;Nakamura et al, 2002;Imanishi et al, 2002), seismic observations (Nakajima et al, 2004), and receiver function analyses (Yoshimoto et al, 2001). Utilizing these observational results, we constructed a first-order approximation model of the stress accumulation process of the Nagamachi-Rifu Fault Zone (NRFZ) with the finite element method.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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A two-dimensional finite element model was constructed along a cross section almost perpendicular to the Nagamachi-Rifu Fault Zone, in order to clarify the stress accumulation process on an intraplate earthquake fault. We explain the surface deformations observed by the dense GPS network and leveling surveys using models with heterogeneities in the crust. These heterogeneities are identified from various geophysical surveys in the region. We found that the observed surface deformations cannot be explained by a model having a weak zone in the upper crust, but can be explained by models having a weak zone in the lower crust. Models having an aseismic fault or fault zone in the lower crust can reproduce the spatial pattern of the observed deformations, but amplitudes predicted by these models are smaller than those observed. The weak zone in the lower crust probably plays an important role in the stress accumulation process on the Nagamachi-Rifu fault zone.

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Introduction to the Gravity Database (GALILEO) Compiled by the Geological Survey of Japan, AIST

Miyakawa

Nawa

Murata

et al. 2015

International Association of Geodesy Symposia

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Caldera structure inferred from gravity anomalies west of Nagamachi-Rifu Fault, Northeast Japan

Cited by 4 publications

References 2 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

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

Introduction to the Gravity Database (GALILEO) Compiled by the Geological Survey of Japan, AIST

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