Gravity Maps and CD-ROM of Japan by Geological Survey of Japan

Komazawa, Masao; Hiroshima, Toshio; Murata, Yoshinori; Morijiri, Rie; Makino, Masahiko

doi:10.6010/geoinformatics1990.11.2_86

Cited by 6 publications

(9 citation statements)

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“…5 and 6 are the difference between the northern and the southern parts of the region, and low velocities along the coast. These features and the average velocities in the northern and the southern areas are consistent with the result of Piao et al (1996a) (Komazawa, 2000). Contour interval is 1.0 mGal.…”

Section: Discussionsupporting

confidence: 80%

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Three-dimensional P wave velocity structure of shallow crust beneath the northern Awaji Island derived from refraction seismic explosion

et al. 2014

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After the 1995 Hyogo-ken Nanbu (Kobe) earthquake (M7.2), the Research Group for Explosion Seismology (RGES) conducted a refraction seismic experiment in the northern part of the Awaji Island in order to investigate a detailed structure around the source region. In the surveyed area, 145 temporal observation stations were deployed two-dimensionally at 200-250 meters intervals, and 7 shots of 150 kg charges were detonated. Using the first arrival times, we derived a three-dimensional P wave velocity structure of the shallow crust in this region. A dominant feature was the low velocity in the northern part of the region as compared with the southern part. The averages of velocities in the northern area were 4.1 km/s (at a depth of 0.09 km) and 4.5 km/s (at 0.49 km). In the southern region, these were 4.9 and 5.2 km/s, respectively. The study region was mostly within the Cretaceous granitic rocks, and we cannot find a difference in geology that corresponds to the velocity variation. On the other hand, the Bouguer anomaly and the resistivity distributions are consistent with the lateral velocity difference.

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Section: Discussionsupporting

confidence: 80%

“…The distribution of Bouguer anomalies (Komazawa, 2000) in the vicinity of the study region is shown in Fig. 8.…”

Section: Discussionmentioning

confidence: 99%

Three-dimensional P wave velocity structure of shallow crust beneath the northern Awaji Island derived from refraction seismic explosion

et al. 2014

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“…Our data set consists of gravity data compiled by the Geological Survey of Japan (Komazawa et al 2013; New Energy and Industrial Technology Development Organization 2013; Metal Mining Agency of Japan 2013). All measured gravity data were referenced to the Japan Gravity Standardization Net 1971 (JGSN75), which is based on the International Gravity Standardization Net 1971 (IGSN71); normal gravities were estimated using Gravity Formula 1980.…”

Section: Methodsmentioning

confidence: 99%

Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture

Miyakawa

Sumita

Okubo

et al. 2016

Earth Planets Space

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We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcano using a three-dimensional inversion with an assumed density contrast of ±0.3 g/cm 3 . The resultant location of the southern low-density body is consistent with a magma reservoir reported in previous studies. No Kumamoto aftershocks occur in the southern low-density body; this aseismic anomaly may indicate a ductile feature due to high temperatures and/or the presence of partial melt. Comparisons of the location of the southern low-density body with rupture models of the mainshock, obtained from teleseismic waveform and InSAR data, suggest that the rupture terminus overlaps the southern low-density body. The ductile features of a magma reservoir could have terminated rupture propagation. On the other hand, a northern low-density body is resolved in the Asodani area, where evidence of current volcanic activity is scarce and aftershock activity is high. The northern low-density body might, therefore, be derived from a thick caldera fill in the Asodani area, or correspond to mush magma or a high-crystallinity magma reservoir that could be the remnant of an ancient intrusion.Keywords: 2016 Kumamoto earthquake, Density structure, Gravity inversion, Volcano-tectonic interactions © The Author(s) 2016. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. BackgroundThe 2016 Kumamoto earthquake (M JMA 7.3) occurred on April 16, 2016, at 01:25 Japan Standard Time (JST, UTC +9) in the Kumamoto region, Kyushu Island, southwestern Japan. The epicenter (32.76°N, 130.76°E) and hypocentral depth (12 km below sea level) determined by the Japan Meteorological Agency (JMA) are very close to Aso volcano, the largest active volcano with a large caldera (15 × 25 km) in Japan (Fig. 1). The rupture process of the 2016 Kumamoto earthquake was resolved by Yagi et al. (2016): Rupture initiated at the hypocenter on the southwest part of the focal plane and propagated east for about 17 s. The area of maximum slip, with a value of ~5.7 m, was centered ~10 km northeast of the epicenter. The effective slip area was about 40 km long and 15 km wide, and the total seismic moment was 5.1 × 10 19 Nm (M w = 7.0). Aftershock distributions and focal mechanism determined by Yagi et al. (2016) indicate that the 2016 Kumamoto earthquake occurred along an active strike-slip fault known as the Futagawa Fault (Research Group for Active Faults of Japan 1991), which bel...

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“…Furthermore, Komazawa (2000) compiled a nationwide gravity map based on these surveys including other agency's data and disclosed gravity data in a CD-ROM. According to a Bouguer gravity map (ρ = 2.67 × 10 3 kg/m 3 ) of the Kitakami Mountains (Fig.…”

Section: Characteristics Of Geophysical Data In the Kitakami Mountainsmentioning

confidence: 99%

“…15). See also Fig This map was created from the gravity database by the GSJ (Komazawa, 2000). See also Fig.…”

Section: Northern Miyagi Earthquake Areamentioning

confidence: 99%

Utility of petrophysical and geophysical data to constrain the subsurface structure of the Kitakami plutons, northeast Japan

Okuma

Kanaya

2005

Earth Planet Sp

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The Geological Survey of Japan (GSJ), AIST has been systematically measuring physical properties of basement rocks in Japan for more than 30 years and has started to construct a petrophysical database called PBRock 21 (Petrophysical Database of Basement rocks in Japan for the 21st Century, http://www.aist.go.jp/RIODB/ PB-Rock21/). The petrophysical data has been integrated with aeromagnetic data to determine the subsurface structure of the Himekami and Sobanokami plutons, members of the Kitakami plutonic belt, northeast Japan. For the Himekami pluton, the result of apparent magnetization intensity mapping clearly shows zonation within subplutons as well as regional rock type differences between the North (felsic) and South (felsic and mafic complex) sub-plutons. The bottom depths of the pluton were estimated by a successive 3-D magnetic modeling to be 1.7 km (North sub-pluton) and 1.5 km below sea level (South sub-pluton), respectively. Magnetic modeling of the Sobanokami pluton, which is partly exposed at the eastern edge of the Ishinomaki Plain, implies that the main part of the pluton extends to the northwest below the surface. Its western edge is cut by the Ishinomaki-wan fault, believed to be the upward extension of the fault plane of the 2003 northern Miyagi earthquake as defined by seismic observations and reflection seismic surveys conducted after the earthquake. Integrated magnetic and gravity modeling suggests that the Kakeyama Formation, a Neogene conglomerate deposited in a half-graben along the Ishinomaki-wan fault during Miocene rifting, contains more granitic fragments toward the south than to the north in the Ishinomaki Plain.

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Gravity Maps and CD-ROM of Japan by Geological Survey of Japan

Cited by 6 publications

References 0 publications

Three-dimensional P wave velocity structure of shallow crust beneath the northern Awaji Island derived from refraction seismic explosion

Three-dimensional P wave velocity structure of shallow crust beneath the northern Awaji Island derived from refraction seismic explosion

Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture

Utility of petrophysical and geophysical data to constrain the subsurface structure of the Kitakami plutons, northeast Japan

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