Gravity survey in the Central Ranges, Honshu, Japan.

Yamamoto, Akihiko; Kozaki, Kyozo; Fukao, Yoshio; Furumoto, Muneyoshi; Shichi, Ryūichi; Ezaka, Teruya

doi:10.4294/jpe1952.30.201

Cited by 23 publications

(16 citation statements)

References 5 publications

(4 reference statements)

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“…However, due to limited resolution in topographic data, terrain corrections have inherent errors. For example, of the 5mgal total error in the Bouguer values in the Central Ranges, Honshu, Japan, roughly 80% was ascribed to the uncertainty in terrain correction (Yamamoto et al, 1982). As the topography is more rugged in Taiwan (Fig.…”

Section: Gravity Reductionmentioning

confidence: 99%

Gravity Survey of Taiwan.

et al. 1995

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A gravity survey of the island of Taiwan was carried out from 1980 to 1987. In a 7-year effort, 603 gravity stations, most of which are located on geodetic stations, have been established. The average spacing between the stations is about 7km. The Bouguer and terrain corrections were made over a distance range of 100km using an average density of 2.57g/cm3. After the reductions, the Bouguer anomaly map was constructed. In general, the isogals of the Bouguer anomaly map trend NNE in consonance with the overall structural trend of the island. Negative anomalies cover a major part of the island; positive anomalies dominate in the eastern part of the Central Range, the Coastal Range and the northern extremity of the island. A high gradient belt, parallel to the trend of the island, is observed in the eastern Central Range across the suture zone between the Philippine Sea and Eurasian plates. In addition, the gravity anomaly data suggests that the island of Taiwan is not in isostatic equilibrium.

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Section: Gravity Reductionmentioning

confidence: 99%

Gravity Survey of Taiwan.

et al. 1995

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“…The density contrast at top surface (depth equal zero) is same as the difference between the average alluvial deposits of density 2.12 g/cm 3 and the average reduction density of 2.645 g/cm 3 in the region after Yamamoto et al (1982), i.e., ρ(0) = −0.525.…”

Section: Geological Materials and Density Contrastsmentioning

confidence: 99%

“…Most of the geological materials used in the synthetic modeling are from Central Ranges in the Japan Alps and therefore the reduction density adopted was 2.645 g/cm 3 , a value closer the average value of 2.64 g/cm 3 by Yamamoto et al (1982).…”

Section: Geological Materials and Density Contrastsmentioning

confidence: 99%

“…The value was obtained by a least squares method that incorporates the topography that covers an extensive 40,000 km 2 with elevation heights ranging from 0 to 3000 m for which the Earth's sphericity cannot be ignored (Yamamoto et al, 1982). Table 1 gives the maximum possible values for density contrasts in the horizontal layers assuming homogenous geological materials.…”

Section: Geological Materials and Density Contrastsmentioning

confidence: 99%

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Determination of density contrasts for a three-dimensional sub-surface intermediate layer

Ateya

Takemoto

2014

Earth Planet Sp

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The quantitative determination of the variable density contrasts for an intermediate horizontal layer has been demonstrated. In particular a sub-surface dipping dike with a priori depth-dependent density contrasts was adopted as a forward model to project gravity anomaly effect above the Earth surface. The sub-surface location and density contrasts in a series of intermediate horizontal layers in the causative dipping dike structure have been recovered by means of inversion analysis. Density contrasts recovery errors of less than 8.0 percent were realized to a depth of 2.00 km on a maximum synthetic gravity anomaly effect of 10.0 mGals that is better in comparison to constant density models. Finally to demonstrate the efficacy of the inverse analysis in the study, the entire process was successfully applied to real field data, i.e., residual gravity anomaly for a micro-gravimetry site and/or localized structures in Matsumoto Basin, Chubu District-Japan.

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“…Spherical Bouguer correction (Hagiwara, 1975) and spherical terrain correction over finite land areas were calculated after Yamamoto et al (1982). The resulting Bouguer anomalies with the terrain corrections for our measurements are listed in Table 6. 3.3 Regional Bouguer anomaly and the Rokko fault system We first show the Bouguer anomaly map in the Rokko area including Awaji Island, the Rokko Mountains, the Osaka Plain and the Sanda Basin in Fig.…”

Section: Evaluation Of Accuracymentioning

confidence: 99%

Two-Dimensional Analysis of Gravity Anomaly across the Rokko Fault System.

et al. 1996

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We carried out dense gravity measurements with the Fast Static GPS positioning along five survey lines across the Rokko fault system. We calculated the Bouguer anomaly to estimate the underground structure relevant to the 1995 Hyogo-ken Nanbu earthquake. We applied the two-dimensional Talwani's method to the modeling, assuming that the density structure is similar for all the five survey lines. All the Bouguer anomaly profiles are characterized by flat areas on the Rokko Mountains and Kobe Plain, with steep gradient between them. The gradient is most likely due to the fault scarps between the Rokko granite and the sedimentary layer of the Osaka and Kobe groups. It also indicates that the faults are vertical or reverse ones, at least just below their surface traces. This finding is consistent with the tectonic background of the Rokko Mountains that have upheaved under the east-west compression in the Quaternary. Moreover, we found the southwestward extension of the Koyo Fault underneath the sedimentary layer. The extension runs on the edge of the earthquake disaster zone. We inferred that the thickness of the sedimentary layer is 1-2 km near the sea, decreasing gradually toward the mountain side. The wedge-like structure and the hidden fault under the Kobe Plain may have served as a focusing lens of seismic rays during the earthquake.

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Gravity survey in the Central Ranges, Honshu, Japan.

Cited by 23 publications

References 5 publications

Gravity Survey of Taiwan.

Gravity Survey of Taiwan.

Determination of density contrasts for a three-dimensional sub-surface intermediate layer

Two-Dimensional Analysis of Gravity Anomaly across the Rokko Fault System.

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