Gravity Map Series 24

Gravity map of Yamaguchi district (Bouguer anomalies) 1:200,000

MORIJIRI Rie, SATOH Hideyuki, NAWA Kazunari, HIROSHIMA Toshio, MURATA Yasuaki, MAKINO Masahiko, KOMAZAWA Masao, JOSHIMA Masato, ISHIHARA Takemi, KISIMOTO Kiyoyuki, OKUMA Shigeo, KOMURO Hiroaki, OHNO Ichiro, SHICHI Ryuichi
published on June 30, 2006

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Gravity Map of Yamaguchi District (Bouguer Anomalies)

A new gravity map of Yamaguchi district has been published. Compiled gravity data within the map area were 16,274 stations including 844 new gravity stations on land. All measured gravitydata were referred to the Japan Gravity Standardization Net 1975 (JGSN75) and normal gravity values were calculated according to the Geodetic Reference System 1980 (GRS80). Bouguer, terrain and other corrections were made by the standard procedure of gravity data processing at the Geological Survey of Japan (SPECG1988). The Bouguer and terrain corrections were carried out as an effect of bounded spherical crust and actual to-pographic undulation relative to the spherical surface, respec-tively, within the same distance range of 60km. The density for both Bouguer and terrain corrections is taken to be 2.3g/cm³. We show gravity maps assumed densities were 2.0g/cm³ (Fig.1) and 2.67g/cm³ (Fig.2), respectively. Regional Bouguer anomalies (Fig.3), a residual Bouguer anomalies with the removal of the 2km upward-continuation (Fig.4) and horizontal derivation (Fig.5) maps were shown in this side. The Bouguer anomalies caused by local geological feature are clearer on the residual map. The horizontal derivation map clearly shows structural boundaries like active faults.

Fig.1 Gravity map (Bouguer anomaly)
Assumed density: 2.0 g/cm³. Contour interval: 1 mGal.Dashed lines indicate negative values.H and L indicate high and low gravity anomalies, respectively.Thick solid lines indicate active faults.

Fig.2 Gravity map (Bouguer anomaly)
Assumed density: 2.67 g/cm³. Contour interval: 1 mGal. See Fig. 1.

Fig.3 Regional Bouguer anomalies continued upward 2km
Contour interval: 1mGal. Gray areas indicate negative values. Thick solid lines indicate active faults.

Fig.4 Residual Bouguer anomalies with the removal of the 2km upward-continuation.
See Fig.3

Fig.5 Horizontal gradients of Bouguer anomaly
Contour interval : 1mGal/km. Gray areas indicate values more than 2mGal/km. See Fig.3